Patent Application
20240036241
The present invention relates to a wire grid polarizing element which has favorable polarization properties, avoids deterioration in heat dissipation and cost in manufacturing, and is excellent in transmissivity for oblique incident light and incident light at wide-range incident angles, and a method for manufacturing the wire grid polarizing element, as well as a projection display device excellent in polarization properties and heat tolerance and a vehicle including the projection display device.
As one of projection display devices, many vehicle head-up display devices have recently been developed which display video on a semi-transmissive plate (hereinafter collectively referred to as a “display surface”) such as a front glass or a combiner of a vehicle. A vehicle head-up display device is a video display device disposed on a dashboard of a vehicle, for example, projects video light on the front glass, and displays driving information as a virtual image. A driver is able to view the virtual image concurrently with a scenery through the front glass. This brings about an advantage that the line of sight of the driver moves less than with display devices such as conventional liquid crystal displays installed outside the range of the front glass.
However, the head-up display device described above outputs a displayed image toward the front glass surface (upward) from below, so that solar light enters the head-up display device oppositely to an output direction of the displayed image and is incident on a display element in some cases. The head-up display device is in many cases provided with a reflector for reflecting and magnifying a displayed image for the purpose of meeting the requirement for size reduction and magnifying the displayed image. In such a case, solar light incident on the head-up display device concentrates on the vicinity of the display element, which might cause degradation or failure of the display element by heat.
Thus, for the purpose of preventing solar light from being incident on a display element, a technology for providing a reflection-type polarizing element in a head-up display device is being developed. For example, Patent Literature 1 discloses ahead-up display device in which a reflection-type polarizing element (a wire grid polarizing plate) is provided between a reflector and a display element.
Herein, examples of a polarizing element provided in the head-up display device as described above include a polarizing element made of a birefringent resin, a wire grid-type polarizing element in which a plurality of conductors (fine metal wires) extend in parallel on a transparent substrate, a polarizing element made of a cholesteric phase liquid crystal, and the like. Among them, the wire grid-type polarizing element excellent in polarization properties is used frequently. In the wire grid-type polarizing element, a wire grid is formed in which conductive wires formed of metal or the like are arrayed in a grid shape at a specific pitch. By setting the array pitch of the wire grid at a pitch smaller than (for example, less than or equal to a half of) the wavelength of incident light (for example, visible light), most of light of an electric field vector component that vibrates in parallel to the conductive wires can be reflected, and most of light of an electric field vector component perpendicular to the conductive wires can be transmitted. As a result, the wire grid-type polarizing element can be used as a polarizing element that creates single polarized light, and can reflect non-transmitted light for reutilization, which is also desirable from the perspective of effective utilization of light. Note that the polarizing element as referred to herein includes a polarizing element that can be used as a polarizing beam splitter that splits incident light into s-polarized light and p-polarized light.
As such a wire grid-type polarizing element, Patent Literature 2, for example, discloses a wire grid polarizing plate including a resin base material having grid-shaped convexities, a dielectric layer provided to cover the grid-shaped convexities of the resin base material, and metal wires provided on the dielectric layer.
In addition, Patent Literature 3 discloses a wire grid polarizing plate which has a base material made of resin or the like and is provided on a surface with a concave-convex structure extending in a specific direction, and a conductor provided to be unevenly located on one of side surfaces of each of convexities of the concave-convex structure. In the wire grid polarizing plate, a pitch which is an interval between adjacent two convexities and a height of the convexities are adjusted in a sectional view in a direction perpendicular to the extending direction of the concave-convex structure.
Further, Patent Literature 4 discloses a projection-type video display device in which a reflection-type liquid crystal display element and a reflection-type wire grid polarizing plate as a polarizing beam splitter are used. In the projection-type video display device in which the reflection-type liquid crystal display element described in Patent Literature 4 is used, the reflection-type wire grid polarizing plate is arranged obliquely at approximately 45° with respect to the optical axis of output light from a light source. The output light from the light source enters the reflection-type wire grid obliquely at an incident angle of approximately 45° to be split into first polarized light (reflected light) and second polarized light (transmitted light). Then, the first polarized light reflected by the reflection-type wire grid polarizing plate is modulated and reflected by the reflection-type liquid crystal display element to become the second polarized light, and the second polarized light is transmitted through the reflection-type wire grid polarizing plate to be projected and displayed.
Moreover, Patent Literature 5 discloses a vehicle front lamp in which a reflection-type wire grid polarizing plate is used as a polarizing beam splitter. Also in the vehicle front lamp described in Patent Literature 5, the reflection-type wire grid polarizing plate is arranged obliquely at approximately 45° with respect to the optical axis of output light from a light source. The output light from the light source enters the reflection-type wire grid obliquely at an incident angle of approximately 45° to be split into first polarized light (reflected light) and second polarized light (transmitted light).
In a case where a reflection-type wire grid polarizing plate is arranged obliquely at approximately 45° with respect to output light from a light source as in the projection-type video display device described in Patent Literature 4 above, the vehicle front lamp described in Patent Literature 5, and the like, incident light is incident on the reflection-type wire grid polarizing plate not only at a single incident angle of 45°, but also at incident angles in a range of approximately 45°±15°.
In addition, Patent Literature 6 discloses a wire grid polarizing beam splitter in which a plurality of grid portions entirely made of silver or aluminum are formed on a substrate in a protruding manner.
Moreover, Patent Literature 7 discloses a wire grid-type polarizer having a light-transmitting substrate, an underlayer, and fine metal wires. In the wire grid-type polarizer of this Patent Literature 7, the light-transmitting substrate has a surface on which a plurality of ridges are formed in parallel to each other at a predetermined pitch. The underlayer is made of a metal oxide present at least on the top of each of the ridges. The fine metal wires are made of a metal laver present on a surface of the underlayer and at least on the top of each of the ridges.
A temperature environment required of equipment commonly used in a vehicle is −40 to 105° C. In a case of considering usage under a high-temperature environment of a device such as a head-up display mounted on a dashboard in a vehicle particularly in the summer, high heat tolerance and heat dissipation are required. In this respect, further improvement has been required of the wire grid polarizing plates described in Patent Literature 1 to Patent Literature 3 in terms of heat tolerance and heat dissipation. In addition, in order to brightly light roads at night with the vehicle front lamp described in Patent Literature 5, it is indispensable to increase luminance of the vehicle front lamp. Therefore, the vehicle front lamp described in Patent Literature 5 is required to have high heat tolerance and heat dissipation against heat from the light source.
Further, a conventional wire grid polarizing element has a concave-convex shape on its surface commonly formed by a photolithography technology or an etching technology, which raises problems of elevated manufacturing cost and unsuitability for mass production.
Then, in a case of splitting incident light into first polarized light (s-polarized light) and second polarized light (p-polarized light) in a projection display device such as a head-up display device using a reflection-type wire grid polarizing element as a polarizing beam splitter, reflectance for the first polarized light and transmittance for the second polarized light are both required to be high. Herein, in a case of using a product (Tp×Rs) of reflection axis reflectance (Rs) for the first polarized light (s-polarized light) and transmission axis transmittance (Tp) for the second polarized light (p-polarized light) as an index of polarization splitting properties, the value of this Tp×Rs preferably is higher. However, handling of polarized light in the polarizing beam splitter varies depending on the type of the projection display device to which the polarizing beam splitter is applied, and there are some cases in which the first polarized light (s-polarized light) becomes transmitted light and the second polarized light (p-polarized light) becomes reflected light.
In addition, the incident angle of incident light on the polarizing beam splitter is not only a single angle of 45°, but also spreads in the range of approximately 45° 15° centering on 45°, and light at wide incident angles is incident on the polarizing beam splitter. Therefore, the polarizing beam splitter is also required to be capable of exerting favorable polarization splitting properties for oblique incident light without depending on the incident angle of incident light incident in an oblique direction (hereinafter referred to as oblique incident light).
However, in the case of the structures of conventional reflection-type wire grid polarizing elements, a problem arises in that the transmission axis transmittance (Tp) for the second polarized light (p-polarized light) decreases as the incident angle of oblique incident light increases, resulting in decrease in polarization splitting properties for oblique incident light. For example, a case of forming all the convexities of a grid by a conductor as described in Patent Literature 6 and a case of providing a conductor (a reflection film) unevenly located entirely on one of the side surfaces of each of the convexities of the wire grid as described in Patent Literature 3 are considered. In these cases, the transmission axis transmittance (Tp) for the second polarized light (p-polarized light) decreases as the incident angle of oblique incident light increases, resulting in decrease in Tp×Rs described above. Therefore, the light utilization efficiency deteriorates, leading to a problem of decreased image quality such as uneven luminance. Consequently, in the structures of the conventional reflection-type wire grid polarizing elements described in Patent Literature 3. Patent Literature 6, and the like, there is a room for improvement in polarization splitting properties for oblique incident light at large and wide-range incident angles.
In addition, Patent Literature 7 describes that a coverage rate of side surfaces of each of the ridges by the metal layer (reflection film) preferably is more than or equal to 50%, more than or equal to 70%, and particularly preferably is 100%. Patent Literature 7 further describes that when the area of the metal layer covering the side surfaces of each of the ridges increases, lower s-polarized light reflectance can be achieved for light incident on the wire grid-type polarizer from the rear surface side, and s-polarized light incident from the front surface side can be efficiently reflected, so that the wire-grid polarizer exerts a high polarization splitting ability.
However, in the case where the area of the metal layer covering the side surfaces of each of the ridges of the wire grid is large as described in Patent Literature 7, the transmission axis transmittance (Tp) for the second polarized light (p-polarized light) decreases considerably when the incident angle of oblique incident light is large, particularly 45 to 60°, so that Tp×Rs described above also decreases considerably. Therefore, the light utilization efficiency deteriorates, leading to the problem of decreased image quality such as uneven luminance. Consequently, also in the structure of the wire grid-type polarizer described in Patent Literature 7, there is a room for improvement in polarization splitting properties for oblique incident light at large and wide-range incident angles.
Although being desired to have excellent polarization splitting properties for oblique incident light at large and wide-range incident angles as described above, the conventional reflection-type wire grid polarizing elements fail to ensure sufficient transmissivity for light at wide-range incident angles, particularly at large incident angles of more than or equal to 45°, so that further improvement in transmissivity for oblique incident light and polarization splitting properties has been desired.
The present invention was therefore made in view of such circumstances, and has an object to provide a wire grid polarizing element excellent in heat dissipation and excellent in transmissivity and polarization splitting properties for oblique incident light at wide-range incident angles, a method for manufacturing the polarizing element, as well as a projection display device including the polarizing element and a vehicle.
The inventor of the present invention has obtained the following knowledge as a result of enthusiastic studies for solving the above-described problems. First, a substrate of a wire grid polarizing element is formed of a transparent inorganic material, and a grid structural body provided on the substrate is integrally formed of a transparent organic material. This can provide the wire grid polarizing element with a hybrid-type structure made of the organic material and the inorganic material. As a result, heat dissipation of the wire grid polarizing element can be improved considerably.
Further, as the above-described grid structural body, a grid structural body in which abase part provided along a surface of the substrate and a plurality of ridge portions protruding from the base part are integrally formed is used. The grid structural body can thereby be formed by a technology such as nano-imprinting. Thus, the grid structural body can be reduced in manufacturing cost as compared with the case of using a photolithography technology or an etching technology, and can also be mass-produced.
Further, when providing a reflection film that reflects light or a functional film such as an absorbing film that absorbs light on ridge portions of the grid structural body, a covered range and a covered form of the ridge portion by the functional film are suitably adjusted. In other words, the leading end and the upper side of one of or both side surfaces of the ridge portion are covered by the functional film in an enfolding manner, and on the other hand, the lower side of the side surfaces of the ridge portion and a surface of the base part are open without being covered by the functional film. Then, the functional film covers and wraps the leading end and the upper side of the side surfaces of the ridge portion in such a rounded shape that bulges in a width direction of the ridge portion. Further, the ridge portion and the functional film are adjusted in shape and size such that a maximum width (WMAX) of a grid portion combining the ridge portion and the functional film covering and wrapping the ridge portion is more than or equal to a bottom width (WB) of the ridge portion. Further, the range of the side surfaces of the ridge portion covered by the functional film preferably is limited to a specific range on the upper side of the side surfaces (for example, a range of more than or equal to 25% and less than or equal to 80% of a height (H) of the ridge portion).
This can restrain the transmittance (Tp) for the second polarized light (p-polarized light) in the wire grid polarizing element from decreasing depending on the incident angles even in a case where oblique incident light at large and wide-range incident angles is incident on the wire grid polarizing element. Consequently, the product (Tp×Rs) of the reflection axis reflectance (Rs) for the first polarized light (s-polarized light) and the transmission axis transmittance (Tp) for the second polarized light (p-polarized light) in the wire grid polarizing element can be maintained at a high value. Thus, in the case of using the wire grid polarizing element as a polarizing beam splitter, for example, sufficient transmissivity and polarization splitting properties can also be obtained for oblique incident light at large and wide-range incident angles.
The inventor of the present invention has yielded the following invention based on the above-described knowledge.
In order to solve the above-described problems, according to an aspect of the present invention, there is provided a wire grid polarizing element of a hybrid type made of an inorganic material and an organic material, including:
The ridge portions each have an upward narrowing shape that narrows in width with distance from the base part.
The functional film covers and wraps a leading end and an upper side of at least one of side surfaces of each of the ridge portions, and does not cover a lower side of both the side surfaces of each of the ridge portions and the base part.
A surface of the functional film covering and wrapping each of the ridge portions is rounded and bulges in a width direction of the ridge portions, and a maximum width (WMAX) of the functional film covering and wrapping each of the ridge portions is more than or equal to a width (WB) of each of the ridge portions at a position of 20% of a height of each of the ridge portions upward from a bottom of each of the ridge portions.
When a coverage rate (Rc) of the side surfaces of each of the ridge portions obtained by the functional film is a proportion of a height (Hx) of a portion of the side surfaces of each of the ridge portions that is covered by the functional film to a height (H) of the ridge portions, the coverage rate (Rc) may be more than or equal to 25% and less than or equal to 80%.
The coverage rate (Rc) may be more than or equal to 30% and less than or equal to 70%.
A product (Tp×Rs) of transmission axis transmittance (Tp) and reflection axis reflectance (Rs) for incident light at an incident angle of 45° with respect to the wire grid polarizing element may be more than or equal to 70%.
The height (H) of each of the ridge portions may be more than or equal to 160 nm.
The functional film covering the leading end of each of the ridge portions may have a thickness (Dt) of more than or equal to 5 nm.
The functional film covering the side surfaces of each of the ridge portions may have a thickness (Ds) of more than or equal to 10 nm and less than or equal to 30 inn.
The base part may have a thickness (TB) of more than or equal to 1 nm.
A sectional shape of each of the ridge portions in a section orthogonal to a reflection axis direction of the wire grid polarizing element may be a trapezoidal shape, a triangular shape, a hanging bell shape, or an elliptical shape that narrows in width with distance from the base part.
The wire grid polarizing element may further include a protection film formed to cover at least the surface of the functional film.
The protection film may include a water-repellent coating or an oleophobic coating.
The functional film may further have a dielectric film.
In a case where θ is more than or equal to 30° and less than or equal to 60°, a difference between transmission axis transmittance (Tp (+)) for incident light at an incident angle of +θ with respect to the wire grid polarizing element and transmission axis transmittance (Tp (−)) for incident light at an incident angle of −θ may be within 3%.
The functional film may be a reflection film configured to reflect incident light.
The wire grid polarizing element may be a polarizing beam splitter configured to split oblique incident light into first polarized light and second polarized light.
In order to solve the above-described problems, according to another aspect of the present invention, there is provided a method for manufacturing a wire grid polarizing element of a hybrid type made of an inorganic material and an organic material, including the steps of:
In the step of forming the grid structural body, the ridge portions each having an upward narrowing shape that narrows in width with distance from the base part are formed.
In the step of forming the functional film, the functional film is formed such that the functional film covers and wraps a leading end and an upper side of at least one of side surfaces of each of the ridge portions and does not cover a lower side of both the side surfaces of each of the ridge portions and the base part, a surface of the functional film covering and wrapping each of the ridge portions is rounded and bulges in a width direction of the ridge portions, and a maximum width (WMAX) of the functional film covering and wrapping each of the ridge portions is more than or equal to a width (WB) of each of the ridge portions at a position of 20% of a height of each of the ridge portions upward from a bottom of each of the ridge portions.
In the step of forming the functional film, deposition may be performed on the ridge portions alternately in a plurality of directions by a sputtering or vapor deposition method.
In order to solve the above-described problems, according to another aspect of the present invention, there is provided a projection display device including:
The polarizing beam splitter is implemented by the wire grid polarizing element.
The incident angle in the predetermined range may be more than or equal to 30° and less than or equal to 60°.
A heat dissipation member may be provided around the wire grid polarizing element.
In order to solve the above-described problems, according to another aspect of the present invention, there is provided a vehicle including the projection display device.
According to the present invention, a wire grid polarizing element which is excellent in heat dissipation and has excellent polarization splitting properties for oblique incident light at wide-range incident angles can be provided.
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the appended drawings. Note that in the present specification and the drawings, structural elements that have substantially the same function and structure are denoted with the same reference numerals, and repeated description is omitted. Note that for convenience of description, the state of each member disclosed in the following drawings may be schematically represented in a scale and shape different from actual ones.
First, an overview of a wire grid polarizing element 1 according to an embodiment of the present invention will be described with reference to
The wire grid polarizing element 1 according to the present embodiment is a polarizing element of a reflection type and is a polarizing element of a wire grid type. The wire grid polarizing element 1 may be a plate-shaped wire grid polarizing plate, for example. The wire grid polarizing plate is a polarizing plate of a wire grid type having a plate shape. The wire grid polarizing plate may be flat plate-shaped, or may be curved plate-shaped, for example. That is, a surface of the wire grid polarizing element 1 (a surface on which light is incident) may be a flat surface or may be curvilinear. Hereinafter, an example in which the wire grid polarizing element 1 according to the present embodiment is a flat plate-shaped wire grid polarizing plate will be described, whilst the wire grid polarizing element of the present invention is not limited to such an example, and can have any shape depending on its application, functions, and the like.
Note that the wire grid polarizing element of the present invention may be used as a polarizer that transmits only light that vibrates in a specific direction, or may be used as a polarizing beam splitter that splits incident light into first polarized light (s-polarized light) and second polarized light (p-polarized light), for example. Hereinafter, the example in which the wire grid polarizing element 1 according to the present embodiment is used as the polarizing beam splitter will be mainly described.
As shown in
Note that “transparent” in the present specification means that light having a wavelength λ belonging to a used band (such as, for example, the band of visible light, the band of infrared light, or the band of visible light and infrared light) has high transmittance, and means that the transmittance for the light is more than or equal to 70%, for example. The wavelength band of visible light is more than or equal to 360 nm and less than or equal to 830 nm, for example. The wavelength band of infrared light (infrared rays) is larger than the wavelength band of visible light, and is more than or equal to 830 nm, for example. From the perspective of a suitable wavelength range of visible light to be projected as a displayed image, the wavelength λ in the used band in the polarizing element 1 according to the present embodiment preferably is more than or equal to 400 nm and less than or equal to 800 nm, for example, and more preferably is more than or equal to 420 nm and less than or equal to 680 nm. The polarizing element 1 according to the present embodiment is formed of a material transparent to light in the used band, so that the polarization properties, light transmissivity, and the like of the polarizing element 1 will not be affected adversely.
The substrate 10 is made of a transparent inorganic material such as glass. The substrate 10 is a flat plate-shaped substrate having a predetermined thickness TS.
The grid structural body 20 is made of a transparent organic material, for example, an organic resin material such as an ultraviolet curable resin or a thermosetting resin excellent in heat tolerance. The grid structural body 20 has a concave-convex structure for achieving the polarizing function of the polarizing element 1. Specifically, the grid structural body 20 has a base part 21 provided along a surface of the substrate 10, and a plurality of ridge portions 22 protruding from the base part 21 in a grid shape. The base part 21 and the plurality of ridge portions 22 of the grid structural body 20 are integrally formed using an identical organic material.
The base part 21 is a thin film having a predetermined thickness TB, and is stacked across the entire principal surface (an X-Y plane shown in
The plurality of ridge portions 22 are arrayed on the base part 21 at regular intervals at a predetermined pitch P in the X direction. Note that the pitch P is an interval at which the plurality of ridge portions 22 arrayed in the X direction of the polarizing element 1 are formed. The plurality of ridge portions 22 are arranged in a grid shape so as to extend in the Y direction in parallel to each other. A predetermined gap is formed between two of the ridge portions 22 adjacent to each other in the X direction. This gap serves as an approach route of incident light. Each of the ridge portions 22 is a wall-like convexity formed in a protruding manner so as to extend elongatedly in a predetermined direction (the Y direction shown in
The functional film is a film for providing a predetermined function for the grid structural body 20 of the polarizing element 1. The functional film is made of an opaque metal material, for example, and is provided to cover part of the ridge portion 22 of the grid structural body 20. The functional film may be the reflection film 30 having a function of reflecting incident light incident on the polarizing element 1, or may be an absorbing film (not shown) having a function of absorbing the incident light, or may be a film having another function, for example. Although an example in which the functional film is the reflection film 30 will be described in the present embodiment, the functional film of the present invention is not limited to the example of the reflection film 30.
The reflection film 30 is a thin film made of a metal material (such as metal or metal oxide) of aluminum, silver, or the like, for example. The reflection film 30 is formed to cover at least the top of the ridge portion 22. The reflection film 30 may be implemented by a metal film that functions as a fine metal wire of the wire grid. The reflection film 30 has the function of reflecting incident light incident on the grid structural body 20.
The ridge portions 22 of the grid structural body 20 and the reflection film 30 constitute a grid of the wire grid polarizing element 1. The pitch Pin the X direction of the plurality of ridge portions 22 in the grid structural body 20 (that is, an array pitch of the grid) is set at a pitch smaller than (for example, less than or equal to a half of) the wavelength λ of incident light (for example, visible light). This enables the polarizing element 1 to reflect most of light (s-polarized light) of an electric field vector component that vibrates in a direction (a reflection axis direction: the Y direction) parallel to the reflection film 30 (a conductive wire) extending in the Y direction, and to transmit most of light (p-polarized light) of an electric field vector component that vibrates in a direction (a transmission axis direction: the X direction) perpendicular to the reflection film 30 (the conductive wire).
As described above, the wire grid polarizing element 1 according to the present embodiment achieves the polarizing function by a combination of the grid structural body having a micro concave-convex structure and the functional film (for example, the reflection film 30) selectively added to the ridge portions 22 of the grid structural body 20. The substrate 10 of the wire grid polarizing element 1 is made of an inorganic material very excellent in heat tolerance, such as glass, and the grid structural body 20 is made of an organic resin material having heat tolerance. In this manner, the wire grid polarizing element 1 according to the present embodiment is a polarizing element of a hybrid type in which the organic material and the inorganic material are combined. Consequently, heat can be efficiently released from the grid structural body 20 having a small thermal resistance R [m2·K/W] to the substrate 10, resulting in excellent heat dissipation. Consequently, the wire grid polarizing element 1 of the hybrid type according to the present embodiment is superior in heat tolerance and heat dissipation to conventional polarizing elements of a film type (heat tolerance: approximately 100° C.) only made of an organic material, and has heat tolerance under a high-temperature environment up to approximately 200° C., for example. Thus, a favorable heat dissipation effect can be maintained while achieving excellent polarization properties.
Further, the wire grid polarizing element 1 according to the present embodiment may include a protection film 40 (see
In addition, the micro concave-convex structure can be achieved by a simple manufacturing process because the grid structural body 20 in which the base part 21 and the ridge portions 22 are integrally configured can be manufactured using a printing technology such as nano-imprinting as described above. Consequently, cost and labor required for manufacturing the grid structural body 20 can be reduced as compared with the case of manufacturing the grid structural body 20 using the photolithography technology or etching technology. Thus, the polarizing element 1 of the hybrid type according to the present embodiment is advantageous in that the manufacturing cost can be reduced considerably and the product unit price of the wire grid polarizing element 1 can be made inexpensive as compared with conventional polarizing elements only made of an inorganic material.
On the other hand, the conventional organic polarizing plates of the film type use many organic materials, and a substrate (base film), a double-faced tape (OCA: optically clear adhesive), and the grid structural body have large thicknesses. Thus, it is considered that the conventional organic polarizing plates of the film type are inferior in heat dissipation and heat tolerance to the polarizing element 1 of the hybrid type according to the present embodiment.
In addition, in the wire grid polarizing element 1 according to the present embodiment, a grid portion composed of the ridge portion 22 of the grid structural body 20 and the reflection film 30 has a special tree shape (details of which will be described later) as shown in
As described above, the wire grid polarizing element 1 according to the present embodiment is excellent in heat tolerance and heat dissipation, can be reduced in manufacturing cost, and is also excellent in transmissivity and polarization splitting properties for oblique incident light at the wide-range and large incident angle θ. Thus, the wire grid polarizing element 1 according to the present embodiment can suitably be applied as various parts of various products. For example, the polarizing element 1 can be applied to a polarizing beam splitter installed in a smart display, and the like. The polarizing element 1 can also be applied to a polarizing element which is installed in a head-up display (HUD) and in which measures against solar light have been taken, a polarizing element in which measures against heat from an LED light source have been taken, a polarizing reflection mirror, and the like. Further, the polarizing element 1 can also be applied to a polarizing beam splitter installed in a headlight such as an adaptive driving beam (ADB), and the like. The polarizing element 1 can also be applied to a lens-integrated phase difference element, a lens-integrated polarizing element, and the like installed in various devices for augmented reality (AR) or virtual reality (VR).
Next, constituent members of the wire grid polarizing element 1 according to the present embodiment will be described in detail with reference to
As shown in
From the perspective of obtaining more excellent heat dissipation and heat tolerance, the material of the substrate 10 preferably is an inorganic material such as various types of glass, quartz, crystal, or sapphire, for example, more preferably is an inorganic material having a thermal conductivity of more than or equal to 1.0 W/m·K, and further preferably is an inorganic material having a thermal conductivity of more than or equal to 8.0 W/m·K.
In addition, the shape of the substrate 10 is not particularly limited, and can be selected as appropriate in accordance with performance and the like required of the polarizing element 1. For example, the substrate 10 can be configured to have a plate shape or a curvilinear surface. In addition, from the perspective of not affecting the polarization properties of the polarizing element 1, the surface of the substrate 10 can be a flat surface. Further, the thickness TS of the substrate 10 is neither particularly limited, and can fall within a range of 0.02 to 10.0 mm, for example.
As shown in
When light is incident on the polarizing element 1 from a surface side on which the grid structural body 20 is formed, part of the incident light is reflected by the reflection film 30. In the light incident on the reflection film 30, light having an electric field component in a direction (that is, the width direction of the ridge portions 22=the transmission axis direction: the X direction) orthogonal to the longitudinal direction of the ridge portions 22 (that is, the direction in which the ridge portions 22 extend=the reflection axis direction: the Y direction) is transmitted through the polarizing element 1 at high transmittance. On the other hand, in the light incident on the reflection film 30, a large part of light having an electric field component in a direction parallel to the longitudinal direction of the ridge portions 22 (that is, the direction in which the ridge portions 22 extend=the reflection axis direction: the Y direction) is reflected by the reflection film 30. Thus, in the present embodiment, the polarizing element 1 can create single polarized light by including the grid structural body 20 partially covered by the reflection film 30. Note that a similar polarization effect can also be obtained for light incident from the rear surface side of the substrate 10.
The grid structural body 20 has the base part 21 as shown in
Note that the thickness TB of the base part 21 is not particularly limited, and from the perspective in which the ridge portions 22 can be supported more reliably and from the perspective of easily performing imprinting molding, preferably is more than or equal to 1 nm, and more preferably is more than or equal to 10 nm. In addition, from the perspective of ensuring favorable heat dissipation, the thickness TB of the base part 21 preferably is less than or equal to 50 μm, and more preferably is less than or equal to 30 μm.
Further, the grid structural body 20 has the plurality of ridge portions 22 protruding from the base part 21 as shown in
Herein, as shown in
In addition, as shown in
Note that the bottom width WB and the top width WT of the ridge portion 22 can be measured by observation with a scanning electron microscope or a transmission electron microscope. For example, the section (the X-Z section) orthogonal to an absorption axis direction or the reflection axis direction of the polarizing element 1 is observed using a scanning electron microscope or a transmission electron microscope. For the ridge portions 22 at any four places, the width of the ridge portion 22 at a height position of 20% of the height H of the ridge portion 22 upward from the bottom of the ridge portion 22 is measured, and their arithmetic mean value can be used as the bottom width WB of the ridge portion 22. In addition, for the ridge portions 22 at any four places, the width of the ridge portion 22 at a height position of 20% of the height H of the ridge portion 22 downward from a leading end 22a of the ridge portion 22 is measured, and their arithmetic mean value can be used as the top width WT of the ridge portion 22.
In addition, as shown in
The shape of the ridge portion 22 of the grid structural body 20 preferably is an upward narrowing shape in order to obtain favorable polarization splitting properties for oblique incident light. Herein, the upward narrowing shape is such a shape that the width W of the ridge portion 22 (the width in the X direction in the X-Z section) gradually narrows with distance from the base part 21, in other words, such a shape that the width W of the ridge portion 22 gradually narrows from the bottom to the top of the ridge portion 22. Consequently, in the case where the ridge portion 22 has the upward narrowing shape, the top width WT of the ridge portion 22 is smaller than the bottom width WB of the ridge portion 22 (WT<WB).
In addition, when the ridge portion 22 has the upward narrowing shape such as a tapered shape, the refractive index of the grid structural body 20 gradually changes. Consequently, an effect of preventing reflection of incident light because of the physical change in refractive index of the grid structural body 20 is obtained similarly to a moth-eye structure. This also enables the effects that the reflectance at the surface of the ridge portion 22 of the grid structural body 20 can be reduced and the transmissivity of the grid structural body 20 can be improved to be expected.
In addition,
In addition, the material constituting the grid structural body 20 is not particularly limited if it is a transparent organic material, and a publicly-known organic material can be used. For example, from the perspectives of ensuring transparency and excellent ease of manufacturing, various thermosetting resins, various ultraviolet curable resins, or the like preferably are used as the material of the grid structural body 20.
Further, from the perspectives of ease of manufacturing and manufacturing cost, a material different from the material of the substrate 10 preferably is used as the material constituting the grid structural body 20. In addition, in the case where the materials of the grid structural body 20 and the substrate 10 are different, their refractive indexes are different. Therefore, in a case where the refractive index of the entire polarizing element 1 is affected, a refractive index adjustment layer may be provided as appropriate between the grid structural body 20 and the substrate 10.
For example, as the material constituting the grid structural body 20, a curable resin such as a polymerizable epoxy compound or a polymerizable acrylic compound can be used. A polymerizable epoxy compound is a monomer, oligomer, or prepolymer having one or multiple epoxy groups in the molecule. Examples of polymerizable epoxy compounds include various bisphenol epoxy resins (such as bisphenol A and F), novolac epoxy resin, various modified epoxy resins such as rubber or urethane, naphthalene epoxy resin, biphenyl epoxy resin, phenol novolac epoxy resin, stilbene epoxy resin, triphenol methane epoxy resin, dicyclopentadiene epoxy resin, triphenyl methane epoxy resin, and prepolymers of the above.
A polymerizable acrylic compound is a monomer, oligomer, or prepolymer having one or multiple acrylic groups in the molecule. Herein, monomers are further classified into monofunctional monomers having one acrylic group in the molecule, bifunctional monomers having two acrylic groups in the molecule, and multifunctional monomers having three or more acrylic groups in the molecule.
Examples of “monofunctional monomers” include carboxylic acids (such as acrylic acids), hydroxy monomers (2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate), alkyl or alicyclic monomers (isobutyl acrylate, t-butyl acrylate, isooctyl acrylate, lauryl acrylate, stearyl acrylate, isobornyl acrylate, cyclohexyl acrylate), other functional monomers (2-methoxyethyl acrylate, methoxyethylene glycol acrylate, 2-ethoxyethyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, ethyl carbitol acrylate, phenoxyethyl acrylate, N,N-dimethylamino ethyl acrylate, N,N-dimethylamino propyl acrylamide, N,N-dimethyl acrylamide, acryloyl morpholine, N-isopropyl acrylamide, N,N-diethyl acrylamide, 2-(perfluorooctyl)ethyl acrylate, 3-perfluorohexyl-2-hydroxypropyl acrylate, 3-perfluorooctyl-2-hydroxypropyl-acrylate, 2-(perfluorodecyl)ethyl-acrylate, 2-(perfluoro-3-methylbutyl)ethyl acrylate), 2,4,6-tribromophenol acrylate, 2,4,6-tribromophenol methacrylate, 2-(2,4,6-tribromophenoxy)ethyl acrylate), and 2-ethylhexyl acrylate.
Examples of “bifunctional monomers” include tri(propylene glycol) di-acrylate, trimethylolpropane-diaryl ether, and urethane diacrylate.
Examples of “multifunctional monomers” include trimethylolpropane tri-acrylate, dipentaerythritol penta- and hexa-acrylate, and ditrimethylolpropane tetra-acylate.
Examples other than the polymerizable acrylic compounds listed above include acrylmorpholine, glycerol acrylate, polyether acrylates, N-vinylformamide, N-vinylcaprolactam, ethoxy diethylene glycol acrylate, methoxy triethylene glycol acrylate, polyethylene glycol acrylate, ethoxylated trimethylolpropane tri-acrylate, ethoxylated bisphenol A di-acrylate, aliphatic urethane oligomers, and polyester oligomers.
In addition, examples of curing initiators for curable resins described above include thermal curing initiators and light curing initiators. A curing initiator may be cured with some energy beam (for example, an electron beam) or the like other than heat and light. In a case where the curing initiator is a thermal curing initiator, a curable resin is a thermosetting resin, and in a case where the curing initiator is a light curing initiator, a curable resin is a light curing resin.
Among them, an ultraviolet-curing initiator preferably is used as the curing initiator. The ultraviolet-curing initiator is a type of light curing initiators. Examples of ultraviolet-curing initiators include 2,2-dimethoxy-1,2-diphenylethane-1-one, 1-hydroxy-cyclohexyl phenyl ketone, and 2-hydroxy-2-methyl-1-phenyl propane-1-one. Consequently, the curable resin preferably is an ultraviolet curable resin. In addition, from the perspective of transparency, the curable resin more preferably is an ultraviolet curable acrylic resin.
Note that a method for forming the grid structural body 20 is not particularly limited if it is a method in which the base part 21 and the ridge portions 22 described above can be formed. For example, a concavity-convexity forming method by a technology such as photolithography or imprinting can be used. Among them, the base part 21 and the ridge portions 22 of the grid structural body 20 preferably are formed by imprinting from the perspective that a concave-convex pattern can be formed in a short time and easily, and further, the base part 21 can be formed reliably.
In the case of forming the base part 21 and the ridge portions 22 of the grid structural body 20 by nano-imprinting, the substrate 10 is coated with a material (a grid structural body material) for forming the grid structural body 20, then a master with concavities and convexities formed thereon is pressed against the grid structural body material, and ultraviolet rays are radiated or heat is applied in that state, so that the grid structural body material can be cured, for example. The grid structural body 20 having the base part 21 and the ridge portions 22 can thereby be formed.
The polarizing element 1 according to the present embodiment includes the reflection film 30 formed on the ridge portions 22 of the grid structural body 20 as shown in
As shown in
The material constituting the reflection film 30 is not particularly limited if it is a material having reflectiveness for light in the used band. Examples of the material include a single metal element such as Al, Ag, Cu, Mo, Cr. Ti, Ni, W, Fe, Si, Ge, or Te and a metal material such as an alloy containing one or more kinds of these elements.
Note that the reflection film 30 may be a single-layer film made of metal described above, or may be a multi-layer film made of a plurality of metal films. In addition, the reflection film 30 may include another layer such as a dielectric film according to necessity if it has the reflective function. The dielectric film is a thin film made of a dielectric. As the material of the dielectric film, a common material such as SiO2, Al2O3, MgF2, or TiO2 can be used. In addition, the dielectric film preferably has a refractive index of more than 1.0 and less than or equal to 2.5. Note that because optical properties of the reflection film 30 are influenced by surrounding refractive indexes as well, polarization properties may be controlled by the material of the dielectric film.
Herein, the special shape of the ridge portion 22 of the grid structural body 20 and the reflection film 30 in the polarizing element 1 according to the present embodiment will be described in detail.
In the polarizing element 1 according to the present embodiment, the reflection film 30 is formed to cover and wrap the leading end 22a and the upper side of at least one of the side surfaces 22b of the ridge portion 22 of the grid structural body 20 and not to cover the lower side of both the side surfaces 22b of the ridge portion 22 and the base part 21, as shown in
Herein, “the state in which the reflection film 30 covers and wraps the leading end 22a and the upper side of at least one of the side surfaces 22b of the ridge portion 22 of the grid structural body 20” is a state in which “the leading end 22a of the ridge portion 22” and “the upper side of the side surfaces 22b connecting the leading end 22a of the ridge portion 22 and the base part 21” are both continuously covered by the reflection film 30, and “the lower side of the side surfaces 22b” and “the base part 21” are exposed without being covered by the reflection film 30, as shown in
Further, the surface of the reflection film 30 covering and wrapping the leading end 22a and the upper side of at least one of the side surfaces 22b of the ridge portion 22 (hereinafter referred to as “the top of the ridge portion 22” in some cases) has a rounded, curved shape (for example, a vertically long, substantially elliptical shape), and bulges in the width direction (the X direction) of the ridge portion 22. In this manner, the surface of the reflection film 30 has a rounded, smoothly curved curvilinear shape, and does not have any angulated corner portion or stepped portion. A maximum width WMAX of the reflection film 30 covering and wrapping the top of the ridge portion 22 in this manner is more than or equal to the bottom width WB of the ridge portion 22. Further, WMAX preferably is larger than WB.
Herein, the maximum width WMAX of the reflection film 30 covering and wrapping the ridge portion 22 is a maximum horizontal width among horizontal widths of both-side outermost surfaces of the reflection film 30 in the width direction (the X direction) of the ridge portion 22. As shown in
The bottom width WB of the ridge portion 22 is the horizontal width of the ridge portion 22 (the width in the X direction) at a height position (a height in the Z direction) of 20% of the height H of the ridge portion 22 upward from the lowermost part of the ridge portion 22 (the upper surface of the base part 21) as shown in
In addition, the top width WT of the ridge portion 22 is a horizontal width of the ridge portion 22 (a width in the X direction) at a height position (a height in the Z direction) of 20% of the height H of the ridge portion 22 downward from the leading end 22a of the ridge portion 22 as shown in
Note that in the following description, a protruding structural body combining the ridge portion 22 and the reflection film 30 is referred to as a “grid portion” and the height of the protruding structural body (that is, the grid portion) combining the ridge portion 22 and the reflection film 30 is referred to as a “grid height” in some cases. In addition, the maximum width WMAX of the reflection film 30 covering and wrapping the ridge portion 22 is referred to as the “grid maximum width WMAX” and the bottom width WB of the ridge portion 22 is referred to as the “grid bottom width WB” in some cases. In addition, the top width WT of the ridge portion 22 is referred to as the “ridge portion top width WT” and the width of the ridge portion 22 at the central position in the height direction is referred to as a “ridge portion central width” in some cases.
In this manner, in the present embodiment, the horizontal width of the ridge portion 22 at the height position of 20% upward from the lowermost part (bottom) of the ridge portion 22 is used as the bottom width We of the ridge portion 22, and the horizontal width of the ridge portion 22 at the height position of 20% downward from the leading end 22a of the ridge portion 22 is used as the top width WT of the ridge portion 22. This is because the width of the lowermost part of the ridge portion 22 on the upper surface of the base part 21 and the width of the leading end 22a of the ridge portion 22 fluctuate significantly depending on manufacturing conditions of the grid structural body 20 and the like, and thus, these widths are difficult to measure precisely.
As described above, in the grid structural body 20 according to the present embodiment, the ridge portions 22 having the upward narrowing shape as well as the reflection film 30 covering and wrapping the leading end 22a and only the upper side of the side surfaces 22b of the ridge portion 22 are formed. Then, the lower side of the side surfaces 22b of the ridge portion 22 is open without being covered by the reflection film 30.
As a result, the sectional shape of the ridge portion 22 covered and wrapped by the curved reflection film 30 (that is, the sectional shape of the grid portion) has a special sectional shape as will be described below. In other words, as shown in
The grid portion of the grid structural body 20 of the polarizing element 1 according to the present embodiment has the special tree shape as described above. An effective grid width WA decreases and a gap width WG increases accordingly in a case where incident light is incident on the polarizing element 1 in an oblique direction as shown in
Hence, the gap width We for oblique incident light increases, and the oblique incident light is likely to pass through the gap between the rounded reflection films 30, 30 to reach the transparent grid structural body 20 to be transmitted because the grid portion of the polarizing element 1 according to the present embodiment has the above-described special tree shape. Consequently, the transmission axis transmittance Tp for oblique incident light is high, and thus, transmissivity for oblique incident light and the polarization splitting properties (Tp×Rs properties) are very excellent. Further, the reflective function for oblique incident light exerted by the reflection film 30 and the transmission function for oblique incident light exerted by the grid structural body 20 can be achieved in a balanced way, and the polarization splitting properties for oblique incident light can be improved further.
Herein, a method for forming the reflection film 30 will be described with reference to
As a method for forming the reflection film 30 such that the reflection film 30 covers the leading end 22a and part of both the side surfaces 22b of the ridge portion 22 of the grid structural body 20, the reflection film 30 preferably is formed by performing sputtering or vapor deposition alternately on the ridge portions 22 of the grid structural body 20 in an oblique direction (at a deposition incident angle ϕ) as shown in
In this manner, in the present embodiment, the reflection film 30 made of a metal material is formed by a sputtering or vapor deposition method after the grid structural body 20 made of a transparent material is formed. This enables the deposition conditions, material, and film thickness of the reflection film 30 to be easily modified. In addition, the case where the reflection film 30 is made of a multi-layer film can also be easily dealt with. Therefore, a film design through use of an interference effect can be made by combining metal, semiconductor, and dielectric, and it is not necessary to consider a material constitution that can be etched and the like when forming the reflection film 30 by etching as in the conventional technology. This also facilitates adjusting the reflectance for a polarization wave parallel to the grid structural body 20 and adjusting the transmittance (a transmitted amount) for polarized light in the direction perpendicular to the grid. In addition, depositing the reflection film 30 after forming the grid structural body 20 eliminates the need for a facility such as a vacuum dry etching device or the like, and eliminates the need for preparing gas, a safety device such as a pretreatment device, and the like in conformity to a complicated process and an etching material. Thus, running cost for facility investment, maintenance, and the like can be saved, so that a cost advantage can also be obtained.
Note that a thickness Dt of the reflection film 30 covering the leading end 22a of the ridge portion 22 and a thickness Ds of the reflection film 30 covering the side surfaces 22b of the ridge portion 22 shown in
In addition, the shape of the reflection film 30 is not particularly limited if it is a shape that can form the special tree shape described above, and can be selected as appropriate in accordance with conditions of a device for forming the reflection film 30 or performance required of the reflection film 30.
For example, a reflection film 30A shown in
In addition, a reflection film 30D covers the top of the substantially wedge-like ridge portion 22D in an enfolding manner, but is unevenly located on the side of one of the side surfaces 22b (the left side surface 22b shown in
Next, a suitable range of the coverage rate Rc of the side surface 22b of the ridge portion 22 obtained by the reflection film 30 according to the present embodiment will be described.
The coverage rate Rc preferably is more than or equal to 25% and less than or equal to 80%. Herein, the coverage rate Rc is a proportion of a height (Hx) of a portion of the side surfaces 22b of the ridge portion 22 covered by the reflection film 30 to the height (H) of the ridge portion 22 shown in
Rc[%]=(Hx/H)×100 (1)
In addition, an open rate Rr is a proportion of a height (H-Hx) of a portion of the side surfaces 22b of the ridge portion 22 that is not covered by the reflection film 30 to the height (H) of the ridge portion 22 shown in
Rr[%]=((H−Hx)/H)×100 (2)
From the above definitions, Rr=100-Rc holds. Thus, in the case where the coverage rate Rc of the side surfaces 22b of the ridge portion 22 obtained by the reflection film 30 is more than or equal to 25% and less than or equal to 80%, the open rate Rr of the side surfaces 22b of the ridge portion 22 obtained by the reflection film 30 is more than or equal to 20% and less than or equal to 75%.
As described above, in the polarizing element 1 according to the present embodiment, the coverage rate Rc of the side surfaces 22b of the ridge portion 22 obtained by the reflection film 30 preferably is more than or equal to 25% and less than or equal to 80% (that is, the open rate Rr is more than or equal to 20% and less than or equal to 75%). In detail, in the present embodiment, the reflection film 30 is formed to cover the leading end 22a and the upper side of both the side surfaces 22b of the ridge portion 22 and not to cover but open the lower side of both the side surfaces 22b. Then, the coverage rate Rc preferably is more than or equal to 25% and less than or equal to 80%, more preferably is more than or equal to 30% and less than or equal to 70%, and still more preferably is more than or equal to 40% and less than or equal to 50%.
Such a configuration enables the polarizing element 1 according to the present embodiment to exert sufficient transmissivity even for oblique incident light at a large incident angle θ (for example, 45 to 60°). For example, when oblique incident light is split by the polarizing element 1 into the s-polarized light (reflected light) and the p-polarized light (transmitted light), the transmittance Tp for the p-polarized light (transmitted light) transmitted through the polarizing element 1 can be maintained at a high value irrespective of the incident angle θ of the oblique incident light. In addition, setting the coverage rate Rc at more than or equal to 25% and less than or equal to 80% enables the reflection function obtained by the reflection film 30 described above to be more reliably exerted without depending on the incident angle θ while maintaining a contrast (CR=Tp/Ts) which is a ratio of the transmission axis transmittance (Tp) to transmission axis reflectance (Ts) at a favorable level. Consequently, high transmissivity for transmitted light can be ensured and the polarization splitting properties can be improved irrespective of the incident angle θ of oblique incident light.
In contrast to this, in a case where the reflection film 30 is formed to cover only the leading end 22a of the ridge portion 22 of the grid structural body 20 and in a case where the reflection film 30 is formed to cover the leading end 22a and the entirety of the side surface 22b on one side of the ridge portion 22 (for example, see
Thus, from the perspective of improving the transmissivity for transmitted light and the polarization splitting properties without depending on the incident angle θ of oblique incident light, the leading end 22a and part of at least one of the side surfaces 22b (the upper side of the side surface 22b) of the ridge portion 22 preferably are covered by the reflection film 30 as in the polarizing element 1 according to the present embodiment.
Further, from the perspective of the Tp×Rs properties required as the polarizing beam splitter (PBS), the coverage rate Rc of the side surfaces 22b of the ridge portion 22 obtained by the reflection film 30 preferably is more than or equal to 25% and less than or equal to 80% in the polarizing element 1 according to the present embodiment (for example, see
In a case where the coverage rate Rc is less than 25%, the transmission axis transmittance Tp for the p-polarized light transmitted through the polarizing element 1 decreases, and the transmittance Tp fluctuates depending on the incident angle θ, so that a sufficiently high value of Tp×Rs cannot be obtained. Therefore, sufficient transmissivity for transmitted light and the polarization splitting properties expressed as Tp×Rs cannot be obtained for oblique incident light at the large incident angle θ. On the other hand, in a case where the coverage rate Rc exceeds 80% (for example, see
Consequently, the coverage rate Rc of the side surfaces 22b of the ridge portion 22 obtained by the reflection film 30 preferably is more than or equal to 25% and less than or equal to 80% (for example, see
From a similar perspective, the coverage rate Rc more preferably is more than or equal to 30% and less than or equal to 70% (that is, the open rate Rr is more than or equal to 30% and less than or equal to 70%). High transmittance Tp of more than or equal to 80% can thereby be obtained in the case of the above-described oblique incident conditions, so that high Tp×Rs of more than or equal to 72% can be obtained. In addition, the coverage rate Rc more preferably is more than or equal to 30% and less than or equal to 60% (that is, the open rate Rr is more than or equal to 40% and less than or equal to 70%). High transmittance Tp of more than or equal to 83% can thereby be obtained in the case of the above-described oblique incident conditions, so that high Tp×Rs of more than or equal to 75% can be obtained. Further, the coverage rate Rc still more preferably is more than or equal to 40% and less than or equal to 50% (that is, the open rate Rr is more than or equal to 50% and less than or equal to 60%). Very high transmittance Tp of more than or equal to 85% can thereby be obtained in the case of the above-described oblique incident conditions, so that very high Tp×Rs of more than or equal to 77% can be obtained.
In addition, as to the reflection axis reflectance Rs, the coverage rate Rc preferably is more than or equal to 20%. High reflectance Rs of more than or equal to 85% is thereby obtained in the case of the above-described oblique incident conditions.
In addition, as to the contrast CR (CR=Tp/Ts) of the transmitted light, sufficient contrast CR is obtained if the coverage rate Rc is more than or equal to 20%. As the coverage rate Rc is higher, higher contrast CR is obtained.
Next, a suitable range of “Tp×Rs” which is an index representing the polarization splitting properties of the wire grid polarizing element 1 according to the present embodiment will be described.
Tp×Rs [%] represents the product of the transmission axis transmittance (Tp) and the reflection axis reflectance (Rs) in percentage. This Tp×Rs serves as the index representing the polarization splitting properties of the wire grid polarizing element 1.
Tp×Rs[%]=(Tp[%]/100)×(Rs[%]/100)×100
Note that as described above, the transmission axis transmittance (Tp) is the transmittance for the second polarized light (p-polarized light) having an electric field component parallel to the transmission axis (the X direction) of the polarizing element 1. The reflection axis reflectance (Rs) is the reflectance for the first polarized light (s-polarized light) having an electric field component parallel to the reflection axis (the Y direction) of the polarizing element 1.
In the case of splitting incident light into the s-polarized light and the p-polarized light using the wire grid polarizing element 1 according to the present embodiment as a polarizing beam splitter (see
The s-polarized light in the reflection axis direction mainly becomes reflected light reflected by the reflection film 30 of the polarizing element 1. The reflectance [%] for the s-polarized light at this time is the reflection axis reflectance (Rs). The reflection axis reflectance (Rs) represents the proportion of the s-polarized light reflected by the polarizing element 1 in the s-polarized light incident on the polarizing element 1. Note that reflection axis transmittance (Rp) represents the proportion of the s-polarized light transmitted through the polarizing element 1 in the s-polarized light incident on the polarizing element 1.
On the other hand, the p-polarized light in the transmission axis direction mainly becomes transmitted light transmitted through the grid structural body 20 and the substrate 10 of the polarizing element 1 which are transparent. The transmittance [%] for the p-polarized light at this time is the transmission axis transmittance (Tp). The transmission axis transmittance (Tp) represents the proportion of the p-polarized light transmitted through the polarizing element 1 in the p-polarized light incident on the polarizing element 1. Note that the transmission axis reflectance (Ts) represents the proportion of the p-polarized light reflected by the polarizing element 1 in the p-polarized light incident on the polarizing element 1.
Consequently, this means that as the transmission axis transmittance Tp is higher, the p-polarized light in the transmission axis direction can efficiently be transmitted. This also means that as the reflection axis reflectance Rs is higher, the s-polarized light in the reflection axis direction can efficiently be reflected. Thus, as the value of Tp×Rs which is the product of Tp and Rs is higher, both the transmissivity for the p-polarized light (transmitted light) and the reflectiveness for the s-polarized light (reflected light) will be high, so that the polarizing element 1 will be excellent in polarization splitting properties as the polarizing beam splitter.
Herein, the suitable range of the value of Tp×Rs according to the present embodiment will be described. A case where light having a wavelength in a predetermined range (for example, 430 to 680 nm) is incident on the polarizing element 1 according to the present embodiment at a predetermined incident angle θ (for example, 45°) in an oblique direction and the light is split into the p-polarized light (transmitted light) and the s-polarized light (reflected light) is considered. In the case of such oblique incident conditions, Tp×Rs preferably is more than or equal to 70% from the perspective of favorable polarization splitting properties of the polarizing element 1.
When Tp×Rs is less than 70%, a display device to which the polarizing element is applied has poor light utilization efficiency to be deficient in brightness of a displayed image and inferior in visibility. In contrast to this, when Tp×Rs is more than or equal to 70%, a display device to which the polarizing element 1 is applied can be increased in light utilization efficiency to ensure sufficient brightness of a displayed image and improve visibility.
Further, Tp×Rs more preferably is more than or equal to 72%, still more preferably is more than or equal to 75%, and particularly preferably is more than or equal to 80%. This enables the light utilization efficiency, the brightness of a displayed image, and the visibility as described above to be further improved.
In a case where incident light is incident on the polarizing element 1 according to the present embodiment at a relatively large incident angle θ (for example, 45°), the height H (see
Specifically, as to the transmittance, when the height H of the ridge portion 22 is more than or equal to 160 nm, the transmission axis transmittance Tp for oblique incident light becomes more than or equal to 80%, so that high transmittance is obtained. Further, when H is more than or equal to 180 nm. Tp of more than or equal to 85% is obtained, which is more preferable. In addition, when H is more than or equal to 220 nm, Tp of more than or equal to 87% is obtained, which is particularly preferable.
In addition, as to the Tp×Rs properties required as the polarizing beam splitter (PBS), when the height H of the ridge portion 22 is more than or equal to 160 nm, excellent Tp×Rs of more than or equal to 70% is obtained. Further, when H is more than or equal to 180 nm, Tp×Rs of more than or equal to 75% is obtained, which is more preferable. In addition, when H is more than or equal to 220 nm, Tp×Rs of more than or equal to 77% is obtained, which is particularly preferable.
In addition, as to the contrast CR (CR=Tp/Ts) of the transmitted light, the height H of the ridge portion 22 should only be more than or equal to 100 nm, and when H is more than or equal to 160 nm, excellent contrast CR of more than or equal to 150 is obtained. Further, when H is more than or equal to 180 nm, excellent CR of more than or equal to 250 is obtained, which is more preferable. In addition, when H is more than or equal to 220 nm, excellent CR of more than or equal to 500 is obtained, which is particularly preferable.
As described above, it is understood that in order to obtain favorable various properties (Tp, Tp×Rs, and CR), particularly Tp, of the polarizing element 1, the height H of the ridge portion 22 preferably is greater. The following is considered to be the reason for this. In other words, in a case where the deposition incident angle ϕ (see
In a case where incident light is incident on the polarizing element 1 according to the present embodiment at a relatively large incident angle θ (for example, 45°), the thickness Dt of the reflection film 30 (the leading end thickness Dt of the reflection film 30: see
When the leading end thickness Dt of the reflection film 30 is more than or equal to 5 nm, both the reflection axis reflectance Rs and the transmission axis transmittance Tp for oblique incident light become more than or equal to 85%, so that high transmittance is obtained. Further, in a case of considering Tp properties and the Tp×Rs properties required as the polarizing beam splitter, Dt more preferably is more than or equal to 15 nm.
In addition, the thickness Ds of the reflection film 30 (the side surface thickness Ds of the reflection film 30: see
Specifically, as to the transmittance, when the side surface thickness Ds of the reflection film 30 is more than or equal to 10 nm and less than or equal to 30 nm, the transmission axis transmittance Tp for oblique incident light becomes more than or equal to 80%, so that high transmittance is obtained. Further, when Ds is more than or equal to 12.5 nm and less than or equal to 25 nm. Tp of more than or equal to 85% is obtained, which is more preferable.
In addition, as to the reflectance, when the side surface thickness Ds of the reflection film 30 is more than or equal to 10 nm, the reflection axis reflectance Rs of oblique incident light becomes more than or equal to 80%, so that high reflectance is obtained. Further, when Ds is more than or equal to 12.5 nm, Rs of more than or equal to 85% is obtained, which is more preferable.
In addition, as to the Tp×Rs properties required as the polarizing beam splitter (PBS), when the side surface thickness Ds of the reflection film 30 is more than or equal to 12.5 nm and less than or equal to 30 nm, excellent Tp×Rs of more than or equal to 70% is obtained. Further, when Ds is more than or equal to 15 nm and less than or equal to 25 nm, Tp×Rs of more than or equal to 76% is obtained, which is more preferable.
In addition, as to the contrast CR (CR=Tp/Ts) of the transmitted light, the side surface thickness Ds of the reflection film 30 should only be more than or equal to 10 nm, and when Ds is more than or equal to 12.5 nm, excellent contrast CR of more than or equal to 50 is obtained. Further, when Ds is more than or equal to 15 nm, CR of more than or equal to 100 is obtained, which is more preferable.
In addition, in the polarizing element 1 according to the present embodiment, the reflection film 30 covering the ridge portion 22 may be unevenly located on one side of the ridge portion 22 to present a bilaterally asymmetric shape in the width direction (the X direction) of the ridge portion 22 (for example, see
In the case of unevenly locating the reflection film 30 on the one side of the ridge portion 22 in this manner, a difference between the transmission axis transmittance Tp (+) for incident light on the polarizing element 1 at an incident angle of +θ (+30° to +60°) and the transmission axis transmittance Tp (−) for incident light at an incident angle of −θ (−30° to −60°) preferably is within 3%. Then, the thickness Ds and the coverage rate Rc of the reflection film 30 covering each of the one of the side surfaces 22b and the other side surface 22b of the ridge portion 22 preferably are adjusted such that the difference between Tp (+) and Tp (−) falls within 3%, thereby unevenly locating the reflection film 30 on the one side of the ridge portion 22 in an appropriate manner.
Note that the incident angle of +θ means that oblique incident light is incident on the ridge portion 22 in a direction inclined to one side in the X direction (the width direction of the ridge portion 22). On the other hand, the incident angle of −θ means that oblique incident light is incident on the ridge portion 22 in a direction inclined to the other side in the X direction (for example, see
As described above, in the case of unevenly locating the reflection film 30 on the one side of the ridge portion 22, the difference between Tp (+) and Tp (−) preferably falls within 3%. This enables high transmission axis transmittance Tp, excellent Tp×Rs properties, and high contrast CR of transmitted light to be obtained even in the case where the reflection film 30 is unevenly located on the one side of the ridge portion 22.
Specifically, as to the transmittance, the transmission axis transmittance Tp for oblique incident light at the incident angles θ of +45° and −45° becomes more than or equal to 85% even in the case where the reflection film 30 is unevenly located on the one side, so that high transmittance is obtained.
In addition, as to the reflectance, the reflection axis reflectance Rs of oblique incident light at the incident angles θ of +45° and −45° becomes more than or equal to 85% even in the case where the reflection film 30 is unevenly located on the one side, so that high reflectance is obtained.
In addition, as to the Tp×Rs properties required as the polarizing beam splitter (PBS), Tp×Rs of oblique incident light at the incident angle θ of 45° becomes more than or equal to 75% even in the case where the reflection film 30 is unevenly located on the one side, so that excellent Tp×Rs properties are obtained.
In addition, as to the contrast CR (CR=Tp/Ts) of the transmitted light, excellent contrast CR is obtained even in the case where the reflection film 30 is unevenly located on the one side. Further, from the perspective of improving the contrast, of the thicknesses Ds of the reflection film 30 covering each of one of the side surfaces 22b and the other side surface 22b of the ridge portion 22, a thinner one of the thicknesses Ds preferably is more than or equal to 5 nm (the coverage rate Rc thereof is more than or equal to 22%), and the thinner one of the thicknesses Ds of the reflection film 30 more preferably is more than or equal to 10 nm (the coverage rate Rc thereof is more than or equal to 33%).
The polarizing element 1 according to the present embodiment can further include constituent members other than the substrate 10, the grid structural body 20, and the reflection film 30 described above.
For example, the polarizing element 1 preferably further includes the protection film 40 formed to cover at least the surface of the reflection film 30 as shown in
In addition, the protection film 40 more preferably further includes a water-repellent coating or an oleophobic coating. This can further increase the antifouling property and waterproofness of the polarizing element 1.
The material constituting the protection film 40 is not particularly limited if it can increase the abrasion resistance, antifouling property, and waterproofness of the polarizing element 1. Examples of the material constituting the protection film 40 include a film made of a dielectric material, and more specifically include inorganic oxides, silane-based water-repellent materials, and the like. Inorganic oxides include Si oxides, Hf oxides, and the like. Silane-based water-repellent materials may contain fluorinated silane compounds such as perfluorodecyltriethoxysilane (FDTS), or may contain non-fluorinated silane compounds such as octadecyl trichlorosilane (OTS).
Among these materials, the protection film 40 more preferably contains at least one of an inorganic oxide and a fluorinated water-repellent material. When the protection film 40 contains an inorganic oxide, the scratch resistance of the polarizing element can be increased further. When the protection film 40 contains a fluorinated water-repellent material, the antifouling property and waterproofness of the polarizing element can be increased further.
Note that the protection film 40 should only be formed to cover at least the surface of the reflection film 30, and more preferably is formed to cover the entire surfaces of the grid structural body 20 and the reflection film 30, as shown in
Further, the polarizing element 1 according to the present embodiment preferably is provided with a heat dissipation member 50 in a manner surrounding the substrate 10, as shown in
Next, an example of the polarizing element 1 according to the present embodiment actually produced and photographed under magnification using a scanning electron microscope (SEM) will be described with reference to
As shown in
Next, a method for manufacturing the wire grid polarizing element 1 according to the present embodiment will be described with reference to
As described above, the polarizing element 1 according to the present embodiment is the wire grid polarizing element 1 of the hybrid type made of an inorganic material (the substrate 10) and an organic material (the grid structural body 20). Hereinafter, the method for manufacturing the wire grid polarizing element 1 of the hybrid type will be described.
As shown in
Grid Structural Body Material Forming Step (S10)
First, in S10, a grid structural body material 23 made of a transparent organic material (for example, an ultraviolet curable resin or a thermosetting resin) is stacked on the substrate 10 made of a transparent inorganic material (for example, glass) by coating or the like. Note that various materials described above can be used as the inorganic material of the substrate 10. In addition, various materials described above can be used as the organic material of the grid structural body 20. Further, the film thickness of the grid structural body material 23 should only be adjusted as appropriate in accordance with the dimensions of the base part 21 and the ridge portions 22 of the grid structural body 20 formed by nano-imprinting in S20.
Nano-Imprinting Step (S12) and Grid Structural Body Forming Step (S14)
Then, the grid structural body material 23 is subjected to nano-imprinting in S12 to form the grid structural body 20 on the substrate 10 in S14. The grid structural body 20 is a micro concave-convex structural body in which the base part 21 provided on the substrate 10 and the plurality of ridge portions 22 protruding from the base part 21 are integrally formed. The micro concave-convex structural body is a structural body having micro convexities and concavities on the order of several nanometers to several tens of nanometers, for example.
In the nano-imprinting step in S12, a master 60 on which a reversed shape of the micro concave-convex shape of the grid structural body 20 has been formed is used to transfer the micro concave-convex shape of the master 60 to a surface of the grid structural body material 23 (S12). A concave-convex pattern composed of the base part 21, the ridge portions 22, and the concavities 24 described above are thereby formed on the grid structural body material 23. Further, in the nano-imprinting step, an energy beam is radiated to the grid structural body material 23 along with the transfer of the above-described concave-convex pattern to cure the grid structural body material 23 to which the concave-convex pattern has been transferred, thereby forming the grid structural body 20 (S14). For example, in the case where the grid structural body material 23 is made of an ultraviolet curable resin, the ultraviolet curable resin to which the concave-convex pattern has been transferred may be cured by radiating ultraviolet rays to the grid structural body material 23 using an ultraviolet radiation device 66. Alternatively, in the case where the grid structural body material 23 is made of a thermosetting resin, the thermosetting resin to which the concave-convex pattern has been transferred may be cured by heating the grid structural body material 23 using a heating device 68 such as a heater.
In the above-described steps S12 and S14, the ridge portions 22 each having the upward narrowing shape that narrows in width with distance from the base part 21 are formed as the ridge portions 22 of the grid structural body 20. The ridge portions 22 in the example of
In this manner, the present embodiment enables the master 60 to easily be peeled from the grid structural body material 23 because the ridge portions 22 each having the upward narrowing shape are imprinted in the nano-imprinting step S12, resulting in excellent mold releasability. In addition, the ridge portions 22 of the grid structural body 20 can be correctly molded into a desired shape without losing their shape.
Reflection Film Forming Step (S16)
Then, in S16, the reflection film 30 covering part of the ridge portion 22 of the grid structural body 20 is formed using a metal material such as Al or Ag. The reflection film 30 is an example of a functional film that provides the polarizing element 1 with a predetermined function. The reflection film 30 is a metal thin film (a grid of fine metal wires) for reflecting incident light incident on the grid structural body 20 of the polarizing element 1.
In this reflection film forming step S16, the reflection film 30 is formed as will be described below. In other words, the reflection film 30 is formed such that the reflection film 30 covers and wraps the leading end 22a and the upper side of at least one of the side surfaces 22b of the ridge portion 22 and does not cover the lower side of both the side surfaces 22b of the ridge portion 22 and the base part 21. Further, the reflection film 30 is formed such that the surface of the reflection film 30 covering and wrapping the ridge portion 22 is rounded and bulges in the width direction of the ridge portion 22. In addition, the reflection film 30 is formed such that the maximum width Wax (the grid maximum width WMAX) of the reflection film 30 covering and wrapping the ridge portion 22 is more than or equal to the aforementioned bottom width We (the grid bottom width WB) of the ridge portion.
As a method for forming this reflection film 30, the sputtering or vapor deposition method can be used as shown in
By forming the reflection film 30 in this manner, the ridge portion 22 of the grid structural body 20 and the reflection film 30 become to have the special tree shape described above. Even in the case where light is incident on the polarizing element 1 in an oblique direction at a relatively large and wide-range incident angle θ (for example, 30 to 60°) as described earlier, the transmission axis transmittance Tp for the p-polarized light included in the oblique incident light can thereby be maintained at a high value, so that the transmissivity for the p-polarized light (transmitted light) can be ensured. Thus, the value of Tp×Rs can be maintained at a high value (for example, more than or equal to 70%), which can improve the polarization splitting properties of the polarizing element 1 for oblique incident light.
Note that the method for manufacturing the polarizing element 1 according to the present embodiment may include a step (a protection film forming step) of forming the protection film 40 that covers the surface of the polarizing element 1 according to necessity after the reflection film forming step S16 shown in
The method for manufacturing the polarizing element 1 according to the present embodiment has been described above. Use of the steps described above enables the polarizing element 1 excellent in polarization properties and heat dissipation to be manufactured without causing elevated manufacturing cost and complicated manufacturing of the polarizing element 1.
Herein, a conventional method for manufacturing a wire grid polarizing element will be briefly described with reference to
As shown in
Then, a resist mask 70 is patterned on the metal film 80 using the photolithography technology (S22). Thereafter, the metal film 80 is subjected to etching using a vacuum dry etching device or the like to form a convex shape made of the metal film 80 (S24). For example, in a case where an etch selectivity between the resist mask 70 and the metal film 80 cannot be achieved at this time, an oxide film of SiO2 or the like is further deposited on the metal film 80 by sputtering or the like, and the resist mask 70 is formed thereon by the photolithography technology. Thereafter, the resist mask 70 is peeled from the metal film 880 (S26), then, the protection film 40 made of an SiO2 film or the like is deposited by CVD or the like, and water repellent/oleophobic coating treatment is also performed according to necessity (S28).
Note that although a process of producing a reflection-type wire grid polarizing element having a basic configuration is shown in steps S20 to S28 of the above-described conventional manufacturing method, a further complicated process is required when considering a case where the metal film 80 is a multi-layer film. Thus, the conventional wire grid polarizing element produced by the process as shown in S20 to S28 of
In contrast to this, by molding the grid structural body 20 using an imprinting technology such as nano-imprinting, the method for manufacturing the polarizing element 1 according to the present embodiment (see
The method for manufacturing the polarizing element 1 according to the present embodiment is not particularly limited in nano-imprinting conditions while the grid structural body material 23 is subjected to nano-imprinting (S12 in
Note that the master 60 used in the nano-imprinting step S12 (
As shown in
Thereafter, the resist mask 70 is peeled from the master metal film 62, thereby obtaining the master 60 (S36). The master 60 has a micro concave-convex structure composed of a plurality of the convexities 63 and concave grooves 65 molded on the master base material 61. The micro concave-convex structure on the surface of the master 60 has an inverted shape of the micro concave-convex structure on the surface of the above-described grid structural body 20 of the polarizing element 1. The concave groove 65 in the master 60 has an inverted shape of the ridge portion 22 of the grid structural body 20, and the convexity 63 of the master 60 has an inverted shape of the concavity 24 between the ridge portions 22, 22 of the grid structural body 20.
Further, the manufacturing method according to the present embodiment may include a step of forming a release film coating 64 on the surface of the micro concave-convex structure of the master 60 according to necessity (S38). By providing the release film coating 64 on the surface of the master 60, the master 60 can easily be peeled from the grid structural body material 23 after subjecting the grid structural body material 23 to nano-imprinting in the nano-imprinting step (S12) shown in
Next, a projection display device to which the wire grid polarizing element 1 according to the present embodiment is applied will be described with reference to
The projection display device according to the present embodiment includes the wire grid polarizing element 1 according to the present embodiment described above. When the projection display device according to the present embodiment includes the polarizing element 1, excellent polarization properties as well as heat tolerance and heat dissipation of the polarizing element 1, and the like can be achieved.
Herein, the projection display device is a device that projects light toward a target, and radiates the light having been projected (projected light) to a to-be-displayed surface (projection surface) of the target, thereby displaying a virtual image such as an image or video. Examples of types of projection display devices include ahead-up display device (HUD), a projector device, and the like.
First, a head-up display device 100 including the wire grid polarizing element 1 according to the present embodiment will be described with reference to
As shown in
As shown in
Herein, the head-up display device 100 may be a vehicle head-up display device provided for a vehicle. The vehicle head-up display device displays video on a semi-transmissive plate (equivalent to “the display surface 5”) such as a front glass or a combiner of the vehicle. The vehicle head-up display device is, for example, a video display device disposed on the dashboard of the vehicle to project video light to the front glass (the display surface 5) and display driving information as a virtual image.
The head-up display device 100 is configured to output a displayed image toward the front glass surface (the display surface 5) from below. Therefore, solar light enters the head-up display device 100 oppositely to the output direction of the displayed image and is incident on the display element 3 in some cases. The head-up display device 100 according to the present embodiment is provided with the reflector 4 for reflecting and magnifying a displayed image for the purpose of meeting the request for size reduction and magnifying the displayed image. In such a case, in the conventional head-up display device, solar light incident on the reflector from the outside concentrates on the vicinity of the display element, which might cause degradation or failure of the display element by heat.
In contrast to this, the head-up display device 100 according to the present embodiment is provided with the polarizing element 1 of the hybrid type excellent in heat dissipation and heat tolerance as described above for the purpose of preventing solar light from being incident on the display element 3. This polarizing element 1 can stably exert the polarizing function even at a high temperature of approximately 200° C., for example. Consequently, even under a high-temperature environment such as the inside of a vehicle in the summer, for example, solar light incident on the reflector 4 from the outside can be shielded by the polarizing element 1 to be prevented from reaching the display element 3. This can restrain degradation or failure of the display element 3.
Note that the constituent members of the head-up display device 100 shown in
In addition, by using the polarizing element 1 as a pre-polarizing plate arranged in front of the display element 3, the polarizing element 1 can restrain solar light from being incident on the display element 3 while transmitting a displayed image output from the display element 3. Consequently, heat tolerance and durability of the head-up display device 100 can be increased further.
In addition, the arrangement of the wire grid polarizing element in the projection display device is not limited to the example of arrangement of the polarizing element 1 in the head-up display device 100 shown in
In addition, the heat dissipation member 50 (see
Next, a projection display device in which the reflection-type wire grid polarizing element 1 according to the present embodiment is used as a polarizing beam splitter 230 will be described with reference to
As shown in
The light source 210 may be a point light source having a single light emitting unit, or may be a light source having a plurality of light emitting units such as LEDs. In addition, light output from the light source 210 may be parallel light, or may be diffused light. Consequently, light of the light source 210 is incident in some cases on the polarizing beam splitter 230 (a reflection-type wire grid polarizing plate) at the incident angle θ in a predetermined range (for example, a range of 45°±15°) centering on 45°, for example.
The PS converter 220 is a polarization conversion element for converting light from the light source 210 into specific polarized light (for example, the p-polarized light or the s-polarized light). The PS converter 220 may convert light from the light source 210 into the p-polarized light or into the s-polarized light.
The polarizing beam splitter 230 is implemented by the reflection-type wire grid polarizing plate. The reflection-type wire grid polarizing plate is an example of the wire grid polarizing element 1 according to the present embodiment. The polarizing beam splitter 230 is arranged such that light from the light source 210 is incident at the incident angle θ in the predetermined range including 45°. This incident angle θ in the predetermined range is, for example, 45°±15° described above, that is, more than or equal to 30° and less than or equal to 60°.
For example, in
The polarizing beam splitter 230 splits incident light into the first polarized light (s-polarized light) and the second polarized light (p-polarized light). For example, the polarizing beam splitter 230 may split the incident light into the s-polarized light and the p-polarized light by reflecting the first polarized light (s-polarized light) in the incident light and transmitting the second polarized light (p-polarized light). To the contrary, the polarizing beam splitter 230 may split the incident light into the s-polarized light and the p-polarized light by reflecting the second polarized light (p-polarized light) in the incident light and transmitting the first polarized light (s-polarized light).
In a case where desired polarized light is reflected by the polarizing beam splitter 230, the polarizing beam splitter 230 is arranged such that light including the polarized light to be reflected is incident on the surface of the polarizing beam splitter 230 (that is, the concave-convex surface on the side where the grid structural body 20 of the polarizing element 1 is formed). For example, in the case where the s-polarized light incident from the PS converter 220 is reflected by the polarizing beam splitter 230 as shown in
The reflection-type liquid crystal display element 240 is a display element that reflects incident light to output light representing a displayed image. As shown in
In addition, the reflection-type liquid crystal display element 240 reflects and modulates the incident first polarized light (s-polarized light) to output the second polarized light (p-polarized light) representing a displayed image as shown in
The lens 250 magnifies light representing a displayed image output from the reflection-type liquid crystal display element 240 for output to the outside. The lens 250 is arranged such that the light representing a displayed image output from the reflection-type liquid crystal display element 240 is incident through the polarizing beam splitter 230. For example, as shown in
As described above, the projection display device 200 according to the present embodiment uses the aforementioned wire grid polarizing element 1 according to the present embodiment as the polarizing beam splitter 230. Consequently, the polarizing beam splitter 230 is excellent in reflectiveness for the s-polarized light, transmissivity for the p-polarized light, and the Tp×Rs properties for oblique incident light at the incident angle θ in a relatively large and wide range (for example, 30 to 60°), and excellent in properties of splitting the oblique incident light into the p-polarized light and the s-polarized light.
Next, the respective specific examples of the projection display devices 200A, 200B, and 200 (shown in
As shown in
Light output from the light source 210 is unpolarized light, and the light includes a p-polarized light component and an s-polarized light component in an identical proportion. Therefore, when only one of the polarized lights is selected and extracted by the polarizing beam splitter 230 implemented by the polarizing element 1, the light volume will decrease to about a half. Thus, the light output from the light source 210 is converted by the PS converter 220 into either the first polarized light (s-polarized light) or the second polarized light (p-polarized light). This can restrain the light volume of polarized light extracted by the polarizing beam splitter 230 from decreasing to improve the light use efficiency. For example, the PS converter 220 shown in
The light converted by the PS converter 220 into the s-polarized light is incident on the polarizing beam splitter 230 arranged at an inclination obliquely at approximately 45°. The polarizing beam splitter 230 reflects the first polarized light (s-polarized light) for output toward the reflection-type liquid crystal display element 240 at an output angle of 45°. The reflection-type liquid crystal display element 240 modulates and reflects the first polarized light (s-polarized light) to generate the second polarized light (p-polarized light) representing a displayed image, and outputs the second polarized light (p-polarized light) toward the polarizing beam splitter 230. The second polarized light (p-polarized light) is transmitted through the polarizing beam splitter 230, magnified by the lens 250, and then projected on the display surface not shown, so that the displayed image is displayed.
The projection display device 200A having the above configuration includes a reflection-type wire grid polarizing plate implemented by the wire grid polarizing element 1 according to the present embodiment as the polarizing beam splitter 230. This can improve the polarization splitting properties of the polarizing beam splitter 230 for oblique incident light and incident light at the wide incident angle θ, and can improve heat dissipation and heat tolerance of the polarizing beam splitter 230 and the projection display device 200A.
In contrast to this, a projection display device (not shown) including a conventional polarizing element as a polarizing beam splitter is inferior in heat dissipation of the polarizing element. Therefore, it is considered that heat tolerance is not sufficient from the perspectives of a long-term use and response to increase in luminance and magnified display. In addition, the incident angle θ of light incident on the polarizing beam splitter is not only 45°, but also every angle within a predetermined range (for example, approximately 45°±15°) centering on 45°. In this manner, even in the case where oblique incident light at the large and wide-range incident angle θ is incident on the polarizing beam splitter, the polarizing beam splitter is required to have performance capable of suitably splitting oblique incident light into the s-polarized light and the p-polarized light irrespective of the incident angle θ. However, the polarizing beam splitter including the conventional polarizing element raises problems of deterioration of the light utilization efficiency and an adverse influence on the image quality of the displayed image, such as uneven luminance, because of poor polarization splitting properties for the above-described oblique incident light.
In this respect, the polarizing beam splitter 230 of the projection display device 200A according to the first specific example of the present embodiment is superior in polarization splitting properties for oblique incident light at the large and wide-range incident angle θ as described above. Consequently, the light utilization efficiency can be improved in the projection display device 200A, and uneven luminance and the like can be reduced to improve the image quality of the displayed image.
In addition, the projection display device is not limited to the example of the projection display device 200A shown in
As shown in
In the projection display device 200B, the PS converter 220 converts light from the light source 210 into the second polarized light (p-polarized light). The light converted by the PS converter 220 into the p-polarized light is transmitted through the polarizing beam splitter 230 arranged at an inclination obliquely at approximately 45° to be incident on the reflection-type liquid crystal display element 240. The reflection-type liquid crystal display element 240 modulates and reflects the second polarized light (p-polarized light) to generate the first polarized light (s-polarized light) representing a displayed image, and outputs the first polarized light (s-polarized light) toward the polarizing beam splitter 230. The polarizing beam splitter 230 reflects the first polarized light (s-polarized light) for output toward the lens 25 at the output angle of 45°. The first polarized light (s-polarized light) is magnified by the lens 250 and then projected on the display surface not shown, so that the displayed image is displayed.
The projection display device 200B having the above configuration is excellent in polarization splitting properties for oblique incident light, the light utilization efficiency can be improved, and uneven luminance and the like can be reduced to improve the image quality of the displayed image, similarly to the projection display device 200A described above (see
In addition, as shown in
In the projection display device 200C, unpolarized light output from the light source 210 is directly incident on the polarizing beam splitter 230 arranged at an inclination obliquely at approximately 45°. The polarizing beam splitter 230 reflects a component of the first polarized light (s-polarized light) in unpolarized light for output toward the reflection-type liquid crystal display element 240 at the output angle of 45°. On the other hand, in the unpolarized light incident on the polarizing beam splitter 230, a component of the second polarized light (p-polarized light) is transmitted through the polarizing beam splitter 230 to be incident on the light absorber 260. Most of this component of the second polarized light (p-polarized light) is absorbed into the light absorber 260. This can restrain the unnecessary second polarized light (p-polarized light) from being incident on another optical system in the projection display device 200C.
The reflection-type liquid crystal display element 240 modulates and reflects the component of the first polarized light (s-polarized light) incident from the polarizing beam splitter 230 to generate the second polarized light (p-polarized light) representing a displayed image, and outputs the second polarized light (p-polarized light) toward the polarizing beam splitter 230. The second polarized light (p-polarized light) is transmitted through the polarizing beam splitter 230, magnified by the lens 250, and then projected on the display surface not shown, so that the displayed image is displayed.
Because the PS converter 220 is not installed in the projection display device 200C having the above configuration, the component of the second polarized light (p-polarized light) in the unpolarized light output from the light source 210 is absorbed into the light absorber 260 and is not utilized for displaying the displayed image. Therefore, the light volume of the displayed image is reduced to about a half. However, cost and installation space required for the PS converter 220 can be saved, and the number of parts of the projection display device 200C can be reduced. This brings about advantages that the projection display device 200C can be reduced in cost and the projection display device 200C can be reduced in size.
The specific examples of the projection display device 200 in which the reflection-type wire grid polarizing element 1 according to the present embodiment is used as the polarizing beam splitter 230 have been described above. Note that the projection display device is not limited to the specific examples of the projection display device 200 shown in
Next, a vehicle including the video display device according to the present embodiment will be described.
The vehicle (not shown) according to the present embodiment includes the projection display device having the wire grid polarizing element 1 according to the present embodiment described above. Note that the vehicle may be various automobiles such as a standard motor vehicle, a light motor vehicle, a bus, a truck, a racing car, a construction-use vehicle, and other large-sized vehicles, for example, or besides may be various rides such as a two-wheeled motor vehicle, a train, a linear motor car, and an attraction vehicle if it is a vehicle in which the projection display device can be installed.
The vehicle according to the present embodiment can project and display a displayed image on a display surface (for example, the display surface 5 shown in
The projection display device provided for the vehicle according to the present embodiment is, for example, the head-up display device 100 shown in
As described above, in the head-up display device 100, solar light is transmitted through the front glass (the display surface 5) from the outside of the vehicle to enter the head-up display device 100 in some cases, as shown in
Similarly, even in the case where the projection display device 200 shown in
In the projection display device provided in the vehicle according to the present embodiment as described above, excellent polarization properties (such as solar light shielding performance and polarization splitting properties) are obtained by the polarizing element 1, and excellent heat tolerance and durability of the projection display device can also be achieved.
Note that the vehicle is not particularly limited if it includes the projection display device and the polarizing element described above, and other conditions can be set and modified as appropriate in accordance with performance required of the vehicle.
Next, examples of the present invention will be described. However, the examples which will be described below are specific examples illustrated for describing the configuration, effects, and the like of the polarizing element 1 according to the present embodiment described above, and the present invention is not limited to the following examples.
As the examples of the present invention, models of the wire grid polarizing element 1 according to the present embodiment described above were produced, and their various properties were simulated to evaluate the wire grid polarizing element 1. In addition, for comparison with the examples of the present invention, models of a wire grid polarizing element according to conventional examples were created, and simulation and evaluation were performed similarly. Note that hereinafter, reference characters representing the constituent members (such as the substrate 10, the grid structural body 20, the base part 21, the ridge portions 22, and the reflection film 30) of the polarizing element and notations representing various dimensions of these constituent members are denoted by identical reference characters and notations both in the examples and the conventional examples for convenience of description.
Note that notations representing various dimensions and the like of the polarizing element 1 which will be used in the following description are described below.
First, Conventional Example 1 will be described with reference to
As shown in
The respective portions of the model of the polarizing element 1 according to Conventional Example 1 had the following dimensions and shapes.
Thereafter, simulation was performed for the model of the polarizing element 1 according to Conventional Example 1 produced as described above while changing the incident angle θ to calculate the transmission axis transmittance (Tp), the reflection axis reflectance (Rs), and Tp×Rs required as the polarizing beam splitter (PBS), respectively. The incident angle θ was set at 0° to +60°. Note that the wavelength λ of incident light was changed in a range of 430 to 680 nm, and average values of a plurality of values of Tp and Rs calculated for incident light having each of the wavelengths λ were used as the values of Tp and Rs. A relationship between each of Tp, Rs, and Tp×Rs calculated as described above and θ is shown in each of graphs of
In Conventional Example 1, the reflection film 30 was unevenly located on one side of the ridge portion 22 and the coverage rate Rc of the one side was 100% as shown in
Next, Conventional Example 2 will be described with reference to
As shown in
The respective portions of the model of the polarizing element 1 according to Conventional Example 2 had the following dimensions and shapes.
Thereafter, simulation was performed for the model of the polarizing element 1 according to Conventional Example 2 produced as described above while changing the incident angle θ to calculate the transmission axis transmittance (Tp), the reflection axis reflectance (Rs), and Tp×Rs required as the polarizing beam splitter (PBS), respectively. On this occasion, Tp, Rs, and Tp×Rs were calculated for each of the case where the incident angle θ is in the positive direction and the case where the incident angle θ is in the negative direction. Note that the wavelength k of incident light was changed in the range of 430 to 680 nm, and average values of a plurality of values of Tp and Rs calculated for incident light having each of the wavelengths were used as the values of Tp and Rs. A relationship between each of Tp, Rs, and Tp×Rs calculated as described above and θ is shown in each of graphs of
As shown in
Specifically, in Conventional Example 2, the difference between Tp (+) and Tp (−) was more than or equal to 5% and the difference between Tp×Rs (+) and Tp×Rs (−) was more than or equal to 4% in the range where the absolute value of θ was 30° to 60°. It was confirmed from this result that in Conventional Example 2, bilateral asymmetry was present in the polarization properties of the polarizing element 1 depending on whether the incident direction of oblique incident light was the positive direction or the negative direction.
It is understood that problems arose in that when the difference in Tp due to the difference in incident direction of oblique incident light (for example, the difference between +45° and −45°) increased as in Conventional Example 2 above, the difference in brightness of a displayed image was recognizable to an observer, and a video state became inappropriate. In addition, it is understood that in the case of using the polarizing element 1 according to Conventional Example 2 as the polarizing beam splitter, problems arose in that the polarization splitting properties (the Tp×Rs properties) were poor for oblique incident light particularly at the large incident angle θ of more than or equal to 45°, so that the Tp×Rs properties required of the polarizing beam splitter failed to be obtained.
Next, Conventional Example 3 will be described with reference to
As shown in
The respective portions of the model of the polarizing element 1 according to Conventional Example 3 had the following dimensions and shapes.
Thereafter, simulation was performed for the model of the polarizing element 1 according to Conventional Example 3 produced as described above while changing the incident angle θ to calculate Tp, Rs, and Tp×Rs, respectively, similarly to Conventional Example 1 described above. The incident angle θ was set at 0° to +60°. A relationship between each of Tp, Rs, and Tp×Rs calculated in this manner and θ is shown in each of graphs of
As shown in
Next, Example 1 of the present invention will be described with reference to
As shown in
The reflection film 30 covering the ridge portions 22 of Example 1 was an Al film. The reflection film 30 was formed to cover the leading end 22a and the upper side of both the side surfaces 22b of the ridge portion 22. However, the reflection film 30 did not cover the lower side of both the side surfaces 22b of the ridge portion 22 and the base part 21. The coverage rate Rc of both the side surfaces 22b of the ridge portion 22 obtained by the reflection film 30 was 40%. In this manner, the reflection film 30 of Example 1 roundly covered and wrapped the top of the ridge portion 22 (the leading end 22a and the upper side of the side surfaces 22b). The surface of the reflection film 30 had a substantially elliptical shape having such roundness that expanded to the outside, and bulged in the width direction (the X direction) of the ridge portion 22.
As a result, the grid portion (the structural body combining the ridge portion 22 and the reflection film 30) according to Example 1 had the special tree shape described above. The grid maximum width WMAX of the special tree shape (the width of the grid at a portion where the reflection film 30 bulged most) was more than or equal to the bottom width WB of the ridge portion 22 (the width of the ridge portion 22 at a height position of 20% upward from the bottom of the ridge portion 22).
The respective portions of the model of the polarizing element 1 according to Example 1 had the following dimensions and shapes.
Thereafter, simulation was performed for the model of the polarizing element 1 according to Example 1 produced as described above while changing the incident angle θ to calculate the transmission axis transmittance (Tp), the transmission axis reflectance (Ts), the reflection axis transmittance (Rp), the reflection axis reflectance (Rs), and Tp×Rs required as the polarizing beam splitter (PBS), respectively. The incident angle θ was set at 0° to +60°. Note that the wavelength λ of incident light was changed in the range of 430 to 680 nm, and average values of a plurality of values of Tp, Ts, Rp, and Rs calculated for incident light having each of the wavelengths λ were used as values of Tp, Rs, Ts, and Rp. In addition, by dividing the transmission axis transmittance (Tp) by the transmission axis reflectance (Ts), the contrast (CR) (CR=Tp/Ts) of transmitted light was also calculated.
A relationship between each of Tp, Rs, Ts, Rp, CR, and Tp×Rs calculated as described above and λ is shown in a table of
Note that the table of
As shown in
Consequently, it is understood that in Example 1. Tp was more than or equal to 80% and Rs was more than or equal to 90% irrespective of the wavelength λ as shown in
Further, as shown in
Further, as is understood from the result of comparison between Example 1 and Conventional Example 2 shown in
In addition, as to the reflection axis reflectance Rs, Example 1 was able to obtain high reflectance having no significant difference from Conventional Examples 1 and 2.
In addition, as to the Tp×Rs properties required as the polarizing beam splitter (PBS), Example 1 was superior to Conventional Examples 1 and 2, and the highest Tp×Rs properties were obtained in the case where the incident angle θ=45°. In addition, also in the range where the incident angle θ=30° to 60°, Example 1 was able to obtain more favorable properties than in Conventional Examples 1 and 2, and was superior to Conventional Examples 1 and 2 in the Tp×Rs properties for oblique incident light at the incident angle θ in the large and wide range. Further, in Example 1, the Tp×Rs properties were in good balance for oblique incident light at the incident angle θ in the range of 45° 15°. Therefore, in a case of projecting an image using the polarizing element 1 according to Example 1 as the polarizing beam splitter, the brightness of the displayed image is in good balance when seen from the observer, and the video state also becomes favorable.
In this manner, it is understood that in the case of using the polarizing element 1 according to Example 1 as the polarizing beam splitter, the transmissivity (transmittance Tp) for the p-polarized light and the polarization splitting properties (the Tp×Rs properties) were significantly excellent for oblique incident light at the incident angle θ in the large and wide range of 30° to 60°, particularly for oblique incident light at 45°. Thus, it can be said that the polarization splitting properties required of the polarizing beam splitter were able to be sufficiently satisfied for the oblique incident light.
In addition, as to the contrast CR (CR=Tp/Ts) of transmitted light, it is understood that excellent contrast CR of more than or equal to 100 was obtained in Example 1.
Next, Example 2 of the present invention will be described with reference to
As shown in
The reflection film 30 covering the ridge portions 22 of Example 2 was an Al film. The reflection film 30 was formed to cover the leading end 22a and the upper side of both the side surfaces 22b of the ridge portion 22. However, the reflection film 30 did not cover the lower side of both the side surfaces 22b of the ridge portion 22 and the base part 21. The coverage rate Rc of both the side surfaces 22b of the ridge portion 22 obtained by the reflection film 30 was 45%. In this manner, the reflection film 30 of Example 2 roundly covered and wrapped the top of the ridge portion 22 (the leading end 22a and the upper side of the side surfaces 22b). The surface of the reflection film 30 had a substantially elliptical shape having such roundness that expanded to the outside, and bulged in the width direction (the X direction) of the ridge portion 22. In this manner, the grid portion (the structural body combining the ridge portion 22 and the reflection film 30) according to Example 2 had the special tree shape described above similarly to the grid portion of Example 1.
The respective portions of the model of the polarizing element 1 according to Example 2 had the following dimensions and shapes.
Thereafter, simulation was performed for the model of the polarizing element 1 according to Example 2 produced as described above while changing the incident angle θ to calculate the transmission axis transmittance (Tp), the reflection axis reflectance (Rs), and Tp×Rs required as the polarizing beam splitter (PBS), respectively. Note that the wavelength λ of incident light was changed in the range of 430 to 680 nm, and average values of a plurality of values of Tp and Rs calculated for incident light having each of the wavelengths were used as the values of Tp and Rs. A relationship between each of Tp, Rs, and Tp×Rs calculated as described above and θ is shown in each of graphs of
As shown in
Consequently, as shown in
It is understood that even in the case where the shape of the ridge portion 22 of the grid structural body 20 was different from that of Example 1 as in Example 2 described above, favorable transmissivity and polarization splitting properties as compared with Conventional Examples 1 to 3 were able to be obtained. However, in a case where the incident angle θ was 60°, Example 1 was superior to Example 2 in Tp and Tp×Rs properties.
Next, Example 3 of the present invention will be described with reference to
As shown in
The respective portions of the model of the polarizing element 1 according to Example 3 had the following dimensions and shapes.
Thereafter, simulation was performed for the model of the polarizing element 1 according to Example 3 produced as described above while changing the height H of the ridge portion 22 to calculate Tp, Rs, and Tp×Rs, respectively. The incident angle θ was set at +45°. Note that the wavelength λ, of incident light was changed in the range of 430 to 680 nm, and average values of a plurality of values of Tp and Rs calculated for incident light having each of the wavelengths λ were used as the values of Tp and Rs. In addition, the contrast CR of transmitted light was also calculated by dividing Tp by Ts.
A relationship between each of Tp, Rs, Tp×Rs, and CR calculated as described above and H is shown in each of graphs of
As shown in
Specifically, as to Tp, when H was more than or equal to 160 nm. Tp was more than or equal to 80% as shown in
In addition, as to the Tp×Rs properties, when H was more than or equal to 160 nm, excellent Tp×Rs of more than or equal to 70% was obtained as shown in
In addition, as to the contrast CR, H should only be more than or equal to 100 nm as shown in
Next, Example 4 of the present invention will be described with reference to
As shown in
The respective portions of the model of the polarizing element 1 according to Example 4 had the following dimensions and shapes.
Thereafter, simulation was performed for the model of the polarizing element 1 according to Example 4 produced as described above while changing the leading end thickness Dt of the reflection film 30 to calculate Tp, Rs, Tp×Rs, and CR, respectively. The incident angle θ was set at +45°. A relationship between each of Tp, Rs, Tp×Rs, and CR calculated as described above and Dt is shown in each of graphs of
As shown in
Specifically, as to Tp, when Dt was more than or equal to 5 nm, Tp was more than or equal to 85% as shown in
In addition, as to the Tp×Rs properties, when Dt was more than or equal to 15 nm, excellent Tp×Rs of more than or equal to 78% was obtained as shown in
In addition, as to the contrast CR, when Dt was more than or equal to 5 nm, excellent CR of more than or equal to 100 was obtained as shown in
Next, Example 5 of the present invention will be described with reference to
As shown in
The respective portions of the model of the polarizing element 1 according to Example 5 had the following dimensions and shapes.
Thereafter, simulation was performed for the model of the polarizing element 1 according to Example 5 produced as described above while changing the side surface thickness Ds of the reflection film 30 to calculate Tp, Rs, Tp×Rs, and CR, respectively. The incident angle θ was set at +45°. A relationship between each of Tp, Rs, Tp×Rs, and CR calculated as described above and Dt is shown in each of graphs of
As shown in
Specifically, as to Tp, when Ds was more than or equal to 10 nm and less than or equal to 30 nm, Tp was more than or equal to 80% as shown in
In addition, as to Rs, when Ds was more than or equal to 10 nm, Rs was more than or equal to 80% as shown in
In addition, as to the Tp×Rs properties, when Ds was more than or equal to 12.5 nm and less than or equal to 30 nm, excellent Tp×Rs of more than or equal to 70% was obtained as shown in
In addition, as to the contrast CR. Ds should only be more than or equal to 10 nm, and when Ds was more than or equal to 12.5 nm, excellent CR of more than or equal to 50 was obtained as shown in
Next, Example 6 of the present invention will be described with reference to FIG. 27. In Example 6, a relationship between the coverage rate Rc of the side surfaces 22b of the ridge portion 22 obtained by the reflection film 30 and the polarization properties of the polarizing element 1 was inspected.
As shown in
The respective portions of the model of the polarizing element 1 according to Example 6 had the following dimensions and shapes.
Thereafter, simulation was performed for the model of the polarizing element 1 according to Example 6 produced as described above while changing the coverage rate Rc to calculate Tp, Rs, Tp×Rs, and CR, respectively. The incident angle θ was set at +45°. A relationship between each of Tp, Rs, Tp×Rs, and CR calculated as described above and Dt is shown in each of graphs of
As shown in
Specifically, as to Tp, when Rc was more than or equal to 25% and less than or equal to 80%, Tp was more than or equal to 75% as shown in
In addition, as to Rs, when Rc was more than or equal to 20%, Rs was more than or equal to 85% as shown in
In addition, as to the Tp×Rs properties, when Rc was more than or equal to 25% and less than or equal to 80%, Tp×Rs was more than or equal to 70% as shown in
In addition, as to the contrast CR, Rc should only be more than or equal to 20% as shown in
Next, Example 7 of the present invention will be described with reference to
As shown in
The respective portions of the model of the polarizing element 1 according to Example 7 had the following dimensions and shapes.
Thereafter, simulation was performed for the model of the polarizing element 1 according to Example 7 produced as described above while changing the side surface thickness Ds of the reflection film 30 and the incident angle θ to calculate Tp, Rs, and Tp×Rs, respectively. The incident angle θ was changed stepwise every 150 in the range of 0 to +600. A relationship between each of Tp, Rs, and Tp×Rs calculated as described above and Dt is shown in each of graphs of
As shown in
Specifically, as to Tp, when θ fell within the range of +30° to +60° even when Ds was changed in the range of 17.5 to 25 nm, Tp was more than or equal to 75% as shown in
In addition, as to Rs, Rs was more than or equal to 85% in the range of the wide incident angle θ of 0° to +60° as shown in
In addition, as to the Tp×Rs properties, when θ fell within the range of +30° to +60° even when Ds was changed in the range of 17.5 to 25 nm, Tp×Rs was more than or equal to 70% as shown in
Next, Example 8 of the present invention will be described with reference to
As shown in
In Example 8, as to the left side surface 22b of the ridge portion 22, the side surface thickness Ds (left side) of the reflection film 30 covering the side surface 22b was fixed at 22.5 nm, the height Hx (left side) of the covered range was fixed at 99 nm, and the coverage rate Rc (left side) was fixed at 45%. On the other hand, the side surface thickness Ds (right side) of the reflection film 30 covering the right side surface 22b of the ridge portion 22 was changed stepwise in a range of 0 to 22.5 nm. At the same time, as to the right side surface 22b of the ridge portion 22, the height Hx (right side) of the covered range of the right side surface 22b was changed stepwise in a range of 0 to 99 nm, and the coverage rate Rc (right side) was changed stepwise in a range of 0 to 45%. As a result, the grid maximum width WMAX changed stepwise in a range of 32.5 to 55 nm.
In addition, in Example 8, two directions of an incident angle (0=0° to +60°) in the positive direction incident on the left side of the ridge portion 22 in an oblique direction and an incident angle (0=0° to −60°) in the negative direction incident on the right side of the ridge portion 22 in an oblique direction were used for the incident angle θ.
The respective portions of the model of the polarizing element 1 according to Example 8 had the following dimensions and shapes.
Thereafter, simulation was performed for the model of the polarizing element 1 according to Example 8 produced as described above while changing Ds (right side) and Rc (right side) for the left side surface 22b of the reflection film 30 to calculate Tp, Rs, Tp×Rs, and CR, respectively. The incident angle θ was changed stepwise every 150 in the range of 0 to +60°. A relationship between each of Tp, Rs, Tp×Rs, and CR calculated as described above and Dt is shown in each of graphs of
As shown in
Specifically, as to Tp, even in a case where oblique incident light was incident in either the positive direction or the negative direction on the grid portion in which the reflection film 30 was unevenly located, both Tp (+) and Tp (−) were more than or equal to 85% as shown in
In addition, as to Rs as well, even in the case where oblique incident light was incident in either the positive direction or the negative direction on the grid portion in which the reflection film 30 was unevenly located, both Rs (+) and Rs (−) were more than or equal to 85% as shown in
In addition, as to the Tp×Rs properties as well, even in the case where oblique incident light was incident in either the positive direction or the negative direction on the grid portion in which the reflection film 30 was unevenly located, Tp×Rs was more than or equal to 75% as shown in
In addition, as to the contrast CR as well, even in the case where oblique incident light was incident in either the positive direction or the negative direction on the grid portion in which the reflection film 30 was unevenly located, excellent CR was obtained as shown in
Next, a result of comparison between Example 9 of the present invention (in which the reflection film 30 was round-shaped) and Conventional Example 4 (in which the reflection film 30 was rectangular-shaped) and inspection of a relationship between the shape of the reflection film 30 covering the ridge portion 22 and the polarization properties of the polarizing element 1 will be described with reference to
As shown in
The model of the polarizing element 1 according to Example 9 had the special tree shape described above similarly to the model of Example 1 (see
On the other hand, the model of the polarizing element 1 according to Conventional Example 4 was different from the model of Example 9 in terms of the shape of the reflection film 30. The reflection film 30 of Conventional Example 4 was rectangular-shaped and had two angulated corner portions on both the left and right ends of the top of the reflection film 30, which was different from a rounded bulging shape (the round-shaped reflection film) like the reflection film 30 of Example 9 described above. Hereinafter, the reflection film 30 of this Conventional Example 4 will be referred to as a rectangular-shaped reflection film. Note that the model of the polarizing element 1 of this Conventional Example 4 is equivalent to the wire grid-type polarizer disclosed in Patent Literature 7 described above.
In this manner, Conventional Example 4 was different from Example 9 in terms of the shape of the reflection film 30, but was identical to Example 9 in terms of other requirements.
The respective portions common to the models of the polarizing elements 1 of Example 9 and Conventional Example 4 had the following dimensions and shapes.
Simulation was performed for the models of the polarizing element 1 of Example 9 and Conventional Example 4 produced as described above while changing the incident angle θ to calculate Tp. Rs, and Tp×Rs, respectively. The incident angle θ was set at 0° to +60°.
A relationship between each of Tp, Rs, and Tp×Rs calculated as described above and θ is shown in each of graphs of
As shown in
Further, in Conventional Example 4, Tp and Tp×Rs decreased as the incident angle θ increased in a range where θ>30°, and Tp and Tp×Rs sharply decreased particularly in a range where θ>45°, as is understood from the result of comparison between Example 9 and Conventional Example 4 shown in
In contrast to this, in Example 9, Tp and Tp×Rs rather rose as θ increased in a range where 0°≤θ≤45°, so that high values of Tp and Tp×Rs were able to be maintained. Further, in Example 9, the degree of decrease in Tp and Tp×Rs was restrained considerably as compared with Conventional Example 4 even when θ increased in a range where 45°<θ≤60°, so that high values of Tp and Tp×Rs were able to be maintained. Particularly in the case where θ=45°, Example 9 was able to obtain Tp and Tp×Rs higher than in the case of Conventional Example 4 even by more than or equal to 5%. In addition, in the case where θ=60°, Example 9 was able to obtain Tp and Tp×Rs higher than in the case of Conventional Example 4 even by more than or equal to 7%. In this manner, in Example 9, significantly excellent transmissivity (transmittance Tp) and Tp×Rs properties were obtained in the large and wide range of the incident angle θ (30° to 60°, particularly 45° to 60°).
In addition, as to Rs, Example 9 was able to obtain high reflectance having no significant difference as compared with Conventional Example 4.
In addition, as to the Tp×Rs properties required as the polarizing beam splitter (PBS), Example 9 was superior to Conventional Example 4, and in the case where the incident angle θ=45°, the highest Tp×Rs properties were obtained. In addition, Example 9 was also able to obtain more favorable properties than in Conventional Example 4 in the range where the incident angle θ=30° to 60°, and was superior to Conventional Example 4 in the Tp×Rs properties for oblique incident light at the incident angle θ in the large and wide range. Further, in Example 9, the Tp×Rs properties were in good balance for oblique incident light at the incident angle θ in the range of 45°±15°. Therefore, in a case of projecting an image using the polarizing element 1 according to Example 9 as the polarizing beam splitter, the brightness of the displayed image was in good balance when seen from the observer, and the video state also became favorable.
In this manner, it is understood that in the case of using the polarizing element 1 as the polarizing beam splitter, Example 9 was significantly superior to Conventional Example 4 in the transmissivity (transmittance Tp) for the p-polarized light and the polarization splitting properties (the Tp×Rs properties) for oblique incident light at the incident angle θ in the large and wide range of 30° to 60°, particularly for oblique incident light at 45°. Thus, it can be said that the polarization splitting properties required of the polarizing beam splitter were able to be sufficiently satisfied for the oblique incident light.
As described above, Example 9 having the round-shaped reflection film 30 was less dependent on the incident angle θ of oblique incident light than Conventional Example 4 having the rectangular-shaped reflection film 30, and was superior in the transmissivity for oblique incident light and the polarization splitting properties (the Tp×Rs properties) as the polarizing beam splitter. The reason will be described below with reference to
As shown in
Herein, as shown in
From the above reason, it can be said that Example 9 having the round-shaped reflection film 30 was less dependent on the incident angle θ of oblique incident light than Conventional Example 4 having the rectangular-shaped reflection film 30, and was superior to Conventional Example 4 in the transmissivity for oblique incident light and the polarization splitting properties (the Tp×Rs properties) as the polarizing beam splitter.
(Result of Inspection of Heat Dissipation)
Next, a result of comparison between the wire grid polarizing element 1 of the hybrid type made of an inorganic material and an organic material according to the examples of the present invention and a wire grid polarizing element of a film type made of an organic material according to a conventional example and inspection of heat dissipation of the polarizing element 1 will be described.
As described above, in the wire grid polarizing element 1 according to the present embodiment described above, the substrate 10 was made of an inorganic material very excellent in heat tolerance, such as glass. Further, the base part 21 and the plurality of ridge portions 22 of the grid structural body 20 provided on the substrate 10 were integrally formed of an organic material having heat tolerance. In this manner, the wire grid polarizing element 1 according to the present embodiment was the polarizing element of the hybrid type in which an organic material and an inorganic material were combined. Consequently, it is considered that the thermal resistance R [m2·K/W] of the entire polarizing element 1 was small, and heat was able to be efficiently released from the grid structural body 20 to the substrate 10, resulting in excellent heat dissipation.
On the other hand, the wire grid polarizing element of the film type of the conventional example was mainly made of an organic material, and had low heat tolerance (approximately 100° C.). In addition, it is considered that because of an increased total thickness of an organic material layer composed of a substrate (base film), a double-faced tape (OCA), and a grid structural body, the thermal resistance R of the organic material layer also increased.
Consequently, the wire grid polarizing element 1 of the hybrid type according to the present embodiment was superior in heat tolerance and heat dissipation to the conventional polarizing element of the film type (heat tolerance: approximately 100° C.) made of an organic material, and had heat tolerance under a high-temperature environment up to approximately 200° C., for example. Thus, it is considered that the wire grid polarizing element 1 of the hybrid type according to the present embodiment was able to exert favorable heat dissipation properties while achieving excellent polarization properties.
Thus, an example of the wire grid polarizing element of the hybrid type of the present invention and the wire grid polarizing element of the film type of the conventional example were actually produced, and the thermal resistance R and heat dissipation thereof were inspected.
Table 1 shows types of materials of common base materials and thermal conductivity λ[W/m·K]. Table 2 shows the thickness of each layer made of an organic material (PMMA), the thickness (a total thickness DALL) of all of a plurality of layers made of an organic material (PMMA), and the thermal resistance R [m2·K/W] for the wire grid polarizing element 1 of the hybrid type according to the example of the present invention and the wire grid polarizing element of the film type according to the conventional example.
In the polarizing element 1 of the hybrid type according to the example as shown in Table 2, the base part 21 and the ridge portions 22 constituting the grid structural body 20 were formed of an organic material, and the substrate was formed of an inorganic material. On the other hand, in the polarizing element of the film type according to the conventional example, the substrate, the base part constituting the grid structural body, and the double-faced tape for bonding the base part and the substrate were entirely formed of an organic material. Herein, PMMA (Poly Methyl Methacrylate) was used as the organic material. As a result, the total thickness DALL of the PMMA material of the polarizing element 1 of the hybrid type according to the example was 30200 [nm]. On the other hand, the total thickness DALL of the PMMA material of the polarizing element of the film type according to the conventional example was 255000 [nm], which is considerably larger than DALL in the example.
As shown in Table 1, the thermal conductivity λ of PMMA was 0.21 [W/m·K]. The thermal resistance R was obtained by dividing “the thickness DALL of material” by “the thermal conductivity λ” (R=DALL/λ). Thus, the thermal resistance R of the grid structural body 20 of the polarizing element 1 of the hybrid type according to the example was 0.000144 [m2·K/W]. On the other hand, the thermal resistance R of the polarizing element of the film type according to the conventional example was 0.001214 [m2·K/W].
Consequently, use of the polarizing element 1 of the hybrid type according to the example of the present invention enabled the value of the thermal resistance R of the grid structural body 20 made of the PMMA material to be reduced to about 1/8.4 as compared with the polarizing element of the film type according to the conventional example. Thus, the polarizing element 1 of the hybrid type according to the example of the present invention enabled heat of the grid structural body 20 made of an organic material (for example, PMMA) to be efficiently released to the outside for heat dissipation via the substrate 10 made of an inorganic material superior in heat tolerance and heat dissipation to the inorganic material. Hence, the polarizing element 1 of the hybrid type according to the example of the present invention had very excellent heat tolerance and heat dissipation as compared with the conventional example.
Note that although PMMA was used as the material of the grid structural body 20 in the example described above, the material of the grid structural body of the present invention is not limited to such an example, and various organic materials other than PMMA may be used.
The preferred embodiment(s) of the present invention has/have been described above in detail with reference to the accompanying drawings, whilst the present invention is not limited to the above examples. A person skilled in the art may find various alterations and modifications within the scope of the appended claims, and it should be understood that they will naturally come under the technical scope of the present invention.
According to the present embodiment, a polarizing element which has favorable polarization properties, avoids deterioration in heat dissipation and cost in manufacturing, and is excellent in transmissivity for light at wide-range incident angles as well as a method for manufacturing the polarizing element can be provided. In addition, according to the present embodiment, a projection display device excellent in polarization properties and heat tolerance as well as a vehicle including the projection display device can be provided.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-219456 | Dec 2020 | JP | national |
| 2021-211457 | Dec 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/048576 | 12/27/2021 | WO |
