Patent Application
20080094718
In the following, embodiments of the present invention will be described with reference to the accompanying drawings.
With reference to
The micro-lens array 1 according to the present embodiment configured to be unified with a translucent array substrate 2 such as glass, transparent resin and the like includes plural micro-lenses 3 arranged at constant intervals. The micro-lenses 3 are minute optical elements having a light condensing function with respect to the incident light according to a convex curved shape thereof. The micro-lens array 1 of the present embodiment is characterized such that each of the micro-lenses 3 of the micro-lens array 1 has substantially a flat part 3a in a part including the top of the curved shape so that each of the micro-lenses 3 is configured to include the flat part 3a at a center thereof and a curved part 3b around the flat part 3a. That is, the flat part 3a forms a flat surface against an incident light.
Generally, a principal axis is rotated excluding a case of vertical incidence, and the extent thereof depends on an incident angle. When a light is injected to a spherical lens, as the light goes from the top of the lens to the surrounding parts, the incident angle becomes greater. However, in a case of a flat surface, the incident angle dose not change, and thus, the rotation of the principal axis can be kept small.
Accordingly, each of the micro-lenses 3 includes the flat part 3a forming substantially a flat surface against the incident light, which contributes to a reduction of the change of the polarization state. It should be noted that in a case of a configuration of a flat surface where the entire micro-lenses 3 comprise a completely flat part, the change of the polarization state is kept small. However, an intrinsic light condensing effect by the micro-lenses 3 cannot be expected. Accordingly, effects such as an improvement of the optical utilization ratio, the numerical aperture, image quality, and a reduction of pixel size described below are not hoped for.
In regard to this point, the light condensing function of the micro-lenses 3 is maintained by a curved part 3b provided around the flat part 3a.
That is, in the present embodiment, a part of the spherical surface is flattened to be the flat part 3a, and the intrinsic light condensing function is partially vitiated. However, the light condensing function of the micro-lenses 3 is sacrificed within the limits of tolerance so as to reduce the change of the polarization state as small as possible and improve the contrast ratio.
Accordingly, the micro-lens array 1 including the flat part 3a can be easily produced.
When the material of the micro-lens array 1 is glass, the micro-lens array 1 is produced according to a method of, for example, mainly a photo lithography technology and a dry etching technology disclosed in Japanese Laid-Open Patent Application Publication No. 6-194502 and Japanese Laid-Open Patent Application Publication No. 6-250002.
When producing the micro-lenses 3 including the flat part 3a from spherical micro-lenses, it is possible to flatten the top of the micro-lenses by polishing.
When CMP is used as a polishing technology, it is possible to correspond to a mass production. Thus, production cost can also be reduced. In addition, roughness of the surface can be kept less so as to fashion optically problem-free micro-lenses.
A description is given of a method of forming the flat part without polishing the micro-lenses. First, a photomask including a desired flat part is produced. Then, by a spin coater, resist is applied on the substrate 2 on which the micro-lenses are provided. When patterning of the resist according to the photo lithography, the micro-lenses including the flat part 3a are produced. In this case, it is possible to form a flat part not only at a top of the lenses but also at a surrounding of the lenses. Moreover, it is possible to provide flat parts at both the top and the surrounding of the lenses. Accordingly, it is possible to design with high flexibility.
With reference to
The micro-mirror array 11 according to the present embodiment is, for example, configured to be a mirror where plural micro-mirrors 13 are arranged at constant intervals on a dielectric substrate 12 such as Sio2, and a metal foil layer such as Al is evaporated on the surface of the micro-mirrors 13. The micro-mirrors 13 are micro-optical devices having a light condensing function with respect to an incident light according to a concave curved surface thereof.
The micro-mirror array 11 according to the present embodiment features including each of the micro-mirrors 13 configured to include a flat part 13a at a part including a curved bottom and a curved part 13b around the flat part 13a compared to a conventional spherical shape as shown by virtual lines in
Generally, the rotation of the principal axis is caused by a linearly polarized light injected to a surface, forming an angle.
Accordingly, even if the incident angle is fixed, when the surface is curved to which the light is injected, the rotation of the principal axis becomes greater. On the contrary, if the surface is flat, the rotation of the principal axis becomes smaller.
Therefore, since each of the micro-mirrors 13 has the flat part 13a configured to be even against the incident light, this contributes to a reduction of the change of the polarization state. It should be noted that in a case of a configuration of a flat surface where the entire micro-mirrors 13 comprise a completely flat part, the change of the polarization state is kept small. However, an intrinsic light condensing effect by the micro-mirrors 13 cannot be expected. Accordingly, effects such as an improvement of the optical utilization ratio, the numerical aperture, image quality, and a reduction of pixel size described below are not hoped for.
In regard to this point, the light condensing function of the micro-lenses 13 is maintained by a curved part 13b provided around the flat part 13a.
In the present embodiment, as a part of the spherical surface is flattened to be the flat part 13a, the intrinsic light condensing function is partially vitiated. However, the light condensing function of the micro-mirrors 13 is sacrificed within the limits of tolerance so as to reduce the change of the polarization state as small as possible and improve the contrast ratio.
With reference to
More specifically, for example, the substrate 2 including micro-lenses 3 is made of glass having a refractive index of 1.54. As for the adhesive layer 22, an adhesive having a refractive index of 1.42 is used. As for the flat layer 23, a cover glass having a refractive index of 1.52 is used. The difference is small between the refractive index of the substrate 2 including the micro-lenses 3 and the refractive index of the adhesive layer 22. Thus, it is possible to reduce optical loss according to an interface of the two indexes in comparison to the interface between the glass (refractive index of 1.54) and the air (refractive index of 1.0). It is true that the light condensing function is sacrificed, but spherical aberration can also be reduced. Therefore, the efficiency of the optical utilization can be improved. As for an adhesive of the adhesive layer 22, for example, ultraviolet curing resin can be used. In addition to this, if the elements are configured to include the flat layer 23 of a cover glass, for example, it is possible to position the pixel array of the reflection liquid crystal spatial optical modulator easily.
With reference to
According to a configuration of the micro-mirror array 31 of the present embodiment, the light having an angle excluding vertical (the light having a lighting angle) injected into the micro-mirror array 31 can be reflected to a direction where the angle thereof becomes smaller in accordance with Snell's Law. Since the light can be reflected by the micro-mirror 13 at a smaller lighting angle, the light condensing characteristic of the micro-mirror 13 can be improved. Accordingly, the efficiency of optical utilization can be improved.
With reference to
The reflection liquid crystal optical modulator 41, as described in the third embodiment, features using the micro-lens array 21 including the flat layer 23. The micro-lens array 21 is mounted on a liquid crystal layer 44 including pixel electrodes 43 formed on a Si substrate 42.
In the micro-lens array 21, each of the micro-lenses 3 is arranged corresponding to a position of a corresponding one of the pixel electrodes 43. The pixel electrodes 43 and the micro-lenses 3 specifically correspond to, for example, XGA standard so as to be arranged as a two-dimensional array of 1,024×768 dots.
According to the reflection liquid crystal spatial optical modulator 41 of the present embodiment, since the micro-lens array 21 is used for enabling a reduction of the change of the polarization and an improvement of the efficiency of the optical utilization, it is possible to provide a reflection liquid crystal spatial optical modulator realizing a high contrast ratio and high efficiency of optical utilization.
With reference to
The reflection liquid crystal spatial optical modulator 51 features using a micro-mirror array 31 including, for example, a flat layer 32 as described in the fourth embodiment. The micro-mirror array 31 is mounted on a Si substrate 53 where an electric circuit part 52 such as a transistor for driving liquid crystal is incorporated. On the flat layer 32, a liquid crystal layer 55 provided between a couple of transparent electrodes 54a and 54b, and a cover glass 56 as a surface layer are formed. The electric circuit part 52 comprises a MOS (Metal Oxide Semiconductor) transistor 500a including a source, a drain, a gate and wirings thereof, and a retention volume 500b.
Moreover, an electrically-conductive shielding layer 501 such as a metal is provided for preventing the light entering from a gap 504 between the micro-mirror arrays 31 from reaching the electric circuit part 52. Furthermore, a dielectric layer 503 is provided between the electric circuit part 52 and the shielding layer 501. The electric circuit part 52 and the transparent electrode 54a are electrically connected via the conductive shielding layer 501 through the through-hole 502.
In a case of the micro-lens array 21 according to the fifth embodiment, it is necessary to position the micro-lenses corresponding to the positions of the array of the pixel electrodes 43. On the other hand, in a case of the micro-mirror array 31 according to the present embodiment, as for a pixel of the liquid crystal spatial optical modulator 51, each of the micro-mirrors 13 of the micro-mirror array 31 can be formed as the pixel thereof. That is, in a case where the micro-mirrors 13 of the micro-mirror array 31 are utilized for the pixel arrangement of the liquid crystal spatial optical modulator 51, as for the production, the micro-mirrors 13 including the flat part 13a are produced in a process where the pixels of the liquid crystal spatial optical modulator 51 are produced.
According to the present embodiment, the micro-mirrors 13 of the micro-mirror array 31 are used as pixels, enabling a reduction of the change of the polarization and an improvement of the efficiency of the optical utilization, so that it is possible to provide a reflection liquid crystal spatial optical modulator 51 realizing a high contrast ratio and high efficiency of optical utilization.
Accordingly, in the micro-optical devices of the above described embodiments, the substantial flat part described as a feature of the configuration includes a case such that a part of the minute optical element is completely flat and a case such that a part of the minute optical element can be considered as flat, even if it is not completely flat. In other words, this is the case where the curvature radius is large in the micro-lens.
In
In
This can be said in the same way as the micro-mirrors. The convex shape of the micro-lens can be replaced by the concave shape of the micro-mirror (
Next, a description is given of an embodiment. In the micro-lens array 21 partially including a flat part 3a as above described, the effects of reducing the change of the polarization state, improving the contrast ratio, and maintaining the light condensing function are quantitatively obtained by a ray tracing calculation and checked.
In the present embodiment, first, the ratio between the size (area) of one micro-lens 3 and the size (area) of the flat part 3a (hereinafter, referred to as area ratio) is obtained. Then, the relationship between the area ratio and the contrast ratio is obtained. The shape in a surface vertical to an optical axis of the micro-lenses 3 is a square. The size of the square is 13.2 μm×13.2 μm. Moreover, since the micro-lens has a spherical shape, the cross-sectional shape of the micro-lens perpendicular to the optical axis is circular. Thus, the shape of the flat part 3a is also circular. However, when a diameter of a circle of the flat part 3a becomes greater than a side of the square equal to 13.2 μm, the flat part 3a becomes a shape where the square is cut out from the circle. The curvature radius of the micro-lens 3 is equal to 10 μm. The refractive index of the glass member is equal to 1.54. Further, the refractive index of the resin layer (adhesive layer) 22 is equal to 1.42. The refractive index of the cover glass (flat layer) 23 is equal to 1.52.
In the ray tracing calculation for obtaining the contrast ratio, an optical system model of a liquid crystal projector as shown in
In
Accordingly, the light from the light source 61 attenuated by the aperture 68 is divided into linearly polarized components by the linear polarizer 62 and reflected by the polarization beam splitter 63 in accordance with the polarization direction to a side where the micro-lens array 21 and the reflection surface (pixel electrode) 65 are provided. The reflected light is given luminosity corresponding to a state of the reflection surface (pixel electrode) 65 which is controlled in accordance with the image data. Then, the light is again injected to a side where the polarized beam splitter 63 is provided, transmitted through a polarization split thereof, and projected onto the screen (photo detector) 67 via the analyzer 66. The retarder plate 64 is rotated so as to model the light in the bright state and the light in the dark state. The ratio of modeling the light in the bright state and the light in the dark state is adopted as the contrast ratio. The light source 61 has an orientation distribution.
The horizontal axis is the area ratio, while the vertical axis is the contrast ratio. As shown in the graph, it is obvious that the contrast ratio is improved as the area of the flat part 3a increases.
The improvement of the contrast ratio draws a gentle curve under the area ratio substantially less than or equal to 0.8, but rapidly increases when the area ratio becomes greater than 0.8.
This may be because the rotation of the principal axis around the micro-lens 3 is large.
Next, a ray tracing calculation is performed referring to an evaluation of the image of the pixels of the reflection liquid crystal spatial optical modulator 41 projected onto the screen 67.
A projection lens 71 and a screen (photo detector) 67 are provided against the micro-lens array 21 on which the cover glass 23 is mounted via the adhesive layer 22 in the same way as the above described micro-lens array 21.
The MTF (Modulation Transfer Function) of the projection lens 71 is equal to 50%. In this model, a light source is supposed to be provided within the micro-lens array 21.
The horizontal axes (x, y) are defined as a spatial spreading (arbitrary), while the vertical axis is defined as an illuminance (or strength, arbitrary)
Hereinafter, the illuminance profile of the projected pixel is referred to as “projected pixel profile.” The projected pixel profile is quoted in one axis direction, and one side thereof is plotted. The result is shown by a graph in
In
The projected pixel profiles almost do not vary when the area ratio is less than 0.34. This is because the area around the center of the micro-lens 3 does not influence the light condensing effect very much. However, as the area ratio is equal to 0.64 and 0.92, the width of the projected pixel profile becomes wider. This is because the light condensing effect of the lens is reduced as the area of the flat part 3a increases.
As a result, the contrast ratio is improved substantially 1.23 times greater, i.e., from 358 to 440 in a range where the projected pixel profile does not vary (the area ratio is in a range between 0.0 and 0.34). Further, if permitting a little spread of the projected pixel profile, the contrast ratio is improved substantially 1.8 times greater, i.e., from 358 to 643. Accordingly, the effect of the improvement of the contrast ratio by providing the flat part 3a can be found. In addition, it can be also found that the quality of the projected image is not degraded very much.
In regard to the spread of the projected pixel profile as above described, the result of the present embodiment is compared with the conventional technology below.
A result similar to the present embodiment is disclosed in a document (Takao Endo and others, Selection of Drafts of Lecture Meeting for 28th Optics Symposium (Lecture Meeting of Optical Technology and Science), pp. 21 through 22, published in 2003 by Ouyou Butusri Gakkai Bunkakai of Nihon Kogakkai). The result is on an evaluation of a projected image of pixels of a projector.
In this document, a description is mainly given of a result obtained from an experiment in respect of a projected image of one pixel. According to the description of the result, the reason why one pixel is used is that in a case such that there is an image of the adjacent pixel (in a diagonal direction), in the illuminance, the image profiles, especially foot parts thereof, are piled up, and thus, the evaluation of one pixel cannot be performed accurately. The piled up foot parts of the image profile in this case are equal to 25%, when the maximum illuminance is normalized as 100%. The pixel of a light bulb (spatial optical modulator) is a square, one side thereof being equal to 13.7 μm. Moreover, the spread of the foot parts generated by the optical system of the projector expresses a degradation of the image quality. As the value of the degradation becomes greater, the differentiation between the adjacent pixels becomes ill-defined. Accordingly, the CTF (Contrast Transfer Function) of the image becomes less.
In the present comparison, the piled up foot parts of the projected pixels are evaluated in the same way as the above description when there is an image of an adjacent pixel in the diagonal direction. The result is shown in
As shown in
As for the projected image of the reduced pixel, for example, in the spatial optical modulator, even an entirely white image where all of the pixels are in the bright state is recognized as an image (regularly) including a gap by an observer.
However, even the projected image including a gap as described above can be projected as a gapless image if a pixel shifting device is utilized, regularly shifting a light path of light flux into the projector (Drawing is omitted. See Japanese Laid-Open Patent Application Publication No. 2002-174852.).
With reference to
In this description, an example is given of two F values, but the number of the F values can be three or more.
The refractive index of the micro-lens is equal to n1. The refractive index of an adjacent member on the incident light side is equal to n0. The member may be replaced by air.
The size of the micro-lens is equal to D. If the micro-lens is single, D is equal to the size of the micro-lens. On the other hand, in a case of a micro-lens array, D shows a pitch. The length of the micro-lens along the optical axis is equal to L.
Further, the micro-lens includes two different curvature radii r1 and r2. The first curvature radius r1 is in effect in a range d against a half of the pitch, i.e., D/2. The second curvature radius r2 is in effect in a range of D/2−d.
Furthermore, the micro-lens includes a shielding part. The shielding part is a black matrix.
On a side of the shielding part, a liquid crystal layer of a spatial optical modulating element is provided (drawing is omitted). The aperture size of the shielding part is equal to A compared to the pitch of D of the micro-lens. The numerical aperture is defined as A2/D2. A focal distance fl in the part d of the micro-lens is obtained by an equation using r1, n0 and n1:
f1=(n0/(n1−n0))×r1.
Another focal distance f2 in the part D/2−d of the micro-lens is obtained by an equation using r2, n0 and n1:
f2=(n0/(n1−n0))×r2
The F numbers are defined as below, in each of the ranges of the lens including the plural focal distances according to the present embodiment. That is, in the range of radius d, the F number is defined as F1=f1/D. In the range between d and D/2, the F number is defined as F2=f2/D.
In addition, a position P1 is at an edge part of the lens having a radius r1. On the other hand, a position P2 is at an edge part of the lens having a radius r2.
The radius r1 is increased so that the lens becomes approximately flat, while the r2 is kept small so that the lens keeps a spherical shape. As described above, on the substantially flat part, the polarization state is maintained to be optimum so that the contrast ratio is improved and the light condensing function around the spherical surface is maintained.
The incident light has a lighting angle defined as θ. The light around the center is parallel to the optical axis. The position P1 is varied by d, while the position P2 fixed to the edge of the micro-lens is not changed.
When the light having a lighting angle θ is injected to the positions P1 and P2, the light is reflected by an angle according to the curvature radii and the indexes of refraction of each of the members.
If the parameters are properly determined, as shown in
However, the light is shielded by the shielding part depending on the parameters, and thus, the efficiency of optical utilization is decreased.
Now, it is determined as:
(These are fixed.)
(These are variable.)
(θ is fixed.)
Then, the ray tracing calculation is performed.
Finally, the coordinates (x, y) are obtained where the light reaches at an end part of the micro-lens.
When a length between the optical axis and the coordinates (x, y) is less than the aperture size, the light is not shielded, and thus, projected through the micro-lens. Further, a lighting angle θ′ when the light is projected through the micro-lens is also obtained.
As for the light which is not shielded, and thus projected through the micro-lens, the light path thereof is sometimes shielded by the following optical system.
In a case such that a projection lens is provided on a light projection side of the micro-lens (drawing is omitted), if θ′ is small compared to the F value of the projection lens, the light reaches the following screen. However, in a reverse case, the light is shielded by the projection lens.
As shown in
In
As for the upper limit of F1, since it may be a completely flat surface, the upper limit of F1 is not laid down.
The number of light rays passing through corresponds to efficiency of the optical utilization, i.e., equal to or greater than 67%. The light condensing function is taken into consideration.
From the examination in respect to the above described contrast ratio, the curvature radius of the micro-lens is found to have a relationship with the contrast ratio as shown in
That is, the greater the curvature radius is, the more the contrast ratio is improved. This can be approximated by a natural logarithm 1n.
(The Contrast Ratio)=a×1n(r)+b
In the equation, a and b are coefficients depending on the optical system. In the example of
For example, the contrast ratio of an arbitrary r or F value is obtained from the graph. In the micro-lens including two different F values according to the present invention, the contrast ratio is in a range between the contrast ratio obtained when the micro-lens is entirely F1 and the contrast ratio obtained when the entire micro-lens is entirely F2.
In the range, the contrast ratio depends on the area ratio between the areas where F1 is effective and where F2 is effective. That is, the contrast ratio depends on the area ratio between an area S1 where F1 is effective: S1=d2Π (Π is the ratio of the circumference of a circle to its diameter) and an area S2 where F2 is effective: S2=D2−S1. Moreover, when these are expressed by a ratio against the entire area of the micro-lens: S′1=S1/D2, and S′2=S2/D2. Accordingly, the contrast ratio CR of the micro-lens including two different F values is: CR(F1)×S′1+CR(F2)×S′2.
The contrast ratio (r1 and r2) shown in
Accordingly, without depending on the value of the optical system, a comparison can be performed. Further, the contrast ratio (r1) and the contrast ratio (r2) are also shown.
It can be found that the contrast ratio (r1 and r2) is in the range between the contrast ratio (r1) and the contrast ratio (r2).
In the cases of F values where the number of the light rays passing through is not small, the contrast ratio is also not small (equal to latter half of 2 or more than 3).
Any of the efficiency of optical utilization, the light condensing function, and the contrast ratio is excellent.
Such a micro-lens, as described above, can be produced in the same way as the method where the flat part is produced without polishing, i.e., the method including the steps of producing a photomask having a desired flat part, spreading resist by a spin coater on a substrate where the micro-lens is provided, and patterning the resist by lithography.
According to at least one of the embodiments of the present invention, the micro-lens array includes minute optical elements. Each of the minute optical elements is a transmission lens element having a curved surface including a substantially flat part. The curved surface is convex. Accordingly, the change of the polarization state can be reduced by the flat part. The curved surface maintains a light condensing function.
According to at least one of the embodiments of the present invention, the micro-mirror array includes minute optical elements. Each of the minute optical elements is a reflection mirror element having a curved surface including substantially a flat part. The curved surface is concave. Accordingly, the change of the polarization state can be reduced by the flat part. The curved surface maintains a light condensing function.
According to at least one of the embodiments of the present invention, the change of the polarization state can be reduced in the transmission micro-lens array. Moreover, it is possible to improve the efficiency of optical utilization since the difference of the refractive indexes is kept small so that the optical loss due to the reflection on the interface can be reduced. Furthermore, with the flat layer, it becomes easy to install the spatial optical modulator.
According to at least one of the embodiments of the present invention, the change of the polarization state can be reduced in the reflection micro-lens array. Moreover, the light condensing feature is improved so as to improve the efficiency of optical utilization. Furthermore, with the flat layer, it becomes easy to install the spatial optical modulator.
According to at least one of the embodiments of the present invention, optimum F values are predetermined so as to further improve the contrast ratio and the efficiency of optical utilization, and maintain the light condensing function.
According to at least one of the embodiments of the present invention, the projector includes the pixel shifting device for realizing a high contrast ratio, high efficiency of optical utilization and high-definition of the image.
Further, the present invention is not limited to these embodiments, but variations and modifications may be made without departing from the scope of the present invention.
The present application is based on Japanese Priority Application No. 2005-171151 filed on Jun. 10, 2005, with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-171151 | Jun 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP05/23001 | 12/8/2005 | WO | 00 | 2/8/2007 |
