Patent Application
20070263137
The best mode for carrying out the invention will now be described with reference to the drawings
The illuminating device according to the present invention is a illuminating device employed in the display device related to the present invention described subsequently, that lights the display (liquid crystal layer) of a reflective type liquid crystal display device.
As shown in
This display device operates as a projection type display device (projector) when the optical imaging system 4 forms an actual image of the image display surface 3 of the liquid crystal display device 2 on a image display surface not shown in the drawing, while when the optical imaging system 4 forms a virtual image of the image display surface 3 of the liquid crystal display device 2 this display device operates as a bead mount display (HMD) or an electronic viewfinder (EVF).
The liquid crystal display device 2 is the same as that utilized in the conventional display device described previously comprised having liquid crystals enclosed between a drive substrate and an opposing electrode. A plurality of reflective type pixel electrodes (reflecting electrodes) are formed in a matrix configuration on the surface of the drive substrate. In this reflective type liquid crystal display device each pixel electrode is separated by a precise, determined pixel interval, and is arranged in a matrix configuration in the longitudinal and horizontal directions, thus the plurality of pixels are arranged in a matrix configuration in the longitudinal and horizontal directions.
This illuminating device 1 of the display device performs illuminating of the image display surface 3 of the liquid crystal display device 2, the illuminating device 1 has a light source 5 arranged in a lateral position to the image display surface 3 of the liquid crystal display device 2. The light source 5 emits parallel light rays of linear polarization to the image display surface 3.
The light source 5 may be provided in the form of a light source that is a laser diode or a light emitting diode (LED: Light Emitting Diode).
If the light source is provided in the form of a laser diode the light emitted from the light source is of linear polarization If the light source is provided in the form of an LED, the light emitted from the light source passes a polarizing filter or the like and becomes light of linear polarization.
In the illuminating device 1, light emitted from the light source 5 is reflected and there are a plurality of reflecting members 6 that inject this light substantially vertically in relation to the image display surface 3 of the liquid crystal display device 2. These reflecting members 6 are arranged to the front of the image display surface 3 of the liquid crystal display device 2 and separate from the image display surface 3, moreover, the reflecting members 6 are arranged to the front of a region of a part, that comprises a very small proportion of the area in relation to the entirety of the image display surface 3 of the liquid crystal display device 2. Light reflected by the reflecting members 6 is not injected in a direction that is perfectly perpendicular in relation to the image display surface 3, but light reflected from the liquid crystal display device 2 passes between each of the reflecting members 6 so that it is injected having a slight, but determined angle (inclination). This slight, determined angle means that the light reflected at each of the reflecting members 6 maintains a direction of polarization, and moreover, must be of an angle (for injection into the optical imaging system 4) that enables compatibility with the optical imaging system 4 described subsequently.
In the case of this embodiment, as shown in
The plane parallel plate 7 can be formed for example of glass the refractive index n of which is 1.73. On the front part (the side having the optical imaging system 4) of the plane parallel plate 7 a plurality of V-shaped groove parts 8 the side wall faces of which comprise reflective members 6 are formed at determined intervals. The light source 5 is arranged so as to direct light towards these V-shaped grooves 8 and to pass inside the plane parallel plate 7, this being the optical beam configuration.
As shown in
In this way, as shown in
Note that a part of the light input to the plane parallel plate 7 reaches the frontal surface part of the plane parallel plate 7, regions where the V-shaped grooves 8 are not formed, and here a part of the light is reflected, while the remainder is considered as passing the frontal side. Further, part of the light that enters the edge parts of the V-shaped grooves 8 is emitted to the frontal side opposite the liquid crystal display device 2. Moreover, if there is any light that enters at an angle so as not to undergo total reflection at the side wall faces of the V-shaped grooves 8, this light can pass the side wall faces and be emitted to the frontal surface side of the plane parallel plate 7. Such light cannot be used as illuminating light and is unusable.
Such unusable light as well as light that is reflected while not being modulated at the liquid crystal display device 2 is absorbed by polarizing plate 9 disposed to the front of the plane parallel plate 7. The polarizing plate 9 is disposed so as only to pass light that is polarized in a direction orthogonal to light from the light source 5.
Light that is polarization modulated at the liquid crystal display device 2 and reflected and that passes the plane parallel plate 7 and the polarizing plate 9, enters the optical imaging system 4. As described above, the light entering the optical imaging system 4 forms either an actual or a virtual image for producing an image display.
When, in this illuminating device, light emitted from the light source 5 is not a perfect parallel beam, it enters as light beams having a spread, and as shown in
If scattering is used in order to increase the spread angle of the light a deterioration in the contrast ratio of the displayed image results due to increased randomness in the polarization direction of the light. Accordingly, it is preferable to avoid the emergence of scattered light as much as possible. In this illuminating device the scattering effect is avoided and illuminating irregularity is reduced by providing a sufficient distance between each of the reflecting member's 6 and the image display surface 3 of the liquid crystal display device 2.
Further, when the light entering the liquid crystal display device 2, modulated at the liquid crystal layer and reflected travels toward the optical imaging system 4, if each of the reflecting members 6 operate to obstruct passage of the light black lines will develop projected layered over the displayed image, resulting in a deterioration in the quality of the displayed image.
In this display device, when the optical imaging system 4 keeps the image display surface 3 of the liquid crystal display device 2 within the focus depth the plurality of the reflecting members 6 are removed from the focus depth. That is to say, the image display surface 3 and each of the reflecting members 6 are separated by a sufficient distance. For example, in the case of this embodiment, the gap between the image display surface 3 and each of the reflecting members 6 is approximately 5 mm The focus surface of the optical imaging system 4 matches that of the image display surface 3 of the liquid crystal display device 2 and as each of the reflecting members 6 (V-shaped grooves 8) is outside the focus depth, the image on each of the reflecting members 6 (dark lines) is formed sufficiently blurred. That is to say, the image on each of the reflecting members 6 is not dark lines but is formed such that the darkness appears uniform over the entirety of the displayed image, thereby preventing a deterioration in the quality of the displayed image.
The decrease in the brightness of the displayed image from the image of each of the reflecting members 6 is proportionate to the width w (area) of each of the reflecting members 6. Accordingly, it is preferable that the pitch a of the reflecting members 6 (the V-shaped grooves 8), the width w and the setting of the distance of the reflecting members 6) from the image display surface 3 be determined with consideration of the balance of the light emitting efficiency of the light source 5 and the illuminating irregularity (how readily visible the black lines are) in coordination with the objective for which the display device is to be used. Here, it follows naturally that the black lines become less visible to the extent that the width w of the reflecting members 6 narrows, but if the width w is not greater than 1 μm the spread angle of the light becomes excessively large due to diffraction and it becomes difficult to inject all of the light into the optical imaging system 4. Accordingly, the width w of the reflecting members 6 should preferably be between 1 μm and 10 μm. Further, the plurality of reflecting members 6 should be disposed to the front of not more than one half of the region of the image display surface 3 of the liquid crystal display device 2, that is to say, the total image projected area of the plurality of the reflecting members 6 should preferably be not more than one half of the area of the image display surface 3.
The ghosting effect (double or multiple layered images) will now be described
The illuminating device 1 related to the first embodiment of the present invention is disposed at a determined distance from a liquid crystal display device 2.
With this arrangement, the reflective member 6 acts as an obstruction that prevents reflected light from passing an image formed by the liquid crystal display device 2, and if each reflective member 6 is disposed at a determined interval there are cases when the ghosting effect can be observed due to the effect of the resulting diffractive grating. Especially in the case of contrast ratio imaging systems that are employed for home theaters and the like, this can lead to a deterioration in the quality of the displayed images.
In contrast to 0 order light that is light used in image display, the first order diffracted light is the main cause of the ghosting effect. The result of the assessment of the images obtained indicate that no practical problem exists where the ratio DR of first order diffracted light to 0 order light is not greater than 0.5%. Accordingly, as evidenced by the graph shown in
Here, in the case of the V-shaped groove part 8 of the form shown in
Moreover, in the case of the V-shaped groove part 8 of the form shown in
Again, the pitch a of the reflective member 6 need not be at constant intervals, and it is sufficient to consider this pitch in terms of an average value where variations exist.
The material for the plane parallel plate 7 should preferably be highly refractive material in order to reduce the angle of total reflection. For example, if the plane parallel plate 7 is formed from materials such as silica glass having a low refractive index total reflection will not occur at the reflecting members 6 (side walls of the V-shaped grooves 8) due to the angle of incidence of the light.
In this case, as shown in
As shown in
Note that the reflecting members 6 may be comprised not of the side wall parts of a V-shaped groove 8 as described above, but by embedding a reflective plate such as a metal alloy plate or the like inside the plane parallel plate 7.
Note that in the following description of the display device that provides a illuminating device according to the second embodiment, like reference numerals identify elements that are the same as those comprising the display device having a illuminating device according to the first embodiment.
In this illuminating device related to the present invention, as shown in
Here, as shown in
The plane parallel plate 7a is formed for example of a transparent plastic or the like. A plurality of the convex parts 12 the side wall faces of which comprise the reflecting members 6A are formed at determined intervals on the rear surface part (that side on which the liquid crystal display device 2 is disposed) of this plane parallel plate 7a. The light source 5 is disposed so as to direct light having an optimum beam formation to the convex part 12 from the rear surface part of the plane parallel plate 7A.
These reflective members 6A are disposed to the front of the image display surface 3 of the liquid crystal display device 2 and removed from the image display surface 3. Moreover, the reflecting members 6A are disposed to the front of part of the region of the image display surface 3 of the liquid crystal display device 2.
As shown in
In this way, as shown in
Note that a part of the light input to the plane parallel plate 7A reaches the frontal surface part of the plane parallel plate 7A, regions where the convex part 12 are not formed, and here a part of the light is reflected, while the remainder is considered as passing the plane parallel plate 7A and being emitted into the atmosphere from the surface on the opposing side at an angle that is the same as the angle of incidence. Further, part of the light that enters the edge parts of the convex part 12 is emitted to the frontal side opposite the liquid crystal display device 2. Such light cannot be used as illuminating light and is unusable
Such unusable light as well as light that is not modulated at the liquid crystal display device 2 is absorbed by polarizing plate 9 disposed to the front of the plane parallel plate 7A. The polarizing plate 9 is disposed so as only to pass light that is polarized in a direction orthogonal to light from the light source 5.
Light that is polarization modulated at the liquid crystal display device 2 and reflected and that passes the plane parallel plate 7A and the polarizing plate 9, enters the optical imaging system 4. As described above, the light entering the optical imaging system 4 forms either an actual or a virtual image for producing an image display.
When, in this illuminating device, light reflected at each of the reflecting members 6A is not a perfect parallel beam, as shown in
If scattering is used in order to increase the spread angle of the light a deterioration in the contrast ratio of the displayed image results due to increased randomness in the direction of polarization of the light. Accordingly, it is preferable to avoid the emergence of scattered light as much as possible. In this illuminating device the scattering effect is not used and illuminating irregularity is reduced by providing a sufficient distance between each of the reflecting members 6A and the image display surface 3 of the liquid crystal display device 2.
Further, when light entering the liquid crystal display device 2, modulated at the liquid crystal layer and reflected travels toward the optical imaging system 4, if each of the reflecting members 6A operate to obstruct passage of the light black lines will develop projected layered over the displayed image, resulting in a deterioration in the quality of the displayed image.
In this illuminating device, when the optical imaging system 4 keeps the image display surface 3 of the liquid crystal display device 2 within the focus depth the plurality of the reflecting members 6A are outside the focus depth. That is to say, the image display surface 3 and each of the reflecting members 6A are separated by a sufficient distance. For example, in the case of this embodiment, the gap between the image display surface 3 and each of the reflecting members 6A is approximately 5 mm. The focus surface of the optical imaging system 4 matches that of the image display surface 3 of the liquid crystal display device 2 and as each of the reflecting members 6A (the convex part 12) is outside the focus depth, the image on each of the reflecting members 6A (dark lines) is formed sufficiently blurred. That is to say, the image on each of the reflecting members 6A is not dark lines but is formed such that the darkness appears uniform over the entirety of the displayed image, thereby preventing a deterioration in the quality of the displayed image.
The decrease in the brightness of the displayed image from the image of each of the reflecting members 6A is proportionate to the width w (area) of each of the reflecting members 6A. Accordingly, it is preferable that the pitch a of the reflecting members 6A (the convex part 12), the width w and the setting of the distance of the reflecting members 6A) from the image display surface 3 be determined with consideration of the balance of the light emitting efficiency of the light source 5 and the illuminating irregularity (how readily visible the black lines are) in coordination with the objective for which the display device is to be used. Here, it follows naturally that the black lines become less visible to the extent that the width w of the reflecting members 6A narrows, but if the width w is not greater than 1 μm the spread angle of the light becomes excessively large due to diffraction and it becomes difficult to inject all of the light into the optical imaging system 4. Accordingly, the width w of the reflecting members 6A should preferably be between 1 μm and 10 μm. Further, the plurality of reflecting members 6A should be disposed to the front of not more than one half of the region of the image display surface 3 of the liquid crystal display device 2, that is to say, the total image projected area of the plurality of the reflecting members 6A should preferably be not more than one half of the area of the image display surface 3.
As shown in
Note that the reflecting members 6A may be comprised not of the side wall parts of a convex part 12 as described above, but by joining a reflective plate such as a metal alloy plate or the like over the rear surface part of the plane parallel plate 7A.
As shown in
This display device operates as a projection type display device (projector) when the optical imaging system 24 forms an actual image of the image display surface 23 of the reflective type liquid crystal display device 22 on a image display surface not shown in the drawing, and operates as a head mount display (HMD) or an electronic viewfinder (EVF) when the optical imaging system 24 forms a virtual image of the image display surface 23 of the reflective type liquid crystal display device 22.
The reflective type liquid crystal display device 22 is the same as those used in display devices of the conventional technology as described above, and is configured having liquid crystals enclosed between a drive substrate and a transparent opposing electrode.
A plurality of reflective type pixel electrodes (reflecting electrodes) are formed in a matrix configuration on the surface of the drive substrate. In this reflective type liquid crystal display device 22 each of the pixel electrodes is separated exactly by a determined pixel interval and is arranged forming a matrix configuration in the longitudinal and horizontal directions, such that the arrangement of the plurality of pixels forms a matrix configuration in the longitudinal and horizontal directions.
The illuminating device 21 of this display device provides illuminating for the image display surface 23 of the reflective type liquid crystal display device 22. This illuminating device 21 is a light source 25 arranged in a lateral position with respect to the image display surface 23 of the reflective type liquid crystal display device 22. The light source 25 emits light substantially parallel to the image display surface 23. The light source 25 can be provided in the form of a laser diode or an LED or the like.
When a laser diode is used to provide this light source the light emitted from the light source is linear polarized light.
When an LED is used to provide the light source the light emitted from the light source can be made into linear polarized light by passing it through a polarizing filter or the like.
The illuminating device 21 has hologram elements 26 that diffract light emitted from the optical imaging system 24 and inject this light into the image display surface 23 of the reflective type liquid crystal display device 22, The hologram elements 26 are arranged to the front of the image display surface 23 of the reflective type liquid crystal display device 22 and removed from the image display surface 23, and are disposed extending over substantially the whole of the image display surface 23 of the reflective type liquid crystal display device 22.
In the case of this embodiment, as shown in
The light source 25 is arranged and configured including an optical system, so as to direct light having an optimum beam formation toward the hologram elements 26. The light from the light source 25 is injected in the side surface part of the plane parallel plate 27, passes inside the plane parallel plate 27 and irradiates toward the hologram elements 26 at a determined angle of incidence θ.
Substantially parallel light entering from the light source 25 is diffracted at the hologram elements 26 and injected to the image display surface 23 of the reflective type liquid crystal display device 22. The hologram elements 26 has a chirping structure, therefore the diffracted light converges and diverges within a determined angle and enters the image display surface 23. On the other hand, all of the light that is not diffracted at the hologram elements is reflected into the atmosphere and does not reach the reflective type liquid crystal display device 22.
Light input to the reflective type liquid crystal display device 22 is polarized and modulated in coordination with the image signal at the image display surface 23 (liquid crystal layer) of the reflective type liquid crystal display device 22 and reflected. The modulated light reflected in this way returns to the hologram elements 26. These hologram elements 26 diffract light of a determined polarization (S polarized light) input from the light source 25, with a high degree of efficiency, while light that is of a polarization that is orthogonal to the S polarized light (P polarized light) is basically not diffracted and is passed.
Accordingly, modulated light modulated and reflected at the reflective type liquid crystal display device 22 passes the hologram elements 26 and the plane parallel plate 27 in that condition, and passes a polarizing plate 29 disposed to the front side of the plane parallel plate 27. This polarizing page 29 is disposed so as only to pass polarized light the direction of polarization of which is a direction orthogonal to light emitted from the light source 25.
Modulated light that is polarization modulated at the reflective type liquid crystal display device 22 and reflected and that passes the hologram elements 26, the plane parallel plate 27 and the polarizing plate 29 enters the optical imaging system 24. As described above, modulated light entering the optical imaging system 24 forms either an actual or a virtual image for producing an image display.
Part of the light that is not modulated at the reflective type liquid crystal display device 22 may pass the plane parallel plate 27, however such light is cut at the polarizing plate 29 therefore there is no deterioration in the quality of the displayed image.
In the case of this illuminating device according to the third embodiment, as shown in
A method for producing hologram elements (hologram lens) 26 furnishing these lens effects will be described.
In the basic design of the hologram lens, the lens pattern can be obtained from the following basic formula (equation 1), that shows the relationship between the angle of outward travel (θ out) of diffracted light and the grating pitch (interference band intervals d).
θout=asin (mλ/nd−sin (θ in)) Equation 1
In this Equation 1, θ out is the angle of outward travel of diffracted light, m is the order of diffraction, λ is the wavelength of incident light n is the refractive index of the medium, d is the grating pitch and θ in shows the angle of incidence of incident light
In order that the angle of outward travel of diffracted light as determined by this Equation 1 be kept within a determined range, it is possible, by making the grating pitch variable (chirping), to provide characteristics to the hologram elements 26, such as the focus and diffusion and the like, that can be changed.
Further, with thick film hologram elements, known as a volume hologram, it is possible to obtain almost 100% diffraction efficiency by optimizing the refractive index differential Δ n of the interference band and the thickness To produce a volume hologram having the desired chirping structure it is necessary to produce a master hologram having the calculated pattern design. Then, a method for transcription to a hologram sensitive material such as a photo polymer can be used to employ this master hologram.
As shown in (a) in
Next, as shown in (b) in
Thereafter, as shown in (c) in
Then, as shown in (d) in
As shown in
The master hologram 35 is then placed over the hologram photosensitive material 36, moreover, a light incidence prism 38 is then placed over the master hologram 35. Next, recording light is irradiated via the prism 38 and a fluid the refractive index of which matches that light, not shown in the drawing The light source for this recording light can be provided in the form of Ar lasers having for example an emission wavelength of 488 nm and an emission wavelength of 514.5 nm.
By irradiating this recording light, 0 order light that directly passes the master hologram lens 35 and first order diffracted light that is diffracted by the master hologram lens 35 interact, and interference bands are formed on the hologram photosensitive material 36. These interference bands are transferred to and recorded on the hologram photosensitive material 36. This is known as light interference exposure method.
Thereafter, a fixing process is performed using ultraviolet light exposure and, after increasing sensitivity to refractive index difference by performing a beating process applying heat at not less than 100 degrees Celsius, a volume hologram is obtained having high refractive index difference.
Besides the amplitude modulated hologram produced using electron beam etching as described above, this hologram used for the interference exposure method can also be provided by a volume hologram produced by transference from this kind of amplitude modulated hologram using the interference exposure method.
Consider as an example of hologram elements 26 the case having a designed angle of incidence of 72 degrees, and being a photo polymer having a refractive index difference Δ n of 0.05. The film thickness is 2.4 μm. As shown in
Further, consider as another example of hologram elements 26 the case having a designed angle of incidence of 60°, and being a photo polymer having a refractive index difference triangle symbol n of 0.05 The film thickness is 1 μm. As shown in
The above simply provide examples of what the hologram elements 26 could be. By changing the settings as appropriate to determine the angle of incidence of incident light, the refractive index difference Δ n of the hologram material and the film thickness d for example, it is possible to produce a hologram elements 26 having the appropriate properties for the desired objective with respect to the diffraction efficiency and angle dependence for P polarized light and S polarized light
As shown in
In this case, light entering the side surface part of the plane parallel plate 47 from the light source 45 enters the hologram elements 46 and a part of that light is diffracted, and reflected to the reflective type liquid crystal display elements 42. The light that is not diffracted at the hologram elements 46 is totally reflected when the surface (rear surface) of the hologram elements 46 are in contact with the atmosphere. The light that is totally reflected in this way travels through the plane parallel plate 47 and again undergoes total reflection via the front surface part of this plate 47 before entering the hologram 46 where it is diffracted.
In this way, in the case of this illumination device light that is not diffracted at the hologram elements 46 is reused for lighting thereby enabling an improvement in the efficiency of light usage.
Further, as shown in
In this case, light from the light source 55 that enters the plane parallel plate 57 undergoes total reflection at the front surface part of the plane parallel plate 57 and thereafter, enters the hologram elements 56, where a part of this light is diffracted and enters the reflective type liquid crystal display device 52, That light which is not diffracted at the hologram elements 56 undergoes total reflection when the surface of these hologram elements 56 are in contact with the atmosphere. The light that undergoes total reflection in this way proceeds through the plane parallel plate 57 and again undergoes total reflection in the front surface part of this plane parallel plate 57, before entering the hologram elements 56 where it is diffracted.
In this way, in the case of this illuminating device, the efficiency with which the light is used can be improved by reusing light that is not diffracted at the hologram elements 56 and provides increased freedom in the positioning of the light source 55.
As shown in
The light of these colors via each of the reflective type liquid crystal display devices 62 R, 62 G and 62 B travels via a plane parallel plate 66 and polarizing plate 69, is input from the three directions comprising both side surfaces and the rear surface of a cross dichroic prism 61 and undergoes color composition in this cross dichroic prism 61 before being emitted from the front surface. The polarizing plate 69 is disposed so as to pass the light of a polarization direction orthogonal to the polarization direction of the linear polarized light emitted from the laser array.
Light emitted from this cross dichroic prism 61 is injected into a projection lens 64a that is an optical imaging system 64. This projection lens 64a provides an image display by forming the incoming light into an image on a image display surface not shown in the drawing
This display device can be provided in a configuration that is of small size and moreover can perform high brightness, high contrast and high-definition image display.
As shown in
An LED array having a configuration in which LED of the three primary colors are arranged such that a plurality of these are alternately disposed can be used to provide the light source 85 that emits light of the three primary colors. The light emitted from this LED array passes a beam forming lens (not shown in the drawing), then travels via a polarizing plate 92 and enters a plane parallel plate 87. This plane parallel plate 87 and reflective type liquid crystal display elements 82 are disposed not tightly adjacent but arranged having a determined layer of atmosphere interposed therebetween.
Light (modulated light) of each of these colors that passes the reflective type liquid crystal display device 82, passes the plane parallel plate 87 and the polarizing plate 89 and is injected into an Lupe 84a. The polarizing plate 89 is disposed so as to pass linearly polarized light of a direction orthogonal to the direction of polarization of linearly polarized light that is passed by the polarizing plate 92 of the illuminating device. Further, the Lupe 84a performs image display by forming a virtual image of the input light.
In this display device image display is performed by the field sequential system as the three primary colors of the LED array light on and off sequentially. When displaying a monochrome image a white LED can be used as the light source.
LED used as light sources emit light beams that are not polarized light and moreover have a poor parallel aspect, thus providing low light use efficiency. However, where the purpose is direct observation of an expanded image (virtual image) expanded by an Lupe as in the case of an electronic viewfinder, this can provide sufficient light brightness for image display.
For such an electronic viewfinder a configuration that employs as the light source a laser light source with field sequencing can be used, while a projection lens may be used to provide the optical imaging system aching for enabling this to be used as a protector
| Number | Date | Country | Kind |
|---|---|---|---|
| P2006-130864 | May 2006 | JP | national |
| P2006-162319 | Jun 2006 | JP | national |
