# Patent

## Title
Projection device and projection-type video display device

## Abstract

An illumination device includes an optical element including a hologram recording medium capable of diffusing a coherent light beam, the hologram recording medium comprising a plurality of regions, each region diffusing a coherent light beam to an illuminated region corresponding to that region, and an irradiation device configured to irradiate the optical element with the coherent light beam so as to allow the coherent light beam to scan the hologram recording medium. The coherent light beam incident to a position existing in each region of the hologram recording medium is diffused to an entire region of the illuminated region corresponding to the region in order to illuminate the entire region of the illuminated region.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. application Ser. No. 13/821,091, filed Mar. 6, 2013, the entirety of which is incorporated herein by reference, which in turn is the National Stage of International Application No. PCT/JP2011/070515, filed Sep. 8, 2011, which designated the United States.


FIELD OF THE INVENTION
The present invention relates to a projection device and a projection-type video display device displaying a plurality of videos by using a coherent light beam, and more particularly, to a projection device and a projection-type video display device capable of allowing occurrence of speckles to be inconspicuous.
BACKGROUND OF THE INVENTION
A projection-type video display device, including a screen and a projection device which projects a video image on the screen, has been widely used. In a typical projection-type video display device, a two-dimensional image as a basic image is generated by using a spatial light modulator such as a liquid crystal micro display or a DMD (digital micromirror device), and the two-dimensional image is magnified and projected on a screen by using a projection optical system, so that a video is displayed on the screen.
As the projection device, various types including a commercialized product called an “optical type projector” have been proposed. In a general optical type projector, the spatial light modulator such as a liquid crystal display is illuminated by using an illumination device including a white light source such as a high pressure mercury lamp, and an obtained modulation image is magnified and projected on the screen by using lenses. For example, Patent Literature 1 listed below discloses a technique where a white light beam generated by a supper-high pressure mercury lamp is divided into three primary color components R, G, and B by a dichiroic mirror, the light beams are guided to spatial light modulators corresponding to the primary colors, generated modulation images corresponding to the primary colors are combined by a cross dichiroic prism to be projected on the screen.
As an application of the projection device and the projection-type video display device, a projection device which projects video image corresponding to each screen on a plurality of the screens is known. In addition, a technique where signals representing different images can be output from one information processing terminal is also known, and video is displayed on a plurality of the screens by using the technique and the projection device.
A plurality of the projection devices are needed in order to project the video image corresponding to each screen on a plurality of the screens. At this time, although a plurality of the spatial light modulators and a plurality of the projection optical systems are needed, it has been considered that the projection device can be miniaturized by commonly using the illumination device illuminating the spatial light modulators.
However, the illumination device of the related art uses a high pressure mercury lamp, an LED, or the like as a light source to spread a light beam of the light source and transmit the light beam. In the illumination device of the related art, since the light beam is spread, there is a loss in light intensity, and there is a problem in that an optical system becomes large.
Further, high intensity discharge lamp such as a high pressure mercury lamp has a relatively short lifecycle, and in the case where the lamp is used for an optical type projector or the like, the lamp needs to be frequently replaced. In addition, since a relatively large optical system such as a dichiroic mirror is needed in order to extract the light beams of the primary color components, there is a problem in that the size of the whole apparatus is increased as described above.
In order to cope with this problem, a type using a coherent light source such as a laser is also proposed. For example, a semiconductor laser which is widely used in industries has a very long lifecycle in comparison with the high intensity discharge lamp such as a high pressure mercury lamp. In addition, since the laser source is a light source capable of generating light having a single wavelength, a spectroscopic apparatus such as a dichiroic mirror is unnecessary, so that there is an advantage in that the whole apparatus can be miniaturized. Further, since the diameter of the light beam of the laser can be easily controlled, a loss of light may not easily occur.
On the other hand, in the type using the coherent light source such as a laser source, there is another problem in that speckles occur. The speckle is a punctate pattern which occurs when the coherent light beam such as a laser beam is irradiated on a scattering plane. If the speckle occurs on the screen, it is observed as punctate luminance irregularity (brightness irregularity), so that it becomes a factor of exerting physiologically bad influence on the observer. The reason why the speckles occur in the case of using the coherent light beam is that the coherent light beams reflected from portions of the scattering reflecting plane such as a screen have very high coherency, and the speckles are generated through interference therebetween. For example, in Non Patent Literature 1 listed below, theoretical review of the occurrence of speckles is made in detail.
In the type of using the coherent light source, since there is an intrinsic problem in that the speckles occur, techniques for suppressing the occurrence of speckles have been proposed. For example, Patent Literature 2 listed below discloses a technique where a scattering plate is irradiated with a laser beam, an obtained scattered light beam is guided to a spatial light modulator, and the scattering plate is driven to rotate by a motor, so that speckles are reduced.
CITATION LIST
Patent Literature


    Patent Literature 1: JP 2004-264512 A
    Patent Literature 2: JP 6-208089 A


Non Patent Literature


    Non Patent Literature 1: Speckle Phenomena in Optics, Joseph W. Goodman, Roberts & Co., 2006


SUMMARY OF THE INVENTION
As described above, with respect to the projection device and the projection-type video display device using the coherent light source, the techniques for reducing speckles which have been proposed up to now may not effectively and sufficiently suppress the speckles. For example, in the method disclosed in Patent Literature 2 described above, since the laser beams irradiated on the scattering plate are scattered, a portion of the laser beams are lost without contribution to video display. In addition, the scattering plate needs to be rotated in order to reduce the speckles, the mechanical rotation mechanism becomes a relatively large apparatus, and the power consumption is increased. Moreover, although the scattering plate is rotated, the position of the optical axis of the illumination light beam is not changed, so that the speckles occurring due to the diffusion on the screen may not be sufficiently suppressed.
The inventors have researched based on the problems described hereinbefore, so that the inventors contrived a projection device and a projection-type video display device displaying a plurality of videos by using a coherent light beam, which are capable of allowing speckles to be inconspicuous and miniaturizing optical systems. In other words, the present invention is to provide a projection device and projection-type video display device which can display a plurality of videos and which are capable of allowing speckles to be inconspicuous and miniaturizing optical systems.
According to the present invention, there is provided a first projection device displaying video corresponding to each screen on a plurality of the screens, including:

    
    
        an optical element including a hologram recording medium where information is multiplexedly recorded in each position so as to allow a coherent light beam to be diffused to a plurality of regions;
        an irradiation device configured to irradiate the optical element with the coherent light beam so as to allow the coherent light beam to scan the hologram recording medium;
        spatial light modulators configured to be illuminated with the coherent light beam which is incident from the irradiation device to the hologram recording medium to be diffused to the plurality of regions; and
        projection optical systems, each projection optical system projecting modulation image obtained on each spatial light modulator on corresponding screen,
        wherein the coherent light beam, which is incident to each position of the hologram recording medium to be diffused, is illuminated on a plurality of the spatial light modulators.
    
    


According to the present invention, there is provided a second projection device displaying video corresponding to each screen on a plurality of the screens, including:

    
    
        an optical element including a hologram recording medium capable of reproducing an image of a scattering plate corresponding to each illuminated region in a plurality of the illuminated regions, and the images of the scattering plates being multiplexedly recorded at each position of the hologram recording medium;
        an irradiation device configured to irradiate the optical element with the coherent light beam so as to allow the coherent light beam to scan the hologram recording medium;
        spatial light modulators, each spatial light modulator disposed to position which overlap each illuminated region; and
        projection optical systems, each projection optical system projecting modulation image obtained on each spatial light modulator on corresponding screen,
        wherein the coherent light beam, which is incident from the irradiation device to each position of the hologram recording medium, reproduces the image of each scattering plate in each illuminated region.
    
    


According to the present invention, there is provided a third projection device displaying video corresponding to each screen on a plurality of the screens, including:

    
    
        an optical element including a hologram recording medium capable of diffusing a coherent light beam, the hologram recording medium including a plurality of regions;
        an irradiation device configured to irradiate the optical element with the coherent light beam so as to allow the coherent light beam to scan the hologram recording medium;
        spatial light modulators, each spatial light modulator being illuminated with the coherent light beam which is incident from the irradiation device to each region of the hologram recording medium to be diffused; and
        projection optical systems, each projection optical system projecting modulation image obtained on each spatial light modulator on corresponding screen,
        wherein the coherent light beam, which is incident to each position existing in each region of the hologram recording medium to be diffused, is overlappedly illuminated on the corresponding spatial light modulator.
    
    


According to the present invention, there is provided a fourth projection device displaying video corresponding to each screen on a plurality of the screens, including:

    
    
        an optical element including a hologram recording medium capable of reproducing an image of a scattering plate corresponding to each illuminated region in a plurality of the illuminated regions, and the hologram recording medium including a plurality of regions corresponding to the images of the scattering plates;
        an irradiation device configured to irradiate the optical element with the coherent light beam so as to allow the coherent light beam to scan the hologram recording medium;
        spatial light modulators, each spatial light modulator disposed to position which overlap each illuminated region; and
        projection optical systems, each projection optical system projecting modulation image obtained on each spatial light modulator on corresponding screen,
        wherein the coherent light beam, which is incident from the irradiation device to each position existing in each region of the hologram recording medium, reproduces the image of the scattering plate corresponding to each region in the corresponding illuminated region.
    
    


In any one of the first to fourth projection device of the present invention, the irradiation device may include:

    
    
        a light source configured to generate the coherent light beam; and
        a scan device configured to change a propagation direction of the coherent light beam from the light source and allow the coherent light beam to scan the hologram recording medium.
    
    


In any one of the first to fourth projection device of the present invention, the coherent light beam from the light source may be irradiated to one point of the scan device, the coherent light beam reflected from the one point of the scan device may constitute a diverging flux from the one point, and the diverging flux may be incident on the hologram recording medium.
In any one of the first to fourth projection device of the present invention,

    
    
        the coherent light beam from the light source may be irradiated to one point of the scan device, and the coherent light beam reflected from the one point of the scan device may constitute a diverging flux from the one point, and
        the projection device may further include a parallel light generation unit which propagates each light beam constituting the diverging flux in a certain direction to generate parallel light flux and allows the parallel light flux to be incident on the hologram recording medium.
    
    


In the third or fourth projection device of the present invention, the irradiation device may include:

    
    
        a light source configured to generate the coherent light beam; and
        a scan device configured to change a propagation direction of the coherent light beam from the light source and allow the coherent light beam to scan the hologram recording medium,
        the light source may include a plurality of light source units which emit a plurality of coherent light beams,
        a plurality of the coherent light beams emitted from a plurality of the light source units may be illuminated to the same point on the scan device, and
        each coherent light beam reflected from the same point on the scan device may constitute diverging flux from the same point, and each diverging flux may be incident on the corresponding region of the hologram recording medium.
    
    


In the third or fourth projection device of the present invention, the irradiation device may include:

    
    
        a light source configured to generate the coherent light beam; and
        a scan device configured to change a propagation direction of the coherent light beam from the light source and allow the coherent light beam to scan the hologram recording medium,
        the light source may include a plurality of light source units which emit a plurality of coherent light beams in substantially parallel directions,
        each coherent light beam emitted from a plurality of the light source units may be irradiated at corresponding point on the scan device, and
        each coherent light beam reflected at each point on the scan device may constitute diverging flux from the corresponding each point, and each diverging flux may be incident on the corresponding region of the hologram recording medium.
    
    


According to the present invention, there is provided a fifth projection device displaying video corresponding to each screen on a plurality of the screens, including:

    
    
        an optical element including a plurality of light diffusion elements, each light diffusion element capable of changing a propagation direction of an incident light beam;
        an irradiation device configured to irradiate the optical element with the coherent light beam so as to allow the coherent light beam to scan each light diffusion element;
        spatial light modulators, each spatial light modulator being illuminated with the coherent light beam which is incident from the irradiation device to each light diffusion element so that a propagation direction thereof is changed, and
        projection optical systems, each projection optical system projecting modulation image obtained on each spatial light modulator on corresponding screen, and
        wherein the propagation direction of the coherent light beam incident to each position of the optical element is changed by the corresponding light diffusion element so that the coherent light beam is overlappedly illuminated on the corresponding spatial light modulator.
    
    


According to the present invention, there is provided a sixth projection device displaying video corresponding to each screen on a plurality of the screens, including:

    
    
        an optical element including a plurality of light diffusion elements, each light diffusion element capable of changing a propagation direction of an incident light beam and illuminating a corresponding illuminated region among a plurality of illuminated regions;
        an irradiation device configured to irradiate the optical element with the coherent light beam so as to allow the coherent light beam to scan each light diffusion element;
        spatial light modulators, each spatial light modulator disposed to position which overlap each illuminated region; and
        projection optical systems, each projection optical system projecting modulation image obtained on each spatial light modulator on corresponding screen,
        wherein the propagation direction of the coherent light beam incident to each position of the optical element is changed by the corresponding light diffusion element so that the coherent light beam is illuminated on the corresponding illuminated region.
    
    


In the fifth or sixth projection device of the present invention, the irradiation device may include:

    
    
        a light source configured to generate the coherent light beam; and
        a scan device configured to change the propagation direction of the coherent light beam from the light source and allow the coherent light beam to scan each light diffusion element.
    
    


In the fifth or sixth projection device of the present invention, the light diffusion element may be a lens array.
According to the present invention, there is provided a projection-type video display device including:

    
    
        any one of the first to sixth projection device; and
        screens on which modulation images obtained on the spatial light modulators are projected.
    
    


According to the present invention, it is possible to display a plurality of videos, to allow speckles to be inconspicuous, and to miniaturize an optical system.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram illustrating configurations of an illumination device, a projection device, and a projection-type video display device according to a specific example of a first basic embodiment as a diagram illustrating the first basic embodiment among embodiments of the present invention.
FIG. 2 is a diagram illustrating the illumination device illustrated in FIG. 1.
FIG. 3 is a diagram illustrating an exposing method for manufacturing a hologram recording medium constituting an optical element of the illumination device illustrated in FIG. 2.
FIG. 4 is a diagram illustrating functions of the hologram recording medium manufactured by the exposing method illustrated in FIG. 3.
FIG. 5 is a perspective diagram illustrating functions of the illumination device illustrated in FIG. 1.
FIG. 6 is a schematic diagram illustrating configurations of an illumination device, a projection device, and a projection-type video display device according to a specific example of a second basic embodiment as a diagram illustrating the second basic embodiment among embodiments of the present invention.
FIG. 7 is a diagram illustrating an exposing method for manufacturing a hologram recording medium constituting an optical element of the illumination device illustrated in FIG. 6.
FIG. 8 is a diagram illustrating functions of the hologram recording medium manufactured by the exposing method illustrated in FIG. 7.
FIG. 9 is a schematic diagram illustrating configurations of an illumination device, a projection device, and a projection-type video display device according to a first modified example of the second basic embodiment.
FIG. 10 is a schematic diagram illustrating configurations of an illumination device, a projection device, and a projection-type video display device according to a second modified example of the second basic embodiment.
FIG. 11 is a perspective diagram illustrating a modified example of the irradiation device and functions thereof as a diagram corresponding to FIG. 5.
FIG. 12 is a perspective diagram illustrating another modified example of the irradiation device and functions thereof as a diagram corresponding to FIG. 2.



DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that, in the drawings attached to the specification, for the better understanding and the convenience of illumination, reduction scales, aspect ratios, and the like are exaggerated differently from those of real objects.
A projection device and a projection-type video display device according to the embodiments of the present invention have a basic configuration capable of effectively preventing speckles from occurring.
In the description hereinafter, first, a configuration which is capable of allowing speckles to be inconspicuous and displaying a plurality of videos and functions and effects which can be obtained based on the configuration will be described as a first basic embodiment with reference to a projection-type video display device including a projection device illustrated in FIGS. 1 to 5. Next, a second basic embodiment having configurations different from those of the first basic embodiment will be described with reference to FIGS. 6 to 8. Next, modified embodiments of the configurations will be described.
First Basic Embodiment
Configuration of First Basic Embodiment
First, a configuration of a projection-type video display device which includes an illumination device and a projection device projecting coherent light beams and which is capable of allowing speckles to be inconspicuous to display a plurality of videos will be described mainly with reference to FIGS. 1 to 5.
The projection-type video display device 10 illustrated in FIG. 1 includes three screens 15-1, 15-2, and 15-3 and a projection device 20 which projects video images including coherent light beams. The projection device 20 includes an illumination device 40 which simultaneously illuminates three illuminated regions LZ1, LZ2, and LZ3 located on a virtual plane with the coherent light beams, three spatial light modulators 30-1, 30-2, and 30-3 which are disposed at positions overlapping the illuminated regions LZ1 to LZ3 and are illuminated with the coherent light beams by the illumination device 40, and three projection optical systems 25-1, 25-2, and 25-3 which project each modulation image obtained on each of the spatial light modulators 30-1 to 30-3 to the corresponding screen 15-1 to 15-3 respectively.
For example, a transmission-type liquid crystal micro display may be used as the spatial light modulators 30-1 to 30-3. In this case, each of the spatial light modulators 30-1 to 30-3 which are illuminated in a planar shape by the illumination device 40 selectively transmits the coherent light beam for each pixel, so that each of the modulation images are formed on the screen of each display constituting each of the spatial light modulators 30-1 to 30-3. The modulation images (video images) obtained in this manner are changed in magnification and projected to the corresponding screens 15-1 to 15-3 by the projection optical systems 25-1 to 25-3. Therefore, the modulation images are displayed on the screens 15-1 to 15-3 with changed magnification (generally, enlargement), so that an observer can observe the three images.
Note that, a reflection-type micro display may be used as the spatial light modulators 30-1 to 30-3. In this case, the modulation images are formed by reflected light beams of the spatial light modulators 30-1 to 30-3, and the plane irradiated with the coherent light beams illuminated from the illumination device 40 to the spatial light modulators 30-1 to 30-3 and the plane of the video images constituting the modulation images progressing from the spatial light modulators 30-1 to 30-3 are the same plane. In the case where the reflected light beams are used, a MEMS element such as a DMD (Digital Micromirror Device) may be used as the spatial light modulators 30-1 to 30-3. In the apparatus disclosed in the Patent Literature 2 described above, the DMD is used as a spatial light modulator.
In addition, it is preferable that the incidence planes of the spatial light modulators 30-1 to 30-3 have the same shape and size as those of the illuminated regions LZ1 to LZ3 which are illuminated with the coherent light beams by the illumination device 40. This is because, in this case, the coherent light beams of the illumination device 40 can be used to display videos on the screens 15-1 to 15-3 with high use efficiency.
The screens 15-1 to 15-3 may be configured as transmission-type screens or as reflection-type screens. In the case where the screens 15-1 to 15-3 are configured as reflection-type screens, an observer observes a video displayed by the coherent light beams reflected by the screens 15-1 to 15-3 from the same side as the projection device 20 with respect to the screens 15-1 to 15-3. On the other hand, in the case where the screens 15-1 to 15-3 are configured as transmission-type screens, the observer observes a video displayed by the coherent light beams passing through the screens 15-1 to 15-3 from the side opposite to the projection device 20 with respect to the screens 15-1 to 15-3.
The coherent light beams projected on the screens 15-1 to 15-3 are diffused to be recognized as videos by an observer. At this time, the coherent light beams projected on the screens interfere with each other due to the diffusion, so that speckles occur. However, in the projection-type video display device 10 described herein, the illumination device 40 described hereinafter is configured to illuminate the illuminated regions LZ1 to LZ3, where the spatial light modulators 30-1 to 30-3 are overlapped, with the coherent light beams of which angles are changed in time. More specifically, although the illumination device 40 described hereinafter illuminates the illuminated regions LZ1 to LZ3 with diffused light beams including the coherent light beams, the incident angle of the diffused light beams is changed in time. As a result, the diffusion pattern of the coherent light beams on the screens 15-1 to 15-3 is also changed in time, and the speckles occurring due to the diffusion of the coherent light beams overlap in time, so that the speckles are inconspicuous. Hereinafter, the illumination device 40 will be described more in detail.
The illumination device 40 illustrated in FIGS. 1 and 2 includes an optical element 50 which divides a coherent light beam into three light beams and directs propagation directions of the divided light beams toward the illuminated regions LZ1 to LZ3 and an irradiation device 60 which irradiates the optical element 50 with the coherent light beam. The optical element 50 includes a hologram recording medium 55 which can reproduce the images 5-1 to 5-3 of the scattering plates 6-1 to 6-3. In the example illustrated, the optical element 50 is composed of the hologram recording medium 55.
In the example illustrated, the hologram recording medium 55 constituting the optical element 50 receives the coherent light beam illuminated from the irradiation device 60 as the reproduction illumination light beam La, diffracts the coherent light beam with high efficiency, and divides the coherent light beam. Particularly, the hologram recording medium 55 diffracts the coherent light beam which is incident to each position thereof, that is, a micro region which is to be called each point thereof, and the coherent light beam is divided into three light beams, the image 5-1 of the scattering plate 6-1, the image 5-2 of the scattering plate 6-2, and the image 5-3 of the scattering plate 6-3 can be simultaneously reproduced.
In other words, the hologram recording medium 55 allows the image of the scattering plate corresponding to each illuminated region to be reproduced in the illuminated regions LZ1 to LZ3. In addition, the images 5-1 to 5-3 of the scattering plates 6-1 to 6-3 are multiplexedly recorded at each position of the hologram recording medium 55. In other words, in the hologram recording medium 55, information is multiplexedly recorded in each position so as to allow a coherent light beam to be diffused to a plurality of regions.
On the other hand, the irradiation device 60 irradiates the optical element 50 with the coherent light beam so as to allow the coherent light beam of the hologram recording medium 55 to scan the hologram recording medium 55 of the optical element 50. Therefore, in some instant, a region of the hologram recording medium 55 which is irradiated with the coherent light beam by the irradiation device 60 is a portion of the surface of the hologram recording medium 55, and particularly, in the example illustrated, the region is the micro region which is to be called a point.
Next, the coherent light beam which is irradiated from the irradiation device 60 to scan the hologram recording medium 55 is incident to each position (each point or each region (the same will apply hereinafter)) on the hologram recording medium 55 with an incident angle satisfying a diffraction condition of the hologram recording medium 55. Particularly, as illustrated in FIG. 2, the coherent light beam incident from the irradiation device 60 to each position of the hologram recording medium 55 is allowed to reproduce the images 5-1 to 5-3 of the scattering plates 6-1 to 6-3 corresponding to each illuminated region on the illuminated regions LZ1 to LZ3. In other words, the coherent light beam incident from the irradiation device 60 to each position of the hologram recording medium 55 is diffused (spread) and divided by the optical element 50 to be incident on the illuminated regions LZ1 to LZ3. In other words, in some instant, the coherent light beam incident to certain position of the hologram recording medium 55 is illuminated on the entire region of each of the illuminated regions LZ1 to LZ3. In other words, the spatial light modulators 30-1 to 30-3 are illuminated with the coherent light beam which is incident from the irradiation device 60 to the hologram recording medium 55 to be diffused to a plurality of the illuminated regions LZ1 to LZ3.
In the example illustrated, a transmission-type volume hologram using a photopolymer is used as the hologram recording medium 55 which enables the diffraction function of the coherent light beam. As illustrated in FIG. 3, the hologram recording medium 55 is manufactured by using scattered light beams from the scattering plates 6-1 to 6-3 of a real object as the object light beams Lo1, Lo2, and Lo3. FIG. 3 illustrates a state where the hologram photosensitive material 58 having photosensitivity which is to constitute the hologram recording medium 55 is exposed by the reference light beams Lr1, Lr2 and Lr3 and the object light beams Lo1 to Lo3 which are the coherent light beams having mutual coherence.
For example, laser beams from three laser sources which oscillate the laser beams in a specific wavelength range are used as the reference light beams Lr1 to Lr3, and the reference light beams Lr1 to Lr3 pass through the light collection element 7 including lenses to simultaneously be incident on the hologram photosensitive material 58. In the example illustrated in FIG. 3, the laser beams constituting the reference light beams Lr1 to Lr3 are incident on the light collection element 7 as the parallel light flux which is parallel to the optical axis of the light collection element 7. The reference light beams Lr1 to Lr3 pass through the light collection element 7, so that the reference light beams Lr1 to Lr3 are shaped (transformed) from the parallel light flux to a converging light flux to be incident on the hologram photosensitive material 58. At this time, the focal points FP of converging light fluxes Lr1 to Lr3 are located beyond the hologram photosensitive material 58. In other words, the hologram photosensitive material 58 is disposed between the light collection element 7 and the focal points FP of converging light fluxes Lr1 to Lr3 which are collected by the light collection element 7.
Next, the object light beams Lo1 to Lo3 as scattered light beams from the scattering plates 6-1 to 6-3 made of, for example, an opal glass, on which the illumination light beams L1 to L3 are incident, are incident on the hologram photosensitive material 58. Since the hologram recording medium 55 which is to be manufactured herein is a transmission-type hologram recording medium, the object light beams Lo1 to Lo3 are incident from the same plane as those of the reference light beams Lr1 to Lr3 to the hologram photosensitive material 58. The object light beam Lo1 needs to have coherence with the reference light beam Lr1. Similarly, the object light beam Lo2 needs to have coherence with the reference light beam Lr2, and the object light beam Lo3 needs to have coherence with the reference light beam Lr3. On the other hand, it is preferable that the object light beam Lo1 have no coherence with the reference light beams Lr2 and Lr3. Similarly, it is preferable that the object light beam Lo2 have no coherence with the reference light beams Lr1 and Lr3, and the object light beam Lo3 have no coherence with the reference light beams Lr1 and Lr2. Therefore, for example, the laser beam oscillated from the same first laser source may be divided into two light beams, the one divided light beam may be used as the reference light beam Lr1 described above, and the other may be used as the illumination light beam L1. Similarly, the reference light beam Lr2 and the illumination light beam L2 may be generated by using the second laser source, and the reference light beam Lr3 and the illumination light beam L3 may be generated by using the third laser source. The laser beams from the first to third laser sources have the same wavelength.
In the example illustrated in FIG. 3, with respect to the scattering plate 6-1, the parallel light flux of the illumination light beam L1 parallel to the normal direction of the plate plane of the scattering plate 6-1 is incident on the scattering plate 6-1 and scattered, and the scattered light beam passing through the scattering plate 6-1 is incident on the hologram photosensitive material 58 as the object light beam Lo1. According to this method, in the case where an isotropic scattering plate which is generally available at low cost is used as the scattering plate 6-1, the object light beam Lol from the scattering plate 6-1 can be incident on the hologram photosensitive material 58 with a substantially uniform light amount distribution. In addition, according to this method, although the light amount distribution depends on the degree of scattering of the scattering plate 6-1, the object light beam Lo1 is easily incident from the entire area of the light emitting plane 6a of the scattering plate 6-1 to each position of the hologram photosensitive material 58 with a substantially uniform light amount. In this case, it can be realized that the light beam, which is incident to each position of the hologram recording medium 55 obtained, reproduces the image 5-1 of the scattering plate 6-1 with the same brightness, and the reproduced image 5-1 of the scattering plate 6-1 is observed with substantially uniform brightness. The same description can be made with respect to the scattering plates 6-2 and 6-3.
In this manner, if the hologram recording material 58 is exposed by the reference light beams Lr1 to Lr3 and the object light beams Lo1 to Lo3, the interference fringe is generated by interference between the reference light beam Lr1 and the object light beam Lo1, the interference fringe is generated by interference between the reference light beam Lr2 and the object light beam Lot, and the interference fringe is generated by interference between the reference light beam Lr3 and the object light beam Lo3. The interference fringes of these light beams are multiplexedly recorded in the hologram recording material 58 as a certain pattern (in the volume hologram, as an example, a refractive index modulation pattern). After that, appropriate post processes corresponding to the type of the hologram recording material 58 are performed, so that the hologram recording medium 55 is obtained.
In addition, the hologram recording medium 55 may be manufactured as follows. In the manufacturing method, the reference light beam Lr1 and the illumination light beam L1 which are generated by using one laser source are used. First, interference fringe is generated on the hologram recording material 58 by the reference light beam Lr1 and the object light beam Lo1 obtained from the illumination light beam L1 by using only the diffusion plate 6-1 of FIG. 3. Next, interference fringe is generated on the hologram recording material 58 by the reference light beam Lr1 and the object light beam Lot obtained from the illumination light beam L1 by using only the diffusion plate 6-2. Finally, interference fringe is generated on the hologram recording material 58 by the reference light beam Lr1 and the object light beam Lo3 obtained from the illumination light beam L1 by using only the diffusion plate 6-3. After that, appropriate post processes corresponding to the type of the hologram recording material 58 are performed, so that the hologram recording medium 55 is obtained. With respect to the diffusion plates 6-1 to 6-3, the same diffusion plate may be used.
FIG. 4 illustrates a diffraction function (reproduction function) of the hologram recording medium 55 obtained through the exposing process of FIG. 3. As illustrated in FIG. 4, with respect to the hologram recording medium 55 formed from the hologram photosensitive material 58 of FIG. 3, the light beam having the same wavelength as that of the laser beam used for the exposing process, which propagates in the reverse direction along the optical path of the reference light beam Lr in the exposing process, satisfies the Bragg condition. In other words, as illustrated in FIG. 4, the diverging flux, which diverges from the standard point SP located with respect to the hologram recording medium 55 which has the same positional relationship as the relative position (refer to FIG. 3) of the focal point FP with respect to the hologram photosensitive material 58 during the exposing process and has the same wavelength as that of the reference light beam Lr during the exposing process, is diffracted as the reproduction illumination light beam La by the hologram recording medium 55, so that the reproduced images 5-1 to 5-3 of the scattering plates 6-1 to 6-3 are generated at a specific positions with respect to the hologram recording medium 55 which have the same positional relationship as the relative positions (refer to FIG. 3) of the scattering plates 6-1 to 6-3 with respect to the hologram photosensitive material 58 during the exposing process.
The reproduced image 5-1 of the scattering plate 6-1 will be considered. At this time, the reproduction light beam (light beam obtained by diffracting the reproduction illumination light beam La with the hologram recording medium 55) Lb1 which generates the reproduced image 5-1 of the scattering plate 6-1 reproduces each point of the image 5-1 of the scattering plate 6-1 as a light beam which propagates in the reverse direction along the optical path of the object light beam Lo1 which propagates from the scattering plate 6-1 toward the hologram photosensitive material 58 during the exposing process. Then, as described above, as illustrated in FIG. 3, the object light beam Lo1 as the scattered light beam which emits from each position of the light emitting plane 6a of the scattering plate 6-1 during the exposing process is diffused (spread) so as to be incident on the substantially entire region of the hologram photosensitive material 58. In other words, the object light beam Lo1 from the entire region of the light emitting plane 6a of the scattering plate 6-1 is incident to each position on the hologram photosensitive material 58, so that information of the entire light emitting plane 6a is recorded in each position of the hologram recording medium 55. Therefore, each light beam constituting the diverging flux from the standard point SP which function as the reproduction illumination light beam La illustrated in FIG. 4 is individually incident to each position of the hologram recording medium 55, so that the images 5-1 of the scattering plate 6-1 having the same contour can be reproduced at the same position (illuminated region LZ1). The same description can be made with respect to the images 5-2 and 5-3 of the scattering plates 6-2 and 6-3.
On the other hand, the irradiation device 60 which irradiates the optical element 50 including the hologram recording medium 55 with the coherent light beam may be configured as follows. In the example illustrated in FIGS. 1 and 2, the irradiation device 60 includes a laser source 61a which generates a coherent light beam and a scan device 65 which changes the propagation direction of the coherent light beam from the laser source 61. The scan device 65 changes the propagation direction of the coherent light beam in time, so that the propagation direction of the coherent light beam is not a constant direction but various directions. As a result, the coherent light beam of which the propagation direction is changed by the scan device 65 is allowed to scan the incidence plane of the hologram recording medium 55 of the optical element 50.
Particularly, in the example illustrated in FIG. 2, the scan device 65 includes the reflection device 66 having the reflection plane 66a which can rotate about one axial line RA1. More specifically, the reflection device 66 is configured as a mirror device having a mirror as the reflection plane 66a which can rotate about one axial line RA1. Then, as illustrated in FIGS. 2 and 5, the mirror device 66 changes the orientation of the mirror 66a to change the propagation direction of the coherent light beam from the laser source 61a. At this time, as illustrated in FIG. 2, the mirror device 66 substantially receives the coherent light beam from the laser source 61a at the standard point SP. Therefore, the coherent light beam of which the propagation direction is finally adjusted by the mirror device 66 can be incident on the hologram recording medium 55 of the optical element 50 as the reproduction illumination light beam La (refer to FIG. 4) which can constitute one light beam of the diverging flux from the standard point SP. As a result, the coherent light beam from the irradiation device 60 is allowed to scan the hologram recording medium 55, and the coherent light beam incident to each position of the hologram recording medium 55 is allowed to reproduce the image 5-1 of the scattering plate 6-1 having the same contour at the same position (illuminated region LZ1), to reproduce the image 5-2 of the scattering plate 6-2 having the same contour at the same position (illuminated region LZ2), and to reproduce the image 5-3 of the scattering plate 6-3 having the same contour at the same position (illuminated region LZ3).
Note that, the mirror device 66 illustrated in FIG. 2 is configured to rotate the mirror 66a along one axial line RA1. FIG. 5 is a perspective diagram illustrating a configuration of the illumination device 40 illustrated in FIG. 2. In the example illustrated in FIG. 5, the rotation axial line RA1 of the mirror 66a is extended in parallel to the Y axis of the XY coordinate system defined on the plate plane of the hologram recording medium 55 (that is, the XY coordinate system where the XY plane is parallel to the plate plane of the hologram recording medium 55). Then, since the mirror 66a rotates about the axial line RA1 which is parallel to the Y axis of the XY coordinate system defined on the plate plane of the hologram recording medium 55, the incidence point IP of the coherent light beam from the irradiation device 60 to the optical element 50 is reciprocally moved in the direction which is parallel to the X axis of the XY coordinate system defined on the plate plane of the hologram recording medium 55. In other words, in the example illustrated in FIG. 5, the irradiation device 60 irradiates the optical element 50 with the coherent light beam so that the coherent light beam is allowed to scan the hologram recording medium 55 along the straight line path.
Note that, as a practical problem, there is a case where the hologram recording material 58 is contracted during the manufacturing of the hologram recording medium 55. In this case, by taking into consideration the shrinkage of the hologram recording material 58, it is preferable that the recording angles of the coherent light beams, which is irradiated on the optical element 50 by the irradiation device 60, is adjusted. Therefore, the wavelength of the coherent light beam generated by the coherent light source 61a needs not to be strictly equal to the wavelength of the light beam used in the exposing process (recording process) of FIG. 3, but the wavelengths thereof may be substantially equal to each other.
In addition, for the same reason, although the propagation directions of the light beams incident on the hologram recording medium 55 of the optical element 50 are not taken to be strictly equal to the one light beam constituting the diverging flux from the standard point SP, the images 5-1 to 5-3 can be reproduced in the illuminated regions LZ1 to LZ3. Actually, in the example illustrated in FIGS. 2 and 5, the mirror (reflection plane) 66a of the mirror device 66 constituting the scan device 65 is necessarily shifted from the rotation axial line RA1. Therefore, in the case where the mirror 66a is allowed to rotate about the rotation axial line RA1 which does not pass through the standard point SP, the light beam incident on the hologram recording medium 55 may not be one light beam constituting the diverging flux from the standard point SP. However, in a practical case, the coherent light beam from the irradiation device 60 having the illustrated configuration is allowed to substantially overlappedly reproduce the image 5-1 in the illuminated region LZ1. The same description can be made with respect to the images 5-2 and 5-3.
Functions and Effects of First Basic Embodiment
Next, the functions of the illumination device 40, the projection device 20, and the projection-type video display device 10 having the configuration described hereinbefore will be described.
First, the irradiation device 60 irradiates the optical element 50 with the coherent light beam so as to allow the coherent light beam to scan the hologram recording medium 55 of the optical element 50. More specifically, the laser source 61a generates a coherent light beam having a specific wavelength which propagates in a constant direction, and the scan device 65 can change a propagation direction of the coherent light beam. The scan device 65 allows the coherent light beam having a specific wavelength to be incident to each position of the hologram recording medium 55 with an incident angle satisfying the Bragg Condition of the position. As a result, due to the diffraction and division on the hologram recording medium 55, the coherent light beam incident to each position overlappedly reproduces the image 5-1 of the scattering plate 6-1 in the illuminated region LZ1, overlappedly reproduces the image 5-2 of the scattering plate 6-2 in the illuminated region LZ2, and overlappedly reproduces the image 5-3 of the scattering plate 6-3 in the illuminated region LZ3. In other words, the coherent light beam incident to a certain position is simultaneously illuminated on the illuminated regions LZ1 to LZ3. In other words, the coherent light beam incident from the irradiation device 60 to each position of the hologram recording medium 55 is diffused (spread) by the optical element 50 and divided so as to be incident on the entire region of each of the illuminated regions LZ1 to LZ3. In this manner, the irradiation device 60 irradiates the illuminated regions LZ1 to LZ3 with the coherent light beams.
As illustrated in FIG. 1, in the projection device 20, the spatial light modulators 30-1 to 30-3 are disposed at the positions which overlap the illuminated regions LZ1 to LZ3 of the illumination device 40. Therefore, with respect to the spatial light modulators 30-1 to 30-3, the planes thereof are illuminated by the illumination device 40, and each pixel is allowed to selectively transmit the coherent light beam, so that three videos are formed. Each video is projected on the corresponding screens 15-1 to 15-3 by the corresponding projection optical systems 25-1 to 25-3. The coherent light beams projected on the screens 15-1 to 15-3 are diffused and recognized as videos by an observer. However, at this time, the coherent light beams projected on the screen interfere with each other due to the diffusion, so that speckles occur.
However, according to the illumination device 40 of the first basic embodiment described herein, as described below, it is possible to very effectively allow the speckles to be inconspicuous. Since the speckles can be allowed to be inconspicuous according to the same principle with respect to the illuminated regions LZ1 to LZ3, the description hereinafter is made on only the illuminated region LZ1.
The Non Patent Literature 1 described above discloses that multiplexing of parameters of polarization, phase, angle, and time and increasing of modes are effective to allow the speckles to be inconspicuous. Herein, the modes denote speckle patterns having no correlation therebetween. For example, in the case where the coherent light beams from a plurality of the laser sources are projected on the same screen in different directions, the number of the modes is equal to the number of the laser sources exist. In addition, in the case where the coherent light beam from the same laser source is projected on the screen in different directions in a time division manner, the number of the modes is equal to the number of changing of the incident direction of the coherent light beam within a time which may not be resolved by human eyes. Then, it is considered that, in the case where a plurality of the modes exist, the interference patterns of light beams overlap each other with no correlation to be averaged, so that the speckles observed with observer's eyes are inconspicuous.
In the irradiation device 60 described above, the coherent light beam is irradiated on the optical element 50 so as to scan the hologram recording medium 55. In addition, with respect to the coherent light beams incident from the irradiation device 60 to the positions of the hologram recording medium 55, although the entire region of the same illuminated region LZ1 is illuminated with the coherent light beam, the illumination directions of the coherent light beams which are illuminated on the illuminated region LZ1 are mutually different. Then, since the position on the hologram recording medium 55 where the coherent light beam is incident is changed in time, the incident direction of the coherent light beam incident on the illuminated region LZ1 is also changed in time.
If the illuminated region LZ1 is considered as a standard, although the coherent light beam is consistently incident to the positions inside the illuminated region LZ1, the incident direction is always continuously changed as indicated by arrow A1 in FIG. 1. As a result, the light beam constituting each pixel of the video formed by the transmitted light beam of the spatial light modulator 30-1 is projected on specific position of the screen 15-1 while the optical path is changed in time as indicated by arrow A2 in FIG. 1.
Note that, the coherent light beam is allowed to continuously scan the hologram recording medium 55. Accordingly, the incident direction of the coherent light beam incident from the irradiation device 60 to the illuminated region LZ1 is also continuously changed, and the incident direction of the coherent light beam incident from the projection device 20 to the screen 15-1 is also continuously changed. Here, if the incident direction of the coherent light beam incident from the projection device 20 to the screen 15-1 is changed by only a small amount (for example, several deci-degrees), the pattern of speckles occurring on the screen 15-1 is also greatly changed, so that speckle patterns having no correlation overlap. In addition, the frequency of the scan device 65 such as a MEMS mirror or a polygon mirror which is actually commercially available is typically several hundred Hz or more, and in some cases, the frequency of the scan device 65 may be several tens of thousands of Hz.
Hereinbefore, according to the first basic embodiment described above, the incident direction of the coherent light beam is changed in time at each position of each of the screens 15-1 to 15-3 displaying videos, and the speed of the change thereof is such a speed that the change may not be distinguished by human eyes, and thus, the multiplexed scattering patterns of the coherent light beams having no correlation are observed by human eyes. Therefore, the speckles occurring corresponding to the scattering patterns overlap to be averaged and are observed by an observer. Therefore, with respect to the observer who observes the videos displayed on the screens 15-1 to 15-3, the speckles are very effectively allowed to be inconspicuous.
Note that, with respect to the speckles observed by human in the related art, the speckles of the screen side may occur due to the scattering of the coherent light beams on the screens 15-1 to 15-3, and the speckles of the projection device side may occur due to the scattering of the coherent light beams before projection on the screens. The speckle pattern occurring at the projection device side is projected on the screens 15-1 to 15-3 through the spatial light modulators 30-1 to 30-3, so that the speckle pattern can be recognized by the observer. However, according to the basic embodiment described above, the coherent light beam is allowed to continuously scan the hologram recording medium 55, and the coherent light beam which is incident to each position of the hologram recording medium 55 is illuminated on the entire regions of the illuminated regions LZ1 to LZ3 which the spatial light modulators 30-1 to 30-3 overlap. In other words, the hologram recording medium 55 forms a new wavefront differently from the existing wavefront which forms the speckle pattern, and illuminates complicatedly and uniformly the illuminated regions LZ1 to LZ3 and the screens 15-1 to 15-3 through the spatial light modulators 30-1 to 30-3. Due to the formation of the new wavefront by the hologram recording medium 55, the speckle pattern occurring at the projection device side may not be visually perceived.
The Non Patent Literature 1 described above discloses a method of using a numerical value called speckle contrast as a parameter indicating a degree of speckles occurring on the screen. When a video of a test pattern which needs to have an originally uniform luminance distribution is displayed, the video on the screen actually have a variation in luminance. The speckle contrast is a quantity defined as a value obtained by dividing a standard deviation of the variation in luminance by an average value of luminance. As the value of the speckle contrast is increased, the degree of occurrence of speckles on the screen is increased, and thus, a punctate luminance irregularity pattern is more remarkably represented to an observer.
Hereinafter, the speckle contrast on the screen 15-1 will be described. In the projection-type video display device 10 according to the basic embodiment described with reference to FIGS. 1 to 5, the speckle contrast on the screen 15-1 is measured to be 3.0% (Condition 1). In addition, in the case where, instead of the reflection-type volume hologram, a relief type hologram which is a computer generated hologram (CGH) having a convex-concave shape designed by using a computer so as to generate an image 5-1 of the scattering plate 6-1 when a specific reproduction illumination light beam is received is used as the optical element 50 described above, the speckle contrast is measured to be 3.7% (Condition 2). In the application of HDTV (high definition TV) video display, although a criterion that the speckle contrast is equal to or less than 6.0% is set (for example, refer to WO/2001/081996) as a level that an observer may not almost recognize the luminance irregularity pattern through visual observation, the basic embodiment described above satisfies the criterion. In addition, actually, in visual observation, luminance irregularity (brightness irregularity) to a degree that it can be visually perceived does not occur.
On the other hand, in the case where the laser beam from the laser source is shaped to be in the parallel light flux and is incident on the spatial light modulator 30-1, that is, in the case where the coherent light beam from the laser source 61a as the parallel light flux is incident on the spatial light modulator 30-1 of the projection-type video display device 10 illustrated in FIG. 1 without use of the scan device 65 and the optical element 50, the speckle contrast becomes 20.7% (Condition 3). Under the condition, punctate luminance irregularity patterns are very conspicuously observed through visual observation.
In addition, in the case where the light source 61a is replaced with a green LED (incoherent light source) and the light beam from the LED light source is incident on the spatial light modulator 30-1, that is, in the case where the incoherent light beam from the LED light source as the parallel light flux is incident on the spatial light modulator 30-1 of the projection-type video display device 10 illustrated in FIG. 1 without use of the scan device 65 and the optical element 50, the speckle contrast becomes 4.0% (Condition 4). Under the condition, luminance irregularity (brightness irregularity) to a degree that it can be perceived through visual observation does not occur.
The results of Conditions 1 and 2 are much better than the result of Condition 3, and the results of Conditions 1 and 2 are better than the measurement result of Condition 4. As described above, the problem of occurrence of speckles is practically an intrinsic problem occurring in the case of using a coherent light source such as a laser source, and thus, the problem needs not be considered in the case of an apparatus using an incoherent light source such as an LED. In addition, in comparison with Condition 4, in Conditions 1 and 2, the optical element 50 which may cause occurrence of speckles is added. In terms of this point, it is considered that it is possible to sufficiently cope with the speckle defect according to Conditions 1 and 2.
In addition, according to the first basic embodiment described above, the following advantages can be obtained.
According to the first basic embodiment described above, the optical element 50 for allowing the speckles to be inconspicuous may also function as an optical member for dividing the coherent light beam irradiated from the irradiation device 60 into three light beams, changing the angles of the divided light beams, and shaping and adjusting the shapes of the divided light beams. Therefore, it is possible to miniaturize and simplify the optical system. In addition, the transmission of the light becomes easy.
In addition, according to the first basic embodiment described above, since the videos corresponding to the screens can be simultaneously displayed on the three screens 15-1 to 15-3, it is possible to increase an amount of display information in comparison with the projection-type video display device displaying video on only one screen. In addition, it is possible to perform panorama display where one video is displayed over the three screens 15-1 to 15-3 in a seamless manner. Therefore, the projection-type video display device according to the basic embodiment can be used as a display having a high sense of realization.
In addition, according to the first basic embodiment described above, the coherent light beam which is incident to each position of the hologram recording medium 55 allows the image 5-1 of the scattering plate 6-1 to be generated at the mutually same first position, allow the image 5-2 of the scattering plate 6-2 to be generated at the mutually same second position, and allow the image 5-3 of the scattering plate 6-3 to be generated at the mutually same third position. Further, the spatial light modulators 30-1 to 30-3 are disposed to overlap the images 5-1 to 5-3. Therefore, the light beam diffracted by the hologram recording medium 55 can be used for video formation with high efficiency, so that use efficiency of the light from the light source 61a is excellent.
Second Basic Embodiment
A second basic embodiment relates to a projection device and a projection-type video display device displaying a plurality of videos by using a hologram recording medium different from that of the first basic embodiment. More specifically, the hologram recording medium according to the second basic embodiment includes three regions, and an image of a diffusion plate is recorded in each region.
Configuration of Second Basic Embodiment
First, the configuration of the projection-type video display device will be described with reference to FIG. 6, and the description is made mainly on different components from the first basic embodiment.
As illustrated in FIG. 6, the optical element 50 includes the hologram recording medium 55a which can reproduce the image of the scattering plate corresponding to each illuminated region on the illuminated regions LZ1 to LZ3. In addition, the hologram recording medium 55a includes three regions 55a-1, 55a-2, and 55a-3 corresponding to the images 5-1 to 5-3 of the scattering plates 6-1 to 6-3. In other words, on the hologram recording medium 55a, in the region 55a-1, the image 5-1 of the corresponding scattering plate 6-1 is recorded, in the region 55a-2, the image 5-2 of the corresponding scattering plate 6-2 is recorded, and in the region 55a-3, the image 5-3 of the corresponding scattering plate 6-3 is recorded. In the example illustrated, the optical element 50 is composed of the hologram recording medium 55a. Other configurations are the same as those of the first basic embodiment of FIG. 1. Therefore, the same components are denoted by the same reference numerals, and the description thereof is not repeated.
In the example illustrated, the hologram recording medium 55a receives the coherent light beam irradiated from the irradiation device 60 as the reproduction illumination light beam La to diffract the coherent light beam with high efficiency. Particularly, the hologram recording medium 55a diffracts the coherent light beam which is incident to each position existing in the region 55a-1, that is, a micro region which is to be called each point existing in the region 55a-1, so that the image 5-1 of the scattering plate 6-1 can be reproduced in the illuminated region LZ1. Similarly, the hologram recording medium 55a diffracts the coherent light beam which is incident to each position of the region 55a-2, so that the image 5-2 of the scattering plate 6-2 can be reproduced in the illuminated region LZ2; and the hologram recording medium 55a diffracts the coherent light beam which is incident to each position of the region 55a-3, so that the image 5-3 of the scattering plate 6-3 can be reproduced in the illuminated region LZ3.
On the other hand, the irradiation device 60 irradiates the optical element 50 with the coherent light beam so as to allow the coherent light beam of the hologram recording medium 55a to scan the hologram recording medium 55a of the optical element 50. Therefore, in some instant, a region of the hologram recording medium 55a which is irradiated with the coherent light beam by the irradiation device 60 is a portion of the surface of the hologram recording medium 55a, and particularly, in the example illustrated, the region is the micro region which is to be called a point. In other words, in some instant, the micro region of any one of the regions 55a-1 to 55a-3 of the hologram recording medium 55a is irradiated with the coherent light beam.
Next, as illustrated in FIG. 6, the coherent light beam incident from the irradiation device 60 to each position existing in each of the regions 55a-1 to 55a-3 of the hologram recording medium 55a overlappedly reproduces the images 5-1 to 5-3 of the scattering plates 6-1 to 6-3 corresponding to each of the regions 55a-1 to 55a-3 in the corresponding illuminated regions LZ1 to LZ3. In other words, the coherent light beam incident from the irradiation device 60 to each position of the region 55a-1 of the hologram recording medium 55a is diffused (spread) by the optical element 50 so as to be incident on the illuminated region LZ1. Similarly, the coherent light beam incident to each position of the region 55a-2 of the hologram recording medium 55a is diffused (spread) by the optical element 50 so as to be incident on the illuminated region LZ2. In addition, the coherent light beam incident to each position of the region 55a-3 of the hologram recording medium 55a is diffused (spread) by the optical element 50 so as to be incident on the illuminated region LZ3. In other words, in some instant, the coherent light beam incident to a certain position of the hologram recording medium 55a is illuminated on the entire region of any one of the illuminated regions LZ1 to LZ3. In this manner, each of the spatial light modulators 30-1 to 30-3 is illuminated with the coherent light beam which is incident from the irradiation device 60 to each of the regions 55a-1 to 55a-3 of the hologram recording medium 55a to be diffused.
As illustrated in FIG. 7, the hologram recording medium 55a is manufactured by using the scattered light beams from the scattering plates 6-1 to 6-3 of real objects as the object light beams Lo1, Lo2, and Lo3. FIG. 7 illustrates a state where the hologram photosensitive material 58 having photosensitivity which is to constitute the hologram recording medium 55a is exposed by the reference light beam Lr and the object light beam Lo1 which are mutually coherent. Herein, an example of three divided steps of exposing the hologram photosensitive material 58 will be described. In other words, as illustrated in FIG. 7, in a first step, the regions 55a-2 and 55a-3 are covered with a mask 100 blocking light, and only the region 55a-1 is exposed by the reference light beam Lr and the object light beam Lo1 obtained from the scattering plate 6-1. In a second step, the regions 55a-1 and 55a-3 are covered with the mask 100 blocking light, and only the region 55a-2 is exposed by the reference light beam Lr and the object light beam Lo2 obtained from the scattering plate 6-2 (not illustrated). In a third step, the regions 55a-1 and 55a-2 are covered with the mask 100 blocking light, and only the region 55a-3 is exposed by the reference light beam Lr and the object light beam Lo3 obtained from the scattering plate 6-3 (not illustrated).
For example, a laser beam from the laser source which oscillates a laser beam in a specific wavelength range is used as the reference light beam Lr, and the reference light beam Lr passes through the light collection element 7 including lenses to be incident on the hologram photosensitive material 58.
In the first step, the object light beam Lo1 as a scattered light beam from the scattering plate 6-1 made of, for example, an opal glass, on which the illumination light beam L is incident, is incident on the hologram photosensitive material 58. The object light beam Lo1 needs to have coherence with the reference light beam Lr. Therefore, for example, a laser beam oscillated from the same laser source may be divided, one of the divided beams may be used as the reference light beam Lr described above, and the other may be used as the illumination light beam L.
In this manner, if the hologram recording material 58 is exposed by the reference light beam Lr and the object light beam Lo1, the interference fringe is generated by interference between the reference light beam Lr and the object light beam Lo1, and the interference fringe of the light beams is recorded in the hologram recording material 58 as a certain pattern (for example, in the case of a volume hologram, a refractive index modulated pattern). After that, similarly, the above-described second and third steps of exposure are performed. At the last, appropriate post processes corresponding to the type of the hologram recording material 58 are performed, so that the hologram recording medium 55a is obtained.
FIG. 8 illustrates a diffraction function (reproduction function) of the hologram recording medium 55a obtained through the exposing process of FIG. 7. As illustrated in FIG. 8, with respect to the hologram recording medium 55a formed from the hologram photosensitive material 58 of FIG. 7, the light beam having the same wavelength as that of the laser beam used for the exposing process, which propagates in the reverse direction along the optical path of the reference light beam Lr in the exposing process, satisfies the Bragg condition. In other words, as illustrated in FIG. 8, the diverging flux, which diverges from the standard point SP located with respect to the hologram recording medium 55a which has the same positional relationship as the relative position (refer to FIG. 7) of the focal point FP with respect to the hologram photosensitive material 58 during the exposing process and has the same wavelength as that of the reference light beam Lr during the exposing process, is diffracted as the reproduction illumination light beam La by the hologram recording medium 55a, so that the reproduced images 5-1 to 5-3 of the scattering plates 6-1 to 6-3 are generated at a specific positions with respect to the hologram recording medium 55 which have the same positional relationship as the relative positions (refer to FIG. 7) of the scattering plates 6-1 to 6-3 with respect to the hologram photosensitive material 58 during the exposing process.
The region 55a-1 of the hologram recording medium 55a will be considered. At this time, the reproduction light beam (light beam obtained by diffracting the reproduction illumination light beam La with the hologram recording medium 55) Lb1 which generates the reproduced image 5-1 of the scattering plate 6-1 reproduces each point of the image 5-1 of the scattering plate 6-1 as a light beam which propagates in the reverse direction along the optical path of the object light beam Lol which propagates from the scattering plate 6-1 toward the hologram photosensitive material 58 during the exposing process. Then, as described above, as illustrated in FIG. 7, the object light beam Lo1 as the scattered light beam which emits from each position of the light emitting plane 6a of the scattering plate 6-1 during the exposing process is diffused (spread) so as to be incident on the substantially entire region of the region 55a-1 of the hologram photosensitive material 58. In other words, the object light beam Lo1 from the entire region of the light emitting plane 6a of the scattering plate 6-1 is incident to each position of the region 55a-1 on the hologram photosensitive material 58, so that information of the entire light emitting plane 6a is recorded in each position of the region 55a-1 of the hologram recording medium 55a. Therefore, each light beam constituting the diverging flux from the standard point SP which function as the reproduction illumination light beam La illustrated in FIG. 8 is individually incident to each position of the region 55a-1 of the hologram recording medium 55a, so that the images 5-1 of the scattering plate 6-1 having the same contour can be reproduced at the same position (illuminated region LZ1). The same description can be made with respect to the regions 55a-2 and 55a-3.
Functions and Effects of Second Basic Embodiment
Next, the functions of the illumination device 40, the projection device 20, and the projection-type video display device 10 having the configuration described hereinbefore will be described.
First, the irradiation device 60 irradiates the optical element 50 with the coherent light beam so as to allow the coherent light beam to scan the hologram recording medium 55a of the optical element 50. More specifically, the laser source 61a generates a coherent light beam having a specific wavelength which propagates in a constant direction, and the scan device 65 can change a propagation direction of the coherent light beam. The scan device 65 allows the coherent light beam having a specific wavelength to be incident to each position of the hologram recording medium 55a with an incident angle satisfying the Bragg Condition of the position. As a result, the coherent light beam incident to each position existing in each of the regions 50a-1 to 50a-3 overlappedly reproduces the images 5-1 to 5-3 of the scattering plates 6-1 to 6-3 corresponding to each of the regions 55a-1 to 55a-3 in the corresponding illuminated regions LZ1 to LZ3. More specifically, due to the diffraction on the hologram recording medium 55a, the coherent light beam incident to each position existing in the region 50a-1 overlappedly reproduces the image 5-1 of the scattering plate 6-1 in the illuminated region LZ1. Similarly, the coherent light beam incident to each position existing in the region 50a-2 overlappedly reproduces the image 5-2 of the scattering plate 6-2 in the illuminated region LZ2, and the coherent light beam incident to each position existing in the region 50a-3 overlappedly reproduces the image 5-3 of the scattering plate 6-3 in the illuminated region LZ3. In other words, the coherent light beam incident from the irradiation device 60 to each position which exists in each of the regions 50a-1 to 50a-3 of the hologram recording medium 55a is diffused (spread) by the optical element 50 so as to be incident on the entire region of the corresponding illuminated regions LZ1 to LZ3. In this manner, the irradiation device 60 irradiates the illuminated regions LZ1 to LZ3 with the coherent light beams.
As described above, in some instant, the coherent light beam incident to a certain position existing in the region 50a-1 of the hologram recording medium 55a is illuminated on the entire region of the illuminated region LZ1. Therefore, at this time, the illuminated regions LZ2 and LZ3 are not illuminated. In other words, the coherent light beam is allowed to scan the hologram recording medium 55a, so that any one of the illuminated regions LZ1 to LZ3 is illuminated one by one. If the scan speed of the coherent light beam scanning the hologram recording medium 55a is appropriately set, the existence of the time period when the illuminated regions LZ1 to LZ3 are not illuminated cannot be recognized by an observer.
As described in the first basic embodiment, in the projection device 20 illustrated in FIG. 6, the spatial light modulators 30-1 to 30-3 are disposed at the positions which overlap the illuminated regions LZ1 to LZ3 of the illumination device 40. Therefore, with respect to the spatial light modulators 30-1 to 30-3, the planes thereof are illuminated by the illumination device 40, and each pixel is allowed to selectively transmit the coherent light beam, so that three videos are formed. Each video is projected on the corresponding screens 15-1 to 15-3 by the corresponding projection optical systems 25-1 to 25-3. The coherent light beams projected on the screens 15-1 to 15-3 are diffused and recognized as videos by an observer. However, at this time, the coherent light beams projected on the screen interfere with each other due to the diffusion, so that speckles occur.
However, according to the illumination device 40 of the second basic embodiment described herein, it is possible to very effectively allow the speckles to be inconspicuous by the same principle as that of the first basic embodiment.
In other words, according to the second basic embodiment described above, the incident direction of the coherent light beam is changed in time at each position of each of the screens 15-1 to 15-3 displaying videos, and the speed of the change thereof is such a speed that the change may not be distinguished by human eyes, and thus, the multiplexed scattering patterns of the coherent light beams having no correlation are observed by human eyes. Therefore, the speckles occurring corresponding to the scattering patterns overlap to be averaged and are observed by an observer. Therefore, with respect to the observer who observes the videos displayed on the screens 15-1 to 15-3, the speckles are very effectively allowed to be inconspicuous.
In addition, according to the second basic embodiment described above, similarly to the first basic embodiment, the following advantages can be obtained.
According to the second basic embodiment described above, optical element 50 for allowing the speckles to be inconspicuous may also function as an optical member for dividing the coherent light beam irradiated from the irradiation device 60 into three light beams, changing the angles of the divided light beams, and shaping and adjusting the shapes of the divided light beams. Therefore, it is possible to miniaturize and simplify the optical system.
In addition, according to the second basic embodiment described above, since the videos corresponding to the screens can be simultaneously displayed on the three screens 15-1 to 15-3, it is possible to increase an amount of display information in comparison with the projection-type video display device displaying video on only one screen. In addition, it is possible to perform panorama display where one video is displayed over the three screens 15-1 to 15-3 in a seamless manner. Therefore, the projection-type video display device according to the basic embodiment can be used as a display having a high sense of realization.
In addition, according to the second basic embodiment described above, the coherent light beam which is incident to each position of the region 55a-1 of the hologram recording medium 55a allows the image 5-1 of the scattering plate 6-1 to be generated at the mutually same first position. Similarly, the coherent light beam which is incident to each position of the region 55a-2 allows the image 5-2 of the scattering plate 6-2 to be generated at the mutually same second position, and the coherent light beam which is incident to each position of the region 55a-3 allows the image 5-3 of the scattering plate 6-3 to be generated at the mutually same third position. Further, the spatial light modulators 30-1 to 30-3 are disposed so as to overlap the images 5-1 to 5-3. Therefore, the light beam diffracted by the hologram recording medium 55a can be used for video formation with high efficiency, so that use efficiency of the light from the light source 61a is excellent.
Note that, instead of the hologram recording medium 55a having the regions 55a-1 to 55a-3, three hologram recording media corresponding to the regions 55a-1 to 55a-3 may be combined.
Modifications of First and Second Basic Embodiments
The first and second embodiments described above based on one specific example exemplified in FIGS. 1 to 8 can be modified in various forms. Hereinafter, modified examples will be described with reference to the drawings. In the drawings used for the description hereinafter, the components corresponding to those of the embodiments described above are denoted by the same reference numerals, and the description thereof will not be repeated.
Projection Device
In the basic embodiment, the example where each of the spatial light modulators 30-1 to 30-3 is disposed at the position which overlaps the corresponding illuminated regions LZ-1 to LZ-3 is described. However, each of the spatial light modulators 30-1 to 30-3 may not be disposed at the position which strictly overlaps the corresponding illuminated regions LZ-1 to LZ-3. For example, in the configuration of the first basic embodiment of FIG. 1, the spatial light modulator 30-1 may be disposed to the optical element 50 side rather than the illuminated region LZ-1, and the spatial light modulator 30-1 may be disposed to the projection optical system 25-1 side rather than the illuminated region LZ-1. The same description can be made with respect to the spatial light modulators 30-2 and 30-3. In other words, in the first basic embodiment, the hologram recording medium 55 and the spatial light modulators 30-1 to 30-3 may be disposed so that the coherent light beam, which is incident to each position of the hologram recording medium 55 to be diffused, overlappedly illuminates on a plurality of the spatial light modulators 30-1 to 30-3. In addition, in the second basic embodiment, the hologram recording medium 55a and the spatial light modulators 30-1 to 30-3 may be disposed so that the coherent light beam, which is incident to each position existing in each of the regions 55a-1 to 55a-3 of the hologram recording medium 55a to be diffused, overlappedly illuminates on the corresponding spatial light modulators 30-1 to 30-3.
First Modified Example of Second Basic Embodiment
In the second basic embodiment, the coherent light beam is allowed to scan the hologram recording medium 55a, so that any one of the illuminated regions LZ1 to LZ3 is illuminated one by one. On the contrary, as illustrated in FIG. 9, the three laser sources (light source units) 61a-1 to 61a-3 may be configured to be used to allow the coherent light beams to simultaneously scan the regions 55a-1 to 55a-3 of the hologram recording medium 55a, so that all the illuminated regions LZ1 to LZ3 can be simultaneously illuminated.
In the example illustrated in FIG. 9, the mirror device 66 receives the coherent light beams from the laser sources 61a-1 to 61a-3 roughly at the standard point SP. Therefore, the coherent light beams of which the propagation directions are finally adjusted by the mirror device 66 can be incident on the hologram recording medium 55a as the reproduction illumination light beams La1 to La3, each of which can constitute one light beam of the diverging flux from the standard point SP. As a result, the region 55a-1 of the hologram recording medium 55a receives the coherent light beam irradiated from the laser source 61a-1 as the reproduction illumination light beam La1. Similarly, the region 55a-2 of the hologram recording medium 55a receives the coherent light beam irradiated from the laser source 61a-2 as the reproduction illumination light beam La2, and the region 55a-3 receives the coherent light beam irradiated from the laser source 61a-3 as the reproduction illumination light beam La3.
Therefore, the coherent light beams from the irradiation device 60 can be allowed to simultaneously scan the regions 55a-1 to 55a-3 of the hologram recording medium 55a. In addition, the coherent light beam incident to each position of the region 55a-1 of the hologram recording medium 55a is allowed to reproduce the image 5-1 of the scattering plate 6-1 having the same contour at the same position (illuminated region LZ1), the coherent light beam incident to each position of the region 55a-2 is allowed to reproduce the image 5-2 of the scattering plate 6-2 at the same position (illuminated region LZ2), and the coherent light beam incident to each position of the region 55a-3 is allowed to reproduce the image 5-3 of the scattering plate 6-3 at the same position (illuminated region LZ3).
According to this modified example, since all the illuminated regions LZ1 to LZ3 are simultaneously illuminated, the illumination device 40 can illuminate the illuminated regions LZ1 to LZ3 more brightly. Therefore, brighter videos can be formed on the screens 15-1 to 15-3.
In addition, the same effects as those of the second basic embodiment can be obtained.
Second Modified Example of Second Basic Embodiment
As illustrated in FIG. 10, the three laser sources 61a-1 to 61a-3 may be disposed to be parallel to each other so that the reproduction illumination light beams La1 to La3 are allowed to be incident on the hologram recording medium 55a as diverging light beams. In other words, in this configuration, the coherent light beams emitted from the laser sources 61a-1 to 61a-3 are incident to three positions of the scan device 65 as parallel light beams, and the coherent light beam is reflected from each position toward the hologram recording medium 55a as diverging light beam.
In this configuration, the region 55a-1 of the hologram recording medium 55a also receives the coherent light beam irradiated from the laser source 61a-1 as the reproduction illumination light beam La1. Similarly, the region 55a-2 of the hologram recording medium 55a receives the coherent light beam irradiated from the laser source 61a-2 as the reproduction illumination light beam La2, and the region 55a-3 receives the coherent light beam irradiated from the laser source 61a-3 as the reproduction illumination light beam La3.
According to this modified example, the coherent light beams irradiated on the mirror plane of the scan device 65 are dispersed, and thus, strong light beam is not irradiated on specific position of the mirror plane, so that durability of the scan device 65 is improved.
In addition, it is possible to obtain the same effects as those of the second basic embodiment and the first modified example of the second basic embodiment.
Note that, a laser array configured by integrating three laser sources may be used as the laser sources 61a-1 to 61a-3.
A portion of the coherent light beam from the irradiation device 60 passes through the hologram recording medium 55a without diffraction by the hologram recording medium 55a. The light beam is called a zeroth-order light beam. If the zeroth-order light beam is incident on the illuminated regions LZ1 to LZ3, abnormal regions (punctate region, linear region, planar region) where brightness (luminance) is sharply increased in comparison with peripheral regions occur in the illuminated regions LZ1 to LZ3.
In case of using the reflection-type hologram recording medium (not illustrated), since the spatial light modulators 30-1 to 30-3 and the projection optical systems 25-1 to 25-3 are not disposed in the direction where the zeroth-order light beam propagates, the zeroth-order light beam can be relatively easily avoided. However, in the case of using the transmission-type hologram recording medium 55a illustrated in FIG. 9 or the like, since the spatial light modulator 30 and the projection optical system 25 are highly likely to be disposed in the direction close to the direction where the zeroth-order light beam propagates, careful treatment is necessary.
In the case of using the transmission-type hologram recording medium 55a, for example, in the configuration illustrated in FIG. 10, although the zeroth-order light beam passes through the hologram recording medium, since the spatial light modulators 30-1 to 30-3 and the projection optical systems 25-1 to 25-3 are not disposed in the direction, the zeroth-order light beam is highly likely to be avoided. However, in the configuration illustrated in FIG. 9, since the optical path of the coherent light beam reflected by the light scan unit 50 may be changed, the zeroth-order light beam may pass through the spatial light modulators 30-1 to 30-3 or the projection optical system 25. Therefore, even in the case of employing the configuration illustrated in FIG. 9, the light scan unit 50, the spatial light modulators 30-1 to 30-3, and the projection optical systems 25-1 to 25-3 are designed to be disposed according to the propagating path of the zeroth-order light beam so that the zeroth-order light beam cannot pass through the spatial light modulators 30-1 to 30-3 or the projection optical systems 25-1 to 25-3.
Spatial Light Modulator, Projection Optical System, and Screen
According to the first and second embodiments described above, it is possible to effectively allow speckles to be inconspicuous. However, the functions and effects are obtained mainly from the illumination device 40. Then, in the case where the illumination device 40 is configured as a combination of various existing spatial light modulators, projection optical systems, screens, and the like, the speckles are effectively allowed to be inconspicuous. Due to this point, the spatial light modulators, the projection optical systems, and the screens are not limited to the exemplified ones, but various existing members, parts, apparatuses, and the like may be used.
Projection-Type Video Display Device
In addition, although the example where the hologram recording medium 55 (55a) is manufactured by using the planar scattering plates 6-1 to 6-3 having a shape corresponding to the incidence planes of the spatial light modulators 30-1 to 30-3 and by an interference exposing method is illustrated, the present invention is not limited thereto. The hologram recording medium 55 (55a) may be manufactured by using a scattering plate having some pattern and by an interference exposing method. In this case, the image of the scattering plate having some pattern is reproduced by the hologram recording medium 55 (55a). In other words, the optical element 50 (hologram recording medium 55 (55a)) illuminates the illuminated regions LZ1 to LZ3 having some patterns. In the case where the optical element 50 is used, the spatial light modulators 30-1 to 30-3 and the projection optical systems 25-1 to 25-3 may be omitted from the first and second basic embodiments described above, and the screens 15-1 to 15-3 are disposed at the positions which overlap the illuminated regions LZ1 to LZ3, so that some patterns recorded in the hologram recording medium 55 (55a) can be displayed on the screens 15-1 to 15-3. In this display device, the irradiation device 60 irradiates the optical element 50 with the coherent light beams so that the coherent light beams are allowed to scan the hologram recording medium 55 (55a), so that it is possible to allow the speckles to be inconspicuous on the screens 15-1 to 15-3.
Irradiation Device
In the first and second embodiments described above, an example where the irradiation device 60 includes the laser source 61a and the scan device 65 is illustrated. Although the scan device 65 which is configured with one-axis-rotation type mirror device 66 which changes the propagation direction of the coherent light beam by reflection is exemplified, the scan device 65 is not limited thereto. As illustrated in FIG. 11, the scan device 65 may be configured so that the mirror(reflection plane 66a) of the mirror device 66 can rotate about the first rotation axial line RA1 as well as about the second rotation axial line RA2 intersecting the first rotation axial line RA1. FIG. 11 illustrates an example where the modified example is applied to the first basic embodiment. In the example illustrated in FIG. 11, the second rotation axial line RA2 of the mirror 66a is perpendicular to the first rotation axial line RA1 which is extended in parallel to the Y axis of the XY coordinate system defined on the plate plane of the hologram recording medium 55. Then, since the mirror 66a can rotate about both of the first axial line RA1 and the second axial line RA2, the incidence point IP of the coherent light beam from the irradiation device 60 incident on the optical element 50 can be moved on the plate plane of the hologram recording medium 55 in two-dimensional directions. Therefore, as an example, as illustrated in FIG. 11, the incidence point IP of the coherent light beam incident on the optical element 50 may also be configured to be moved along a circumference. At this time, similarly to the first basic embodiment, the coherent light beam incident to each incidence point IP can be simultaneously illuminated on the illuminated regions LZ1 to LZ3. Note that, in FIG. 11, for better understanding, the reproduction light beams to the illuminated regions LZ1 and LZ3 are not illustrated.
In the case where the modified example is applied to the second basic embodiment, the scan path may be configured so that the incidence point IP is moved in the regions 55a-1 to 55a-3 of the hologram recording medium 55a. 
In addition, the scan device 65 may include two or more mirror devices 66. In this case, although the mirror 66a of the mirror device 66 can rotate about only one axial line, the incidence point IP of the coherent light beam from the irradiation device 60 incident on the optical element 50 can be moved on the plate plane of the hologram recording media 55 and 55a in the two-dimensional directions.
Note that, as a specific example of the mirror devices 66a included in the scan device 65, there are a MEMS mirror, a polygon mirror, and the like.
In addition, the scan device 65 may be configured to include a device besides a reflection device (for example, the mirror device 66 described above) which changes the propagation direction of the coherent light beam through reflection. For example, the scan device 65 may include a refraction prism or lens or the like.
Essentially, the scan device 65 is not a necessary component. The light source 61a of the irradiation device 60 is configured so that the light source can be displaced (moved, oscillated, and rotated) with respect to the optical element 50 and so that the coherent light beams irradiated from the light source 61a are allowed to scan the hologram recording medium 55 (55a) according to the displacement of the light source 61a with respect to the optical element.
Further, although the description hereinbefore is made under the presumption that the light source 61a of the irradiation device 60 oscillates a laser beam which is shaped as a linear light beam, the preset invention is not limited thereto. Particularly, in the first basic embodiment described above, the coherent light beam irradiated on each position of the optical element 50 is shaped as the light fluxes which are to be incident on the illuminated regions LZ1 to LZ3 by the optical element 50. In addition, in the second basic embodiment described above, the coherent light beam irradiated on each position existing in each region of the optical element 50 is shaped as the light flux which is to be incident on the entire region of the illuminated regions LZ1 to LZ3 corresponding to each region by the optical element 50. Therefore, even in the case where the coherent light beam irradiated from the light source 61a of the irradiation device 60 on the optical element 50 is not accurately shaped, no problem occurs. For this reason, the coherent light beam generated from the light source 61a may be a diverging light beam. In addition, the shape of cross section of the coherent light beam generated from the light source 61a may be an ellipse or the like instead of a circle. In addition, the transverse mode of the coherent light beam generated from the light source 61a may be a multi-mode.
Note that, in the case where the light source 61a generates the diverging flux, when the coherent light beam is incident on the hologram recording medium 55 (55a) of the optical element 50, the light beam is incident on not a spot but a region having somewhat area. In this case, the light beam which is diffracted by the hologram recording medium 55 (55a) to be incident to each position of the illuminated regions LZ1 to LZ3 is multiplexed in terms of angle. In other words, in each instant, the coherent light beams are incident from the directions of certain angle ranges to each position of the illuminated regions LZ1 to LZ3. Due to the multiplexing in terms of angle, it is possible to more effectively allow the speckles to be inconspicuous.
Further, in the first and second embodiments described above, although the example where the irradiation device 60 allows the coherent light beam to be incident on the optical element 50 so as to trace the optical path of the one light beam constituting the diverging flux is described, the present invention is not limited thereto. For example, in the first and second embodiments described above, as illustrated in FIG. 12, the scan device 65 may be configured to further include a collection lens (parallel light generation unit) 67 disposed at the lower stream side of the mirror device 66 along the optical path of the coherent light beam. FIG. 12 illustrates an example where the modified example is applied to the first basic embodiment. In this case, the light beam from the mirror device 66, which propagates along the optical path of the light beam constituting the diverging flux, is allowed by the collection lens 67 to become the light beam which propagates in a certain direction. In other words, the irradiation device 60 allows the coherent light beam to be incident on the optical element 50 so as to trace the optical path of the light beam constituting the parallel light flux. In this example, in the exposing process during the manufacturing of the hologram recording medium 55, instead of the converging light flux described above, the parallel light flux is used as the reference light beam Lr. The hologram recording medium 55 can be more simply manufactured and replicated.
The modified example may be applied to the second basic embodiment.
In the first and second embodiments described above, the example that the irradiation device 60 includes only one laser source 61a is described. However, the present invention is not limited thereto. As already described as the first and second modified examples of the second basic embodiment, in the first basic embodiment, for example, the irradiation device 60 may include a plurality of the light sources which oscillate light beams having the same wavelength range. In this case, the illumination device 40 can illuminate the illuminated regions LZ1 to LZ3 more brightly. In addition, the coherent light beams from different solid-state laser sources have no mutual coherency. Therefore, the multiplexing of the scattering patterns further progresses, so that it is possible to allow the speckles to be more inconspicuous.
In addition, the irradiation device 60 may include a plurality of the light sources which generate the coherent light beams having different wavelength ranges. According to this example, a color which is hard to display by using a single laser beam is generated through additive color mixing, and the illuminated regions LZ1 to LZ3 can be illuminated with the generated color. In addition, in this case, in the projection device 20 or the transmission-type video display device 10, in the case where the spatial light modulators 30-1 to 30-3 include, for example, color filters and are capable of forming modulation image with respect to each coherent light beam having each wavelength range, the video can be displayed in a plurality of colors. Alternatively, although the spatial light modulators 30-1 to 30-3 do not include color filters, in the case where the irradiation device 60 irradiates the coherent light beam having each wavelength range in a time division manner and the spatial light modulators 30-1 to 30-3 operate in a time division manner so as to form modulation image corresponding to the irradiated coherent light beam having the wavelength range, the video can be displayed in a plurality of colors. Particularly, in the projection device 20 or the transmission-type video display device 10, in the case where the irradiation device 60 includes a light source which generates the coherent light beam having a wavelength range corresponding to red light, a light source which generates the coherent light beam having a wavelength range corresponding to green light, and a light source which generates the coherent light beam having a wavelength range corresponding to blue light, the video can be displayed in full colors.
Note that, the hologram recording medium 55 (55a) included in the optical element 50 has wavelength selectivity. Therefore, in the case where the irradiation device 60 includes light sources having different wavelength ranges, the hologram recording medium 55 (55a) may be configured to include hologram components corresponding to the wavelength ranges of the coherent light beams generated from the light sources in a laminated state. The hologram components for the coherent light beams having the wavelength ranges may be manufactured by using the coherent light beams having the corresponding wavelength ranges as the light beams for exposing (reference light beams Lr1 to Lr3 and object light beams Lo1 to Lo3 or reference light beam Lr and object light beams Lo1 to Lo3), for example, in the method described above with reference to FIGS. 3, 4, 7, and 8. In addition, instead of manufacturing the hologram recording medium 55 (55a) by laminating the hologram components for the wavelength ranges, the hologram photosensitive material 58 is simultaneously exposed with the object light beam and reference light beam which are obtained from the coherent light beams having the wavelength ranges, and a plurality of light beams having wavelength ranges are diffracted by a single hologram recording medium 55 (55a).
Optical Element
In the embodiment described above, although the example where the optical element 50 is configured with the reflection-type volume hologram recording medium 55 (55a) using photopolymer is described, the present invention is not limited thereto. As described above, the optical element 50 may include a plurality of the hologram recording media 55 (55a). In addition, the optical element 50 may include a type of a volume hologram recording medium where recording is performed by using a photosensitive medium including a silver halide material. Further, the optical element 50 may include a reflection-type volume hologram recording medium, and the optical element 50 may include a relief type (emboss type) hologram recording medium.
With respect to the relief type (emboss type) hologram recording medium, hologram interference fringe is recorded by using a convex-concave structure of a surface thereof. However, in the case of the relief type hologram recording medium, since scattering due to the convex-concave structure of the surface may also cause occurrence of new speckles, the volume hologram recording medium is preferred. In the case of the volume hologram recording medium, hologram interference fringe is recorded by using a refractive index modulation pattern (refractive index distribution) of an inner portion of the medium, there is no influence of the scattering due to the convex-concave structure of the surface.
However, even in the case of the volume hologram recording medium, if recording is performed by using a photosensitive medium including a silver halide material, scattering due to silver halide particles may also cause occurrence of speckles. Therefore, as the hologram recording medium 55 (55a), the volume hologram recording medium using a photopolymer is preferred.
The reflection-type hologram recording medium is higher than the transmission-type hologram recording medium in terms of the wavelength selectivity. In other words, in the reflection-type hologram recording medium, although interference fringes corresponding to a different wavelength are laminated, a coherent light beam having a desired wavelength can be diffracted by using only a desired layer. In addition, in terms of removing the influence of the zeroth-order light beam, the reflection-type hologram recording medium is excellent.
On the other hand, although the transmission-type hologram recording medium has a wide diffractable spectrum range and a high degree of allowance of the laser source, if interference fringes corresponding to different wavelengths are laminated, layers other than a desired layer also diffract the coherent light beam having a desired wavelength. Therefore, in general, it is difficult to configure the transmission-type hologram recording medium in a lamination structure.
In addition, in the exposing process illustrated in FIGS. 3 and 7, although a so-called Fresnel type hologram recording medium is manufactured, a Fourier transform type hologram recording medium which can be obtained through recording using lenses may be manufactured. However, in the case of using a Fourier transform type hologram recording medium, the lenses can be used even during the reproduction.
In addition, a striped pattern (refractive index modulation pattern or convex-concave pattern) which is to be formed on the hologram recording medium 55 (55a) may be designed by using a computer based on wavelengths or incident directions of predetermined reproduction illumination light beam La, shapes or positions of to-be-reproduced images, and the like without use of the actual object light beam Lo and the reference light beam Lr. The hologram recording medium 55 (55a) obtained in this manner is called computer generated hologram recording medium. In addition, similarly to the modified example described above, in the case where a plurality of the coherent light beams having mutually different wavelength ranges are irradiated from the irradiation device 60, the hologram recording medium 55 (55a) as the computer generated hologram recording medium may be configured so as to be partitioned two-dimensionally into a plurality of regions disposed corresponding to the coherent light beams having the wavelength ranges, and the coherent light beams having the wavelength ranges are diffracted by the corresponding regions to reproduce images.
Further, in the second basic embodiment described above, although the example where the optical element 50 includes the hologram recording medium 55a which spreads the coherent light beam irradiated to each position existing in each of the regions 55a-1 to 55a-3 and illuminates the entire region of the corresponding illuminated regions LZ1 to LZ3 with the spread coherent light beam is described, the present invention is not limited thereto. Instead of the hologram recording medium 55a or in addition to the hologram recording medium 55a, the optical element 50 may include a plurality of lens arrays (light diffusion elements) as optical components capable of changing the propagation direction of the incident light beam and diffusing the light beam and illuminating the corresponding illuminated region among a plurality of the illuminated regions LZ1 to LZ3. As a specific example of the lens array, a total reflection-type or refraction-type Fresnel lens added with a diffusion function, a fly-eye lens, or the like may be exemplified. In the illumination device 40, the irradiation device 60 and the optical element 50 may also be configured so that the irradiation device 60 allows the coherent light beam to scan each lens array, irradiates the optical element 50 with the coherent light beam and so that the propagation direction of the coherent light beam incident from the irradiation device 60 to each position of the optical element 50 is changed by the corresponding lens array to be illuminated on the corresponding illuminated regions LZ1 to LZ3. Therefore, it is possible to effectively allow the speckles to be inconspicuous.
Illuminating Method
In the first and second basic embodiments described above, as an example, the irradiation device 60 is configured so as to allow the coherent light beam to scan the optical element 50 in one-dimensional direction, and the hologram recording medium 55 (55a) (or lens arrays) of the optical element 50 are configured so as to diffuse (spread, diverge) the coherent light beam irradiated to each position in two-dimensional directions, so that the illumination device 40 illuminates the illuminated regions LZ1 to LZ3 in a two-dimensional manner. However, as already explained, the present invention is not limited thereto. For example, the irradiation device 60 may be configured so as to allow the coherent light beam to scan the optical element 50 in two-dimensional directions, and the hologram recording medium 55 (55a) (or lens arrays) of the optical element 50 may be configured so as to diffuse (spread, diverge) the coherent light beam irradiated to each position in two-dimensional directions, so that the illumination device 40 illuminates the illuminated regions LZ1 to LZ3 in a two-dimensional manner (described above with reference to FIG. 11).
Combination of Modified Examples
Note that, although several modified examples of the first and second basic embodiments are described hereinbefore, it is obvious that a combination of a plurality of the modified examples is available.
Number of Screens
In the description hereinbefore, although the example where the projection-type video display device 10 includes the three screens 15-1 to 15-3 is described, the projection-type video display device 10 may include two screens or four or more screens. In this case, in the first basic embodiment, the projection device may include the hologram recording medium where images of the scattering plates, of which the number is equal to the number of screens, are multiplexedly recorded and the spatial light modulators and the projection optical system, of which the respective number is equal to the number of screen. In addition, in the second basic embodiment, the projection device may include the hologram recording medium which is partitioned into regions, of which the number is equal to the number of screens, and the spatial light modulator and the projection optical system, of which the respective number is equal to the number of screens. In addition, the image of the scattering plate may be recorded in each region of the hologram recording medium.

## Claims

1. An illumination device comprising:
an optical element comprising a hologram recording medium capable of diffusing a coherent light beam, the hologram recording medium comprising a plurality of hologram recording medium regions, each hologram recording medium region diffusing a coherent light beam to an illuminated region corresponding to the hologram recording medium region; and
an irradiation device including a light source configured to generate the coherent light beam and a scan device configured to distribute the coherent light beam from the light source to the plurality of hologram recording medium regions included in the hologram recording medium, the irradiation device being configured to irradiate the plurality of hologram recording medium regions with the coherent light beam distributed from the light source to the plurality of hologram recording medium regions so as to allow the coherent light beam to scan the plurality of hologram recording medium regions,
wherein each hologram recording medium region comprises a plurality of positions in such hologram recording medium region, and for each hologram recording medium region, each coherent light beam incident to a position in such hologram recording medium region is diffused to an entirety of the respective illuminated region corresponding to the hologram recording medium region in order to illuminate the entirety of the illuminated region.

2. The illumination device according to claim 1, wherein an illuminated region corresponding to a hologram recording medium region is shifted from an illuminated region corresponding to another hologram recording medium region.

3. The illumination device according to claim 1, wherein the scan device is configured to change a propagation direction of the coherent light beam from the light source and allow the coherent light beam to scan the hologram recording medium.

4. The illumination device according to claim 3, wherein the coherent light beam from the light source is irradiated to one point of the scan device, the coherent light beam reflected from the one point of the scan device constitutes a diverging flux from the one point, and the diverging flux is incident on the hologram recording medium.

5. The illumination device according to claim 3,
wherein the coherent light beam from the light source is irradiated to one point of the scan device, and the coherent light beam reflected from the one point of the scan device constitutes a diverging flux from the one point, and
wherein the illumination device further comprises a parallel light generation unit which propagates each light beam constituting the diverging flux in a certain direction to generate parallel light flux and allows the parallel light flux to be incident on the hologram recording medium.

6. The illumination device according to claim 1,
wherein the scan device is configured to change a propagation direction of the coherent light beam from the light source and allow the coherent light beam to scan the hologram recording medium,
wherein the light source comprises a plurality of light source units which emit a plurality of coherent light beams,
wherein a plurality of the coherent light beams emitted from a plurality of the light source units are illuminated to the same point on the scan device, and
wherein each coherent light beam reflected from the same point on the scan device constitutes diverging flux from the same point, and each diverging flux is incident on the corresponding hologram recording medium region.

7. The illumination device according to claim 1,
wherein the scan device is configured to change a propagation direction of the coherent light beam from the light source and allow the coherent light beam to scan the hologram recording medium,
wherein the light source comprises a plurality of light source units which emit a plurality of coherent light beams in substantially parallel directions,
wherein each coherent light beam emitted from a plurality of the light source units is irradiated at corresponding point on the scan device, and
wherein each coherent light beam reflected at each point on the scan device constitutes diverging flux from the corresponding each point, and each diverging flux is incident on the corresponding hologram recording medium region.

8. An illumination device comprising:
an optical element comprising a plurality of light diffusion elements, each light diffusion element capable of changing a propagation direction of an incident light beam, each light diffusion element diffusing a coherent light beam to an illuminated region corresponding to the light diffusion element; and
an irradiation device including a light source configured to generate the coherent light beam and a scan device configured to distribute the coherent light beam from the light source to the plurality of light diffusion elements included in the optical element, the irradiation device being configured to irradiate the plurality of light diffusion elements with the coherent light beam distributed from the light source to the plurality of light diffusion elements so as to allow the coherent light beam to scan the plurality of light diffusion elements,
wherein each light diffusion element comprises a plurality of positions in said light diffusion element, and for each light diffusion element, each coherent light beam incident to a position in such light diffusion element is diffused to an entirety of the respective illuminated region corresponding to the light diffusion element in order to illuminate the entirety of the illuminated region.

9. The illumination device according to claim 8, wherein an illuminated region corresponding to a light diffusion element is shifted from an illuminated region corresponding to another light diffusion element.

10. The illumination device according to claim 8, wherein the scan device is configured to change the propagation direction of the coherent light beam from the light source and allow the coherent light beam to scan each light diffusion element.

11. The illumination device according to claim 8, wherein the optical element comprises a lens array.