JP2012230307A - Projection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a projection device by which speckles on a diffusion screen are made inconspicuous, and the entire configuration of which can be downsized and simplified.SOLUTION: A projection device 20 comprises: an optical element 50 which can diffuse coherent light; an irradiation device 40 for irradiating the optical element with the coherent light so that the coherent light scans on the optical element; an optical modulator 30 which is illuminated by the coherent light made incident from the irradiation device to each position of the optical element and diffused; a diffusion member 15 having a diffusion surface for causing a modulation image generated by the optical modulator to diffuse; and a magnification projection optical system 80 which forms a virtual image of the modulation image diffused by the diffusion surface and allows an observer to visually recognize the virtual image. The rays of coherent light made incident on respective positions of the optical element 50 and diffused illuminate the optical modulator 30 so as to overlap each other on the optical modulator 30.

Description

  The present invention relates to a projection apparatus using a light source that emits coherent light.

  A technique for configuring a vehicle head-up display device using a laser light source has been proposed (see Patent Document 1). The head mounted display device described in this publication proposes a technique for preventing blurring of a projected image projected on a screen by a projection optical system including a divergence angle conversion element and a deflection optical element.

  However, when a laser is used as a light source, speckles are generated due to high coherence. A speckle is a speckled pattern that appears when a scattering surface is irradiated with laser light or other coherent light. When it appears on a screen, it is observed as speckled brightness irregularities (brightness irregularities). It becomes a factor having a physiological adverse effect on the person. The reason why speckles occur when coherent light is used is that coherent light reflected by each part of a scattering reflection surface such as a screen interferes with each other because of its extremely high coherence. . For example, the following non-patent document 1 gives a detailed theoretical consideration on the generation of speckle.

  Patent Document 1 described above does not take any measures against speckles generated by a laser light source. Therefore, even if the blur of the projected image can be prevented, the projected image itself includes speckles, and the image quality cannot be improved.

  As described above, in the method using a coherent light source such as a laser light source, a problem inherent to the generation of speckles occurs, and thus a technique for suppressing the generation of speckles has been proposed. For example, the following Patent Document 2 discloses a technique for reducing speckle by irradiating a scattering plate with laser light, guiding scattered light obtained therefrom to an optical modulator, and rotating the scattering plate by a motor. Is disclosed.

JP 2009-282083 A Japanese Patent Laid-Open No. 6-208089

Speckle Phenomena in Optics, Joseph W. Goodman, Roberts & Co., 2006

  Speckle is a problem not only in the vehicle head-up display device described above, but also in various devices in which an illumination device that illuminates coherent light in an illuminated area. As represented by laser light, coherent light has excellent straightness and can be irradiated as light having a very high energy density. Therefore, it is preferable that the light path of the coherent light is designed as an illuminating device actually developed corresponding to the characteristics of the coherent light.

  The inventors of the present invention have made extensive studies based on the above points, and as a result, when illuminating the illuminated area with coherent light and diffusing this illumination light to the outside, speckles are inconspicuous. It came to invent the projection apparatus which can be made to do. In addition, the present inventors have further researched and improved the projection apparatus so that it is possible to stably prevent a bright area from being projected and brightened in the illuminated area illuminated with coherent light. We were able to. That is, an object of the present invention is to provide a projection device that can prevent speckles from being noticeable and can effectively suppress the occurrence of uneven brightness in an illuminated area.

In order to solve the above problems, in one embodiment of the present invention, an optical element capable of diffusing coherent light;
An irradiation device for irradiating the optical element with the coherent light so that coherent light scans the optical element;
A light modulator that is illuminated by the coherent light that is incident and diffused from the irradiation device to each position of the optical element;
A diffusion member having a diffusion surface for diffusing a modulated image generated by the light modulator;
Forming a virtual image of the modulated image diffused on the diffusion surface, and an enlarged projection optical system that allows the observer to visually recognize the virtual image,
A coherent light that has been incident and diffused at each position of the optical element is illuminated by overlapping the light modulator.

  According to the present invention, speckles on the diffusing screen can be made inconspicuous, the overall configuration can be reduced in size and simplified, and the image quality of the virtual image formed by the enlarged projection optical system can be improved, Wide field of view.

The block diagram which shows schematic structure of the projection apparatus which concerns on one Embodiment. The figure explaining a mode that the image of a scattering plate is formed in the hologram recording medium 55 as an interference fringe. The figure explaining a mode that the image of a scattering plate is reproduced | regenerated using the interference fringe formed in the hologram recording medium 55 obtained through the exposure process of FIG. The figure explaining the scanning path | route of the scanning device 65. FIG. The figure which shows the example which rotates the mirror device 66 to a biaxial direction.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings attached to the present specification, for convenience of illustration and understanding, the scale, the vertical / horizontal dimensional ratio, and the like are appropriately changed or exaggerated from those of the actual ones.

  The projection device according to an embodiment of the present invention can be applied to, for example, a vehicle head-up display device, but can also be applied to various projection devices other than the vehicle head-up display device, such as a projector. .

  FIG. 1 is a block diagram showing a schematic configuration of a projection apparatus 20 according to an embodiment. The projection apparatus 20 in FIG. 1 includes an optical element 50, an irradiation apparatus 60, a light modulator 30, a relay optical system 70, a diffusion screen 15, and an enlarged projection optical system 80. In the present specification, a combination of the optical element 50 and the irradiation device 60 is referred to as an illumination device 40.

  The irradiation device 60 irradiates the optical element 50 with coherent light so that the coherent light scans the surface of the optical element 50. The irradiation device 60 includes a laser light source 61 that emits coherent light, and a scanning device 65 that scans the surface of the optical element 50 with the coherent light emitted from the laser light source 61.

  The optical element 50 has a hologram recording medium 55 that can reproduce the image of the scattering plate in the illuminated area LZ. Details of the hologram recording medium 55 will be described later. Coherent light reflected by the scanning device 65 is incident on the hologram recording medium 55. The hologram recording medium 55 is formed with interference fringes. When coherent light is incident, the coherent light diffracted by the interference fringes is emitted as divergent light (diffused light).

  The scanning device 65 varies the reflection angle of the incident coherent light at a constant period so that the reflected coherent light scans on the hologram recording medium 55.

  The coherent light incident on each point on the hologram recording medium 55 becomes diffused light and forms a scattering plate image in the illuminated area LZ. The light modulator 30 is disposed at a position overlapping the illuminated area. As a result, the light modulator 30 is illuminated by the irradiation device 60.

  As the light modulator 30, for example, a transmissive liquid crystal micro display (for example, LCOS: Liquid Crystal on Silicon) can be used. In this case, the liquid crystal micro display illuminated in a planar shape by the illumination device 40 selects and transmits coherent light for each pixel, thereby forming a modulated image on the liquid crystal micro display. The modulated image (video light) obtained in this way is scaled as necessary by the relay optical system 70 and projected onto the diffusion screen 15. Since the speckle pattern of the modulated image projected on the diffusing screen 15 changes with time, the speckle is invisible.

  As the light modulator 30, a reflection type micro display can be used. In this case, a modulated image is formed by the reflected light from the light modulator 30, the surface on which the coherent light is irradiated from the illumination device 40 to the light modulator 30, and the image light (the modulated image generated by the light modulator 30 ( The exit surface of the (reflected light) is the same surface. When using such reflected light, a MEMS (Micro Electro Mechanical Systems) element such as DMD (Digital Micromirror Device) can be used as the optical modulator 30. In the apparatus disclosed in Patent Document 2 described above, DMD is used as an optical modulator. In addition, a transmissive liquid crystal panel can be used as the optical modulator 30. In this case, the enlarged projection optical system 80 can be omitted if the screen size of the liquid crystal panel is increased.

  Moreover, it is preferable that the incident surface of the light modulator 30 has the same shape and size as the illuminated region LZ where the illumination device 40 emits coherent light. In this case, it is because the coherent light from the illuminating device 40 can be utilized with high utilization efficiency for displaying the image on the diffusion screen 15.

  The relay optical system 70 that projects the modulated image generated by the light modulator 30 onto the diffusing screen 15 has a convex lens, for example, and the modulated image generated by the light modulator 30 is refracted by the convex lens and is on the diffusing screen 15. A modulated image 71 is projected onto the screen. The size of the modulated image 71 projected on the diffusion screen 15 can be adjusted by the diameter of the convex lens, the distance between the convex lens and the light modulator 30, and the distance between the convex lens and the diffusion screen 15. The diffusing screen 15 in FIG. 1 is a transmission type, and diffuses the projected modulated image light. The diffusing screen 15 may be a reflective type.

  The modulated image diffused by the diffusing screen 15 enters the enlarged projection optical system 80. The magnifying projection optical system 80 includes a half mirror 81, for example. The half mirror 81 reflects a part of the modulated image light diffused by the diffusion screen 15 to form a virtual image 82 of the modulated image and also transmits a part of the external light. 82 will be visually recognized.

  As the half mirror 81, for example, a vehicle windshield can be used, and the observer can view the virtual image 82 while viewing the scenery outside the vehicle through the windshield by sitting in the driver's seat and facing forward. Alternatively, a hologram recording medium or a prism may be used instead of the half mirror 81.

  Moreover, a concave mirror may be provided in the magnifying projection optical system 80 to enlarge the size of the modulated image more greatly. The concave mirror is preferably provided between the diffusing screen 15 and the half mirror 81.

  The optical modulator 30 can generate various modulated images. The modulated optical image is generated by the optical modulator 30 and illuminated by the illuminated region LZ, so that the relay optical system 70 and the enlarged projection optical system 80 are illuminated. Thus, an arbitrary virtual image 82 corresponding to the modulated image can be formed.

  In the present embodiment, the optical element 50 including the hologram recording medium 55 is used to illuminate the illuminated area LZ. The hologram recording medium 55 is a reflection type volume hologram using, for example, a photopolymer. FIG. 2 is a diagram for explaining how the image of the scattering plate is formed on the hologram recording medium 55 as interference fringes.

  As shown in FIG. 2, the hologram recording medium 55 is manufactured using the scattered light from the actual scattering plate 6 as the object light Lo. FIG. 2 shows a state in which the reference light Lr and the object light Lo made of coherent light having coherence are exposed on the photosensitive hologram photosensitive material 58 that forms the hologram recording medium 55. Has been.

  As the reference light Lr, for example, laser light from a laser light source 61 that oscillates laser light in a specific wavelength region is used. The reference light Lr passes through the condensing element 7 made of a lens and enters the hologram photosensitive material 58. In the example shown in FIG. 2, the laser light for forming the reference light Lr is incident on the condensing element 7 as a parallel light beam parallel to the optical axis of the condensing element 7. The reference light Lr passes through the condensing element 7, so that it is shaped (converted) into a convergent light beam from the parallel light beam so far, and is incident on the hologram photosensitive material 58. At this time, the focal position FP of the convergent light beam Lr is at a position past the hologram photosensitive material 58. That is, the hologram photosensitive material 58 is disposed between the light condensing element 7 and the focal position FP of the convergent light beam Lr condensed by the light condensing element 7.

  On the other hand, the object light Lo is incident on the hologram photosensitive material 58 as scattered light from a scattering plate 6 made of, for example, opal glass. In the example of FIG. 2, the hologram recording medium 55 to be manufactured is a transmission type, and the object light Lo is incident on the hologram photosensitive material 58 from the surface on the same side as the reference light Lr. The object light Lo is premised on having coherency with the reference light Lr. Therefore, for example, the laser light oscillated from the same laser light source 61 can be divided, and one of the divided light can be used as the reference light Lr and the other can be used as the object light Lo.

  In the example shown in FIG. 2, a parallel light beam parallel to the normal direction to the plate surface of the scattering plate 6 is incident on the scattering plate 6 and scattered, and the scattered light transmitted through the scattering plate 6 is the object light Lo. The light enters the hologram photosensitive material 58. According to this method, when an isotropic scattering plate that is usually available at a low cost is used as the scattering plate 6, the object light Lo from the scattering plate 6 is incident on the hologram photosensitive material 58 with a substantially uniform light amount distribution. Can do. Further, according to this method, although depending on the degree of scattering by the scattering plate 6, the object light Lo is incident on each position of the hologram photosensitive material 58 with a substantially uniform light amount from the entire area of the exit surface 6 a of the scattering plate 6. It becomes easy. In such a case, the light incident on each position of the obtained hologram recording medium 55 reproduces the image 5 of the scattering plate 6 with the same brightness, and the reproduced image of the scattering plate 6. Observing 5 with substantially uniform brightness can be realized.

  As described above, when the hologram recording material 58 is exposed to the reference light Lr and the object light Lo, an interference fringe formed by the interference of the reference light Lr and the object light Lo is generated. For example, in a volume hologram, the pattern is recorded on the hologram recording material 58 as a refractive index modulation pattern. Thereafter, appropriate post-processing corresponding to the type of the hologram recording material 58 is performed, and the hologram recording material 55 is obtained.

  FIG. 3 is a diagram for explaining how the image of the scattering plate is reproduced using the interference fringes formed on the hologram recording medium 55 obtained through the exposure process of FIG. As shown in FIG. 3, the hologram recording medium 55 formed of the hologram photosensitive material 58 of FIG. 2 is light having the same wavelength as the laser beam used in the exposure process, and the optical path of the reference light Lr in the exposure process The light traveling in the opposite direction satisfies the Bragg condition. That is, as shown in FIG. 3, the reference point SP positioned with respect to the hologram recording medium 55 in the same positional relationship as the relative position of the focal point FP (see FIG. 2) with respect to the hologram photosensitive material 58 during the exposure process. The divergent light beam that diverges from the light beam and has the same wavelength as the reference light Lr during the exposure process is diffracted by the hologram recording medium 55 as the reproduction illumination light La, and is relative to the hologram photosensitive material 58 during the exposure process. The reproduced image 5 of the scattering plate 6 is generated at a specific position with respect to the hologram recording medium 55 that has the same positional relationship as the position (see FIG. 2).

  At this time, the reproduction light for generating the reproduction image 5 of the scattering plate 6, that is, the light Lb formed by diffracting the reproduction illumination light La by the hologram recording medium 55 travels from the scattering plate 6 toward the hologram photosensitive material 58 during the exposure process. Each point of the image 5 of the scattering plate 6 is reproduced as light traveling in the opposite direction along the optical path of the object light Lo that has been emitted. Here, as shown in FIG. 2, the object light Lo emitted from each position of the emission surface 6 a of the scattering plate 6 during the exposure process is diffused so as to enter almost the entire region of the hologram photosensitive material 58. Yes. That is, the object light Lo from the entire area of the exit surface 6 a of the scattering plate 6 is incident on each position on the hologram photosensitive material 58, and as a result, information on the entire exit surface 6 a is placed on each position of the hologram recording medium 55. Each is recorded. For this reason, each light that forms a divergent light beam from the reference point SP functioning as the reproduction illumination light La shown in FIG. 3 is incident on each position of the hologram recording medium 55 independently and has the same contour. The image 5 of the scattering plate 6 can be reproduced at the same position (illuminated area LZ).

  Since the light incident on the hologram recording medium 55 is diffracted in the direction of the illuminated area LZ, useless scattered light can be effectively suppressed. Therefore, all the reproduction illumination light La incident on the hologram recording medium 55 can be effectively used to form an image of the scattering plate 6.

  Next, the configuration of the irradiation device 60 that irradiates the optical element 50 including the hologram recording medium 55 with coherent light will be described. In the example shown in FIGS. 1 to 3, the irradiation device 60 includes a laser light source 61 that generates coherent light and a scanning device 65 that changes the traveling direction of the coherent light from the laser light source 61. .

  As the laser light source 61, for example, a plurality of laser light sources 61 that emit laser beams of different wavelength bands may be used. When a plurality of laser light sources 61 are used, the laser light from each laser light source 61 irradiates the same point on the scanning device 65. Thereby, the hologram recording medium 55 is illuminated with the reproduction illumination light in which the illumination colors of the laser light sources 61 are mixed.

  The laser light source 61 may be a monochromatic laser light source or a plurality of laser light sources having different emission colors. For example, a plurality of red, green, and blue laser light sources may be used. In the case of using a plurality of laser light sources, if each laser light source is arranged so that coherent light from each laser light source is irradiated to one point on the scanning device 65, it corresponds to the incident angle of the coherent light from each laser light source. The light is reflected at the reflection angle, is incident on the hologram recording medium 55, is diffracted separately from the hologram recording medium 55, and is superimposed on the illuminated area LZ to be a composite color. For example, when a plurality of red, green, and blue laser light sources are used, the color becomes white. Alternatively, a separate scanning device 65 may be provided for each laser light source.

  For example, when illuminating in white, it may be possible to reproduce a color closer to white by separately providing a laser light source that emits light other than red, green, and blue, for example, a laser light source that emits yellow light. Therefore, the type of laser light source provided in the irradiation device 60 is not particularly limited.

When forming the color virtual image 82, various realization methods can be considered. When the light modulator 30 is composed of LCOS or the like and has a color filter for each pixel, the modulated image generated by the light modulator 30 is colored by making the illuminated area LZ white light. can do.
Alternatively, for example, an optical modulator 30 that generates a red modulated image, an optical modulator 30 that generates a green modulated image, and an optical modulator 30 that generates a blue modulated image are arranged close to each other. The three illuminated areas that illuminate each of the light modulators 30 may be sequentially illuminated with diffused light from the hologram recording medium 55. As a result, the three color modulation images generated by the three light modulators 30 are combined to generate a color modulation image. Instead of such time-division driving, three color modulation images generated simultaneously by the three optical modulators 30 may be combined using a prism or the like to generate a color modulation image.

  The relay optical system 70 described above is provided mainly for projecting the modulated image of the light modulator 30 onto the diffusion screen 15. The enlarged projection optical system 80 is provided in order to adjust the size of the modulated image so that when the observer visually recognizes the virtual image 82, the virtual image 82 can be easily viewed with human eyes. .

  In the case where a sufficiently large virtual image 82 can be formed using only the enlarged projection optical system 80, the relay optical system 70 may be omitted. In this case, it is desirable to dispose the diffusing screen 15 as close to the light modulator 30 as possible. This is because, when the relay optical system 70 is not provided, if the distance between the light modulator 30 and the diffusion screen 15 is large, the modulated image projected on the diffusion screen 15 is blurred.

  By the way, even if the relay optical system 70 is provided or omitted, the diffusion screen 15 is essential. By providing the diffusion screen 15, speckles are overlapped and averaged, and as a result, speckles are not noticeable.

  The scanning device 65 changes the traveling direction of the coherent light with time, and directs it in various directions so that the traveling direction of the coherent light is not constant. As a result, the coherent light whose traveling direction is changed by the scanning device 65 scans the incident surface of the hologram recording medium 55 of the optical element 50.

  FIG. 4 is a diagram for explaining the scanning path of the scanning device 65. The scanning device 65 according to the present embodiment includes a reflecting device 66 having a reflecting surface 66a that can be rotated about one axis RA1. The reflection device 66 includes a mirror device having a mirror as a reflection surface 66a that can be rotated about one axis RA1. This mirror device 66 changes the traveling direction of coherent light from the laser light source 61 by changing the orientation of the mirror 66a. At this time, as shown in FIG. 3, the mirror device 66 generally receives coherent light from the laser light source 61 at the reference point SP.

  The coherent light whose traveling direction is finally adjusted by the mirror device 66 is incident on the hologram recording medium 55 of the optical element 50 as reproduction illumination light La (see FIG. 3) that can form one light beam diverging from the reference point SP. obtain. As a result, the coherent light from the irradiation device 60 scans on the hologram recording medium 55, and the image of the scattering plate 6 in which the coherent light incident on each position on the hologram recording medium 55 has the same contour. 5 is reproduced at the same position (illuminated area LZ).

  As shown in FIG. 4, the reflection device 66 is configured to rotate the mirror 66a along one axis RA1. In the example shown in FIG. 4, the rotation axis RA <b> 1 of the mirror 66 a has an XY coordinate system defined on the plate surface of the hologram recording medium 55 (that is, the XY plane is parallel to the plate surface of the hologram recording medium 55. It extends parallel to the Y axis of the (XY coordinate system). Then, since the mirror 66a rotates around the axis line RA1 parallel to the Y axis of the XY coordinate system defined on the plate surface of the hologram recording medium 55, the coherent light from the irradiation device 60 is applied to the optical element 50. The incident point IP reciprocates in a direction parallel to the X axis of the XY coordinate system defined on the plate surface of the hologram recording medium 55. That is, in the example shown in FIG. 4, the irradiation device 60 irradiates the optical element 50 with coherent light so that the coherent light scans on the hologram recording medium 55 along a linear path.

  As described above, the scanning device 65 configured by the mirror device 66 or the like is a member that can rotate at least around the axis line RA1, and is configured by using, for example, MEMS. The scanning device 65 periodically rotates, but in applications such as a liquid crystal display device that is directly observed by humans, it is 1/30 seconds per cycle, which is more coherent at a higher speed depending on the type of screen to be displayed. If it can scan with light, there will be no restriction | limiting in particular in the rotation frequency.

  As a practical problem, the hologram recording material 58 may shrink when the hologram recording medium 55 is produced. In such a case, it is preferable to adjust the incident / exit angle of the coherent light irradiated from the irradiation device 60 to the optical element 50 in consideration of the shrinkage of the hologram recording material 58. Therefore, the wavelength of the coherent light generated by the coherent light source 61 does not need to be exactly the same as the wavelength of the light used in the exposure process of FIG. 2, and may be substantially the same.

  For the same reason, even if the traveling direction of the light incident on the hologram recording medium 55 of the optical element 50 does not take exactly the same path as the one light beam included in the divergent light beam from the reference point SP, it is illuminated. The image 5 can be reproduced in the region LZ. Actually, in the example shown in FIGS. 3 and 4, the mirror (reflection surface) 66a of the mirror device 66 constituting the scanning device 65 is inevitably deviated from the rotation axis RA1. Therefore, when the mirror 66a is rotated around the rotation axis RA1 that does not pass through the reference point SP, the light incident on the hologram recording medium 55 may not be a single light beam that forms a divergent light beam from the reference point SP. is there. However, in practice, the image 5 can be substantially reproduced by being superimposed on the illuminated region LZ by coherent light from the irradiation device 60 having the illustrated configuration.

  By the way, the scanning device 65 does not necessarily need to be a member that reflects the coherent light, and may be scanned on the optical element 50 by causing the coherent light to be refracted or diffracted instead of being reflected.

(Operational effect of this embodiment)
Next, the operation and effect of the projection apparatus 20 having the above configuration will be described.

  The projection apparatus 20 according to the present embodiment scans the hologram recording medium 55 with coherent light by the scanning device 65 and illuminates the illuminated region LZ with coherent light diffracted by the hologram recording medium 55. Using this illumination, the modulated image generated by the light modulator 30 is adjusted in size by the relay optical system 70 and projected onto the diffusion screen 15. Further, a virtual image 82 of the modulated image is formed using the magnifying projection optical system 80 so that the viewer can visually recognize it.

  As described above, in this embodiment, a modulated image is generated using the scanning device 65, the optical element 50 including the hologram recording medium 55, and the optical modulator 30, and thus the modulated image is generated using, for example, a normal liquid crystal display device. Compared with the case where it produces | generates, the hardware constitutions until it produces | generates a modulated image can be reduced in size significantly. In the present embodiment, the scanning device 65 scans the hologram recording medium 55 with coherent light and projects a modulated image onto the diffusion screen 15, so that speckle is not conspicuous while using coherent light. Thus, the projection device 20 capable of displaying a high-quality image can be realized. In addition, by providing the diffusion screen 15, the viewing angle can be widened.

  The scanning device 65 makes each position on the hologram recording medium 55 incident coherent light of a corresponding specific wavelength at an incident angle that satisfies the Bragg condition at the position. As a result, the coherent light incident on each position is reproduced by the diffraction by the interference fringes recorded on the hologram recording medium 55 so as to overlap the entire illuminated area LZ and reproduce the image 5 of the scattering plate 6. That is, the coherent light incident on each position of the hologram recording medium 55 from the irradiation device 60 is diffused (expanded) by the optical element 50 and enters the entire illuminated area LZ.

  In this way, the irradiation device 60 illuminates the illuminated area LZ with coherent light. For example, when the laser light source 61 has a plurality of laser light sources 61 that emit light in different colors, the image 5 of the scattering plate 6 is reproduced in each color in the illuminated region LZ. Therefore, when these laser light sources 61 emit light at the same time, the illuminated area LZ is illuminated with white in which three colors are mixed.

  In the present embodiment, as described below, a light image can be formed on the illuminated area LZ without conspicuous speckles.

  According to the aforementioned Non-Patent Document 1, it is effective to multiplex parameters such as polarization, phase, angle, and time and increase the mode in order to make speckle inconspicuous. The mode here refers to speckle patterns that are uncorrelated with each other. For example, when coherent light is projected from different directions onto the same screen from a plurality of laser light sources 61, there are as many modes as the number of laser light sources 61. Further, when coherent light from the same laser light source 61 is projected onto the screen from different directions every unit time, the number of times the incident direction of the coherent light has changed during the time that cannot be resolved by the human eye Will exist. When there are a large number of these modes, it is considered that the interference patterns of light are overlapped uncorrelatedly and averaged, and as a result, speckles observed by the observer's eyes become inconspicuous.

  The irradiation device 60 described above irradiates the optical element 50 with coherent light so that the coherent light scans on the hologram recording medium 55. Further, the coherent light incident on the arbitrary position in the hologram recording medium 55 from the irradiation device 60 illuminates the entire illuminated area LZ, but the illumination directions of the coherent light illuminating the illuminated area LZ are different from each other. Since the position on the hologram recording medium 55 where the coherent light enters changes with time, the incident direction of the coherent light to the illuminated region LZ also changes with time.

  As described above, in this embodiment, coherent light continuously scans on the hologram recording medium 55. Along with this, the incident direction of coherent light incident on the illuminated area LZ from the irradiation device 60 via the optical element 50 also changes continuously. Here, if the incident direction of the coherent light from the optical element 50 to the illuminated area LZ changes only slightly (for example, several degrees), the pattern of speckles generated on the illuminated area LZ also changes greatly, and is uncorrelated. A speckle pattern is superimposed. In addition, the frequency of scanning devices 65 such as MEMS mirrors and polygon mirrors that are commercially available is usually several hundred Hz or higher, and scanning devices 65 that reach tens of thousands of Hz are not uncommon.

  From the above, according to the present embodiment, the incident direction of coherent light changes temporally at each position of the illuminated region LZ, and this change is a speed that cannot be resolved by the human eye. It is. Accordingly, if a screen is arranged in the illuminated area LZ, speckles generated corresponding to each incident angle are overlapped and averaged and observed by the observer, so that the image displayed on the screen Speckle can be made very inconspicuous for an observer who observes the above. In the case of this embodiment, the light modulator 30 is arranged so as to overlap the position of the illuminated area LZ, and the light modulator 30 projects onto the diffusion screen 15 via the relay optical system 70. Similarly, since speckles generated on the diffusion screen 15 are overlapped and averaged, the speckles generated on the diffusion screen 15 become inconspicuous.

  As described above, in the embodiment of the present invention, the scanning device 65 is used to scan the coherent light on the hologram recording medium 55, and the coherent light diffracted by the hologram recording medium 55 is incident on the entire illuminated area LZ. The lighting device 40 can be realized with a very simple configuration.

(Other features of this embodiment)
Non-Patent Document 1 mentioned above proposes a method using a numerical value called speckle contrast (unit%) as a parameter indicating the degree of speckle generated on the screen. This speckle contrast is defined as a value obtained by dividing the standard deviation of the actual luminance variation on the screen divided by the average luminance value when displaying a test pattern image that should have a uniform luminance distribution. Amount. The larger the speckle contrast value is, the larger the speckle occurrence level on the screen is, which indicates that the spot-like luminance unevenness pattern is more prominently presented to the observer.

  In addition, according to the above-described embodiment, the following advantages can be obtained.

  According to this embodiment described above, the optical element 50 for making speckles inconspicuous can also function as an optical member for shaping and adjusting the beam form of coherent light emitted from the irradiation device 60. Therefore, the optical system can be reduced in size and simplified.

  Further, according to the present embodiment described above, coherent light incident on a specific position of the hologram recording medium 55 generates the image 5 of the scattering plate 6 in each color in the entire illuminated area LZ. For this reason, all the light diffracted by the hologram recording medium 55 can be used for illumination, and the use efficiency of the light from the laser light source 61 is excellent.

(Avoiding zero-order light)
A part of the coherent light from the irradiation device 60 passes through the hologram recording medium 55 without being diffracted by the hologram recording medium 55. Such light is called zero order light. When the zero-order light enters the illuminated area LZ, abnormal areas such as point-like areas, linear areas, and planar areas whose brightness (luminance) increases sharply compared to the surroundings are illuminated area LZ. Will occur within.

  In the case of using the reflection type hologram recording medium 55 (hereinafter referred to as reflection type holo), the illuminated region LZ is not arranged in the direction in which the 0th order light travels, so that the 0th order light can be avoided relatively easily. When a hologram recording medium 55 (hereinafter referred to as a transmission type holo) is used, it is difficult to take a configuration that avoids zero-order light. Therefore, in the case of a transmission type holo, it is desired to increase the diffraction efficiency as much as possible and suppress the influence of zero-order light as much as possible.

(Reflective and transmissive hologram recording medium 55)
The reflection type holo has higher wavelength selectivity than the transmission type holo. That is, the reflection type holo can diffract coherent light having a desired wavelength only by a desired layer even if interference fringes corresponding to different wavelengths are laminated. The reflection type holo is also excellent in that it is easy to remove the influence of zero-order light.

  On the other hand, the transmission type holo has a wide diffractable spectrum and a wide tolerance of the laser light source 61. However, when interference fringes corresponding to different wavelengths are laminated, coherent light of a desired wavelength is generated even in layers other than the desired layer. It will be diffracted. Therefore, in general, it is difficult to make the transmission type holo a laminated structure.

(Irradiation device 60)
In the above-described embodiment, the example in which the irradiation device 60 includes the laser light source 61 and the scanning device 65 has been described. Although the scanning device 65 is an example of the uniaxial rotation type mirror device 66 that changes the traveling direction of the coherent light by reflection, the scanning device 65 is not limited thereto. As shown in FIG. 5, the scanning device 65 has a second rotation in which the mirror (reflection surface 66a) of the mirror device 66 intersects not only the first rotation axis RA1 but also the first rotation axis RA1. It may be rotatable about the axis RA2. In the example shown in FIG. 5, the second rotation axis RA2 of the mirror 66a is a first rotation axis RA1 extending in parallel with the Y axis of the XY coordinate system defined on the plate surface of the hologram recording medium 55. Are orthogonal. Since the mirror 66a is rotatable about both the first axis RA1 and the second axis RA2, the incident point IP of the coherent light from the irradiation device 60 to the optical element 50 is the plate of the hologram recording medium 55. It is possible to move in a two-dimensional direction on the surface. For this reason, as shown in FIG. 5 as an example, the incident point IP of the coherent light to the optical element 50 can be moved on the circumference.

  Further, the scanning device 65 may include two or more mirror devices 66. In this case, even if the mirror 66a of the mirror device 66 can be rotated only about a single axis, the incident point IP of the coherent light from the irradiation device 60 to the optical element 50 is expressed by the hologram recording medium 55. It can be moved in a two-dimensional direction on the plate surface.

  Specific examples of the mirror device 66a included in the scanning device 65 include a MEMS mirror, a polygon mirror, and a galvano scanner.

  The scanning device 65 may include a reflection device that changes the traveling direction of coherent light by reflection, that is, a device other than the mirror device 66 described above as an example in the present embodiment. For example, the scanning device 65 may include a refractive prism, a lens, and the like.

  In the first place, the scanning device 65 is not essential, and the light source 61 of the irradiation device 60 is configured to be displaceable (movable, swinging, rotating) with respect to the optical element 50, and the light source 61 is displaced by the displacement of the light source 61 with respect to the optical element 50. The coherent light irradiated from the above may be scanned on the hologram recording medium 55.

  Furthermore, although the light source 61 of the irradiation apparatus 60 has been described on the assumption that the laser light shaped as a linear light beam is oscillated, the present invention is not limited to this. In particular, in the above-described form, the coherent light irradiated to each position of the optical element 50 is shaped by the optical element 50 into a light beam that enters the entire illuminated area LZ. Therefore, there is no inconvenience even if the coherent light irradiated from the light source 61 of the irradiation device 60 to the optical element 50 is not accurately shaped. For this reason, the coherent light generated from the light source 61 may be diverging light. Further, the cross-sectional shape of the coherent light generated from the light source 61 may not be a circle but an ellipse or the like. Furthermore, the transverse mode of the coherent light generated from the light source 61 may be a multimode.

  When the light source 61 generates a divergent light beam, the coherent light is incident on a region having a certain area instead of a point when entering the hologram recording medium 55 of the optical element 50. In this case, the light diffracted by the hologram recording medium 55 and incident on each position of the illuminated area LZ is multiplexed in angle. In other words, at each moment, coherent light is incident on each position of the illuminated area LZ from a certain angle range. Speckle can be made more inconspicuous by such multiplexing of angles.

  Further, FIG. 1 shows an example in which the coherent light reflected by the scanning device 65 is directly incident on the optical element 50. However, a condensing lens is provided between the scanning device 65 and the optical element 50, and the light is condensed. You may make it make coherent light into a parallel light beam with a lens, and inject into the optical element 50. FIG. In such an example, a parallel light beam is used as the reference light Lr instead of the above-described convergent light beam in the exposure process when the hologram recording medium 55 is manufactured. Such a hologram recording medium 55 can be produced and duplicated more easily.

(Optical element 50)
In the embodiment described above, an example in which the optical element 50 includes the reflective volume hologram 55 using a photopolymer has been described, but the present invention is not limited thereto. Further, the optical element 50 may include a volume hologram that is recorded using a photosensitive medium including a silver salt material. Furthermore, the optical element 50 may include a transmissive volume hologram recording medium 55 or a relief (embossed) hologram recording medium 55.

  However, in the relief (embossed) hologram, hologram interference fringes are recorded by the concavo-convex structure on the surface. However, in the case of this relief-type hologram, scattering due to the uneven structure on the surface may cause a loss of light amount and may cause a new unintended speckle generation. In this respect, the volume-type hologram is preferable. . In the volume hologram, since the hologram interference fringe is recorded as a refractive index modulation pattern (refractive index distribution) inside the medium, it is not affected by scattering due to the uneven structure on the surface.

  However, even volume holograms that are recorded using a photosensitive medium containing silver salt material may cause light loss due to scattering by silver salt particles, and may cause unintended new speckle generation. There is sex. In this respect, the hologram recording medium 55 is preferably a volume hologram using a photopolymer.

  In addition, in the recording process shown in FIG. 2, a so-called Fresnel type hologram recording medium 55 is produced, and a Fourier transform type hologram recording medium 55 obtained by performing recording using a lens is produced. It doesn't matter. However, when the Fourier transform type hologram recording medium 55 is used, a lens may also be used during image reproduction.

  Further, the striped pattern to be formed on the hologram recording medium 55, for example, the refractive index modulation pattern or the uneven pattern, does not use the actual object light Lo and the reference light Lr, but the planned wavelength and incident direction of the reproduction illumination light La. In addition, it may be designed using a computer based on the shape and position of the image to be reproduced. The hologram recording medium 55 obtained in this way is also called a computer-generated hologram. When a plurality of coherent lights having different wavelength ranges are irradiated from the irradiation device 60 as in the above-described modification, the hologram recording medium 55 as a computer-generated hologram corresponds to each coherent light in each wavelength range. The coherent light in each wavelength region may be diffracted in the corresponding region to reproduce an image.

  Furthermore, in the embodiment described above, an example is shown in which the optical element 50 includes the hologram recording medium 55 that expands the coherent light irradiated to each position and illuminates the entire illuminated area LZ using the expanded coherent light. However, it is not limited to this. The optical element 50 changes the traveling direction of the coherent light irradiated to each position and diffuses instead of the hologram recording medium 55 or in addition to the hologram recording medium 55 so that the entire area to be illuminated LZ is coherent light. You may make it have a lens array as an optical element illuminated with. Specific examples include a total reflection type or refractive type Fresnel lens provided with a diffusion function, a fly-eye lens, and the like. Note that “diffusion” in the optical element in the present invention means that incident light is angularly expanded in a predetermined direction and emitted, and the diffusion angle is sufficiently controlled as in a diffractive optical element or a lens array. In addition, the case where the emission angle is expanded by scattering particles such as opal glass is also included. Also in such an illuminating device 40, the irradiating device 60 scans the lens array with the coherent light so as to irradiate the optical element 50 with the coherent light. By configuring the irradiation device 60 and the optical element 50 so that the traveling direction of the coherent light incident on the position is changed by the lens array to illuminate the illuminated area LZ, speckles are effectively inconspicuous. Can be made.

  In addition to the hologram recording medium 55 and the lens array, the optical element 50 can also be composed of a diffusion plate. As the diffusion plate, a glass member such as an opal glass file or a resin diffusion plate can be considered. Since the diffusion plate diffuses the coherent light reflected by the scanning device 65, the illuminated region LZ can be illuminated from various directions as in the case of using the hologram recording medium 55 or the lens array.

(Lighting method)
In the embodiment described above, the irradiation device 60 is configured to be able to scan the coherent light in the one-dimensional direction on the optical element 50, and the hologram recording medium 55 or the lens array of the optical element 50 is irradiated to each position. An example is shown in which the coherent light is configured to diffuse in a two-dimensional direction, whereby the illumination device 40 illuminates the two-dimensional illuminated region LZ. However, as described above, the present invention is not limited to such an example. For example, the irradiation device 60 is configured to be able to scan the coherent light on the optical element 50 in a two-dimensional direction, and The hologram recording medium 55 or the lens array of the optical element 50 is configured to diffuse the coherent light irradiated to each position in a two-dimensional direction. As a result, as shown in FIG. The illuminated area LZ may be illuminated.

  Further, as already mentioned, the irradiation device 60 is configured to be able to scan the coherent light on the optical element 50 in a one-dimensional direction, and each of the hologram recording medium 55 or the lens array of the optical element 50 includes The coherent light irradiated to the position may be configured to diffuse in a one-dimensional direction, so that the illumination device 40 may illuminate the one-dimensional illuminated area LZ. In this aspect, the scanning direction of the coherent light by the irradiation device 60 and the diffusing direction of the hologram recording medium 55 or the lens array of the optical element 50 may be parallel to each other.

  Furthermore, the irradiation device 60 is configured to be able to scan the coherent light in the one-dimensional direction or the two-dimensional direction on the optical element 50, and each position is irradiated with the hologram recording medium 55 or the lens array of the optical element 50. The coherent light may be configured to diffuse in a one-dimensional direction. In this aspect, the optical element 50 has a plurality of hologram recording media 55 or lens arrays, and the illumination area 40 is sequentially illuminated by illuminating the illuminated area LZ corresponding to each hologram recording medium 55 or lens array. A dimensional area may be illuminated. At this time, each illuminated area LZ may be sequentially illuminated at a speed as if it were illuminated simultaneously by the human eye, or it can be recognized that the illuminated area LZ is also illuminated sequentially by the human eye. It may be illuminated sequentially at such a slow speed.

  The aspect of the present invention is not limited to the individual embodiments described above, and includes various modifications that can be conceived by those skilled in the art, and the effects of the present invention are not limited to the contents described above. That is, various additions, modifications, and partial deletions can be made without departing from the concept and spirit of the present invention derived from the contents defined in the claims and equivalents thereof.

  DESCRIPTION OF SYMBOLS 15 Diffusing screen, 20 Projection apparatus, 30 Spatial light modulator, 40 Illumination apparatus, 50 Optical element, 55 Hologram recording medium, 58 Hologram photosensitive material, 60 Irradiation apparatus, 61 Light source, 65 Scanning device, 66 Mirror device (reflection device) , 66a Mirror (reflective surface), 67 condenser lens, 70 relay optical system, 80 enlarged projection optical system, LZ illuminated area

Claims (15)

An optical element capable of diffusing coherent light;
An irradiation device for irradiating the optical element with the coherent light so that coherent light scans the optical element;
A light modulator that is illuminated by the coherent light that is incident and diffused from the irradiation device to each position of the optical element;
A diffusion member having a diffusion surface for diffusing a modulated image generated by the light modulator;
Forming a virtual image of the modulated image diffused on the diffusion surface, and an enlarged projection optical system that allows the observer to visually recognize the virtual image,
The coherent light that is incident and diffused at each position of the optical element illuminates the light modulator in an overlapping manner.   The projection apparatus according to claim 1, wherein the light modulator transmits or reflects coherent light from the irradiation device to generate a modulated image. The light modulator is a transmissive light modulator that transmits a coherent light from the irradiation device to generate a modulated image,
The projection apparatus according to claim 1, wherein the diffusing member is disposed in proximity to the optical modulator.   The projection apparatus according to claim 1, further comprising a relay optical system that projects a modulated image generated by the light modulator onto the diffusion surface.   The projection apparatus according to claim 4, wherein the relay optical system adjusts the size of the modulated image generated by the light modulator and projects the modulated image onto the diffusion surface.   The projection apparatus according to claim 1, wherein the diffusing member transmits or reflects a modulated image generated by the light modulator.   The magnifying projection optical system includes a half mirror that reflects a part of the modulated image light diffused by the diffusion surface to form a virtual image of the modulated image and guides the modulated image light in the direction of the observer together with external light. The projection apparatus according to claim 1.   The projection device according to claim 7, wherein the half mirror is a windshield of a vehicle.   The projection apparatus according to claim 1, wherein the enlargement projection optical system includes a concave mirror, a hologram recording medium, or a prism.   The projection apparatus according to claim 1, wherein the light modulator is a micromirror device, a reflective or transmissive LCOS, or a transmissive liquid crystal panel. The irradiation device includes:
A light source that emits coherent light;
The scanning device that changes the traveling direction of the coherent light emitted from the light source and scans the coherent light on the optical element. Projection device.   The projection apparatus according to claim 1, wherein the optical element is a reflection-type or transmission-type hologram recording medium.   The projection apparatus according to claim 1, wherein the optical element is a microlens array.   The projection apparatus according to claim 1, wherein the optical element is a diffusion plate.   The projection device according to claim 14, wherein the diffusion plate is a glass member or a resin member.

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