JP2010197916A - Projection type video display device and video display method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently and sufficiently suppress the occurrence of a speckle, even when coherent light is adopted. <P>SOLUTION: The coherent light from a laser 210 is enlarged and made a parallel luminous flux LL. A hologram recording medium 220 on which the hologram image of a scattering plate is recorded is irradiated with the parallel luminous flux LL. The hologram reproduced real image 235 of the scattering plate is produced by using the parallel luminous flux LL as reproduced illumination light. A spatial light modulator 240 comprising a liquid crystal display, etc. is arranged to overlap the position of the hologram reproduced real image 235, and to obtain a modulated image on the surface of the reproduced real image 235 of the scattering plate. The modulated image is projected onto a screen 260 by a projection optical system 250. It is configured such that the light distribution angle θ of light made incident on one point Q1 on the screen 260 is 0.4° or more and the hologram recording medium 220 is periodically moved in an X-Y plane by a motor 225, so that the linear velocity of the light scanning on the screen 260 is 200 mm/sec. or more. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a projection-type image display device and an image display method, and more particularly to a technique for displaying an image on a screen by illuminating a spatial light modulator using light from a coherent light source.

  Various types of projection-type image display devices that display images by projecting light onto a screen have been proposed, including commercially available products called “optical projectors”. The basic principle of such a projection-type image display device is to generate an original two-dimensional image using a spatial light modulator such as a liquid crystal micro display or DMD (Digital Micromirror Device), and project the two-dimensional image. The image is enlarged and projected on a screen using an optical system.

  In general optical projectors, a white light source such as a high-pressure mercury lamp is used to illuminate a spatial light modulator such as a liquid crystal display, and the resulting modulated image is enlarged and projected onto a screen by a lens. For example, in Patent Document 1 below, white light generated by an ultra-high pressure mercury lamp is divided into three primary color components of R, G, and B by a dichroic mirror, and these lights are guided to a spatial light modulator for each primary color. A technique is disclosed in which a generated modulated image for each primary color is synthesized by a cross dichroic prism and projected onto a screen.

  However, high-intensity discharge lamps such as high-pressure mercury lamps have a relatively short life and require frequent lamp replacement when used in optical projectors and the like. Further, since it is necessary to use a relatively large optical system such as a dichroic mirror in order to extract the light of each primary color component, there is a problem that the entire apparatus becomes large. Thus, a method using a coherent light source such as a laser has been proposed. For example, a semiconductor laser widely used in the industry has a very long life compared to a high-intensity discharge lamp such as a high-pressure mercury lamp. In addition, since the light source can generate light having a single wavelength, a spectroscopic device such as a dichroic mirror is not necessary, and the entire device can be reduced in size.

  On the other hand, a method using a coherent light source such as a laser has a new problem of speckle generation. Speckle is a speckled pattern that appears when a diffused surface is irradiated with coherent light such as laser light. When speckle is generated on a screen, it is observed as speckled luminance unevenness, which is physiological to the observer. It becomes a factor that has a bad influence. The reason why speckle is generated when coherent light is used is that coherent light reflected by each part of a diffuse 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 speckle generation.

  As described above, in the system using the coherent 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, in Patent Document 2 below, the speckle is reduced by irradiating a scattering plate with laser light, guiding the scattered light obtained therefrom to a spatial light modulator, and rotating the scattering plate by a motor. Technology is disclosed.

JP 2004-264512 A Japanese Patent Laid-Open No. 6-208089

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

  As described above, a technique for reducing speckles has been proposed in a projection-type image display device using a coherent light source. However, with the conventionally proposed methods, speckles can be efficiently and sufficiently suppressed. Can not. For example, in the method disclosed in the above-mentioned Patent Document 2, laser light is irradiated on the scattering plate and scattered, and therefore, part of the laser light is wasted without contributing to video display at all. Moreover, although it is necessary to rotate a scattering plate for speckle reduction, such a mechanical rotation mechanism becomes a comparatively large apparatus, and also power consumption becomes large. Furthermore, even if the scattering plate is rotated, the position of the optical axis of the illumination light does not change, so that speckles generated on the diffusing surface of the screen cannot be sufficiently suppressed.

  Therefore, an object of the present invention is to provide a technique for efficiently and sufficiently suppressing the generation of speckles in a projection display apparatus using a coherent light source.

(1) According to a first aspect of the present invention, there is provided a projection-type image display device that displays an image by projecting light onto a screen.
Coherent light generating means for generating coherent light composed of substantially parallel light bundles;
A hologram recording medium that generates a hologram reproduction real image of the scattering plate by receiving the coherent light as reproduction illumination light;
A spatial light modulator arranged so as to be superimposed on the generation position of the hologram reproduction real image;
A projection optical system that projects a modulated image obtained on the spatial light modulator onto a screen;
Is provided.

(2) According to a second aspect of the present invention, in the projection display apparatus according to the first aspect described above,
Coherent light generation means
A laser light source that emits and emits laser light;
A light beam expanding means for expanding the laser light emitted from the laser light source into a substantially parallel light beam having a predetermined cross-sectional area;
It is made to have.

(3) According to a third aspect of the present invention, in the projection display apparatus according to the first or second aspect described above,
A hologram recording medium is constituted by a volume hologram using a photopolymer.

(4) According to a fourth aspect of the present invention, in the projection display apparatus according to the first to third aspects described above,
The coherent light generating means generates coherent light having substantially the same wavelength as that of the light used for recording the image of the scattering plate on the hologram recording medium,
The hologram recording medium is arranged in “the direction in which the incident angle of the coherent light with respect to the hologram recording medium and the incident angle of the reference light used when recording the image of the scattering plate are the same”. It is a thing.

(5) According to a fifth aspect of the present invention, in the projection display apparatus according to the first to fourth aspects described above,
The spatial light modulator is constituted by a transmissive or reflective liquid crystal display or a digital micromirror device.

(6) According to a sixth aspect of the present invention, in the projection display apparatus according to the first to fifth aspects described above,
The projection optical system performs forward projection to project a modulated image on the observation surface side of the screen.

(7) According to a seventh aspect of the present invention, in the projection-type image display device according to the first to sixth aspects described above,
The characteristics and arrangement of the spatial light modulator and the characteristics and arrangement of the projection optical system are set so that the light distribution angle with respect to an arbitrary point on the screen is 0.4 ° or more.

(8) According to an eighth aspect of the present invention, in the projection-type image display device according to the first to sixth aspects described above,
A drive mechanism for periodically moving the hologram recording medium is further provided.

(9) According to a ninth aspect of the present invention, in the projection display apparatus according to the eighth aspect described above,
The drive mechanism periodically translates the hologram recording medium within a plane parallel to the recording surface.

(10) According to a tenth aspect of the present invention, in the projection display apparatus according to the ninth aspect described above,
When the drive mechanism defines an XY two-dimensional orthogonal coordinate system on the recording surface of the hologram recording medium, the driving mechanism causes the hologram recording medium to vibrate simply in the X-axis or Y-axis direction, or the hologram recording medium is circled on the XY plane. It is intended to move or move elliptically.

(11) An eleventh aspect of the present invention is the projection type video display device according to the eighth to tenth aspects described above,
The characteristics and arrangement of the spatial light modulator and the characteristics and arrangement of the projection optical system are set so that the light distribution angle with respect to any one point on the screen is 0.4 ° or more.
The hologram recording medium is driven by the drive mechanism so that the linear velocity of light scanning on the screen is 200 mm / second or more.

(12) According to a twelfth aspect of the present invention, in the projection-type image display device according to the first to sixth aspects described above,
A drive mechanism is further provided for periodically moving the lens constituting the projection optical system in a plane perpendicular to the optical axis.

(13) According to a thirteenth aspect of the present invention, in the projection display apparatus according to the first to sixth aspects described above,
A drive mechanism for periodically moving the spatial light modulator along the modulated image forming surface is further provided.

(14) According to a fourteenth aspect of the present invention, in the projection display apparatus according to the first to sixth aspects described above,
A drive mechanism for periodically and periodically moving the apparatus main body constituted by the coherent light generation means, the hologram recording medium, the spatial light modulator, and the projection optical system is further provided.

(15) According to a fifteenth aspect of the present invention, in the projection-type image display device that projects light on a screen and performs color image display,
First coherent light generating means for generating coherent light in a first wavelength range composed of parallel light bundles;
A first hologram recording medium for generating a first hologram reproduction real image of the scattering plate by receiving coherent light in the first wavelength region as reproduction illumination light;
A first spatial light modulator that is arranged so as to overlap the formation position of the first hologram reproduction real image and that performs modulation based on an image having a first primary color component corresponding to the first wavelength range;
Second coherent light generating means for generating coherent light in a second wavelength range composed of parallel light bundles;
A second hologram recording medium that generates a second hologram reproduction real image of the scattering plate by receiving coherent light in the second wavelength region as reproduction illumination light;
A second spatial light modulator that is arranged so as to overlap the formation position of the second hologram reproduction real image and that performs modulation based on an image having a second primary color component corresponding to the second wavelength range;
Third coherent light generating means for generating coherent light in a third wavelength range composed of parallel light bundles;
A third hologram recording medium that generates a third hologram reproduction real image of the scattering plate by receiving coherent light in the third wavelength region as reproduction illumination light;
A third spatial light modulator that is arranged so as to overlap the formation position of the third hologram reproduction real image and that performs modulation based on an image having a third primary color component corresponding to the third wavelength range;
The first modulated image obtained on the first spatial light modulator, the second modulated image obtained on the second spatial light modulator, and the third modulated image obtained on the third spatial light modulator A combined projection optical system for projecting onto the screen,
Is provided.

(16) According to a sixteenth aspect of the present invention, in the projection-type image display method for displaying an image by projecting light on a screen,
Creating a hologram recording medium recording a hologram image of the scattering plate;
Irradiating the hologram recording medium with coherent light to generate a hologram reproduction real image of the scattering plate;
Placing the spatial light modulator superimposed on the hologram reproduction real image generation position;
Projecting the modulated image obtained on the spatial light modulator onto a screen;
Is to do.

(17) According to a seventeenth aspect of the present invention, in the projection-type image display method according to the sixteenth aspect described above,
While the modulated image is projected on the screen, the hologram recording medium is periodically translated in a plane parallel to the recording surface.

(18) According to an eighteenth aspect of the present invention, in the projection-type image display method according to the seventeenth aspect described above,
The light distribution angle with respect to an arbitrary point on the screen is 0.4 ° or more, and the linear velocity of light scanning on the screen is 200 mm / second or more.

  In the present invention, a hologram reproduction real image of the scattering plate is formed so as to be superimposed on the position of the existing spatial light modulator. For this reason, the modulated image obtained on the spatial light modulator is projected on the screen with the same behavior as the scattered light directly scattered from the scattering plate, and the generation of speckle on the screen is efficiently performed. It becomes possible to suppress sufficiently. Further, in the embodiment provided with a drive mechanism that periodically moves the hologram recording medium, light flux scanning is performed on the screen, so that it is possible to further reduce the generation of speckle.

It is a top view which shows an example of the projection type video display apparatus of the coherent light type | mold with the function which suppresses generation | occurrence | production of the speckle conventionally proposed. It is a top view for showing the problem of the projection type video display apparatus shown in FIG. It is a top view which shows basic embodiment of the projection type video display apparatus concerning this invention. It is a top view which shows the preparation methods of the hologram recording medium 220 in the apparatus shown in FIG. It is a top view which shows the mode of the real image reproduction | regeneration by the hologram recording medium 220 in the apparatus shown in FIG. It is a top view which shows an example of the drive mode of the hologram recording medium 220 in the projection type video display apparatus shown in FIG. It is a top view which shows another example of the drive mode of the hologram recording medium 220 in the projection type video display apparatus shown in FIG. It is a top view for showing the advantage of the projection type video display shown in Drawing 3. It is a table | surface which shows the generation | occurrence | production degree of the speckle when experimenting on various conditions. It is a graph of the experimental result which shows the generation | occurrence | production degree of the speckle when using the light distribution angle (theta) and the linear velocity of light beam scanning as a parameter. It is a top view which shows embodiment which applied this invention to the color image display apparatus.

  Hereinafter, the present invention will be described based on the illustrated embodiments.

<<< §1. Previously proposed projection display device >>>
Here, for convenience of explanation, for example, the basic principle of a coherent light projection type image display apparatus proposed in the above-mentioned Patent Document 2 will be described with reference to the plan view of FIG.

  As shown in the figure, in this projection type image display device, coherent light generated from a coherent light source 110 such as a laser is irradiated onto a transmission type scattering plate 120, and the obtained scattered light is collected by a condensing lens 130, and spatial light modulation is performed. Leading to vessel 140. If, for example, a transmissive liquid crystal microdisplay is used as the spatial light modulator 140, a modulated image can be obtained on the screen of this display. When the modulated image obtained in this manner is projected onto the screen 160 by the projection optical system 150, the enlarged modulated image is displayed on the screen 160.

  As the spatial light modulator 140, a reflective micro display can be used. In that case, the coherent light source 110, the scattering plate 120, and the condenser lens 130 are disposed obliquely above the spatial light modulator 140 in FIG. 1, and reflected light from the spatial light modulator 140 is reflected by the projection optical system 150 on the screen 160. Will be projected to. When using such reflected light, it is also possible to use a MEMS element such as DMD (Digital Micromirror Device) as the spatial light modulator 140. In fact, the embodiment disclosed in the above-mentioned Patent Document 2 is This is a reflection type device using a DMD as the spatial light modulator 140.

  The illustrated example is a front projection type device that observes the viewpoint E placed on the front side of the screen 160, but a rear projection type device that observes the viewpoint E placed on the other side of the screen 160 (so-called Rear projector devices) are also widely used.

  As already described, the apparatus using the coherent light source 110 such as a laser has a problem that speckles are generated on the screen 160. The speckle is a speckled pattern that appears when the scattering surface is irradiated with coherent light, and is caused by the interference of the coherent light reflected by each part of the scattering surface. Therefore, in the embodiment disclosed in the above-mentioned Patent Document 2, the scattering plate 120 is rotationally driven by the rotation mechanism 125 with the optical axis of the laser light as the central axis, thereby devising the generation of speckle. Has been.

  According to the aforementioned Non-Patent Document 1, it is considered effective to multiplex modes such as polarization, phase, angle, and time in order to reduce the generation of speckle. When the scattering plate 120 is driven to rotate, the modes of scattered light emitted from the scattering plate 120 are multiplexed, and as a result, generation of speckles on the screen 160 can be reduced.

  However, it has already been pointed out that it is difficult to efficiently and sufficiently suppress the generation of speckles in this type of apparatus that has been proposed in the past. FIG. 2 is a plan view for illustrating problems of the projection display apparatus shown in FIG. The configuration of the apparatus shown in FIG. 2 is exactly the same as that of the apparatus shown in FIG. Hereinafter, some problems of the conventional apparatus will be described in detail with reference to FIG.

  First, since the laser light applied to the scattering plate 120 is scattered in various directions, the light is collected by the condenser lens 130 like the light exemplified as the scattered light Ls in FIG. There is also scattered light that goes in a direction that is not illuminated. As described above, a part of the laser light is wasted without contributing to the image display at all, which causes a problem in terms of energy use efficiency.

  Secondly, rotating the scattering plate 120 by the rotation mechanism 125 for speckle reduction is not necessarily an efficient method. That is, the greater the mass of the scattering plate 120, the greater the power consumption required for rotating the scattering plate. In fact, the electric power necessary to always give a rotational moment to the scattering plate 120 cannot be ignored, and a mechanical rotating structure is required, which also hinders downsizing of the apparatus.

  Thirdly, even if the scattering plate 120 is rotated, the position of the optical axis of the illumination light supplied from the coherent light source 110 to the screen 160 does not change, so speckles generated on the scattering surface of the screen 160 are reduced. It cannot be suppressed sufficiently. In the case of the apparatus shown in FIG. 2, the scattering of light that contributes to the generation of speckle occurs at two locations of the scattering plate 120 and the screen 160. If the scattering plate 120 is rotated, speckles caused by scattering on the scattering plate 120 (so-called speckles caused by the light source side of the illumination light) can be reduced. However, speckles generated due to scattering on the screen 160 (in other words, speckles generated due to the screen side) cannot be reduced.

  Here, let us focus on the light distribution angle of the projection light L1 that reaches an arbitrary projection point Q1 on the screen 160 shown in the drawing (the distribution range of the incident angle on the screen 160, as will be described later). In the case of the illustrated apparatus, the spatial light modulator 140 performs the function of modulating the illumination light incident from the condenser lens 130 side and then transmitting it to the projection optical system 150. Accordingly, the pixel information of the video point P1 is projected as it is onto the projection point Q1 on the screen 160 by the projection light L1. This means that the light distribution angle is extremely narrow when the projection optical system 150 is desired from the projection point Q1 side. Even if the scattering plate 120 is rotated, there is no change in the optical path of the projection light L1 that illuminates the projection point Q1, and the incident angle is always constant. As described above, when the surface of the screen 160 is always irradiated with coherent light from the same direction, it becomes a major factor for generating speckle, and the speckle generated due to such a screen side is reduced. Above, the rotational drive of the scattering plate 120 is not useful at all.

  The present invention proposes a new technique for solving such problems of the conventional apparatus. The basic embodiment will be described below.

<<< §2. Basic embodiment of the present invention >>
FIG. 3 is a plan view showing a basic embodiment of a projection-type image display apparatus according to the present invention. Also in this projection type image display apparatus, coherent light generated from the coherent light source 210 is used. In this apparatus, a laser light source that generates and emits laser light is used as the coherent light source 210, and the emitted laser light is blocked by a light beam enlarging unit including a magnifying lens 211 and a collimating lens 212. It is expanded to a parallel light beam with an area. In practice, there is no problem even if a substantially parallel beam bundle is used instead of a strictly parallel beam bundle.

  Thus, the illustrated coherent light source 210 (laser light source), the magnifying lens 211, and the collimating lens 212 function as coherent light generating means for generating coherent light composed of parallel light beams. As shown in the figure, coherent light composed of parallel light beams enters the hologram recording medium 220 with a predetermined incident angle φ. As will be described later, the coherent light composed of this parallel light beam functions as reproduction illumination light for the hologram recording medium 220. Therefore, the magnifying lens 211 and the collimating lens 212 magnify the light beam of the laser beam so that the reproduction illumination light composed of parallel light beams is irradiated on the entire recording surface of the hologram recording medium 220. In other words, the cross section of the parallel light beam has an area necessary and sufficient to irradiate the entire recording surface of the hologram recording medium 220. However, since each point of the hologram recording medium 220 has a function of reproducing the image of the scattering plate, the reproduction illumination light does not necessarily have a cross-sectional area necessary for irradiating the entire recording surface.

  A hologram image of a scattering plate (optical diffusion plate) is recorded in advance on the hologram recording medium 220, and when the coherent light composed of the parallel light bundle is irradiated as reproduction illumination light, the scattering is performed. A real hologram reproduction image of the plate is generated.

  FIG. 4 is a plan view showing a method for producing this hologram recording medium 220. The scattering plate 230 shown in the figure is a transmission type scattering plate (for example, an opal glass plate) in which fine particles (light scatterers) for scattering light are incorporated, and the hologram photosensitive medium 222 is a hologram. It is a photosensitive medium used for recording an image. In the illustrated example, laser light having a predetermined wavelength λ is irradiated as illumination light L from below the scattering plate 230, and hologram recording is performed using the scattered light generated by scattering by the scattering plate 230 as object light Lo. . At this time, a laser beam having the same wavelength λ as the illumination light L is used as the reference light Lr so as to irradiate the hologram photosensitive medium 222 at an incident angle φ, and the interference fringe pattern between the object light Lo and the reference light Lr becomes a hologram photosensitive. It is recorded on the recording surface of the medium 222.

  FIG. 5 is a plan view showing how a real image is reproduced by the hologram recording medium 220 created in this way. A hologram recording medium 220 shown in FIG. 5 corresponds to the hologram photosensitive medium 222 shown in FIG. 4 (recording of the hologram is completed), but the upper and lower surfaces in the drawing are reversed. That is, the hologram recording medium 220 shown in FIG. 5 is the one in which the recorded hologram photosensitive medium 222 is turned upside down after the hologram recording is completed in the process shown in FIG.

  As shown in FIG. 5, a laser beam having a wavelength λ (the same wavelength as that of the illumination light L and the reference light Lr used in the recording process of FIG. 4) from the lower side of the hologram recording medium 220 is used as the reproduction illumination light LL. When irradiation is performed at an incident angle φ, a hologram reproduction real image 235 of the scattering plate is generated above the figure. This hologram reproduction real image 235 is a reproduction image using the scattering plate (opal glass plate) shown in FIG. 4 as an original image.

  A coherent light source (laser light source) 210 used in the apparatus shown in FIG. 3 is a light source for generating the reproduction illumination light LL shown in FIG. 5, and the illumination light L and the reference light used in the recording process of FIG. Coherent light having the same wavelength λ as the wavelength of Lr is generated. As described above, this coherent light is applied to the hologram recording medium 220 at an incident angle φ. Here, the incident angle φ is equal to the incident angle φ of the reference light Lr in the hologram recording process shown in FIG. Therefore, in FIG. 3, a hologram reproduction real image 235 is obtained at a position above the hologram recording medium 220. Actually, in the process of creating the hologram recording medium 220, the medium material may shrink. In such a case, it is preferable to adjust the wavelength of the reproduction illumination light LL in consideration of material shrinkage. Therefore, the wavelength of the coherent light generated by the coherent light source 210 does not have to be exactly the same as the wavelength of the light used in the recording process of FIG.

  An important feature of the present invention is that the spatial light modulator 240 is arranged so as to be superimposed on the generation position of the hologram reproduction real image 235. Here, the spatial light modulator 240 is a real device such as a liquid crystal micro display or a DMD (Digital Micromirror Device), whereas the hologram reproduction real image 235 is an optical reproduction image, and both are in the same space. It is possible to overlap with each other. In FIG. 3, only the real spatial light modulator 240 is depicted, but the hologram reproduction real image 235 of the scattering plate reproduced by the hologram recording medium 220 is superposed on this same spatial position.

  However, the actual hologram reproduction real image 235 obtained in this way is coherent light diffracted by the interference fringes formed on the hologram recording medium 220, and the spatial light modulator 240 performs illumination with such coherent light. Then, a predetermined modulated image is generated. For example, when a transmissive liquid crystal microdisplay is used as the spatial light modulator 240, a modulated image is obtained as a grayscale pattern of illumination light transmitted through the display.

  The projection optical system 250 performs a function of projecting the modulated image thus obtained on the spatial light modulator 240 onto the screen 260. If a transmissive liquid crystal microdisplay is used as the spatial light modulator 240, the modulated image formed on the display is projected onto the screen 260, and video display is performed.

  In the apparatus shown in FIG. 3, a drive mechanism 225 for moving the hologram recording medium 220 periodically is further provided. More specifically, the drive mechanism 225 functions to periodically translate the hologram recording medium 220 in a plane parallel to the recording surface. For example, as shown in the figure, an XYZ three-dimensional orthogonal coordinate system is defined in which the X axis is in the right direction of the drawing, the Z axis is in the upward direction of the drawing, and the Y axis is in the vertical direction of the drawing. Assuming that the recording surface is arranged so as to be included in the XY plane, the drive mechanism 225 periodically causes the hologram recording medium 220 to remain in a state where the recording surface is included in the XY plane. It performs the function of translating. Here, “parallel movement” means a movement that does not include a rotation factor, and the hologram recording medium 220 performs a movement that changes only the position on the XY plane while maintaining the same posture. .

  6 and 7 are plan views showing an example of a driving mode of the hologram recording medium 220 on such an XY plane. FIG. 6 shows an example in which the hologram recording medium 220 is simply vibrated along the X-axis direction as indicated by the arrow Mx, or is simply vibrated along the Y-axis direction as indicated by the arrow My. In any case, the movement of the hologram recording medium 220 does not include a rotation factor, and is a periodic parallel movement along the arrow Mx or the arrow My. FIG. 7 shows an example in which the hologram recording medium 220 is circularly moved on the XY plane. The hologram recording medium 220 moves along a circular orbit indicated by an arrow Mc. In this case as well, the hologram recording medium 220 is also moved. The movement does not include the rotation factor, it is just a translation. Elliptic motion may be used instead of circular motion.

  In such a periodic motion, the recording surface of the hologram recording medium 220 always maintains the position on the XY plane, and therefore, the incident angle φ of the parallel light flux that has exited the collimating lens 212 to the hologram recording medium 220 is increased. There will be no change. Of course, if the hologram recording medium 220 is moved along the XY plane, the position of the reproduced image to be obtained also moves in parallel, but the spatial light modulator 240 disposed at a predetermined distance from the hologram recording medium 220. The point at which the hologram reproduction real image 235 of the scattering plate is obtained at the same position remains unchanged.

  In the hologram recording process shown in FIG. 4, the plane size of the scattering plate 230 used as the original image is set larger than the plane size of the image forming surface of the spatial light modulator 240 by a predetermined amount Δ, and the simple vibrations Mx, My If the amplitude and the diameter of the circular motion Mc are suppressed to the predetermined amount Δ or less, even if the hologram recording medium 220 is moved, the scattering plate is always on the image forming surface of the spatial light modulator 240. 230 reproduction real images 235 are obtained.

  Thus, the reason why the hologram recording medium 220 is periodically moved by the drive mechanism 225 is to reduce speckles generated on the screen 260. The basic principle will be described in §4. The exercise conditions for efficiently reducing speckle will be described in detail in §5.

<<< §3. Examples and modifications showing specific configurations of individual elements >>
Next, a specific configuration example of each element of the projection type video display device shown in FIG. 3 will be described based on the device according to the embodiment actually manufactured by the inventor of the present application.

  First, as the coherent light source 210, a DPSS (Diode Pumped Solid State) laser capable of emitting laser light having a wavelength λ = 532 nm (green) was used. The DPSS laser is suitable as a coherent light source for use in a projection display apparatus such as the present invention because it can obtain laser light having a desired wavelength with a relatively high output while being small. As the magnifying lens 211 and the collimating lens 212, any lens may be used as long as it can magnify the luminous flux of the laser light emitted from the DPSS laser and generate a parallel light beam. .

  On the other hand, as described above, the hologram recording medium 220 is produced by the hologram recording process shown in FIG. As the scattering plate 230 to be an original image, an opal glass plate (which is generally commercially available as an optical diffusion plate) having a slightly larger planar size than the spatial light modulator 240 was used. In order to generate the illumination light L and the reference light Lr used in the hologram recording process, the above-described DPSS laser capable of emitting the laser light having the wavelength λ = 532 nm (green) was used.

  Eventually, the coherent light source 210 that functions as a means for generating coherent light is a light source that generates coherent light having the same wavelength as that of the light used when the image of the scattering plate 230 is recorded. The hologram recording medium 220 shown in FIG. 3 indicates that “the incident angle φ of the coherent light with respect to the hologram recording medium 220 (the angle φ in FIG. 3) and the reference light Lr used when recording the image of the scattering plate 230. The incident angle φ (the angle φ in FIG. 4) is arranged in the same direction.

  Here, as the hologram recording medium 220, a volume hologram using a photopolymer is preferably used. In general, a hologram used as an anti-counterfeit seal on a cash card or a cash voucher is called a relief (emboss) type hologram, and hologram interference fringes are recorded by a concavo-convex structure on the surface. However, in the case of this relief type hologram, the scattering due to the uneven structure on the surface may become a new speckle generation factor, so that it is not suitable for use in the projection type video display apparatus as in the present invention. In the volume hologram, since the hologram interference fringes are recorded as the refractive index distribution inside the medium, the volume hologram is not affected by scattering due to the uneven structure on the surface.

  Of course, volume holograms that are recorded using a photosensitive medium containing a silver salt material are preferably avoided because scattering by silver salt particles may be a new speckle generation factor. . For these reasons, the present inventor believes that a volume hologram using a photopolymer is optimal as the hologram recording medium 220 used in the present invention. A specific chemical composition of a volume hologram using such a photopolymer is exemplified in, for example, Japanese Patent No. 2849021.

  In the embodiment shown in FIG. 3, the transmission type hologram recording medium 220 that transmits the reproduction illumination light and generates the hologram reproduction real image is shown. However, the hologram reproduction real image is reflected by reflecting the reproduction illumination light. A reflection type hologram recording medium to be generated may be used. In this case, the coherent light source 210, the magnifying lens 211, and the collimating lens 212 may be arranged so that the reproduction illumination light is irradiated obliquely from above the hologram recording medium 220 shown in FIG.

  In the embodiment shown in FIG. 3, the light source 210 and the lenses 211 and 212 are arranged obliquely downward with respect to the hologram recording medium 220, but the incident angle with respect to the hologram recording medium 220 is φ. If such a device can be applied, these may be arranged directly under the hologram recording medium 220. For example, if a polarizing element plate or the like is attached to the lower surface side of the hologram recording medium 220, even if an arrangement in which the reproduction illumination light is incident on the polarizing element plate from vertically below, If the incident angle with respect to the hologram recording medium 220 is φ due to the polarization action, no particular problem occurs.

  In the recording process shown in FIG. 4, a so-called Fresnel type hologram recording medium is produced. However, a Fourier transform type hologram recording medium obtained by performing recording using a lens may be produced. Absent. However, when a Fourier transform type hologram recording medium is used, a lens is also required during image reproduction.

  On the other hand, as the spatial light modulator 240, a transmissive liquid crystal microdisplay was used as described above. In this display, the light transmittance can be controlled for each pixel by the phase change of the liquid crystal based on the electrical signal, so that a modulated image corresponding to the given image data is generated on the display surface of the display. Can do. Note that a reflective liquid crystal microdisplay can be used as the spatial light modulator 240. In this case, light from the hologram recording medium 220 is incident on the spatial light modulator 240 obliquely from above. It is necessary to adopt such a configuration.

  Of course, the spatial light modulator 240 that can be used in the present invention is not limited to a liquid crystal microdisplay, and uses elements such as DMD (Digital Micromirror Device) and LCOS (Liquid Crystal On Silicon). It doesn't matter.

  As the projection optical system 250, any optical system having a function of projecting the modulated image obtained on the spatial light modulator 240 onto the screen 260 may be used. Usually, it is composed of a plurality of lenses so that the focal length can be adjusted. The illustrated example is a forward projection type apparatus that observes the viewpoint E placed on the front side of the screen 260. However, the projection type video display apparatus according to the present invention places the viewpoint E on the other side of the screen 260. It is also possible to use it for a rear projection type device (so-called rear projector device).

  However, in general, in a rear projection type apparatus, it is possible to suppress the generation of speckles by devising the material of the screen. That is, in the case of a rear projection type device, the light that the observer sees is light that has passed through the screen. Therefore, by taking measures to embed scattering particles inside the screen, it is possible to deal with speckle generation. It becomes possible. Therefore, in practice, the speckle reduction technique according to the present invention exhibits its true value in a front projection type apparatus that performs forward projection in which a modulated image is projected onto the observation surface side of the screen.

  As shown in FIGS. 6 and 7, the driving mechanism 225 may use any mechanism as long as it can move the hologram recording medium 220 on the XY plane. In an apparatus actually manufactured by a person, a stepping motor for driving in the X-axis direction and the Y-axis direction was provided, and a simple vibration or circular motion was performed by a digital drive signal. In addition, the drive mechanism 225 can be configured using a piezoelectric element, a voice coil, an ultrasonic motor, or the like.

<<< §4. Advantages of the present invention >>
Here, advantages of the present invention over the conventional apparatus illustrated in FIG. 1 will be described. FIG. 8 is a plan view for illustrating the advantages of the embodiment shown in FIG. 3, and the configuration of the apparatus shown here is exactly the same as the configuration of the apparatus shown in FIG. Here, for the sake of convenience, the conventional apparatus shown in FIG. 2 will be described in comparison with the apparatus according to the embodiment shown in FIG.

  As described in §1, the first problem of the conventional apparatus shown in FIG. 2 is that a part of the laser light applied to the scattering plate 120 contributes to the video display as exemplified by the scattered light Ls. It is a point that becomes useless. On the other hand, in the apparatus shown in FIG. 8, useless scattered light Ld as shown does not occur. This is because the light that has passed through the hologram recording medium 220 is diffracted in the direction in which the hologram reproduction real image 235 is formed, as shown in FIG. Since the hologram recording medium 220 itself is not a scattering plate that randomly scatters incident light, no wasted light is generated in a direction in which a reproduced image is not generated unlike the scattered light Ld shown in the drawing. For this reason, all the light applied to the hologram recording medium 220 is effectively used to form the hologram reproduction real image 235.

  The second problem of the conventional apparatus shown in FIG. 2 is that a large rotating mechanism is required to rotate the scattering plate 120, and this prevents the apparatus from being downsized. On the other hand, in the case of the apparatus shown in FIG. 8, the drive mechanism 225 does not need to rotate the hologram recording medium 220, and can perform simple vibration, circular motion, and elliptical motion as shown in FIGS. Good. Thus, the mechanism for performing a motion that does not include a rotation factor can be reduced in size and consumes less power than the mechanism for performing a rotational motion.

  The third problem of the conventional apparatus shown in FIG. 2 is that the speckles generated due to the light source side of the illumination light can be reduced by the rotational movement of the scattering plate 120, but due to the screen side. The speckles that occur cannot be reduced. As described with reference to FIG. 2, since the spatial light modulator 140 is not a scattering plate, the pixel information of the image point P1 is projected as it is onto the projection point Q1 on the screen 160 by the projection light L1. When the projection optical system 150 is desired from the Q1 side, the direction in which the projection light L1 enters the projection point Q1 is always constant. As described above, when the surface of the screen 160 is always irradiated with coherent light from the same direction, it becomes a major factor in generating speckles.

  On the other hand, in the apparatus shown in FIG. 8, the hologram reproduction real image 235 of the scattering plate is formed so as to be superimposed on the spatial position of the spatial light modulator 240. For this reason, the light incident on each point on the spatial light modulator 240 has already been multiplexed with respect to the angle. That is, as shown in FIG. 5, each point of the hologram reproduction real image 235 of the scattering plate is constituted by light from various points of the hologram recording medium 220. For this reason, the speckle on the light source side is eliminated at this stage.

  Furthermore, since the hologram reproduction real image 235 of the scattering plate is formed on the spatial light modulator 240, the light from the modulated image formed on the spatial light modulator 240 is scattered light as if emitted from the scattering plate. Will behave in the same way. Accordingly, the pixel information of the video point P1 shown in FIG. 8 is propagated as scattered light information directed in various directions, and is imaged at the projection point Q1 on the screen 260 by the lenses constituting the projection optical system 250. Here, there are various optical paths of scattered light from the image point P1 toward the projection point Q1 (two optical paths are illustrated by broken lines in the drawing), and the projection optical system 250 is desired from the projection point Q1 side. In this case, the incident angle of light incident on the projection point Q1 varies.

  Eventually, when the optical paths of incident light incident from various directions are bundled for a certain projection point Q1, a cone having the projection point Q1 as a vertex is formed. Here, the apex angle θ of the triangle obtained by cutting the cone with the central axis is generally called “light distribution angle”. An angle θ formed by the optical path indicated by a broken line in FIG. 8 is a light distribution angle with respect to the projection point Q1. The light distribution angle θ takes a different value for each projection point, and generally increases as the center of the screen 260 decreases toward the end of the screen 260.

  The light distribution angle θ for a certain projection point Q1 is a parameter indicating the multiplicity of the incident angle of light incident on the projection point Q1. The greater the light distribution angle θ, the greater the multiplicity of incident angles, and the more light is incident from various directions. The multiplicity of incident angles is closely related to speckle generation factors. That is, as described in the aforementioned Non-Patent Document 1, if the multiplicity of incident angles is increased, the generation of speckle can be reduced. Therefore, the speckle generation is reduced by increasing the light distribution angle θ as much as possible at any projection point on the screen 260.

  The actual value of the light distribution angle θ depends on the characteristics (especially the size of the modulated image generation surface) and arrangement of the spatial light modulator 240, the characteristics (especially the aperture and focal length of the lens) and arrangement of the projection optical system 250, and Characteristics of the scattering plate 230 recorded on the hologram recording medium 220 (particularly, scattering characteristics such as size and scattering angle determined according to the positional relationship between the maximum capture diameter of the projection lens in the projection optical system 250 and the light valve) However, in the apparatus according to the present invention, the light distribution angle θ for an arbitrary projection point on the screen 260 can be increased as compared with the conventionally proposed apparatus. The reason is that the hologram reproduction real image 235 of the scattering plate is formed so as to be superimposed on the spatial position of the spatial light modulator 240 as shown in FIG.

  As described above, when the apparatus configuration according to the present invention is adopted, the light from the modulated image formed on the spatial light modulator 240 behaves as if it is the scattered light emitted from the scattering plate. The pixel information of the illustrated video point P1 propagates as scattered light information directed in various directions. In the example shown in the drawing, the light distribution angle θ is obtained for the projection point Q1 because scattered light traveling in various directions from the image point P1 is condensed at the projection point Q1 by the projection optical system 250. . As described above, the feature that “the hologram reproduction real image 235 of the scattering plate is formed so as to overlap the position of the spatial light modulator 240” in the present invention is extremely important in reducing speckles caused by the screen side. Fulfills the functions.

  In addition, the device shown in FIG. 8 is devised to further reduce speckles caused by the screen side. This is a mechanism for driving the hologram recording medium 220 by the drive mechanism 225. As described above, in the present invention, the hologram reproduction real image 235 of the scattering plate is formed so as to be superimposed on the position of the spatial light modulator 240, thereby making it possible to secure a larger light distribution angle θ compared to the conventional device. Thus, the effect of reducing speckles can be obtained, but the speckle reduction effect can be further improved by driving the hologram recording medium 220 by the driving mechanism 225.

  As already described, the drive mechanism 225 has a function of periodically moving the hologram recording medium 220 in parallel on the XY plane (that is, on the plane including the recording surface). If the hologram recording medium 220 is translated in this way, the hologram reproduction real image 235 of the scattering plate is also translated. However, since the spatial light modulator 240 remains stationary, the modulated image does not move, and the image projected on the screen 260 does not move. Therefore, the parallel movement of the hologram recording medium 220 on the XY plane has no effect on the original image projected on the screen 260.

  However, the parallel movement of the hologram recording medium 220 on the XY plane serves to reduce speckles generated on the screen 260. The reason why such a speckle reduction effect occurs can be easily understood by considering how the driving of the hologram recording medium 220 affects the light emitted from the video point P1 shown in FIG. That is, since the pixel at the video point P1 (the pixel of the spatial light modulator 240) remains stationary, there is no change in the modulated image information given to the video point P1, but it is superimposed and reproduced at the position of the video point P1. Since the reproduced real image 235 of the scattering plate to be moved moves, the scattering phenomenon at the video point P1 changes with time. Therefore, the characteristic of the scattered light from the video point P1 toward the projection point Q1 also changes with time, and the scattering phenomenon that occurs at the projection point Q1 also changes with time and is multiplexed in time. Thus, speckles generated due to scattering occurring at the projection point Q1 are reduced.

  In the embodiment shown here, the hologram recording medium 220 is periodically moved by the drive mechanism, but instead, the lenses constituting the projection optical system 250 are placed in a plane perpendicular to the optical axis. Even if it is moved periodically, speckles generated due to scattering generated on the screen 260 can be reduced. However, when the lens constituting the projection optical system 250 is moved, the image itself projected on the screen 260 vibrates and the image is blurred. Therefore, in practice, the hologram recording medium 220 is driven. Is preferred.

  In addition, instead of moving the hologram recording medium 220 by the driving mechanism, the spatial light modulator 240 may be moved periodically along the modulated image forming surface due to scattering generated on the screen 260. Speckle generated by the process can be reduced. However, in this method, since the modulated image formed on the spatial light modulator 240 also moves, the image projected on the screen 260 also moves. If the displacement (amplitude) of the image on the screen 260 is suppressed to a very small amount, it is possible to prevent the naked eye from recognizing that the image vibrates. 220 is preferably driven.

  Further, as another method, a coherent light source 210, a magnifying lens 211, a collimating lens 212, a hologram recording medium 220, a spatial light modulator 240, a projection optical system 250, which function as coherent light generation means, are driven by a driving mechanism. The speckles generated due to the scattering generated on the screen 260 can also be reduced by moving the apparatus main body constituted by the above as a whole periodically. However, in this method, the image projected on the screen 260 also moves, and the drive mechanism becomes large. Therefore, it is preferable to drive only the hologram recording medium 220 in practice.

<<< §5. Optimal numerical conditions >>
Next, here, optimum numerical conditions for implementing the basic embodiment described in §2 will be shown. First, in order to investigate what is an important factor in reducing speckles in a projection-type image display apparatus such as the present invention, results of experiments conducted by the present inventor will be presented.

  FIG. 9 is a table showing the degree of speckle occurrence when experiments are performed under various conditions. 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.

  The table in FIG. 9 shows the results of measuring speckle contrast under three conditions using the apparatus configuration shown in FIG. First, the measurement result shown as Condition 1 is a measurement result when a green laser is used as the light source 210 and no diffusing element is provided between the light source 210 and the spatial light modulator 240. In short, this is the result of measurement in the measurement system in which the hologram recording medium 220 is removed from the apparatus shown in FIG. In this case, as shown in the table, a result of speckle contrast of 20.7% was obtained. This is a state in which a spot-like luminance unevenness pattern can be observed quite noticeably when observed with the naked eye.

  On the other hand, the measurement result shown as Condition 2 is the result of measurement without operating the drive mechanism 225 in the apparatus configuration shown in FIG. That is, when a green laser is used as the light source and the hologram recording medium 220 functioning as a diffusing element is disposed between the light source 210 and the spatial light modulator 240, the hologram recording medium 220 is not driven and is kept stationary. This is a measurement result (the measurement result when the hologram recording medium 220 is driven is shown in the graph of FIG. 10 as described later). In this measurement, the condition setting was made such that the light distribution angle θ = 10 ° or more at any point on the screen 260. In this case, as shown in the table, a result of speckle contrast of 17.9% was obtained. This is a state in which a spot-like luminance unevenness pattern can still be observed when observed with the naked eye.

  On the other hand, the measurement result shown as Condition 3 shows that in the apparatus shown in FIG. 3, the light source 210 is replaced with a green LED (non-coherent light source), and no diffusion occurs between the LED and the spatial light modulator 240. This is a measurement result when no element is provided (that is, when the hologram recording medium 220 is removed). In this case, as shown in the table, a result of speckle contrast of 4.0% was obtained. This is a very good state in which a luminance unevenness pattern can hardly be observed when observed with the naked eye.

  The reason why the measurement result under Condition 3 shows significantly better results than the measurement results under Conditions 1 and 2 is that a “non-coherent light source (LED)” is used as the light source. As already mentioned, the problem of speckle generation is a problem inherent in the case of using a “coherent light source” such as a laser in practice, and is considered in an apparatus using a “non-coherent light source” such as an LED. It is a problem that does not need to be done. Therefore, ideally, an apparatus using a “coherent light source” such as a laser preferably has a speckle contrast comparable to that of an apparatus using a “non-coherent light source”.

  In fact, in the case of HDTV (high-definition television) video display applications, a standard of speckle contrast of 6.0% or less is indicated as a level at which an uneven brightness pattern is hardly recognized when an observer observes with the naked eye (see FIG. For example, see WO / 2001/081996). Therefore, in a device using a “coherent light source” such as a laser, one technical goal is to suppress the speckle contrast to 6.0% or less.

  According to the measurement results of FIG. 9, in the apparatus shown in FIG. 3, the speckle contrast can be reduced by 2.8 points by providing the hologram recording medium 220 functioning as a diffusing element (condition 1 → condition). 2). Certainly, it has succeeded in reducing speckles to some extent by inserting the hologram recording medium 220, but the result that the speckle contrast is 17.9% is not a satisfactory result in practical use.

  As described above, the reason that the speckle contrast cannot be sufficiently reduced only by the insertion of the hologram recording medium 220 is that the speckle caused by the light source side of the illumination light can be reduced, but the speckle contrast is caused by the screen side. This is because the speckles that are generated cannot be reduced sufficiently. In the apparatus according to the basic embodiment of the present invention shown in FIG. 3, the following two approaches are taken in order to reduce speckle.

  The first approach is to secure the light distribution angle θ at each projection point. In the case of the conventional apparatus, there is only one optical path of light incident on the projection point Q1 shown in FIG. 2, and the light distribution angle θ = 0 °. For this reason, it is not possible to reduce speckle caused by the screen side. On the other hand, in the case of the apparatus according to the present invention, scattered light from the image point P1 is collected through various optical paths at the projection point Q1 shown in FIG. 8, and a certain degree of light distribution angle θ is ensured. Is possible.

  The second approach is driving by the driving mechanism 225. As described above, the drive mechanism 225 periodically moves the hologram recording medium 220 within its recording surface (within the XY plane). Here, when attention is focused on a single light emitted from a specific point of the hologram recording medium 220 toward a specific direction, the light passes through a predetermined point on the spatial light modulator 240 and passes through the screen 260. It will reach a predetermined projection point. Therefore, when the hologram recording medium 220 moves in the XY plane, the final arrival point of this single light (projection point on the screen 260) also moves, and the screen 260 is scanned. When the hologram recording medium 220 is simply oscillated in a predetermined axis direction as in the example shown in FIG. 6, the projection point by the light also oscillates on the screen. As in the example shown in FIG. When the medium 220 is moved in a circle, the projection point of the light also moves on the screen. In this way, the speckle pattern caused by the screen side can be reduced by scanning the light on the screen 260. The speckle pattern is temporally integrated by the light beam scanning. Because.

  Therefore, the inventor of the present application uses the apparatus according to the embodiment shown in FIG. 3 to perform speckle contrast between the first approach (securing the light distribution angle θ) and the second approach (light beam scanning). I examined how much it can contribute to the reduction. The result is shown in the graph of FIG. This graph is based on the assumption that the hologram recording medium 220 is inserted and driven, and the degree of speckle generation (speckle contrast) when the light distribution angle θ and the linear velocity of light beam scanning are used as parameters. It is an experimental result shown.

  The vertical axis of the graph is the speckle contrast value (unit%) obtained for the image displayed on the screen 260. On the other hand, the movement speed shown on the horizontal axis of the graph is the movement speed of the light scanned on the screen 260. The experiment was performed by circularly moving the hologram recording medium 220 as shown in FIG. At this time, the tangential speed of the circular motion was used as the light motion velocity. Note that the linear velocity shown in units of “mm / second” is only the scanning speed of light on the screen 260, and thus a value obtained by multiplying the velocity in the tangential direction of the circular motion of the hologram recording medium 220 by a predetermined projection magnification. become.

  In the measurement system used in this experiment, the effective diameter of the light emitted from the lens of the projection optical system 250 is 50 mm, the F number is 1.8, the distance between this lens and the screen 260 is about 7 m, and the spatial light modulator 240. The maximum angle at which the hologram recording medium 220 is desired from the center point is set to 15 °, and the maximum angle from the lens of the projection optical system 250 to the spatial light modulator 240 is set to 15 °. In such a setting, the modulated image on the spatial light modulator 240 is enlarged and displayed on the screen 260 by about 80 times. Therefore, light is scanned on the screen 260 at a speed about 80 times the movement speed when the hologram recording medium 220 is driven by the drive mechanism 225.

  This graph shows measurement results for seven light distribution angles θ. That is, seven results of light distribution angles θ = 0 °, 0.2 °, 0.4 °, 0.6 °, 1 °, 3 °, and 5 ° are plotted. As described above, the actual value of the light distribution angle θ is determined depending on the characteristics and arrangement of the spatial light modulator 240, the characteristics and arrangement of the projection optical system 250, and the recorded characteristics of the scattering plate 230. For example, if the planar size of the spatial light modulator 240 is reduced and the projection magnification by the projection optical system 250 is increased, an image having the same size can be obtained on the same screen 260, but the light distribution angle θ becomes larger. Therefore, by changing various parameters such as the characteristics and arrangement of the spatial light modulator 240 and the characteristics and arrangement of the projection optical system 250, settings for obtaining the above seven light distribution angles θ are performed. The contrast value was measured.

  Note that, as described above, the light distribution angle θ takes a different value for each position on the screen 260, and increases as the center of the screen 260 decreases toward the end of the screen 260. Therefore, here, the minimum value of the light distribution angles θ for the respective projection points on the screen 260 is defined as the minimum light distribution angle (the projection point at which the minimum light distribution angle is obtained is the projection point at the end of the screen 260). The seven light distribution angles θ = 0 °, 0.2 °, 0.4 °, 0.6 °, 1 °, 3 °, and 5 ° are projection points at which this minimum light distribution angle can be obtained. Was set as a standard. Therefore, for example, the condition setting that results in the light distribution angle θ = 0.2 ° in the graph of FIG. 10 is the projection point (the end of the screen 260) where the minimum light distribution angle is obtained on the screen 260. This means that the light distribution angle θ = 0.2 ° is obtained (naturally, a light distribution angle θ higher than that is obtained at the center of the screen 260). This means that at least the setting is made so that a light distribution angle θ of 0.2 ° is obtained.

  Now, looking at the graph of FIG. 10, between the result of the light distribution angle θ = 0.2 ° plotted by a circle and the result of the light distribution angle θ = 0.4 ° plotted by a Δ mark, It can be seen that there is a large difference in the speckle contrast value. This means that the effect of remarkably reducing the generation of speckle can be obtained by setting the light distribution angle θ to 0.4 ° or more. In other words, the characteristics and arrangement of the spatial light modulator 240 and the characteristics and arrangement of the projection optical system 250 are set so that the light distribution angle with respect to an arbitrary point on the screen 260 is 0.4 ° or more. If set, an effect of significantly reducing speckle generation can be obtained. This means that in a setting where the light distribution angle is 0.4 ° or more, the incident angle is sufficiently multiplexed at one projection point (a large number of angle modes having no correlation with each other are included). To do.

  Next, when it is assumed that the light distribution angle for any one point on the screen 260 is set to 0.4 ° or more, it is the same level as the apparatus using the “non-coherent light source”. Consider the ideal conditions for obtaining speckle contrast. As described above, in the case of HDTV (high-definition television) video display applications, a standard of speckle contrast of 6.0% or less is indicated as a level at which an uneven luminance pattern is hardly recognized when an observer observes with the naked eye. Yes. As can be seen from the graph shown in FIG. 10, it is impossible to obtain an ideal speckle contrast of 6.0% or less unless the hologram recording medium 220 is moved (the speckle contrast is obtained when the movement speed is 1 mm / second). Are 10% or more). Therefore, in order to obtain an ideal speckle contrast, it is assumed that the hologram recording medium 220 is driven by the drive mechanism 225. As shown in the graph, the speckle contrast decreases as the motion speed increases, but the ideal speckle contrast of 6.0% or less is assumed on the assumption that the light distribution angle is 0.4 ° or more. It can be seen that the motion speed should be 200 mm / second or more in order to obtain

  The inventor of the present application conducted the same experiment using various types of forward projection screens currently on the market, and all obtained results equivalent to the graph shown in FIG. Further, the same experiment was performed on the scattering plate 230 that is an original image recorded on the hologram recording medium 220 by using a plurality of different scattering plates. It was. Therefore, the experimental result shown in the graph of FIG. 10 can be said to be a result having universality that does not depend on the characteristics of the scattering plate used, etc., if it is a front projection screen. It is assumed that it has the necessary and sufficient scattering properties).

  After all, in the case of the forward projection type embodiment shown in FIG. 3, as an ideal numerical condition, the light distribution angle with respect to any one point on the screen is 0.4 ° or more (in other words, , So that a light distribution angle of 0.4 ° or more is obtained at any position on the screen), the characteristics (particularly, the size of the modulated image generation surface) and arrangement of the spatial light modulator 240, and the projection optical system 250 Characteristics (particularly the aperture and focal length of the lens) and arrangement, and the hologram recording medium by the drive mechanism 225 so that the linear velocity of light scanned on the screen 260 is 200 mm / second or more The condition of driving 220 is derived. For example, if the modulated image on the spatial light modulator 240 is enlarged about 80 times on the screen 260, the actual motion speed when the hologram recording medium 220 is driven by the drive mechanism 225 is calculated as follows: What is necessary is just to set to 5 mm / second or more.

  When the hologram recording medium 220 is moved circularly (or moved elliptically) as shown in FIG. 7, the linear velocity of light can be maintained at a constant speed. (Moving speed) may be set to be 200 mm / second or more, but in the case of simple oscillation as shown in FIG. 6, the linear velocity of light cannot be maintained at a constant speed. That is, at the end point of simple vibration, the motion speed temporarily becomes zero, and speckle is observed at this point. Therefore, in the case of simple vibration, it is preferable that the stationary time at the end point is suppressed to a short time in which no speckle is observed. Specifically, in the case of displaying a moving image as a video, it is desirable to suppress the still time at the end point to 1/30 seconds or less which is a normal moving image bit rate.

<<< §6. Application to color video display device >>>
The embodiments described so far are all examples in which a monochromatic laser (specifically, a DPSS laser having a wavelength of λ = 532 nm (green)) is used as the coherent light source 210, and is obtained on the screen 260. The obtained image is a monochrome image corresponding to the color of the laser. However, in order to use it for a general optical projector device, it is desirable that it can be used as a color image display device. Therefore, here, an embodiment in which the device according to the present invention is used as a color image display device will be described.

  FIG. 11 is a plan view showing an embodiment in which the present invention is applied to a color video display device. In order to apply the present invention to a color video display device, basically, the components shown in FIG. 3 except for the projection optical system 250 and the screen 260 are prepared for each of the three primary colors R, G, and B. Then, modulated images for each of the three primary colors R, G, and B may be generated independently, and these may be combined and projected onto the screen.

  A cross dichroic prism 270 shown in the center of FIG. 11 has a function of synthesizing the modulated images for the three primary colors R, G, and B. The synthesized image is screened by the projection optical system 250. 260 is projected onto the screen.

  The components arranged below the cross dichroic prism 270 are components for generating a G (green) modulated image, and include a coherent light source (laser) 210G, a magnifying lens 211G, a collimating lens 212G, and a hologram recording. A medium 220G and a spatial light modulator (for example, a liquid crystal micro display) 240G are included. Each of these components is the same component as the coherent light source 210, the magnifying lens 211, the collimating lens 212, the hologram recording medium 220, and the spatial light modulator 240 shown in FIG. The G color component image is modulated by the spatial light modulator 240G, and a G color modulated image is generated.

  On the other hand, the component arranged on the left side of the cross dichroic prism 270 is a component for generating a modulated image of R color (red), and includes a coherent light source (laser) 210R, a magnifying lens 211R, a collimating lens 212R, A hologram recording medium 220R and a spatial light modulator (for example, a liquid crystal micro display) 240R are included. These components are components corresponding to the coherent light source 210, the magnifying lens 211, the collimating lens 212, the hologram recording medium 220, and the spatial light modulator 240 shown in FIG. However, since it is necessary to generate an R-color modulated image, a laser light source that emits laser light having an R-color wavelength region is used as the coherent light source 210R. In the scattering plate recording process for the hologram recording medium 220R (see FIG. 4), the R illumination light L and the R reference light Lr are used, and the R reproduction illumination light LL is irradiated with the R illumination light L. A color reproduction real image 235 is formed. Then, the R color component image of the color video to be displayed is modulated by the spatial light modulator 240R, and an R color modulated image is generated.

  Similarly, the component arranged on the right side of the cross dichroic prism 270 is a component for generating a B-color (blue) modulated image, and includes a coherent light source (laser) 210B, a magnifying lens 211B, and a collimating lens 212B. The hologram recording medium 220B and a spatial light modulator (for example, a liquid crystal micro display) 240B are included. These components are components corresponding to the coherent light source 210, the magnifying lens 211, the collimating lens 212, the hologram recording medium 220, and the spatial light modulator 240 shown in FIG. However, since it is necessary to generate a B-color modulated image, a laser light source that emits laser light having a B-color wavelength range is used as the coherent light source 210B. In the scattering plate recording process for the hologram recording medium 220B (see FIG. 4), B-color illumination light L and B-color reference light Lr are used, and the B-color reproduction illumination light LL is irradiated to emit B A color reproduction real image 235 is formed. Then, the B color component image in the color video to be displayed is modulated by the spatial light modulator 240B, and a B color modulated image is generated.

  The R color modulation image generated by the spatial light modulator 240R, the G color modulation image generated by the spatial light modulator 240G, and the B color modulation image generated by the spatial light modulator 240B are crossed. The color image synthesized by the dichroic prism 270 is synthesized and projected on the screen 260 by the projection optical system 250.

  After all, when the present invention is applied to a projection-type image display device that projects light on a screen to display a color image, the first wavelength region, the second wavelength region, the third wavelength region corresponding to each of the three primary color components It is only necessary to set a wavelength range and provide an independent modulated image creation unit for each wavelength range.

  Here, the first modulated image creating unit includes a first coherent light generating unit that generates coherent light in the first wavelength region composed of parallel light bundles, and reproduction light for the coherent light in the first wavelength region. As a result, the first hologram recording medium for generating the first hologram reproduction real image of the scattering plate and the first hologram reproduction real image are disposed so as to be superimposed on the first hologram reproduction real image and correspond to the first wavelength region. And a first spatial light modulator that performs modulation based on an image having one primary color component.

  In addition, the second modulated image creation unit includes second coherent light generation means for generating coherent light in the second wavelength region composed of parallel light bundles, and the coherent light in the second wavelength region as reproduction illumination light. By receiving the second hologram recording medium for generating the second hologram reproduction real image of the scattering plate, the second hologram recording medium is arranged so as to overlap with the formation position of the second hologram reproduction real image, and corresponds to the second wavelength region. And a second spatial light modulator that performs modulation based on an image having the primary color components.

  On the other hand, the third modulated image creating unit generates third coherent light generating means for generating coherent light in the third wavelength region composed of parallel light bundles, and uses the coherent light in the third wavelength region as reproduction illumination light. The third hologram recording medium that generates the third hologram reproduction real image of the scattering plate by receiving and a third hologram recording medium that is superimposed on the formation position of the third hologram reproduction real image and corresponds to the third wavelength region And a third spatial light modulator that performs modulation based on an image having the primary color components.

  In addition, the projection type video display device that performs this color video display further includes a first modulated image obtained on the first spatial light modulator and a second modulation obtained on the second spatial light modulator. What is necessary is just to provide the synthetic | combination projection optical system which synthesize | combines an image and the 3rd modulation image obtained on a 3rd spatial light modulator, and projects on a screen. Although a drive mechanism is not shown in the figure, in practice, a drive mechanism is provided that periodically translates each hologram recording medium 220R, 220G, 220B in a plane parallel to the recording surface. Is preferred.

110: Coherent light source 120: Scattering plate 125: Rotating mechanism 130: Condensing lens 140: Spatial light modulator 150: Projection optical system 160: Screen 210, 210R, 210G, 210B: Coherent light source (laser)
211, 211R, 211G, 211B: Magnifying lenses 212, 212R, 212G, 212B: Collimating lenses 220, 220R, 220G, 220B: Hologram recording medium 222: Hologram photosensitive medium 225: Drive mechanism 230: Scattering plate 235: Hologram of scattering plate Real reproduction images 240, 210R, 210G, 210B: spatial light modulator 250: projection optical system 260: screen 270: cross dichroic prism E: viewpoint L, LL: illumination light L1: projection light Ld: scattered light Lo: object light Lr: Reference light Ls: scattered light Mc: circular motion Mx: simple vibration in the X-axis direction My: simple vibration in the Y-axis direction P1: image point Q1: projection points X, Y, Z: coordinate axes θ of the three-dimensional orthogonal coordinate system: Light distribution angle φ: Incident angle of illumination light

Claims (18)

A projection-type image display device that displays images by projecting light on a screen,
Coherent light generating means for generating coherent light composed of substantially parallel light bundles;
A hologram recording medium for generating a hologram reproduction real image of the scattering plate by receiving the coherent light as reproduction illumination light;
A spatial light modulator disposed so as to be superimposed on the generation position of the hologram reproduction real image;
A projection optical system for projecting a modulated image obtained on the spatial light modulator onto the screen;
A projection-type image display device comprising: In the projection type video display device according to claim 1,
Coherent light generation means
A laser light source that emits and emits laser light;
A light beam expanding means for expanding the laser light emitted from the laser light source into a substantially parallel light beam having a predetermined cross-sectional area;
A projection-type image display device comprising: In the projection type video display device according to claim 1 or 2,
A projection-type image display device, wherein the hologram recording medium is constituted by a volume hologram using a photopolymer. In the projection type video display apparatus in any one of Claims 1-3,
The coherent light generating means generates coherent light having substantially the same wavelength as that of the light used for recording the image of the scattering plate on the hologram recording medium,
The hologram recording medium is disposed in the “direction in which the incident angle of the coherent light with respect to the hologram recording medium and the incident angle of the reference light used when recording the image of the scattering plate are the same”. Projection-type image display device characterized by the above. In the projection type video display apparatus in any one of Claims 1-4,
A projection-type image display device, wherein the spatial light modulator is constituted by a transmissive or reflective liquid crystal display or a digital micromirror device. In the projection type video display apparatus in any one of Claims 1-5,
A projection-type image display device, wherein the projection optical system performs forward projection for projecting a modulated image onto the observation surface side of the screen. In the projection type video display apparatus in any one of Claims 1-6,
The characteristics and arrangement of the spatial light modulator and the characteristics and arrangement of the projection optical system are set so that the light distribution angle with respect to any one point on the screen is 0.4 ° or more. Projection-type image display device. In the projection type video display apparatus in any one of Claims 1-6,
A projection-type image display apparatus, further comprising a drive mechanism that periodically moves the hologram recording medium. In the projection type video display device according to claim 8,
A projection-type image display apparatus, wherein the drive mechanism periodically translates the hologram recording medium in a plane parallel to the recording surface. In the projection type video display device according to claim 9,
When the drive mechanism defines an XY two-dimensional orthogonal coordinate system on the recording surface of the hologram recording medium, the driving mechanism causes the hologram recording medium to vibrate simply in the X-axis or Y-axis direction, or the hologram recording medium is circled on the XY plane. Projection type image display device characterized by moving or elliptically moving. In the projection type video display apparatus in any one of Claims 8-10,
The characteristics and arrangement of the spatial light modulator and the characteristics and arrangement of the projection optical system are set so that the light distribution angle with respect to any one point on the screen is 0.4 ° or more.
A projection-type image display apparatus, wherein a hologram recording medium is driven by a drive mechanism so that a linear velocity of light scanning on a screen is 200 mm / second or more. In the projection type video display apparatus in any one of Claims 1-6,
A projection-type image display apparatus, further comprising a drive mechanism for periodically moving a lens constituting the projection optical system in a plane perpendicular to the optical axis thereof. In the projection type video display apparatus in any one of Claims 1-6,
A projection-type image display apparatus, further comprising a drive mechanism that periodically moves the spatial light modulator along the modulated image forming surface. In the projection type video display apparatus in any one of Claims 1-6,
A projection type characterized by further comprising a drive mechanism for periodically and periodically moving the apparatus main body constituted by coherent light generation means, a hologram recording medium, a spatial light modulator, and a projection optical system. Video display device. A projection-type image display device that projects light on a screen to display a color image,
First coherent light generating means for generating coherent light in a first wavelength range composed of parallel light bundles;
A first hologram recording medium for generating a first hologram reproduction real image of a scattering plate by receiving coherent light in the first wavelength region as reproduction illumination light;
A first spatial light modulator that is arranged so as to overlap the formation position of the first hologram reproduction real image and that performs modulation based on an image having a first primary color component corresponding to the first wavelength range;
Second coherent light generating means for generating coherent light in a second wavelength range composed of parallel light bundles;
A second hologram recording medium that generates a second hologram reproduction real image of the scattering plate by receiving coherent light in the second wavelength region as reproduction illumination light;
A second spatial light modulator that is arranged so as to overlap the formation position of the second hologram reproduction real image and that performs modulation based on an image having a second primary color component corresponding to the second wavelength range;
Third coherent light generating means for generating coherent light in a third wavelength range composed of parallel light bundles;
A third hologram recording medium for generating a third hologram reproduction real image of the scattering plate by receiving coherent light in the third wavelength region as reproduction illumination light;
A third spatial light modulator that is arranged to overlap the formation position of the third hologram reproduction real image and performs modulation based on an image having a third primary color component corresponding to the third wavelength range;
A first modulated image obtained on the first spatial light modulator, a second modulated image obtained on the second spatial light modulator, and a third obtained on the third spatial light modulator. A combined projection optical system that synthesizes the modulated image and projects onto the screen;
A projection-type image display device comprising: A projection-type image display method for projecting light onto a screen to display an image,
Creating a hologram recording medium recording a hologram image of the scattering plate;
Irradiating the hologram recording medium with coherent light to generate a hologram reproduction real image of the scattering plate;
Arranging a spatial light modulator superimposed on the generation position of the hologram reproduction real image;
Projecting a modulated image obtained on the spatial light modulator onto the screen;
A projection type image display method characterized by comprising: The projection-type image display method according to claim 16,
A projection-type image display method, wherein a hologram recording medium is periodically translated in a plane parallel to a recording surface while a modulated image is projected on a screen. The projection-type image display method according to claim 17,
Projection-type image display characterized in that the light distribution angle with respect to any one point on the screen is 0.4 ° or more, and the linear velocity of light scanning on the screen is 200 mm / second or more. Method.

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