JP6168116B2 - Stereoscopic image display apparatus and stereoscopic image display method - Google Patents

Description

  The present invention relates to a stereoscopic image display apparatus and a stereoscopic image display method, and more particularly, to a technique for reproducing and displaying a stereoscopic image recorded as a hologram using coherent light.

  As a representative method for displaying a stereoscopic image, a two-dimensional parallax image method has been known for a long time. This method uses a human perception characteristic that when a three-dimensional object is observed with both eyes, a slight parallax occurs in the images obtained in the retinas of the left and right eyes, and the depth is perceived using this parallax as a clue. It is. In order to present a stereoscopic image using this method, a left-eye parallax image to be presented to the left eye and a right-eye parallax image to be presented to the right eye are separately prepared in advance. The eye parallax image may be presented only to the left eye, and the right eye parallax image may be presented only to the right eye. As specific presentation methods, many methods such as an anaglyph method, a liquid crystal shutter method, a polarized glasses method, a parallax barrier method, a lenticular lens method, and a head mounted display method have been proposed and put into practical use.

  However, it is known that this two-dimensional parallax image method generally has a problem called “congestion adjustment contradiction”. This problem is caused by a mismatch between the “eye focus adjustment distance (focus position)” and the “depth angle obtained from the convergence angle (angle formed by the left and right eyes when viewed from the object)”. In other words, since the eye always focuses on the display surface of the two-dimensional image, the focus adjustment distance is fixed, whereas the convergence angle is a different angle depending on the depth of the displayed object. You will recognize the contradiction between them. This contradiction is also said to cause eye strain that occurs when observing a stereoscopic image.

  In contrast, in the method of presenting a stereoscopic image using holography technology, information on the wavefront of light generated from an object is once recorded in the form of a hologram, and at the time of reproduction, the hologram is irradiated with reproduction illumination light. The recorded wavefront will be reproduced. In this method, the information on the wavefront of the object can be accurately reproduced, and thus the above-described “congestion adjustment contradiction” problem does not occur. For this reason, holography is said to be an ideal stereoscopic display technology. In order to create a hologram, usually, object light from an object to be recorded and reference light different from this are superimposed on the recording surface of a medium made of a photosensitive material, and the object light and reference light are combined. A method is used in which interference fringes due to interference are formed on the recording surface.

  Recently, a technique for creating a hologram using a computer has also been put into practical use, and a simulation is performed on a computer using a virtual object created by a CG technique, and an interference fringe pattern formed on a recording surface is obtained. Computer-generated holograms (CGH) created by calculation are also becoming popular. Also, instead of recording the wavefront information from the object as interference fringes (amplitude intensity), a method that records only the phase of the object wave (Kinoform method) or a method that records both the phase and amplitude of the object wave ( A complex amplitude method has also been proposed. Furthermore, the image data such as the interference fringe pattern obtained by the calculation of such a computer is given to a spatial light modulator (SLM) such as a liquid crystal display to modulate the reproduction illumination light, and the object light A method for regenerating the wavefront of this is also proposed. For example, in Patent Document 1 below, a spatial light modulation element for the right eye and a spatial light modulation element for the left eye are prepared, and image data for the right eye and image data for the left eye (hologram and kinoform) are prepared. Etc., and a method of presenting the wavefront of the object light to each of the left and right eyes is disclosed.

  A merit of the stereoscopic image presentation method using the spatial light modulator is that an arbitrary stereoscopic image can be presented based on arbitrary image data. The reproduced image by the hologram recording medium made of a photosensitive material is fixed to a specific three-dimensional image recorded in advance, but the reproduced image by the spatial light modulator can be freely changed depending on the image data to be given. . For this reason, for example, if a plurality of image data arranged in time series is prepared, and these are sequentially supplied to the spatial light modulation element and driven, the image to be presented can be updated temporally. Therefore, a stereoscopic image can be presented as a moving image to the observer.

  On the other hand, when coherent light such as laser light is used for reproducing a hologram, it is known that unpleasant noise called speckle occurs. In order to deal with such a problem, the following Patent Documents 2 and 3 disclose techniques for suppressing the occurrence of speckle.

Japanese Patent Application Laid-Open No. 8-262926 Japanese Patent Laid-Open No. 6-208089 JP 2004-144936 A

  Holograms currently used as anti-counterfeit seals on banknotes and credit cards are premised on reproduction in a general lighting environment, and reproduced images using illumination light obtained in ordinary living spaces Once obtained, it can fulfill its role. On the other hand, in order to present general video content such as movies to viewers, it is necessary to reproduce clear and bright stereoscopic images that can withstand viewing, and in order to reproduce such high-quality stereoscopic images It is indispensable to use coherent light such as laser light as reproduction illumination light.

  However, as described above, when coherent light such as laser light is used as illumination light, a new problem of speckle generation occurs. A speckle is a speckled pattern that appears when a diffused surface is irradiated with coherent light such as laser light. When a laser beam is irradiated on an object to be illuminated, speckles appear as uneven brightness on the irradiated surface. Observed. For example, when one point on the screen is indicated by the laser pointer, the spot of the laser beam appears to shine on the screen. This is because speckle noise is generated on the screen, which causes a physiological adverse effect on the observer. The reason that 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 due to its extremely high coherence. For example, "Speckle Phenomena in Optics, Joseph W. Goodman, Roberts & Co., 2006" provides a detailed theoretical discussion of speckle generation.

  In an application such as a laser pointer, the observer can only see a minute spot, so the generation of speckle is not a big problem. However, when the hologram recording medium is irradiated with laser light as reproduction illumination light, speckles are generated on the hologram recording medium, so that the observer observes the speckles superimposed on the hologram reproduction image. Will be. In this way, when speckle noise occurs on a reproduced image to be displayed, a glaring speckled pattern appears on the image, causing a physiological adverse effect on the observer and making the mood worse. Symptoms appear. Due to such problems, it has been conventionally difficult to commercialize a stereoscopic image display apparatus that obtains a hologram reproduction image using a laser light source.

  Of course, several specific methods for reducing such speckle noise have been proposed. For example, in Patent Document 2 described above, a technique for reducing speckles by irradiating a scattering plate with laser light, using the scattered light obtained therefrom as illumination light, and rotating the scattering plate with a motor. Is disclosed. Further, Patent Document 3 described above discloses a technique for reducing speckles by disposing a light diffusing element between a laser light source and an object to be illuminated and vibrating the light diffusing element. However, in order to rotate the scattering plate or vibrate the light diffusing element, a large mechanical drive mechanism is required, which increases the overall size of the apparatus and increases the power consumption. In addition, such a method cannot always effectively remove speckles.

  Accordingly, an object of the present invention is to efficiently and sufficiently suppress the generation of speckles when a stereoscopic image recorded as a hologram is reproduced using coherent light and displayed.

(1) A first aspect of the present invention is a stereoscopic image display device that reproduces a stereoscopic image recorded as a hologram and displays the same.
A coherent light source that generates a coherent light beam;
An illumination hologram recording medium on which an illumination image is recorded;
A light beam scanning device that irradiates the illumination hologram recording medium with a light beam and performs scanning so that the irradiation position of the light beam with respect to the illumination hologram recording medium changes temporally;
A display hologram recording medium on which a stereoscopic image to be displayed is recorded;
Provided,
On the illumination hologram recording medium, an illumination image is recorded as a hologram,
The coherent light source generates a light beam with a wavelength capable of reproducing an image for illumination and a stereoscopic image,
The light beam scanning device scans the light beam so that an illumination image is reproduced on the illumination hologram recording medium,
The display hologram recording medium is such that a reproduction image of a stereoscopic image is formed by using the reproduction light of the illumination image obtained from the illumination hologram recording medium as the reproduction illumination light.

(2) A second aspect of the present invention provides a stereoscopic image display device that reproduces a stereoscopic image recorded as a hologram and displays it.
A coherent light source that generates a coherent light beam;
An illumination hologram recording medium on which an illumination image is recorded;
A light beam scanning device that irradiates the illumination hologram recording medium with a light beam and performs scanning so that the irradiation position of the light beam with respect to the illumination hologram recording medium changes temporally;
A spatial light modulator that, based on image data indicating the modulation characteristics of each position on the modulation plane, modulates the light incident on the modulation plane and emits it according to the incident position;
An image data storage unit storing a hologram for reproducing a stereoscopic image to be displayed as image data;
A control device for supplying image data read from the image data storage unit to the spatial light modulator;
Provided,
On the illumination hologram recording medium, an illumination image is recorded as a hologram,
The coherent light source generates a light beam with a wavelength capable of reproducing an image for illumination and a stereoscopic image,
The light beam scanning device scans the light beam so that an illumination image is reproduced on the illumination hologram recording medium,
The spatial light modulator uses a reproduction light of an illumination image obtained from an illumination hologram recording medium as a reproduction illumination light to form a three-dimensional hologram reproduction image based on given image data. is there.

(3) According to a third aspect of the present invention, in the stereoscopic image display device according to the second aspect described above,
The light beam scanning device has a function of performing scanning so that a plurality of N irradiation points on the illumination hologram recording medium are sequentially irradiated with the light beam,
The image data storage unit stores a plurality of N types of image data corresponding to the plurality of N types of irradiation points, and the i-th (1 ≦ i ≦ N) image data is the i-th irradiation point. Is a hologram image data that forms a hologram reproduction image of a stereoscopic image to be displayed at a predetermined position when illumination light for reproduction from is applied to the spatial light modulator,
The control device gives a scanning control signal to the light beam scanning device so as to sequentially irradiate a plurality of N irradiation points with light beams, and sequentially gives a plurality of N image data to the spatial light modulator, In addition, when the light beam scanning device performs scanning to irradiate the i-th irradiation point with the light beam, synchronous control is performed so that the i-th image data is given to the spatial light modulator. Is.

(4) According to a fourth aspect of the present invention, in the stereoscopic image display device according to the third aspect described above,
The coherent light source includes three laser light sources that generate monochromatic laser beams having respective wavelengths of the three primary colors, and an optical combiner that combines the laser beams generated by the three laser light sources to generate a combined light beam. And having
The light beam scanning device scans the combined light beam generated by the light combiner on the hologram recording medium for illumination,
In the illumination hologram recording medium, illumination images are recorded as three types of holograms so that reproduced images can be obtained by the respective laser beams generated by the three laser light sources,
The image data storage unit stores a total of (3 × N) monochromatic image data for each of the three primary colors corresponding to each of a plurality of N irradiation points, and is the i-th (1 ≦ i ≦ N). ) Illumination light for reproduction of j-th monochromatic light from the i-th irradiation point is applied to the spatial light modulator in the j-th (1 ≦ j ≦ 3) monochromatic image data corresponding to the irradiation point). Image data of a hologram for forming a hologram reproduction image for the j-th primary color of a stereoscopic image to be displayed at a predetermined position,
The control device gives a scanning control signal to the light beam scanning device so that a plurality of N irradiation points are sequentially irradiated with light beams, and spatially stores each monochrome image data corresponding to the plurality of N irradiation points. When the light beam scanning device performs scanning for irradiating the i-th irradiation point with the light beam, the i-th monochrome image data is sequentially supplied to the spatial light modulator. In addition, each of the laser light sources is selectively operated so that only the laser light source that generates the j-th monochromatic light is selectively operated when the spatial light modulator is supplied with the j-th monochromatic image data. On the other hand, synchronous control for giving an operation control signal is performed.

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

(6) According to a sixth aspect of the present invention, there are three sets of the three-dimensional image display devices according to the first or second aspect described above, and a composition for combining the reproduced images formed by these three sets of the three-dimensional image display devices. An optical system,
The j-th (1 ≦ j ≦ 3) stereoscopic image display apparatus uses a coherent light source that generates a laser beam of monochromatic light having a wavelength of the j-th primary color among the three primary colors. It has a function to form a reproduction image of a primary color stereoscopic image,
A reconstructed image of a color stereoscopic image is formed by synthesizing each reconstructed image of the three primary colors using a combining optical system.

(7) According to a seventh aspect of the present invention, in the stereoscopic image display device according to the first to sixth aspects described above,
A display hologram recording medium or a spatial light modulator is disposed at a reproduction position of an illumination image formed by the illumination hologram recording medium.

(8) According to an eighth aspect of the present invention, in the stereoscopic image display device according to the first to sixth aspects described above,
An optical system having a function of condensing light in the vicinity of a viewpoint assumed to observe a stereoscopic image, and an optical system disposed between an illumination hologram recording medium and a display hologram recording medium or a spatial light modulator. Further provided.

(9) According to a ninth aspect of the present invention, in the stereoscopic image display device according to the eighth aspect described above,
As an optical system, one or more sets arranged between an illumination hologram recording medium and a display hologram recording medium or a spatial light modulator, with the perpendicular extending from the viewpoint to the recording surface of the illumination hologram recording medium as an optical axis A pair of convex lenses is used.

(10) According to a tenth aspect of the present invention, in the stereoscopic image display device according to the ninth aspect described above,
A pair of convex lenses is used as the optical system, and the distance between the hologram recording medium for illumination and the convex lens is set to 2f, and the distance between the convex lens and the viewpoint is set to 2f, where f is the focal length of the convex lens. It is.

(11) An eleventh aspect of the present invention is the stereoscopic image display device according to the ninth aspect described above,
Two sets of convex lenses are used as the optical system, and the focal length of the first convex lens arranged at a position close to the illumination hologram recording medium is set as f1, and the optical system is arranged at a position close to the display hologram recording medium or the spatial light modulator. When the focal length of the second convex lens is f2, the distance between the illumination hologram recording medium and the first convex lens is set to f1, and the distance between the second convex lens and the viewpoint is set to f2. .

(12) A twelfth aspect of the present invention is the stereoscopic image display device according to the ninth to eleventh aspects described above,
A half mirror having a reflecting surface inclined with respect to the optical axis of the convex lens is disposed between the viewpoint position and the display hologram recording medium or the spatial light modulator.

(13) According to a thirteenth aspect of the present invention, in the stereoscopic image display device according to the above eighth to twelfth aspects,
When a virtual pupil is placed at the position of a viewpoint where a stereoscopic image is expected to be observed, “0th-order diffracted light from the display hologram recording medium or spatial light modulator is incident on the inside of the pupil”. The “light beam irradiation range on the hologram recording medium for illumination” that satisfies the condition is defined as a scanning prohibited area, and the light beam scanning device performs scanning of the light beam while avoiding the scanning prohibited area.

(14) According to a fourteenth aspect of the present invention, in the stereoscopic image display device according to the thirteenth aspect described above,
The optical beam scanning device sets a circular scanning trajectory outside the scanning prohibition area so that the light beam spot does not enter the scanning prohibition area during scanning, and the central axis of the light beam moves around the scanning trajectory. Thus, scanning is performed.

(15) According to a fifteenth aspect of the present invention, in the stereoscopic image display device according to the first to fourteenth aspects described above,
The light beam scanning device is bent by bending the light beam at a predetermined scanning base point, irradiating the bent light beam onto the hologram recording medium for illumination, and changing the bending mode of the light beam with time. The irradiation position of the illuminated light beam on the hologram recording medium for illumination is changed over time,
In the hologram recording medium for illumination, an illumination image is recorded as a hologram using reference light that converges at a specific convergence point or reference light that diverges from a specific convergence point,
The light beam scanning device scans the light beam using the convergence point as a scanning base point.

(16) According to a sixteenth aspect of the present invention, in the stereoscopic image display device according to the fifteenth aspect described above,
An illumination image is recorded on the illumination hologram recording medium using reference light that converges or diverges three-dimensionally along the side surface of the cone having the convergence point as a vertex.

(17) According to a seventeenth aspect of the present invention, in the stereoscopic image display device according to the first to fourteenth aspects described above,
By irradiating the illumination hologram recording medium while the light beam scanning device translates the light beam, the irradiation position of the light beam with respect to the illumination hologram recording medium is temporally changed,
On the hologram recording medium for illumination, an image for illumination is recorded as a hologram using a reference beam composed of a parallel light beam,
The light beam scanning device irradiates the illumination hologram recording medium with a light beam from a direction parallel to the reference light to scan the light beam.

(18) An eighteenth aspect of the present invention is the stereoscopic image display device according to the first to seventeenth aspects described above,
A computer-generated hologram is used as the hologram recorded on the illumination hologram recording medium.

(19) According to a nineteenth aspect of the present invention, in the stereoscopic image display device according to the first to eighteenth aspects described above,
As the light beam scanning device, a scanning mirror device, a total reflection prism, a refraction prism, or an electro-optic crystal is used.

(20) According to a twentieth aspect of the present invention, in a stereoscopic image display device for reproducing and displaying a stereoscopic image recorded as a hologram,
A coherent light source that generates a coherent light beam;
A microlens array consisting of a collection of many individual lenses;
A light beam scanning device that irradiates a microlens array with a light beam and scans so that the irradiation position of the light beam with respect to the microlens array changes temporally;
A display hologram recording medium on which a stereoscopic image to be displayed is recorded;
Provided,
Each of the individual lenses constituting the microlens array has a function of refracting the light irradiated from the light beam scanning device to form a predetermined irradiation area on a predetermined reference surface, and any individual lens. The irradiation area formed by is also configured to be substantially the same common area on the reference plane,
The coherent light source generates a light beam having a wavelength capable of reproducing a stereoscopic image,
The display hologram recording medium forms a three-dimensional reproduced image using the refracted light obtained from the microlens array as reproduction illumination light.

(21) According to a twenty-first aspect of the present invention, in a stereoscopic image display device for reproducing a stereoscopic image recorded as a hologram and displaying the same,
A coherent light source that generates a coherent light beam;
A light beam scanning device that performs beam scanning by controlling the direction and / or position of the light beam;
A light diffusing element that diffuses and emits an incident light beam;
A display hologram recording medium on which a stereoscopic image to be displayed is recorded;
Provided,
The light beam scanning device emits the light beam generated by the coherent light source toward the light diffusing element, and scans so that the incident position of the light beam with respect to the light diffusing element changes with time.
The light diffusing element has a function of diffusing an incident light beam to form a predetermined irradiation region on a predetermined reference surface, and the formed irradiation region is a reference regardless of the incident position of the light beam. It is configured to be almost the same common area on the surface,
The coherent light source generates a light beam having a wavelength capable of reproducing a stereoscopic image,
In the display hologram recording medium, a reproduction image of a stereoscopic image is formed by using diffused light obtained from a light diffusing element as reproduction illumination light.

(22) According to a twenty-second aspect of the present invention, in a stereoscopic image display device for reproducing and displaying a stereoscopic image recorded as a hologram,
A coherent light source that generates a coherent light beam;
A microlens array consisting of a collection of many individual lenses;
A light beam scanning device that irradiates a microlens array with a light beam and scans so that the irradiation position of the light beam with respect to the microlens array changes temporally;
A spatial light modulator that, based on image data indicating the modulation characteristics of each position on the modulation plane, modulates the light incident on the modulation plane and emits it according to the incident position;
An image data storage unit storing a hologram for reproducing a stereoscopic image to be displayed as image data;
A control device for supplying image data read from the image data storage unit to the spatial light modulator;
Provided,
Each of the individual lenses constituting the microlens array has a function of refracting the light irradiated from the light beam scanning device to form a predetermined irradiation area on a predetermined reference surface, and any individual lens. The irradiation area formed by is also configured to be substantially the same common area on the reference plane,
The coherent light source generates a light beam having a wavelength capable of reproducing a stereoscopic image,
The spatial light modulator uses a refracted light obtained from a microlens array as a reproduction illumination light to form a three-dimensional reproduction image based on given image data.

(23) A twenty-third aspect of the present invention provides a stereoscopic image display device that reproduces a stereoscopic image recorded as a hologram and displays the same.
A coherent light source that generates a coherent light beam;
A light beam scanning device that performs beam scanning by controlling the direction and / or position of the light beam;
A light diffusing element that diffuses and emits an incident light beam;
A spatial light modulator that, based on image data indicating the modulation characteristics of each position on the modulation plane, modulates the light incident on the modulation plane and emits it according to the incident position;
An image data storage unit storing a hologram for reproducing a stereoscopic image to be displayed as image data;
A control device for supplying image data read from the image data storage unit to the spatial light modulator;
Provided,
The light beam scanning device emits the light beam generated by the coherent light source toward the light diffusing element, and scans so that the incident position of the light beam with respect to the light diffusing element changes with time.
The light diffusing element has a function of diffusing an incident light beam to form a predetermined irradiation region on a predetermined reference surface, and the formed irradiation region is a reference regardless of the incident position of the light beam. It is configured to be almost the same common area on the surface,
The coherent light source generates a light beam having a wavelength capable of reproducing a stereoscopic image,
The spatial light modulator uses a diffused light obtained from a light diffusing element as a reproduction illumination light to form a reproduction image of a stereoscopic image based on given image data.

(24) According to a twenty-fourth aspect of the present invention, in the stereoscopic image display device according to the twenty-second or twenty-third aspect described above,
The light beam scanning device has a function of performing scanning so that a plurality of N irradiation points on the microlens array or the light diffusion element are sequentially irradiated with the light beam,
The image data storage unit stores a plurality of N types of image data corresponding to the plurality of N types of irradiation points, and the i-th (1 ≦ i ≦ N) image data is the i-th irradiation point. Is a hologram image data that forms a hologram reproduction image of a stereoscopic image to be displayed at a predetermined position when illumination light for reproduction from is applied to the spatial light modulator,
The control device gives a scanning control signal to the light beam scanning device so as to sequentially irradiate a plurality of N irradiation points with light beams, and gives a plurality of N image data to the spatial light modulator, and The optical beam scanning device performs a synchronous control so that the i-th image data is given to the spatial light modulator when the i-th irradiation point is scanned with the light beam. It is.

(25) A twenty-fifth aspect of the present invention is a stereoscopic image display method for reproducing and displaying a stereoscopic image recorded as a hologram,
An illumination hologram preparation stage for creating an illumination hologram recording medium by recording an illumination image as a hologram on the recording medium;
Display hologram recording medium having a function of reproducing a stereoscopic image to be displayed by providing reproduction light of an illumination image obtained from the hologram recording medium for illumination as reproduction illumination light, or display hologram recording A display hologram preparation stage in which a spatial light modulator having a diffraction function equivalent to that of a medium is disposed;
A coherent light beam suitable for obtaining an image for illumination is irradiated on the hologram recording medium for illumination from a direction suitable for obtaining an image for illumination, and the irradiation position is changed with time. A hologram reproduction stage in which a light beam is scanned on a hologram recording medium for illumination;
Is to do.

(26) A twenty-sixth aspect of the present invention is a stereoscopic image display method for reproducing and displaying a stereoscopic image recorded as a hologram,
Irradiation consisting of an assembly of a large number of individual lenses each having a function of refracting a light beam irradiated from a specific direction and forming a predetermined irradiation area on a predetermined reference plane, and formed by any individual lens A microlens array preparation stage for preparing a microlens array that is configured so that the area is also substantially the same common area on the reference plane;
By providing refracted light obtained from the microlens array as illumination light for reproduction, a display hologram recording medium having a function of reproducing a stereoscopic image to be displayed, or a diffraction function equivalent to that of a display hologram recording medium A hologram preparation stage for display in which a spatial light modulator is disposed;
The microlens array is irradiated with a coherent light beam having a wavelength suitable for reproducing a stereoscopic image from a specific direction, and scanning is performed so that the irradiation position of the light beam with respect to the microlens array changes with time. Hologram reproduction stage,
Is to do.

(27) A twenty-seventh aspect of the present invention is a stereoscopic image display method for reproducing and displaying a stereoscopic image recorded as a hologram.
It has a function of diffusing a light beam incident from a specific direction to form a predetermined irradiation area on a predetermined reference plane, and the irradiation area to be formed is on the reference plane regardless of the incident position of the light beam. A light diffusing element preparing step of preparing a light diffusing element configured to be substantially the same common region in
By providing diffused light obtained from a light diffusing element as illumination light for reproduction, a display hologram recording medium having a function of reproducing a stereoscopic image to be displayed, or a diffraction function equivalent to that of a display hologram recording medium A hologram preparation stage for display in which a spatial light modulator is disposed;
A hologram reproduction stage in which a light diffusing element is irradiated with a coherent light beam having a wavelength suitable for reproducing a three-dimensional image, and scanning is performed so that the irradiation position of the light beam with respect to the light diffusing element changes with time. When,
Is to do.

(28) According to a twenty-eighth aspect of the present invention, in the stereoscopic image display method according to the above twenty-fifth to twenty-seventh aspects,
In the display hologram preparation stage, a plurality of N types of hologram image data and a spatial light modulator that forms a hologram reproduction image according to the image data by providing reproduction illumination light are prepared,
In the hologram reproduction stage, scanning is performed such that a plurality of N irradiation points are sequentially irradiated with the light beam, and the light beam is irradiated to the i-th (1 ≦ i ≦ N) irradiation point. The optical modulator forms a hologram reproduction image corresponding to the i-th image data,
As the i-th image data, when the reproduction illumination light from the i-th irradiation point is given to the spatial light modulator, a hologram reproduction image that forms a hologram reproduction image of a stereoscopic image to be displayed at a predetermined position is displayed. Image data is used.

(29) According to a 29th aspect of the present invention, in the stereoscopic image display method according to the above 25th to 28th aspects,
When a virtual pupil is placed at the position of a viewpoint where a stereoscopic image is expected to be observed, “0th-order diffracted light from the display hologram recording medium or spatial light modulator is incident on the inside of the pupil”. The irradiation range of the light beam that satisfies the condition is defined as a scanning prohibition region, and scanning of the light beam is performed while avoiding the scanning prohibition region in the hologram reproduction stage.

(30) A 30th aspect of the present invention is the stereoscopic image display method according to the above 25th to 29th aspects,
Reproduction illumination light collected by an optical system that has the function of condensing light in the vicinity of the viewpoint where stereoscopic images are expected to be observed is given to the display hologram recording medium or spatial light modulator. Is.

  In the stereoscopic image display apparatus according to the basic embodiment of the present invention, an illumination hologram recording medium and a display hologram recording medium are prepared. An illumination image is recorded on the illumination hologram recording medium, and a stereoscopic image to be displayed is recorded on the display hologram recording medium. The light beam from the coherent light source is irradiated to one point on the hologram recording medium for illumination, and is scanned so that the irradiation position changes with time. Due to the properties of the hologram, when a coherent light beam is irradiated onto an arbitrary point on the illumination hologram recording medium, a reproduced image of the illumination image is formed. The reproduction light for forming this reproduction image functions as reproduction illumination light for the display hologram recording medium, and a stereoscopic image to be displayed is reproduced. In addition, the light beam from the coherent light source is scanned on the holographic recording medium for illumination, and the irradiation point of the light beam constantly varies with time. For this reason, the optical path of the light forming the reproduction image of the illumination image is temporally changed and multiplexed. Eventually, the incident angle of the reproduction illumination light incident on the display hologram recording medium is temporally multiplexed, and speckle generation can be suppressed.

  As a display hologram recording medium, a physical medium having a fixed hologram interference fringe pattern or the like is not necessarily used, and a spatial light modulator such as a liquid crystal display can be used. If a spatial light modulator is used, an arbitrary stereoscopic image can be displayed by providing image data corresponding to a desired interference fringe pattern or the like. In addition, the scanning angle of the light beam from the coherent light source changes the incident angle of the illumination light for reproduction incident on the spatial light modulator, but the optimum interference is synchronized with the scanning of the light beam. If image data indicating a fringe pattern or the like is provided, a stereoscopic image based on an optimal interference fringe pattern or the like can always be reproduced regardless of the irradiation position of the light beam.

  If a light source that generates a monochromatic light beam of each of the three primary colors is used as the coherent light source, and a reproduced image of the three primary colors is synthesized, a three-dimensional color image can be displayed. In addition, if an optical system for condensing light is added in the vicinity of the viewpoint where a stereoscopic image is expected to be observed, the diffraction capability of the display hologram recording medium (spatial light modulator) will be reduced. Even if it is sufficient, it is possible to reproduce a stereoscopic image having a sufficient viewing angle when observed from the viewpoint position.

  Further, if the scanning of the light beam is performed while avoiding the scanning prohibition region where the 0th-order diffracted light is incident on the inside of the pupil placed at the viewpoint position, the 0th-order diffracted light is observed in the field of view when observed from the viewpoint position. Since it can prevent entering into, it can prevent the bad influence by the speckle contained in the light source.

  Note that even if a microlens array or a light diffusing element is used instead of the illumination hologram recording medium, reproduction illumination light in which the incident angles with respect to the display hologram recording medium or the spatial light modulator are temporally multiplexed is obtained. Therefore, the same effect as described above can be obtained.

It is a side view which shows the general recording method of a hologram. It is a side view which shows the reproducing method of the hologram recorded by the method shown in FIG. It is a side view which shows the general structure of the three-dimensional image display apparatus using a hologram. It is a side view which shows another form of the stereo image display apparatus using a hologram. FIG. 3 is an arrangement diagram of an optical system showing a process of creating an illumination hologram recording medium that is a constituent element of a stereoscopic image display device according to the present invention. FIG. 6 is a plan view showing a positional relationship between a cross section S1 of reference light L23 and the hologram photosensitive medium 40 in the process shown in FIG. 6 is a plan view showing the positional relationship between another section S2 of the reference light L23 and the hologram photosensitive medium 40 in the process shown in FIG. FIG. 6 is a partially enlarged view around the scattering plate 30 and the hologram photosensitive medium 40 in the optical system shown in FIG. 5. It is a figure which shows the process which reproduces | regenerates the image 35 of a scattering plate using the hologram recording medium 45 produced by the process shown in FIG. It is a figure which shows the process which reproduces | regenerates the image 35 of a scattering plate by irradiating only one light beam with respect to the hologram recording medium 45 produced in the process shown in FIG. FIG. 6 is another diagram showing a process of reproducing the image 35 of the scattering plate by irradiating only one light beam to the hologram recording medium 45 created by the process shown in FIG. 5. It is a top view which shows the irradiation position of the light beam in the reproduction | regeneration process shown in FIG. 10 and FIG. It is a side view which shows the structure of the illumination light generation part for reproduction | regeneration in the three-dimensional image display apparatus which concerns on fundamental embodiment of this invention. It is a side view which shows an example of the production method of the hologram recording medium for a display used for the stereo image display apparatus which concerns on fundamental embodiment of this invention. It is a side view showing composition and operation of a stereoscopic image display device concerning a basic embodiment of the present invention. It is another side view which shows the structure and operation | movement of a three-dimensional image display apparatus which concern on basic embodiment of this invention. It is a side view which shows another example of the production method of the hologram recording medium for a display used for the stereo image display apparatus which concerns on fundamental embodiment of this invention. It is a figure which shows the whole structure of the stereo image display apparatus which concerns on practical embodiment of this invention. It is a figure which shows the whole structure of the three-dimensional image display apparatus which concerns on the modification suitable for size reduction of practical embodiment of this invention. FIG. 20 is a side view showing a process for creating an illumination hologram recording medium used in the modification shown in FIG. 19. FIG. 20 is a side view showing a process of creating an illumination hologram recording medium used in the modification shown in FIG. 19 by the CGH technique. FIG. 22 is a front view of a virtual scattering plate 30 ′ shown in FIG. 21. It is a figure which shows the whole structure of the three-dimensional image display apparatus which concerns on the modification which added the lens of practical embodiment of this invention. It is a figure which shows the whole structure of the three-dimensional image display apparatus which concerns on the modification which added two lenses of practical embodiment of this invention. It is a figure which shows the incident position to the viewpoint vicinity of the 0th-order diffracted light in the modification shown in FIG. It is a figure which shows the relationship between the irradiation point of the light beam with respect to the hologram recording medium for illumination in FIG. 25, and the incident position to the viewpoint vicinity of 0th-order diffracted light. FIG. 26 is a plan view showing a condensing position of zero-order diffracted light and an incident range of first-order diffracted light in the stereoscopic image display device shown in FIG. 25. FIG. 26 is another plan view showing a condensing position of 0th-order diffracted light and an incident range of 1st-order diffracted light in the stereoscopic image display device shown in FIG. 25. It is a top view which shows the ideal scanning track | orbit of the light beam with respect to the hologram recording medium for illumination. It is a table | surface which shows the concrete synchronous control of the control apparatus in the modification shown in FIG. It is a table | surface which shows the experimental result by which the reduction effect of the speckle was acquired by this invention. It is a side view which shows the modification which added the half mirror to the modification shown in FIG. FIG. 6 is a layout diagram illustrating a first configuration example for displaying a color stereoscopic image. It is a table | surface for demonstrating the synchronous control in the structural example shown in FIG. It is a top view which shows the 2nd structural example which displays a color stereo image. It is a side view which shows the modification of the light beam scanning apparatus used for this invention. It is a side view which shows the basic composition of the modification which used the microlens array instead of the hologram recording medium for illumination. It is a side view which shows the operation | movement principle of the modification shown in FIG.

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

<<< §1. Basic principles of holograms and speckle generation >>>
First, the basic principle of holograms and speckle generation will be briefly described. FIG. 1 is a side view showing a general hologram recording method, and shows a method of recording an original image F to be recorded (in this example, a cubic object F) on a photosensitive medium M as a hologram. .

  In the figure, the object F is irradiated with coherent illumination light, and coherent object light Lobj is emitted from an arbitrary object point K located on the surface of the object F. Although only the object light Lobj emitted from one object point K is shown in the figure, in practice, the object light Lobj is emitted from every point on the surface of the object F. On the other hand, the photosensitive medium M is irradiated with a coherent reference light Lref having the same wavelength as that of the object light Lobj (in the case of the illustrated example, a parallel light beam from the obliquely upper left direction in the figure), and is generated by the object light Lobj and the reference light Lref. Interference fringes are recorded on the photosensitive medium M. Hereinafter, the photosensitive medium M on which such interference fringes are recorded is referred to as a hologram recording medium H.

  FIG. 2 is a side view showing a method for reproducing a hologram recorded by the method shown in FIG. As shown in the figure, when the reproduction illumination light Lrep composed of parallel light beams is irradiated from the diagonally upper left direction of the hologram recording medium H and viewed from the position of the viewpoint E, the reproduction image FF of the cubic object F is observed as a virtual image. Become. Here, the reproduction illumination light Lrep shown in FIG. 2 is coherent light having the same wavelength as that of the reference light Lref shown in FIG. 1 and irradiated from the same direction. The reason why the reproduced image FF is observed as a virtual image at the position of the viewpoint E is that the reproduction illumination light Lrep is diffracted by the interference fringes recorded on the hologram recording medium H, and the diffracted light Ldif is the object shown in FIG. This is because it is transmitted to the viewpoint E as light having the same wavefront as the object light Lobj from F.

  FIG. 2 shows an example in which the hologram recording medium H is a transmission type medium. However, in the case of a reflection type medium, the diffracted light Ldif is reflected to the left side of the drawing so as to be optically conjugate. By looking at the right side of the figure from the viewpoint placed on the left side of the medium, the reproduced image is observed as a virtual image at the right position of the medium H. In the drawings of the present application, for convenience of explanation, an optical path of light is drawn with a one-dot chain line or a two-dot chain line, and a reproduced image is shown with a broken line.

  Now, as described above, the reproduction illumination light Lrep shown in FIG. 2 needs to be coherent light having the same wavelength as that of the reference light Lref. Therefore, a general configuration of a stereoscopic image display apparatus using a hologram takes the form of a coherent light source S (for example, a laser), a beam expander X, and a hologram recording medium H as shown in FIG. The coherent light beam Ls generated by the coherent light source S is expanded into a parallel light beam by the beam expander X, and is reproduced from the hologram recording medium H as a reproduction illumination light Lrep from a predetermined direction (the same direction as the reference light Lref in FIG. 1). Is irradiated. As described above, the reproduced image FF is observed as a virtual image by the diffracted light Ldif toward the viewpoint E.

  In the example shown in FIG. 1, the photosensitive medium M is irradiated with the reference light Lref from an oblique direction. However, the reference light Lref does not necessarily have to be applied to the photosensitive medium M from an oblique direction when recording a hologram. . The hologram may be recorded by irradiating the reference light Lref from any direction as long as the photosensitive medium M can be irradiated without being disturbed by the original image F (cubic object F). . However, at the time of image reproduction, it is necessary to irradiate the reproduction illumination light Lrep from the irradiation direction (or optically conjugate direction) of the reference light Lref used for recording the hologram.

  Accordingly, for example, in the example shown in FIG. 1, if the reference light Lref is irradiated in the horizontal direction from left to right instead of being obliquely irradiated from the upper left, a stereoscopic image display apparatus for reproducing such a hologram is obtained. Instead of the configuration shown in FIG. 3, the configuration shown in FIG. 4 is obtained. That is, the reproduction illumination light Lrep composed of parallel light beams spread by the beam expander X is irradiated to the hologram recording medium H in the horizontal direction from the left to the right (the same direction as the reference light Lref at the time of recording). .

  As described above, recently, a computer-generated hologram (CGH) technique for creating a hologram using a computer has also been developed. When creating the hologram recording medium H using this CGH method, the optical interference fringe recording process shown in FIG. 1 is executed as a computer simulation. That is, the original image F is given as a CG image to the computer, and a recording surface is defined instead of the photosensitive medium M. Then, the object light Lobj and the reference light Lref are respectively defined by equations indicating wave motion, the combined amplitude value of the object light and the reference light at each sample point on the recording surface is calculated, and interference formed on the recording surface An operation for obtaining the stripe information as image data may be performed. If such a CGH method is used, the reference light Lref is not obstructed by the original image F, so there is no limitation on the irradiation direction of the reference light Lref, and the hologram recording medium H as in the example shown in FIG. A stereoscopic image display device that irradiates the reproduction illumination light Lrep from a direction perpendicular to the recording surface can be easily realized.

  In addition, a stereoscopic image display device using a spatial light modulator such as a liquid crystal display instead of the hologram recording medium H has been proposed. For example, the liquid crystal display itself can be used in place of the hologram recording medium H if the image data obtained by the CGH method described above is applied to the liquid crystal display to display interference fringes on the screen. Moreover, since the interference fringes to be displayed can be freely changed depending on the image data to be given, if a large number of image data is prepared in advance, an arbitrary stereoscopic image can be displayed. It is also possible to present a stereoscopic video.

  However, as described above, such a stereoscopic image display device has a problem of speckle generation. The speckle is a speckled pattern that appears when the diffusing surface is irradiated with coherent light such as laser light, and is observed as flickering speckled luminance unevenness by an observer. In the stereoscopic image display apparatus shown in FIGS. 3 and 4, speckles are generated on the surface of the hologram recording medium H because the hologram recording medium H is irradiated with the coherent illumination light Lrep for reproduction. In addition, speckles are also generated in the reproduced image FF of the hologram. Therefore, when viewed from the viewpoint E, spotted speckle noise is observed in both the reproduced image FF and the background portion. Such a problem of the generation of speckle noise is a problem that similarly occurs when a spatial light modulator such as a liquid crystal display is used instead of the hologram recording medium H.

  Further, in the case of a stereoscopic image display apparatus having the arrangement shown in FIG. 4, in addition to the speckles generated on the hologram recording medium H side, speckles generated on the light source side are further added. That is, when the arrangement shown in FIG. 4 is adopted, since the coherent light source S and the beam expander X are located in the observation direction from the viewpoint E (left direction in the figure), these light sources are looked into from the front. Speckle included on the light source side is also observed.

  As described above, when the hologram is reproduced by using the coherent light source S, there is an advantage that a clear and bright reproduced image FF can be obtained. Noise will be generated, causing a serious problem that the observer has a physiological adverse effect. Even if speckles that are glaring are included in a minute area, such as a spot of a laser pointer, it does not have a significant adverse effect on the viewer, but speckle noise appears in the image presented by the stereoscopic image display device. If included, many observers will experience physiological symptoms such as feeling unwell.

  Thus, the present invention provides a technique for efficiently and sufficiently suppressing the generation of speckles when a stereoscopic image recorded as a hologram is reproduced using coherent light and displayed. is there.

<<< §2. Basic principle of speckle suppression >>>
Next, the basic principle of speckle suppression in the present invention will be described. Here, for the convenience of explanation, first, the characteristics of the “illumination hologram recording medium” used in the stereoscopic image display apparatus according to the basic embodiment of the present invention will be described. This “illumination hologram recording medium” is not an “original hologram recording medium” for recording a stereoscopic image to be displayed, but, in other words, serves to supply reproduction illumination light to the “original hologram recording medium”. This is an auxiliary medium. In the present application, this “original hologram recording medium” is referred to as “display hologram recording medium” and is distinguished from “illumination hologram recording medium”.

  FIG. 5 is a layout diagram of the optical system showing the process of creating this “illumination hologram recording medium”. The purpose of this optical system is to create a hologram recording medium (illumination hologram recording medium) on which an image for illumination (in the embodiment described here, an image of a scattering plate) is recorded. The configuration will be described in detail below.

  The coherent light source 10 shown in the upper right of the figure is a light source that generates a coherent light beam L10. In practice, a laser light source that generates monochromatic laser light having a circular cross section is used. The coherent light beam L10 generated by this laser light source is divided into two beams by the beam splitter 20. That is, a part of the light beam L10 is directly transmitted through the beam splitter 20 and guided downward in the figure, and the remaining part is reflected by the beam splitter 20 and guided to the left in the figure as the light beam L20. It is burned.

  The light beam L10 transmitted through the beam splitter 20 plays a role of generating object light Lobj of the scattering plate. That is, the light beam L10 traveling downward in the figure is reflected by the reflecting mirror 11 to become a light beam L11. Further, the diameter of the light beam L10 is expanded by the beam expander 12 to form a parallel light beam L12. The entire area of the surface is irradiated. The scattering plate 30 is a plate having a property of scattering irradiated light, and is generally called an optical diffusion plate. In the case of the embodiment shown here, a transmission type scattering plate (for example, an opal glass plate) in which fine particles (light scatterers) for scattering light are kneaded is used. Therefore, as illustrated, the parallel light beam L12 irradiated on the right side surface of the scattering plate 30 passes through the scattering plate 30 and is emitted as scattered light L30 from the left side surface. The scattered light L30 constitutes the object light Lobj of the scattering plate 30.

  On the other hand, the light beam L20 reflected by the beam splitter 20 plays a role of generating the reference light Lref. That is, the light beam L20 traveling from the beam splitter 20 to the left in the figure is reflected by the reflecting mirror 21 to become the light beam L21. Further, the diameter of the light beam L20 is expanded by the beam expander 22 to form a parallel light beam L22. After being refracted by the convex lens 23 having a focal point C, the photosensitive medium 40 is irradiated. Note that the parallel light beam L22 is not necessarily a strict set of parallel rays, but if it is a set of substantially parallel rays, there is no practical problem. The photosensitive medium 40 is a photosensitive medium used for recording a hologram image. The irradiation light L23 to the photosensitive medium 40 constitutes the reference light Lref.

  Eventually, the photosensitive medium 40 is irradiated with the object light Lobj of the scattering plate 30 and the reference light Lref. Here, since both the object light Lobj and the reference light Lref are coherent light having the same wavelength λ generated by the coherent light source 10 (laser light source), both interference fringes are recorded on the photosensitive medium 40. Will be. In other words, the image of the scattering plate 30 is recorded on the photosensitive medium 40 as a hologram. The “scattering plate” referred to in the present application is not necessarily limited to articles distributed or used under the name of “scattering plate” in the general industry, but has the property of scattering light. It means a wide range of objects. Therefore, for example, a gypsum board, white paper, a foamed polystyrene plate, or the like can be used as the scattering plate 30. Of course, as will be described later, an image equivalent to an image of an object having the property of scattering light may be recorded on the illumination hologram recording medium by the CGH method. In short, any “illumination image” having an illumination function for the display hologram recording medium or the spatial light modulator need only be recorded as a hologram in the illumination hologram recording medium of the present invention. However, in practice, in order to improve the illumination efficiency, it is preferable to record the image of the above-mentioned opal glass plate or the like as the image of the scattering plate (that is, “image for illumination”).

  FIG. 6 is a plan view showing the positional relationship between the cross section S1 of the reference light L23 (Lref) shown in FIG. Since the parallel light beam L22 whose diameter is expanded by the beam expander 22 has a circular cross section, the reference light Lref collected by the convex lens 23 converges in a conical shape with the focal point C of the lens as the apex. However, in the example shown in FIG. 5, since the photosensitive medium 40 is arranged obliquely with respect to the central axis of the cone, the cross section S1 obtained by cutting the reference light L23 (Lref) at the surface of the photosensitive medium 40 is shown in FIG. It becomes an ellipse as shown in FIG.

  As described above, in the example shown in FIG. 6, the reference light Lref is irradiated only in the entire area of the photosensitive medium 40 that is hatched in the figure, so that the hologram of the scattering plate 30 is subjected to this hatching. It will be recorded only in the area. Of course, if the collimated light beam L22 having a larger diameter is generated by the beam expander 22 and the convex lens 23 having a larger diameter is used, the photosensitive medium 40 looks exactly in the cross section S2 of the reference light Lref as shown in FIG. It can also be included. In this case, the hologram of the scattering plate 30 is recorded on the entire surface of the photosensitive medium 40 as hatched in the drawing. In creating the hologram recording medium for illumination used in the present invention, recording may be performed in any form of FIGS.

  Next, let us look at the optical process in which the image of the scattering plate 30 is recorded on the photosensitive medium 40 in more detail. FIG. 8 is a partially enlarged view of the periphery of the scattering plate 30 and the photosensitive medium 40 in the optical system shown in FIG. As described above, the reference light Lref is obtained by condensing the parallel light beam L22 having a circular cross section with the convex lens 23 having the focal point C, and converges into a conical shape having the focal point C as an apex. Therefore, hereinafter, this focal point C is referred to as a convergence point. The reference light L23 (Lref) irradiated to the photosensitive medium 40 is light that converges at the convergence point C as shown in the figure.

  On the other hand, since the light (object light Lobj) emitted from the scattering plate 30 is scattered light, it goes in various directions. For example, as illustrated, when an object point Q1 is considered at the upper end of the left side surface of the scattering plate 30, scattered light is emitted in all directions from this object point Q1. Similarly, scattered light is emitted from any object point Q2 or Q3 in all directions. Accordingly, focusing on an arbitrary point P1 in the photosensitive medium 40, information on interference fringes between the object lights L31, L32, L33 from the object points Q1, Q2, Q3 and the reference light Lref toward the convergence point C is recorded. It will be. Of course, in reality, the object points on the scattering plate 30 are not limited to Q1, Q2, and Q3, so the information from all the object points on the scattering plate 30 is also the interference fringes with the reference light Lref. Recorded as information. In other words, all information of the scattering plate 30 is recorded at the illustrated point P1. In the same manner, all the information on the scattering plate 30 is recorded at the point P2 shown in the figure. As described above, all information of the scattering plate 30 is recorded in any part of the photosensitive medium 40. This is the essence of the hologram.

  Now, the photosensitive medium 40 on which the information of the scattering plate 30 is recorded by such a method will be referred to as an illumination hologram recording medium 45 hereinafter. In order to reproduce this illumination hologram recording medium 45 and obtain a hologram reproduction image of the scattering plate 30, a coherent light having the same wavelength as the light used at the time of recording is obtained from the direction according to the reference light Lref at the time of recording. What is necessary is just to irradiate as illumination light for reproduction | regeneration.

  FIG. 9 is a diagram showing a process of reproducing the hologram reproduction image 35 of the scattering plate using the illumination hologram recording medium 45 created by the process shown in FIG. As shown in the figure, the illumination light Lrep is irradiated from below to the illumination hologram recording medium 45. The reproduction illumination light Lrep is coherent light that diverges as a spherical wave from the point light source located at the convergence point C, and a part of the reproduction illumination light Lrep radiates the illumination hologram recording medium 45 while spreading in a conical shape as shown in the figure. become. Further, the wavelength of the reproduction illumination light Lrep is equal to the wavelength at the time of recording on the illumination hologram recording medium 45 (that is, the wavelength of the coherent light generated by the coherent light source 10 shown in FIG. 5).

  Here, the positional relationship between the illumination hologram recording medium 45 and the convergence point C shown in FIG. 9 is exactly the same as the positional relationship between the photosensitive medium 40 and the convergence point C shown in FIG. Therefore, the reproduction illumination light Lrep shown in FIG. 9 corresponds to the light traveling backward in the optical path of the reference light Lref shown in FIG. When the reproduction illumination light Lrep satisfying such conditions is irradiated onto the illumination hologram recording medium 45, a hologram reproduction image 35 (shown by a broken line in the figure) of the scattering plate 30 is obtained by the diffracted light L45 (Ldif). . The positional relationship between the illumination hologram recording medium 45 and the reproduced image 35 shown in FIG. 9 is exactly the same as the positional relationship between the photosensitive medium 40 and the scattering plate 30 shown in FIG.

  As described above, a technique for recording an image of an arbitrary object as a hologram and reproducing it is a known technique that has been put into practical use for a long time. However, when creating a hologram recording medium used for general purposes, a parallel light beam is used as the reference light Lref as in the example shown in FIG. Holograms recorded using the reference light Lref consisting of a parallel light beam are excellent in convenience since the reproduction illumination light Lrep consisting of a parallel light beam may be used even during reproduction.

  On the other hand, as shown in FIG. 8, when the light that converges at the convergence point C is used as the reference light Lref, light that diverges from the convergence point C (or at the convergence point C) as shown in FIG. (Converging light) must be used as the reproduction illumination light Lrep. Actually, in order to obtain the reproduction illumination light Lrep as shown in FIG. 9, it is necessary to arrange an optical system such as a lens at a specific position. If the positional relationship between the illumination hologram recording medium 45 and the convergence point C during reproduction does not match the positional relationship between the photosensitive medium 40 and the convergence point C during recording, an accurate reproduced image 35 is obtained. Therefore, the illumination conditions at the time of reproduction are limited (if reproduction is performed using a parallel light beam, the illumination conditions need only satisfy the irradiation angle).

  For these reasons, the hologram recording medium created using the reference light Lref that converges at the convergence point C is not suitable for general applications. Nevertheless, in the embodiment shown here, the reason why the light converged at the convergence point C is used as the reference light Lref is to facilitate the light beam scanning performed during reproduction. That is, in FIG. 9, for convenience of explanation, a method of generating the reproduction image 35 of the scattering plate 30 using the reproduction illumination light Lrep that diverges from the convergence point C is shown. Thus, the reproduction using the reproduction illumination light Lrep spreading in a conical shape is not performed. Instead, a method of scanning the light beam is adopted. Hereinafter, this method will be described in detail.

  FIG. 10 is a diagram showing a process for reproducing the image 35 of the scattering plate 30 by irradiating only one light beam to the illumination hologram recording medium 45 created by the process shown in FIG. That is, in this example, only one light beam L61 directed from the convergence point C to one point P1 in the medium is provided as the reproduction illumination light Lrep. Of course, the light beam L61 is coherent light having the same wavelength as that of the recording light. As already described with reference to FIG. 8, information on the entire scattering plate 30 is recorded at an arbitrary point P <b> 1 in the illumination hologram recording medium 45. Therefore, if the reproduction illumination light Lrep is irradiated on the position of the point P1 in FIG. 10 under the conditions corresponding to the reference light Lref used at the time of recording, only the interference fringes recorded in the vicinity of the point P1 are used. Thus, a reproduced image 35 of the scattering plate 30 can be generated. FIG. 10 shows a state in which the reproduced image 35 is reproduced by the diffracted light L45 (Ldif) from the point P1.

  On the other hand, FIG. 11 shows an example in which only one light beam L62 directed from the convergence point C to another point P2 in the medium is given as the reproduction illumination light Lrep. Also in this case, since the information of the entire scattering plate 30 is recorded at the point P2, the reproduction illumination light Lrep is irradiated to the position of the point P2 under the conditions corresponding to the reference light Lref used at the time of recording. For example, it is possible to generate the reproduced image 35 of the scattering plate 30 using only the interference fringes recorded in the vicinity of the point P2. FIG. 11 shows a state in which the reproduced image 35 is reproduced by the diffracted light L45 (Ldif) from the point P2. Since the reproduced image 35 shown in FIG. 10 and the reproduced image 35 shown in FIG. 11 have the same scattering plate 30 as the original image, they are theoretically the same reproduced image generated at the same position. .

  FIG. 12 is a plan view showing the irradiation position of the light beam in the reproduction process shown in FIGS. A point P1 in FIG. 12 corresponds to the point P1 in FIG. 10, and a point P2 in FIG. 12 corresponds to the point P2 in FIG. A1 and A2 respectively indicate cross sections (light beam spots) of the reproduction illumination light Lrep. The shapes and sizes of the cross sections A1 and A2 depend on the shapes and sizes of the cross sections of the light beams L61 and L62. Further, it also depends on the irradiation position on the hologram recording medium 45 for illumination. Here, for the sake of convenience, circular cross sections A1 and A2 are shown, but actually, when the light beams L61 and L62 having a circular cross section are used, the cross sectional shape becomes a flat ellipse according to the irradiation position.

  As described above, the recorded interference fringes are completely different in the vicinity of the point P1 and in the vicinity of the point P2 shown in FIG. 8, but any point is irradiated with the light beam serving as the reproduction illumination light Lrep. Even in this case, the same reproduced image 35 is obtained at the same position. This is because the reproduction illumination light Lrep is a light beam directed from the convergence point C toward each of the points P1 and P2, and at any point, reproduction in a direction corresponding to the direction of the reference light Lref at the time of recording shown in FIG. This is because the illumination light Lrep is provided.

  FIG. 12 illustrates only two points P1 and P2, but the same can be said of an arbitrary point on the illumination hologram recording medium 45. Therefore, when a light beam is irradiated on an arbitrary point on the hologram recording medium 45 for illumination, the same reproduced image 35 is obtained at the same position as long as the light beam is light from the convergence point C. However, as shown in FIG. 6, when a hologram is recorded only in a partial area of the photosensitive medium 40 (the area shown by hatching in the figure), a reproduced image 35 is obtained when light is applied to a point in the area. Limited to beam irradiation.

  Eventually, the illumination hologram recording medium 45 described here is a medium in which the image of the scattering plate 30 is recorded as a hologram using the reference light Lref that converges to a specific convergence point C, and passes through this convergence point C. When a light beam is irradiated to an arbitrary position as the reproduction illumination light Lrep, a reproduction image 35 of the scattering plate 30 is generated. Therefore, when the light beam passing through the convergence point C is scanned on the illumination hologram recording medium 45 as the reproduction illumination light Lrep, the same reproduction image 35 is placed at the same position by the diffracted light Ldif obtained from each irradiation point. Will be played.

  In the present invention, the reproduction light (diffracted light for forming the reproduction image 35 of the scattering plate) obtained from the “illumination hologram recording medium 45” in this way is used as the “display hologram recording medium” (display target). It is used as illumination light for reproduction with respect to “original hologram recording medium” on which a stereoscopic image is recorded.

  FIG. 13 is a side view showing a configuration of the reproduction illumination light generation unit 100 for generating such reproduction illumination light. As shown in the figure, the reproduction illumination light generation unit 100 includes an illumination hologram recording medium 45, a coherent light source 50, and a light beam scanning device 60.

  Here, as described above, the illumination hologram recording medium 45 is a medium created by a process using the optical system shown in FIG. 5, and the image 35 of the scattering plate 30 is recorded thereon. The coherent light source 50 is a light source that generates a coherent light beam L50 having the same wavelength as that of the light (object light Lobj and reference light Lref) used when the illumination hologram recording medium 45 is produced.

  On the other hand, the light beam scanning device 60 irradiates the illumination hologram recording medium 45 with the light beam L50 generated by the coherent light source 50 bent at a predetermined scanning base point B, and changes the bending state of the light beam L50 in terms of time. This is a device that scans so that the irradiation position of the bent light beam L60 on the illuminating hologram recording medium 45 changes with time. Specifically, the illustrated light beam scanning device 60 is configured by a movable mirror having a reflecting surface on the scanning base point B side, with the V axis (axis perpendicular to the paper surface) and the W axis in the figure as rotation axes. It can be inclined in a desired direction.

  Such an apparatus is generally known as a scanning mirror device. In the figure, for convenience of explanation, the bending mode at time t1 is indicated by a one-dot chain line, and the bending mode at time t2 is indicated by a two-dot chain line. That is, at the time t1, the light beam L50 is bent at the scanning base point B and irradiated to the point P (t1) of the hologram recording medium 45 as the light beam L60 (t1), but at the time t2, the light beam L50 is scanned. Bending at the base point B and irradiating the point P (t2) of the hologram recording medium 45 as a light beam L60 (t2).

  For the sake of convenience, only the bending modes at two points in time t1 and t2 are shown in the figure, but actually, the bending direction of the light beam changes smoothly during the period from time t1 to time t2, and the light beam L60. The irradiation position with respect to the hologram recording medium 45 gradually moves to points P (t1) to P (t2) in the figure. That is, during the period from time t1 to time t2, the irradiation position of the light beam L60 is scanned from the point P (t1) to P (t2) on the illumination hologram recording medium 45.

  Here, if the position of the scanning base point B coincides with the position of the convergence point C shown in FIG. 8 (in other words, the positional relationship between the illumination hologram recording medium 45 and the scanning base point B in FIG. If it is made to be equal to the positional relationship between the photosensitive medium 40 and the convergence point C in FIG. 8), at each irradiation position of the illumination hologram recording medium 45, the light beam L60 corresponds to the reference light Lref shown in FIG. The light is irradiated in the opposite direction (the direction in which the optical path of the reference light Lref shown in FIG. 8 moves backward). Therefore, the light beam L60 functions as correct reproduction illumination light Lrep for reproducing the hologram recorded therein at each irradiation position of the illumination hologram recording medium 45.

  For example, at time t1, a reproduced image 35 of the scattering plate 30 is generated by diffracted light L45 (t1) from the irradiation point P (t1), and at time t2, diffracted light L45 (t2) from the irradiation point P (t2). ), A reproduced image 35 of the scattering plate 30 is generated. Of course, also during the period from time t1 to t2, the reproduced image 35 of the scattering plate 30 is similarly generated by the diffracted light from each position irradiated with the light beam L60. That is, as long as the light beam L60 is light traveling from the scanning base point B to the illumination hologram recording medium 45, no matter where the light beam L60 is irradiated on the illumination hologram recording medium 45, the light beam L60 is diffracted from the irradiation position. The same reproduced image 35 is generated at the same position by the light.

  Such a phenomenon occurs, as shown in FIG. 8, in the illumination hologram recording medium 45, an image of the scattering plate 30 is recorded as a hologram using the reference light L23 that converges at a specific convergence point C. This is because the light beam scanning device 60 scans the light beam L60 with the convergence point C as the scanning base point B. Of course, even if the scanning by the light beam scanning device 60 is stopped and the irradiation position of the light beam L60 is fixed at one point on the illumination hologram recording medium 45, the same reproduced image 35 is continuously generated at the same position. There is no change. Nevertheless, scanning the light beam L60 is none other than to suppress speckle noise.

  As described above, in the present invention, the diffracted light L45 for forming the reproduction image 35 of the scattering plate shown in FIG. 13 is used as reproduction illumination light for the display hologram recording medium. In other words, the reproduction illumination light generation unit 100 shown in FIG. 13 serves as an illumination device that illuminates an object placed at the position of the reproduction image 35.

  Thus, as shown in FIG. 13, a point of interest Q is set at an arbitrary position on the reproduced image 35, and the diffracted light reaching the point of interest Q is considered. First, at time t1, the light beam L50 emitted from the coherent light source 50 is bent at the scanning base point B as indicated by the alternate long and short dash line in the figure, and is irradiated to the point P (t1) as the light beam L60 (t1). A part of the diffracted light L45 (t1) from the irradiation point P (t1) reaches the point of interest Q. On the other hand, at time t2, the light beam L50 emitted from the coherent light source 50 is bent at the scanning base point B as indicated by a two-dot chain line in the drawing, and is irradiated to the point P (t2) as the light beam L60 (t2). A part of the diffracted light L45 (t2) from the irradiation point P (t2) reaches the point of interest Q.

  Eventually, such a diffracted light always generates a reproduced image corresponding to the position of the point of interest Q on the scattering plate 30 at the position of the point of interest Q. The corners are different at time t1 and time t2. In other words, when the light beam L60 is scanned, the reproduced image 35 formed in the space is not changed, but the incident angle of the diffracted light reaching each point of the reproduced image 35 changes with time. Become. Such a change in incident angle with time greatly contributes to reducing speckle.

  As described above, speckles are generated when coherent light is used because the coherent light reflected from each part of the light receiving surface interferes with each other because of its extremely high coherence. However, in the present invention, for example, when the incident angle of the diffracted light with respect to the point of interest Q shown in the drawing is considered, the incident angle varies with time by scanning the light beam L60. This is not only true for the position of the point of interest Q shown in the figure, but is true for any point where the diffracted light from the illumination hologram recording medium 45 arrives. Therefore, the incident angle of the diffracted light with respect to the surface of an arbitrary object arranged in the space where the diffracted light reaches varies with time. For this reason, although it is coherent light, the mode of interference also varies with time and has multiplicity. For this reason, speckle generation factors can be mitigated from the fact that speckled patterns that disperse in time and have physiological adverse effects are constantly observed. This is the basic principle of speckle suppression according to the present invention.

<<< §3. Basic embodiment of the present invention >>
Next, the configuration and operation of the stereoscopic image display apparatus according to the basic embodiment of the present invention will be described. FIG. 14 is a side view showing an example of a method for producing a display hologram recording medium used in this stereoscopic image display apparatus. As shown in FIG. 13, the reproduction illumination light generation unit 100 shown in the figure is configured by the illumination hologram recording medium 45, the coherent light source 50, and the light beam scanning device 60.

  After the reproduction illumination light generation unit 100 is disposed, the photosensitive medium 70 is subsequently disposed at a position where the reproduced image 35 of the scattering plate is formed (position indicated by a broken line in FIG. 13), and further at an arbitrary position. An original image F (cube in this example) to be displayed is arranged. Then, the light beam L50 emitted from the coherent light source 50 is bent at the scanning base point B as indicated by a one-dot chain line in the figure, and irradiated to the irradiation point P (t1) as the light beam L60 (t1), and the irradiation point P (t1 ) Is irradiated to the photosensitive medium 70.

  At this time, scanning by the light beam scanning device 60 is not performed, and the photosensitive medium 70 is continuously irradiated with the diffracted light L45 (t1) from the irradiation point P (t1) (so to speak, a scanning system). Is fixed at the position of time t1). On the other hand, the object light Lobj from the original image F also reaches the photosensitive medium 70 (in the drawing, for convenience of explanation, only the object light Lobj from the representative point K on the original image F is shown). Then, using the diffracted light L45 (t1) as the reference light Lref, interference fringes generated by the reference light Lref and the object light Lobj are recorded on the photosensitive medium 70. In other words, the original image F is recorded on the photosensitive medium 70 as a hologram. Here, the photosensitive medium 70 on which such a hologram is recorded is referred to as a display hologram recording medium 75.

  The above-described process is a process for creating the display hologram recording medium 75 by an optical method, but the display hologram recording medium 75 can also be created by the CGH method. In this case, information indicating the geometrical arrangement of the reproduction illumination light generation unit 100 shown in FIG. 14 is given to the computer as data, and a recording surface is defined at the position of the light receiving surface of the photosensitive medium 70, and the original image is defined. As F, CG data indicating the shape may be given to the computer, and hologram interference fringes formed on the recording surface may be obtained as image data by simulation calculation.

  When the optical method is adopted, it is necessary to devise the arrangement so that the reference light Lref (that is, the diffracted light L45 (t1)) is not obstructed by a physical object constituting the original image F. Can be used to obtain image data indicating hologram interference fringes through computation on a computer, so that there is no problem even if the arrangement is practically impossible. For example, in the geometric condition shown in FIG. 14, a part of the diffracted light L45 (t1) is obstructed by the original image F, which is a problem when an optical method is employed, but the CGH method is used. If so, there will be no problem.

  If the display hologram recording medium 75 can be created in this way, the stereoscopic image display apparatus according to the basic embodiment of the present invention can be configured by taking the arrangement as shown in FIG. That is, the apparatus shown in FIG. 15 is a stereoscopic image display apparatus configured by adding the display hologram recording medium 75 created by the method shown in FIG. 14 to the reproduction illumination light generation unit 100 shown in FIG. . Here, the display hologram recording medium 75 is arranged at a position where the reproduced image 35 of the scattering plate shown by a broken line in FIG. 13 is formed (that is, the position of the photosensitive medium 70 shown in FIG. 14).

  The stereoscopic image display operation by this stereoscopic image display apparatus is as follows. First, as shown in FIG. 15, the light beam L50 emitted from the coherent light source 50 is bent at the scanning base point B as indicated by a one-dot chain line in the figure, and is converted into a light beam L60 (t1) on the illumination hologram recording medium 45. The irradiation point P (t1) is irradiated so that the diffracted light L45 (t1) from the irradiation point P (t1) is irradiated to the display hologram recording medium 75. Since the diffracted light L45 (t1) is equivalent to the diffracted light L45 (t1) that functions as the reference light Lref in the recording process of FIG. 14, the reproduction process of FIG. 15 reproduces the holographic recording medium 75 for display. It functions as an illumination light Lrep. Therefore, the reproduced image FF (t1) is observed as a virtual image by the diffracted light L75 (t1) reaching the viewpoint E, as depicted by a broken line in the figure. The position of the reproduced image FF (t1) is the position of the original image F shown in FIG.

  Of course, when the reproduction state shown in FIG. 15 is maintained as it is, speckle noise is generated, and the viewer observes shining speckled luminance unevenness. This is because the diffracted light L45 (t1), which is coherent light, is reflected on the surface of the display hologram recording medium 75 and interferes with each other. Therefore, in the present invention, scanning by the light beam scanning device 60 is performed when reproducing a stereoscopic image. If such scanning is performed, the irradiation point P of the light beam L60 with respect to the illumination hologram recording medium 45 will fluctuate with time, so that the incident angle of the diffracted light L45 with respect to the display hologram recording medium 75 is temporally changed. fluctuate.

  For example, in FIG. 16, at time t2, the light beam L60 (t2) bent at the scanning base point B by the scanning of the light beam scanning device 60 is irradiated to the irradiation point P (t2) on the illumination hologram recording medium 45, A state in which the diffracted light L45 (t2) from the irradiation point P (t2) is irradiated onto the display hologram recording medium 75 is shown. In this case, the diffracted light L75 (t2) reaching the viewpoint E displays a reproduced image FF (t2) as depicted by a broken line in the figure as a virtual image.

  Actually, due to the scanning function of the light beam scanning device 60, the irradiation point of the light beam L60 gradually increases along the path from the irradiation point P (t1) shown in FIG. 15 to the irradiation point P (t2) shown in FIG. Will move to. Accordingly, the incident angle of the diffracted light L45 with respect to the display hologram recording medium 75 gradually changes with time and is multiplexed. For this reason, speckle generation factors can be mitigated from the fact that speckled patterns that disperse in time and have physiological adverse effects are constantly observed. This is the basic principle of the present invention.

  However, the reproduced image FF (t1) shown in FIG. 15 is a correct reproduced image of the original image F recorded as a hologram, but the reproduced image FF (t2) shown in FIG. It will not be. This is because the display hologram recording medium 75 is a recording process shown in FIG. 14, that is, a medium in which the original image F is recorded using the diffracted light L45 (t1) from the irradiation point P (t1) as the reference light Lref. As shown in FIG. 15, the reproduced image FF (t1) obtained by using the diffracted light L45 (t1) from the irradiation point P (t1) as the reproduction illumination light becomes an original hologram reproduced image. As shown, the reproduced image FF (t2) obtained by using the diffracted light L45 (t2) from the irradiation point P (t2) as the reproduction illumination light does not become an original hologram reproduced image.

  That is, as shown in FIG. 16, the reproduced image FF (t2) obtained by using the diffracted light L45 (t2) from the irradiation point P (t2) as the reproduction illumination light is the original correct hologram reproduction. In order to make an image, in the image recording process for creating the display hologram recording medium 75, as shown in FIG. 17, reference is made to the diffracted light L45 (t2) from the irradiation point P (t2). It is necessary to record the original image F as the light Lref. Of course, when the display hologram recording medium 75 is produced by such a recording process, the diffracted light L45 (t1) from the irradiation point P (t1) is used as reproduction illumination light, as shown in FIG. The reproduced image FF (t1) obtained in this way is no longer the original hologram reproduced image.

  As described above, in the stereoscopic image display device according to the basic embodiment described in §3, since the hologram recording medium 75 for display uses a medium in which the interference fringe pattern is physically fixed, the light beam scanning device is used. The original correct hologram reproduction image FF is displayed only when the light beam L60 irradiates the specific irradiation point P (the irradiation point used in the recording process) with 60, and the correct hologram reproduction image is displayed at other times. The FF is not displayed, and the reproduced image FF whose position and shape are slightly changed is displayed. As a result, when viewed from the viewpoint E, a slightly blurred reproduced image FF is observed. In order to solve such a problem, as described in §5, an arbitrary interference fringe pattern is formed based on the applied image data instead of the display hologram recording medium 75 in which the interference fringe pattern is physically fixed. It is necessary to use a spatial light modulator (eg, a liquid crystal display) that can be made to operate.

  However, in this stereoscopic image display device, since the hologram is reproduced using the same coherent light as that used when the original image F was recorded, it is far more than a reproduced image using a general light source such as indoor lighting. A clear and bright reproduced image can be obtained. Therefore, the stereoscopic image display device according to the basic embodiment described in §3 is capable of displaying a clearer and brighter stereoscopic image than the conventional stereoscopic image display device using a general light source, and is industrially It has sufficient availability.

  In the stereoscopic image display device according to this basic embodiment, the first method for obtaining a clearer reproduced image FF is to display the depth position at which the reproduced image FF appears when viewed from the viewpoint as much as possible. To bring it closer to the position of the recording medium 75. In general, a hologram from which a reproduced image is obtained in the vicinity of a recording medium with respect to depth is called an image hologram. With such an image hologram, even if the incident angle of the reproduction illumination light with respect to the recording medium changes, the position and shape of the reproduction image do not change greatly. Therefore, in the recording process for creating the display hologram recording medium 75, the original image F is arranged in the immediate vicinity of the photosensitive medium (in the case of CGH, the original image F is arranged so as to overlap the recording surface), What is necessary is just to record.

  A second method for obtaining a clearer reproduced image FF is a method for limiting the scanning range on the illumination hologram recording medium 45 by the light beam scanning device 60. As in the example shown in FIG. 15, from the irradiation point P (t1) at the lower end of the illumination hologram recording medium 45, the irradiation point P (t2) at the upper end of the illumination hologram recording medium 45 as in the example shown in FIG. When a wide scanning area up to is set, the incident angle of the reproduction illumination light L45 with respect to the display hologram recording medium 75 changes significantly. As a result, the temporal fluctuation range of the position and shape of the reproduced image FF increases, and the degree of blurring of the observed image also increases. Therefore, if the scanning range by the light beam scanning device 60 is limited to the vicinity of the reference irradiation point, the temporal fluctuation width of the position and shape of the reproduced image FF is suppressed, and the degree of blurring of the observed image is reduced. Can be made. In this case, the reference irradiation point is preferably an irradiation point in a recording process for creating the display hologram recording medium 75.

  However, if the scanning range by the light beam scanning device 60 is limited, the change width of the incident angle of the reproduction illumination light L45 with respect to the display hologram recording medium 75 is reduced, so that the speckle noise is suppressed. There is also a demerit that damages the effect. Therefore, from the viewpoint of suppressing speckle noise, the scanning range by the light beam scanning device 60 should not be so limited. Therefore, in practice, an optimal scanning range may be set depending on whether the sharpness of the reproduced image is emphasized or the reduction of speckle noise is emphasized.

  In the basic embodiments described so far, the example in which the display hologram recording medium 75 is arranged at the position of the reproduction image 35 of the scattering plate obtained by the illumination hologram recording medium 45 is shown. The position of the recording medium 75 is not necessarily limited to the position of the reproduced image 35 of the scattering plate. In other words, in the recording process shown in FIG. 14, the photosensitive medium 70 does not necessarily have to be arranged at the position of the reproduced image 35 of the scattering plate. Since the display hologram recording medium 75 may be irradiated with the light diffracted from the illumination hologram recording medium 45 as reproduction illumination light, the display hologram recording medium 75 is diffracted from the illumination hologram recording medium 45. If it is a position where light can reach, it may be arranged at any position in space.

  However, considering the point of illumination efficiency, the display hologram recording medium 75 is arranged at the position of the reproduction image 35 of the scattering plate obtained by the illumination hologram recording medium 45 as in the basic embodiment described so far. It is preferable to do this. For example, in the case of the example shown in FIG. 15, the light beam L50 emitted from the coherent light source 50 is bent at the scanning base point B, and is applied to the irradiation point P (t1) on the illumination hologram recording medium 45 as the light beam L60 (t1). Irradiated and diffracted light L45 (t1) from the irradiation point P (t1) is irradiated on the entire surface of the display hologram recording medium 75. In this way, the entire surface of the display hologram recording medium 75 is irradiated with the reproduction illumination light because the display hologram recording medium 75 is disposed at the position of the reproduction image 35 of the scattering plate, and the scattering plate. This is because it has the same size as the reproduced image 35.

  Since the diffracted light L45 (t1) from the irradiation point P (t1) is light for forming the reproduction image 35 of the scattering plate, the display hologram recording medium 75 having the same size as the reproduction image 35 is reproduced from the reproduction image 35. If arranged at the same position as 35, it is natural that the display hologram recording medium 75 is irradiated with the diffracted light L45 (t1). This is not limited to the diffracted light L45 (t1) from the irradiation point P (t1), but can be applied to the diffracted light from all the irradiation points P. For example, in the case of the example shown in FIG. 16, the diffracted light L45 (t2) is also light that irradiates the entire surface of the display hologram recording medium 75.

  In this way, if the display hologram recording medium 75 is arranged at the position of the reproduction image 35 of the scattering plate obtained by the illumination hologram recording medium 45 and is a medium having the same size as the reproduction image 35, the coherent light source 50 is used. The entire energy of the light beam L50 emitted from the light beam can be applied to the surface of the display hologram recording medium 75, and energy loss can be prevented. Of course, the display hologram recording medium 75 may be larger than the reproduced image 35. In this case, the periphery of the medium is a useless area where the reproduction illumination light is not irradiated.

<<< §4. Detailed configuration of each part of basic embodiment >>
The basic embodiment of the present invention described in §3 is a stereoscopic image display device that reproduces and displays a stereoscopic image recorded as a hologram, and as shown in FIG. 15, a coherent light beam L50. The illumination hologram recording medium 45 on which the image of the scattering plate is recorded, and the illumination hologram recording medium 45 is irradiated with the light beam L50 as the light beam L60, and the light beam L60 is used for illumination. This is an apparatus including a light beam scanning device 60 that scans so that the irradiation position on the hologram recording medium 45 changes with time, and a display hologram recording medium 75 on which a stereoscopic image to be displayed is recorded. .

  Here, as shown in FIG. 8, the image of the scattering plate 30 is recorded on the illumination hologram recording medium 45 as a hologram using the reference light Lref irradiated along a predetermined optical path. The coherent light source 50 is a light beam having a wavelength capable of reproducing the image of the scattering plate 30 recorded on the illumination hologram recording medium 45 and the three-dimensional image recorded on the display hologram recording medium 75. L50 is generated, and the light beam scanning device 60 scans the light beam so that the irradiation direction of the light beam L60 on the illumination hologram recording medium 45 is in the direction along the optical path of the reference light Lref shown in FIG. . Then, the display hologram recording medium 75 forms a reproduction image FF of a stereoscopic image using the reproduction light L45 of the image of the scattering plate obtained from the illumination hologram recording medium 45 as the reproduction illumination light. Therefore, in the following, these components will be described in more detail.

<§4-1: Coherent light source>
First, as the coherent light source 50, a light source that generates a coherent light beam L50 having the same wavelength as the light (object light Lobj and reference light Lref) used when the illumination hologram recording medium 45 is produced may be used. Good. However, the wavelength of the light beam L50 generated by the coherent light source 50 does not have to be exactly the same as the wavelength of the light used when the hologram recording medium 45 is produced. Can be obtained. In short, the coherent light source 50 used in the present invention may be a light source that generates a coherent light beam L50 having a wavelength capable of reproducing the image 35 of the scattering plate.

  In the case of the embodiment shown here, a DPSS (Diode Pumped Solid State) laser device capable of emitting laser light having a wavelength λ = 532 nm (green) is used as the coherent light source 50. The DPSS laser is a coherent light source suitable for use in the stereoscopic image display apparatus according to the present invention because it can obtain laser light having a desired wavelength with a relatively high output while being small.

  Since this DPSS laser device has a longer coherence length than a general semiconductor laser, speckles are likely to occur, and it has been conventionally considered inappropriate for illumination applications. That is, conventionally, in order to reduce speckle, efforts have been made to increase the oscillation wavelength of laser light and shorten the coherent length as much as possible. On the other hand, in the present invention, even if a light source having a long coherent length is used, the generation of speckle can be effectively suppressed by the above-described principle, so even if a DPSS laser device is used as the light source. In practice, the generation of speckle is no longer a problem. In such a point, if the present invention is used, an effect of further expanding the selection range of the light source can be obtained.

<§4-2: Light beam scanning device>
The light beam scanning device 60 is a device having a function of scanning the light beam on the illumination hologram recording medium 45. As a specific scanning method of the light beam, for example, similarly to scanning of an electron beam in a CRT, the illumination hologram recording medium 45 is scanned in the horizontal direction, and such scanning is repeated in the vertical direction, thereby A method of scanning the entire surface can be taken. However, in practice, it is preferable to scan the illumination hologram recording medium 45 along a circular scanning trajectory.

  As shown in the example of FIG. 6, when recording is performed by irradiating only a part of the photosensitive medium 40 (hatched area) with the reference light Lref, the other area (outer white area) is recorded. ) Has no hologram recorded. In such a case, if the outer white area is scanned, the reproduced image 35 cannot be obtained, and the illumination temporarily becomes dark. Therefore, in this case, it is preferable to scan only the area where the hologram is recorded.

  As shown in FIG. 15, the light beam scanning device 60 scans the light beam L <b> 60 on the illumination hologram recording medium 45. The light beam scanning device 60 has a function of irradiating the illumination hologram recording medium 45 with the light beam L50 from the coherent light source 50 bent at the scanning base point B (convergence point C at the time of hologram recording). Moreover, scanning is performed so that the irradiation position of the bent light beam L60 with respect to the illumination hologram recording medium 45 changes with time by changing the bending mode (the direction of bending and the size of the bending angle) with time. To do. An apparatus having such a function is used in various optical systems as a scanning mirror device.

  For example, in the example shown in FIG. 15, a simple reflecting mirror is drawn as the light beam scanning device 60 for the sake of convenience, but actually, a driving mechanism for rotating the reflecting mirror in two axial directions is provided. Yes. That is, when the scanning base point B is set at the center position of the reflecting surface of the reflecting mirror shown in the figure, and the V axis and the W axis that pass through the scanning base point B and are orthogonal to each other on the reflecting surface are defined, A mechanism for rotating around an axis (axis perpendicular to the paper surface in the figure) and a mechanism for rotating around a W axis (axis indicated by a broken line in the figure) are provided.

  As described above, by using a reflecting mirror that can be rotated independently around the V-axis and the W-axis, the reflected light beam L60 can be scanned in the horizontal direction and the vertical direction on the hologram recording medium 45 for illumination. It is. For example, in the above-described mechanism, when the reflected light is rotated around the V axis, the light beam L60 is scanned from the irradiation point P (t1) shown in FIG. 15 toward the irradiation point P (t2) shown in FIG. be able to. Further, if it rotates around the W axis, it can scan in the direction perpendicular to the paper surface.

  After all, if the light beam scanning device 60 has a function of bending the light beam L60 so as to perform a swinging motion on a plane including the scanning base point B, the light beam L60 on the illumination hologram recording medium 45 will be described. The irradiation position can be scanned in a one-dimensional direction. On the other hand, if the operation of scanning the irradiation position of the light beam L60 on the illumination hologram recording medium 45 in a two-dimensional direction is performed, the light beam scanning device 60 is arranged on the first plane including the scanning base point B. A function of bending the light beam L60 so as to perform a swinging motion, and a function of bending the light beam L60 so as to perform a swinging motion on a second plane including the scanning base point B and orthogonal to the first plane; , Just keep it.

  A polygon mirror is widely used as a scanning mirror device for scanning the irradiation position of a light beam in a one-dimensional direction. As a scanning mirror device for scanning in a two-dimensional direction, a combination of two polygon mirrors can be used, and devices such as a gimbal mirror, a galvano mirror, and a MEMS mirror are known. In addition to a normal mirror device, a total reflection prism, a refraction prism, an electro-optic crystal (such as a KTN crystal), and the like can be used as the light beam scanning device 60.

  Note that the scanning speed of the light beam by the light beam scanning device 60 needs to be set to a speed at which an effect of suppressing speckle noise is generated. For example, even if scanning is performed at such a slow speed that one hour is required for scanning in one direction from the irradiation point P (t1) shown in FIG. 15 to the irradiation point P (t2) shown in FIG. From the viewpoint of resolution, it is the same as when scanning is not performed, and speckle is recognized. The reason that speckle is reduced by scanning the light beam is that, as described above, the incident angles of the light applied to each part of the display hologram recording medium 75 are temporally multiplexed. Therefore, in order to sufficiently obtain the effect of speckle reduction by beam scanning, the time during which the same interference condition that causes speckle is maintained is shorter than human visual time resolution. do it.

  In general, the limit of human visual temporal resolution is about 1/20 to 1/30 seconds, and if a still image of 20 to 30 frames or more is presented per second, a smooth video is displayed to humans. Be recognized. In consideration of such points, if the diameter of the light beam is d, scanning is performed at a scanning speed (speed of 20 d to 30 d per second) that travels a distance of d or more in 1/20 to 1/30 seconds. A sufficient speckle suppressing effect can be obtained.

<§4-3: Hologram recording medium>
In the basic embodiment described in §3, the illumination hologram recording medium 45 and the display hologram recording medium 75 are used. The former may be a medium having a feature that an image of the scattering plate 30 is recorded as a hologram using reference light that converges at a specific convergence point C, and the latter is a diffraction obtained from the former. Any medium may be used as long as a stereoscopic image to be displayed is recorded as a hologram using light as reference light. Here, a specific form of a hologram recording medium suitable for use in the present invention will be described.

  There are several physical forms of holograms. The inventor of the present application considers that a volume hologram is most preferable for use in the present invention. In particular, it is optimal to use a volume hologram using a photopolymer.

  In general, a hologram used as an anti-counterfeit seal on a cash card or a cash voucher is called a surface relief (emboss) hologram, and hologram interference fringes are recorded by a surface uneven structure. Of course, in practicing the present invention, it is possible to use a hologram recording medium (generally called a holographic diffuser) in which an image is recorded as a surface relief hologram. However, in the case of this surface relief hologram, scattering due to the uneven structure on the surface may become a new speckle generation factor, which is not preferable from the viewpoint of reducing speckle. Further, in the surface relief type hologram, since multi-order diffracted light is generated, the diffraction efficiency is lowered, and further, there is a limit to the diffraction performance (how much the diffraction angle can be increased).

  On the other hand, in the volume hologram, since hologram interference fringes are recorded as a refractive index distribution inside the medium, it is not affected by scattering due to the uneven structure on the surface. In general, the diffraction efficiency and the diffraction performance are also superior to the surface relief hologram. Therefore, when practicing the present invention, it is optimal to use a medium on which an image is recorded as a volume hologram.

  However, volume holograms that are recorded using a photosensitive medium containing a silver salt material are preferably avoided because scattering by silver salt particles may cause new speckle generation. . For these reasons, the present inventor believes that a volume hologram using a photopolymer is optimal as a hologram recording medium 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.

  However, the surface relief type hologram is superior to the volume type hologram in terms of mass productivity. The surface relief hologram can be mass-produced by producing an original plate having a concavo-convex structure on the surface and press working using the original plate. Therefore, when it is necessary to reduce the manufacturing cost, a surface relief hologram may be used.

  On the other hand, as a hologram recording method, in addition to the interference fringe recording method that records the amplitude of the combined wave of the object light and the reference light as an interference fringe, the kinoform method that records the phase of the combined wave, or the amplitude and phase There is a complex amplitude method for recording both, and in the present invention, the hologram may be recorded by any of these methods.

  As a physical form of the hologram, an amplitude modulation type hologram in which interference fringes are recorded as a light and shade pattern on a plane is also widely used. However, since this amplitude modulation hologram has low diffraction efficiency and light is absorbed in a dark pattern portion, sufficient illumination efficiency cannot be secured when used in the present invention. However, in the manufacturing process, since a simple method of printing a shading pattern on a flat surface can be adopted, a merit can be obtained in terms of manufacturing cost. Therefore, depending on the application, it is also possible to employ an amplitude modulation hologram in the present invention.

  In the recording methods described so far, a so-called Fresnel type hologram recording medium is produced, but a Fourier transform type hologram recording medium obtained by recording the scattering plate 30 or the original image F through a lens. Can be created.

<<< §5. Practical embodiment of the present invention >>>
In the stereoscopic image display device according to the basic embodiment described in §3, since the medium on which the interference fringe pattern is physically fixed is used as the display hologram recording medium 75, the light beam scanning device 60 uses the light beam. The original correct hologram reproduction image FF is displayed only at the time when L60 is irradiated to a specific irradiation point P (the irradiation point used in the recording process). At other times, the correct hologram reproduction image FF is displayed. As described above, there is a drawback that a slightly blurred reproduction image FF is observed without being performed.

  In the practical embodiment described here, instead of the display hologram recording medium 75 in which the interference fringe pattern is physically fixed, an arbitrary interference fringe pattern or the like can be formed on the basis of the applied image data. By using a vessel (for example, a liquid crystal display), the above disadvantages are solved. Further, by changing the image data applied to the spatial light modulator, an arbitrary stereoscopic image can be displayed, and there is an advantage that a moving image can be displayed as necessary.

  FIG. 18 is a diagram showing an overall configuration of a stereoscopic image display apparatus according to this practical embodiment. Here, the reproduction illumination light generation unit 100 (that is, the coherent light source 50, the light beam scanning device 60, and the illumination hologram recording medium 45) has the same configuration as that of the basic embodiment shown in FIG. . First, the coherent light source 50 is a component that generates a coherent light beam L50 having a wavelength capable of reproducing an image of a scattering plate and a stereoscopic image. The illumination hologram recording medium 45 records an image of the scattering plate 30 as a hologram using reference light irradiated along a predetermined optical path. The light beam scanning device 60 then transmits the light so that the irradiation direction of the light beam L60 on the illumination hologram recording medium 45 is in the direction along the optical path of the reference light used when recording the image of the scattering plate 30. The beam L50 is bent and irradiated to the illumination hologram recording medium 45, and scanning is performed so that the irradiation position of the light beam L60 on the illumination hologram recording medium 45 changes with time.

  On the other hand, a spatial light modulator 80 is used in the practical embodiment shown in FIG. 18 in place of the display hologram recording medium 75 used in the basic embodiment shown in FIG. The spatial light modulator 80 has a predetermined modulation plane, and based on the image data indicating the modulation characteristics at each position on the modulation plane, the spatial light modulator 80 corresponds to the incident position with respect to the light incident on the modulation plane. It has the function of performing injection after applying modulation. The spatial light modulator 80 can be disposed at an arbitrary position as long as the diffracted light from the illumination hologram recording medium 45 can reach. However, as described above, the spatial light modulator 80 improves the illumination efficiency. For this reason, it is preferable to arrange at the position of the reproduced image 35 of the scattering plate obtained by the illumination hologram recording medium 45. The size of the spatial light modulator 80 is preferably set to be approximately the same as the size of the reproduced image 35 of the scattering plate. The example shown in FIG. 18 is an example in which the spatial light modulator 80 is disposed so as to completely overlap the position where the reproduced image 35 is formed.

  As the spatial light modulator 80, for example, a transmissive liquid crystal display can be used. Since the liquid crystal display can display an arbitrary image in accordance with the given image data, the liquid crystal display has a display hologram recording medium 75 used in the basic embodiment shown in FIG. If the recorded interference fringe pattern is displayed, an optical function equivalent to that of the display hologram recording medium 75 can be obtained. In other words, the reproduction light of the image of the scattering plate obtained from the illumination hologram recording medium 45 is used as the reproduction illumination light, and the function of forming a three-dimensional hologram reproduction image FF based on the given image data is achieved.

  In this stereoscopic image display apparatus, a control device 200 and an image data storage unit 250 are further provided as components for driving the spatial light modulator 80. The image data storage unit 250 is a component that stores, as image data, a hologram for reproducing a stereoscopic image to be displayed, and can be configured by, for example, a hard disk device for a computer. On the other hand, the control device 200 is a unit that performs overall control of the stereoscopic image display device, and can be configured by a dedicated digital circuit or a computer incorporating a dedicated program.

  The control device 200 performs supply control for supplying the image data read from the image data storage unit 250 to the spatial light modulator 80, and also provides an operation control signal (a signal for performing power ON / OFF control) to the coherent light source 50. Further, a control for giving a scanning control signal to the light beam scanning device 60 is performed. As described above, the control device 200 has the function of controlling the supply of image data to the spatial light modulator 80 and the function of performing the scanning control of the light beam scanning device 60. It becomes possible. By performing this synchronization control, it is possible to solve the problem of “blurred reproduction image FF” of the basic embodiment described in §3.

  In the basic embodiment described in §3, the reason that the problem of “blurred reproduced image FF” occurs is that, as described above, the light beam scanning device 60 uses the light beam L60 in a specific irradiation point P (recording process). This is because the original correct hologram reproduction image FF is displayed only at the time of irradiation to the irradiation point. For example, in the case of the stereoscopic image display device shown in FIG. 15, the display hologram recording medium 75 uses the diffracted light L45 (t1) from the irradiation point P (t1) as the reference light Lref as shown in FIG. 15, the original hologram reproduction image FF (t1) is obtained at time t1 when the diffracted light L45 (t1) from the irradiation point P (t1) is given as reproduction illumination light, as shown in FIG. As shown in FIG. 16, at the time point t2 when the diffracted light L45 (t2) from the irradiation point P (t2) is provided as the reproduction illumination light, the reproduced image FF (t2) to be formed is formed. ) Is not a correct hologram reproduction image.

  In other words, as shown in FIG. 16, the original correct hologram reproduction image FF (t2) is formed at the time t2 when the diffracted light L45 (t2) from the irradiation point P (t2) is given as the reproduction illumination light. For this purpose, as the hologram recording medium 75 for display, as shown in FIG. 17, a hologram in which the original image F is recorded using the diffracted light L45 (t2) from the irradiation point P (t2) as the reference light Lref is used. That's fine.

  In the spatial light modulator 80 such as a liquid crystal display, the contents of the hologram formed on the modulation surface can be changed by changing the image data to be given. Therefore, different image data is prepared for each irradiation point. In synchronism with the scanning of the light beam scanning device 60, synchronous control for giving the corresponding image data to the spatial light modulator 80 becomes possible.

  For example, in the example shown in FIG. 18, when the light beam scanning device 60 irradiates the irradiation point P (t1) with the light beam L60 (t1) at time t1, the spatial light modulator 80 stores the image data PIC. (T1) is given, and at time t2, when the light beam scanning device 60 irradiates the irradiation point P (t2) with the light beam L60 (t2), the spatial light modulator 80 receives the image data PIC (t2). May be performed such that the synchronization control is given. Here, the image data PIC (t1) is image data for forming a hologram so that a correct reproduced image FF is formed when the spatial light modulator 80 is irradiated with the diffracted light L45 (t1). The image data PIC (t2) is image data for forming a hologram so that a correct reproduced image FF is formed when the spatial light modulator 80 is irradiated with the diffracted light L45 (t2).

  Such image data can be created in advance by computer simulation. For example, the image data PIC (t1) in the above example can be calculated as image data indicating interference fringes formed on the light receiving surface of the photosensitive medium 70 in an optical arrangement state as shown in FIG. Similarly, the image data PIC (t2) in the above example can be calculated as image data indicating interference fringes formed on the light receiving surface of the photosensitive medium 70 in an optical arrangement state as shown in FIG. .

  Actually, a plurality of N irradiation points are set in advance on the illumination hologram recording medium 45, and the light beam scanning device 60 performs scanning so that the light beams are sequentially irradiated to the plurality of N irradiation points. N image data respectively corresponding to the plurality of N irradiation points may be obtained in advance and stored in the image data storage unit 250. That is, the image data storage unit 250 stores a plurality of N types of image data corresponding to a plurality of N types of irradiation points, and the i-th (1 ≦ i ≦ N) image data PIC (ti ) Is a hologram that forms a hologram reproduction image of a stereoscopic image to be displayed at a predetermined position when the illumination light for reproduction from the i-th irradiation point P (ti) is given to the spatial light modulator 80. The image data may be set.

  When a stereoscopic image is actually displayed, the control device 200 gives a scanning control signal to the light beam scanning device 60 so that the light beam L60 is sequentially irradiated to a plurality of N irradiation points. The N-th image data is sequentially applied to the spatial light modulator 80, and the i-th irradiation point P (ti) is being scanned by the light beam scanning device 60 to irradiate the light beam. The synchronization control may be performed so that the image data PIC (ti) is supplied to the spatial light modulator 80.

  In addition, if image data composed of a moving image is prepared in the image data storage unit 250, a stereoscopic image can be displayed as a moving image. In that case, the individual image data is formed by reference light from a specific irradiation point that receives scanning of a light beam at a specific time and object light from a specific original image to be displayed at the specific time. What is necessary is just to make it image data which shows the interference fringe pattern to be performed.

  The spatial light modulator 80 used in the present invention is not limited to the transmissive liquid crystal display as in the above example, and modulates the incident light to a desired shape at each position in the space. Any element may be used as long as the element has a function of emitting light. For example, a transmissive LCOS (Liquid Crystal On Silicon) element may be used as the spatial light modulator 80. Alternatively, a reflective liquid crystal display or a reflective LCOS (Liquid Crystal On Silicon) element can be used (in this case, the position of the viewpoint E is opposite to the example shown in FIG. The reproduced image FF is formed as a virtual image on the right side of the spatial light modulator 80). When using reflected light, a MEMS element such as DMD (Digital Micromirror Device) can be used as the spatial light modulator 80.

<<< §6. Modified example of practical embodiment >>>
Here, some modifications of the practical embodiment described in §5 will be described.

<§6-1: Modification suitable for downsizing>
FIG. 19 is a diagram showing an overall configuration of a stereoscopic image display apparatus according to a modified example in which the practical embodiment shown in FIG. 18 is further miniaturized. The difference from the apparatus shown in FIG. 18 is that an optical axis Z drawn in the horizontal direction of the figure is defined, and on this optical axis Z, a light beam scanning device 60, an illumination hologram recording medium 45, a spatial light modulator. (Liquid crystal display) 80, the viewpoint E is arranged in a line. The scanning base point B of the light beam scanning device 60 is located on the optical axis Z, and the illumination hologram recording medium 45 is arranged so that its light modulation surface is perpendicular to the optical axis Z. As described above, since the main components are arranged on the optical axis Z, the overall size of the apparatus can be reduced. The spatial light modulator 80 is disposed at a position where a reproduced image of the scattering plate reproduced by the illumination hologram recording medium 45 is formed.

  As described above, the modification shown in FIG. 19 is obtained by slightly changing the arrangement of each component of the apparatus shown in FIG. 18, and there is no change in the function of each component. However, with respect to the illumination hologram recording medium 45, since the incident angle of the light beam L60 emitted from the light beam scanning device 60 is different, the recorded holograms are also slightly different. That is, when attention is paid to the positional relationship between the scanning base point B and the hologram recording medium 45 for illumination, in the case of the apparatus shown in FIG. In the case of the apparatus shown, the scanning base point B is arranged on the central axis (optical axis Z) of the medium 45.

  As described above, the hologram recording medium 45 for illumination shown in FIG. 18 is obtained by recording the image of the scattering plate 30 on the photosensitive medium 40 as a hologram by the recording process shown in FIG. The convergence point C of the reference light Lref shown in FIG. 5 corresponds to the scanning base point B shown in FIG. On the other hand, the illumination hologram recording medium 45 shown in FIG. 19 is obtained by recording the image of the scattering plate 30 on the photosensitive medium 40 as a hologram by the recording process shown in FIG. That is, on the photosensitive medium 40, interference fringes between the light L30 (object light Lobj) from the scattering plate 30 and the reference light Lref are recorded. Here, the convergence point C of the reference light Lref shown in FIG. 20 corresponds to the scanning base point B shown in FIG.

  18 and the apparatus shown in FIG. 19 have the same basic principle for scanning the light beam L60. That is, in any case, the light beam scanning device 60 bends the light beam L50 emitted from the coherent light source 50 at a predetermined scanning base point B, and irradiates the illumination hologram recording medium 45 with the bent light beam L60. In addition, by changing the bending mode of the light beam with time, scanning is performed in which the irradiation position of the bent light beam L60 on the illumination hologram recording medium 45 is changed with time. Moreover, in any case, the illumination hologram recording medium 45 uses the reference light Lref that converges to the specific convergence point C (or may be the reference light that diverges from the specific convergence point C). Is recorded as a hologram, and the light beam L60 is scanned with the convergence point C as the scanning base point B.

  More specifically, in any case, the illumination hologram recording medium 45 may be a reference beam (or a diverging reference beam) that converges three-dimensionally along the side surface of the cone having the convergence point C as a vertex. ), The image of the scattering plate 30 is recorded. The reason why the image of the scattering plate 30 is recorded using the reference light along the side surface of the cone with the convergence point C as the apex is that the illustrated light beam scanning device 60 has the cone with the scanning base point B as the apex. This is because it has a function of emitting the light beam L60 in a direction along the side surface.

  The optical path indicated by the alternate long and short dash line in FIG. 19 indicates the optical path of the light at time t1. In other words, the light beam L60 (t1) bent by the light beam scanning device 60 is applied to the irradiation point P (t1) of the illuminating hologram recording medium 45, and the diffracted light therefrom (to reproduce the image of the scattering plate 30). Of reproduction light) is provided to the spatial light modulator 80 as reproduction illumination light. At this time, predetermined image data is given to the spatial light modulator 80 from the control device 200, and the reproduced image FF is observed when viewed from the viewpoint E by the diffraction function by the hologram corresponding to the image data. Will be.

  On the other hand, the two-dot chain line optical path in FIG. 19 indicates the optical path of light at time t2. That is, the light beam L60 (t2) bent by the light beam scanning device 60 is irradiated to the irradiation point P (t2) of the illumination hologram recording medium 45, and the diffracted light (from which the image of the scattering plate 30 is reproduced). Of reproduction light) is provided to the spatial light modulator 80 as reproduction illumination light. At this time, predetermined image data is given to the spatial light modulator 80 from the control device 200, and the reproduced image FF is observed when viewed from the viewpoint E by the diffraction function by the hologram corresponding to the image data. Will be.

  In FIGS. 5 and 20, as a process of creating the holographic recording medium 45 for illumination, the optical medium in which the photosensitive medium 40 is actually irradiated with light and the interference fringes generated there are fixed by the chemical change of the photosensitive medium 40. In this example, the illumination hologram recording medium 45 may be created by the CGH method.

  FIG. 21 is a side view showing the principle of creating the illumination hologram recording medium 45 by the CGH method, and shows a method of simulating the optical phenomenon shown in FIG. 20 on a computer. 21 corresponds to the real scattering plate 30 shown in FIG. 20, and the virtual recording surface 40 ′ shown in FIG. 21 corresponds to the real photosensitive medium 40 shown in FIG. Corresponds to the light receiving surface. The illustrated object light Lobj is virtual light emitted from the virtual scattering plate 30 ', and the illustrated reference light Lref is virtual light having the same wavelength as the object light Lobj. The point that the reference light Lref is light that converges at the convergence point C is exactly the same as the method described so far. At each point on the recording surface 40 ', information on interference fringes between the virtual object light Lobj and the reference light Lref is calculated.

  As the virtual scattering plate 30 ′, for example, a fine three-dimensional model represented by polygons or the like can be used. Here, however, a large number of point light sources D are arranged in a grid on a plane. A simple model is used. FIG. 22 is a front view of the virtual scattering plate 30 ′ shown in FIG. 21, and small white circles indicate the point light sources D, respectively. As shown in the figure, a large number of point light sources D are arranged in a grid pattern with a horizontal pitch Pa and a vertical pitch Pb. The pitches Pa and Pb are parameters that determine the surface roughness of the scattering plate.

  The inventor of the present application calculates the information of interference fringes generated on the recording surface 40 ′ by setting the pitches Pa and Pb of the point light sources D to about 10 μm, respectively. A pattern was formed to produce a surface relief type CGH. And when this CGH was used as the hologram recording medium 45 for illumination, the favorable illumination environment which suppressed the speckle was obtained.

<§6-2: Modified example with lens added>
So far, the configuration example of the stereoscopic image display apparatus according to the practical embodiment of the present invention has been described with reference to FIGS. 18 and 19. A feature of these embodiments is that a spatial light modulator 80 such as a liquid crystal display is used instead of the display hologram recording medium 75, and a hologram reproduction image is generated by light modulation using the spatial light modulator 80. In the point.

  However, considering the provision of a stereoscopic image display device having the configuration shown in FIGS. 18 and 19 as a mass-produced industrial product, at present, spatial light modulation with sufficient performance at a price that is profitable. It is difficult to procure the vessel 80. For example, the cheapest mass-produced spatial light modulator 80 includes a liquid crystal display, and the pixel pitch of a general liquid crystal display currently on the market is about 32 μm. So it cannot be said that it has sufficient resolution. When a hologram is recorded on a photosensitive medium by an optical method, a fine interference fringe pattern having a resolution in the order of the wavelength of light can be recorded. However, a liquid crystal display having a pixel pitch of about 32 μm cannot display such a fine interference fringe pattern.

  Of course, there are some special displays for use in special applications with finer pixel pitches, but such special displays are not mass-produced and are very expensive, so they are mass-produced. It is not suitable for use in the stereoscopic image display apparatus. Therefore, in order to mass-produce the stereoscopic image display device according to the embodiment shown in FIGS. 18 and 19 at a commercial level, there is no choice but to use a general-purpose liquid crystal display.

  Consider a case where light having a wavelength λ is incident on a liquid crystal display having a pixel pitch d and the light is diffracted by interference fringes displayed on the display. Of course, the resolution of the displayed interference fringes is determined by the pixel pitch d. In this case, an expression “2d = mλ / (sin θout−sin θin)” is established between the incident angle θin and the exit angle θout. Here, m is the order of the diffracted light. As a result, the difference between the incident angle θin and the exit angle θout, that is, the diffraction angle of light increases as the pixel pitch d decreases. Conversely, if the pixel pitch d is large, a sufficient diffraction angle cannot be obtained, and incident light cannot be diffracted greatly.

  Therefore, in reality, when a general liquid crystal display having a pixel pitch of about 32 μm is used as the spatial light modulator 80, a sufficient diffraction angle cannot be ensured. For example, in the case of the example shown in FIG. 19, the reproduction illumination light (light indicated by the one-dot chain line on the upper side) from the irradiation point P (t1) toward the upper end of the spatial light modulator 80 is directed toward the viewpoint E at time t1. Although it may be possible to diffract the light, it is diffracted so that the reproduction illumination light (light indicated by the lower one-dot chain line) directed from the irradiation point P (t1) toward the lower end of the spatial light modulator 80 is directed toward the viewpoint E. It is difficult to make it.

  After all, when a general liquid crystal display having a pixel pitch of about 32 μm is used as the spatial light modulator 80 to form a stereoscopic image display device of the type shown in FIG. 18 or FIG. 19, sufficient diffraction capability cannot be expected. When observed from the viewpoint E, a sufficient viewing angle cannot be obtained, and the entire display cannot be used effectively. In order to enlarge the viewing angle, the illumination hologram recording medium 45 and the spatial light modulator 80 are sufficiently separated (in the example shown in FIG. 19, the distance d1 between the position a and the position b is set sufficiently large). The reproduction illumination light incident on the spatial light modulator 80 may be made to be close to a parallel light beam, but it is difficult to set the distance d1 sufficiently large in practice. On the other hand, in order to effectively use the entire surface of the display, the viewpoint E is set at a position sufficiently away from the spatial light modulator 80 (in the example shown in FIG. 19, the distance d2 between the position b and the position c is sufficiently large). Setting) and using only the diffracted light from the vicinity of the optical axis Z of the liquid crystal display to form the reconstructed image FF is necessary. The corner will be further reduced.

  In order to solve such a problem, an optical system having a function of condensing light in the vicinity of the viewpoint E where a stereoscopic image is supposed to be observed is replaced with an illumination hologram recording medium 45 and a spatial light modulator. It may be arranged between 80. By inserting such an optical system, a sufficient viewing angle can be secured during observation. FIG. 23 is a side view showing an example in which a set of convex lenses 110 is added as an optical system in the stereoscopic image display apparatus shown in FIG. The convex lens 110 is a lens having an optical axis Z that is a perpendicular line from the viewpoint E to the recording surface of the illumination hologram recording medium 45, and is disposed between the illumination hologram recording medium 45 and the spatial light modulator 80. Yes.

  When the convex lens 110 is inserted between the illumination hologram recording medium 45 and the spatial light modulator 80, the reproduction illumination light emitted from one irradiation point of the illumination hologram recording medium 45 is condensed by the convex lens 110, and the viewpoint The light is condensed in the vicinity of E. The optical path drawn by the alternate long and short dash line in FIG. 23 indicates the optical path when the reproduction illumination light emitted from the irradiation point P (t1) travels without being diffracted by the spatial light modulator 80 at time t1. Is. In the example shown in the figure, the reproduction illumination light indicated by the alternate long and short dash line is condensed by the convex lens 110 and converges on the condensing point E1 in the vicinity of the viewpoint E. On the other hand, the optical path drawn with a two-dot chain line in FIG. 23 is the case where the reproduction illumination light emitted from the irradiation point P (t2) travels without being diffracted by the spatial light modulator 80 at time t2. It shows the optical path. In the example shown in the figure, the reproduction illumination light indicated by the two-dot chain line is condensed by the convex lens 110 and converges on the condensing point E2 near the viewpoint E.

  Of course, actually, the illumination light for reproduction is diffracted by the spatial light modulator 80, and a part of the illumination light travels to the retina in the eyeball placed at the viewpoint E to form a reproduction image FF. The optical paths of the one-dot chain line and the two-dot chain line shown in the figure indicate the path of light when such diffraction is not performed. This shows the course of the light. Therefore, the condensing points E1 and E2 are the condensing points of the 0th-order diffracted light at times t1 and t2.

  As described above, if the convex lens 110 is inserted, the condensing points E1 and E2 of the 0th-order diffracted light are formed in the vicinity of the viewpoint E. Therefore, the light necessary for obtaining the reproduced image FF is the viewpoint E. The diffraction angle necessary for diffracting to the position can be kept relatively small. Therefore, the reproduced image FF can be observed from the position of the viewpoint E with a sufficient viewing angle even if the diffraction capability of the spatial light modulator 80 is not sufficient.

  In order to enhance the light condensing effect of the convex lens 110, the distance between the hologram recording medium 45 for illumination and the convex lens 110 (position a and position b in FIG. 23) when the focal length of the convex lens 110 is f. The distance between the convex lens 110 and the viewpoint E (the distance between the position b and the position c in FIG. 23) is preferably set to 2f. With such an arrangement, light from the irradiation point P at the position a (light from the point light source) can be collected at the condensing point at the position c, so that an ideal condensing effect can be obtained. become. Of course, even if the convex lens 110 is arranged at a position other than the above, a condensing effect near the viewpoint E can be obtained, but if the above arrangement is adopted, an optimum condensing effect can be obtained.

<§6-3: Modified example with two pairs of lenses>
Of course, it is also possible to focus on the viewpoint E using a plurality of sets of convex lenses. FIG. 24 is a side view showing a modification in which two sets of lenses are added. That is, in this modification, the two sets of lenses 120 and 130 having the optical axis Z as a perpendicular line drawn from the viewpoint E to the recording surface of the illumination hologram recording medium 45 include the illumination hologram recording medium 45 and the spatial light modulator 80. The reproduction image FF is observed between these two sets of lenses.

  In addition, in the illustrated modification, the focal length of the first convex lens 120 disposed near the illumination hologram recording medium 45 is f1, and the second convex lens 130 disposed near the spatial light modulator 80 is used. Is set to f1, and the distance between the illumination hologram recording medium 45 and the first convex lens 120 (the distance between the position a and the position b in FIG. 24) is set to f1. The distance from the viewpoint E (the distance between the position c and the position d in FIG. 24) is set to f2.

  Of course, although the two sets of convex lenses 120 and 130 are not necessarily arranged at the positions as in the above example, a light collecting effect can be obtained. However, if the arrangement as in the above example is taken, from the irradiation point P at the position a. Of the light (light from the point light source) can be made into a parallel light flux by the first convex lens 120, and further, this parallel light flux can be collected at the condensing point at the position d by the second convex lens 130. The position of the condensing point can be freely set.

  For example, at time t1, as shown by a one-dot chain line in FIG. 24, the reproduction illumination light L45 (t1) emitted from the irradiation point P (t1) is converted into a parallel light beam L120 (t1) by the first convex lens 120. Then, the light enters the second convex lens 130. The second convex lens 130 condenses this parallel light beam at a condensing point E1 on the position d. Similarly, at time t2, as indicated by a two-dot chain line in FIG. 24, the reproduction illumination light L45 (t2) emitted from the irradiation point P (t2) is converted into a parallel light beam L120 (t2) by the first convex lens 120. And is incident on the second convex lens 130. The second convex lens 130 condenses this parallel light beam at a condensing point E2 on the position d.

  Here, since the light transmitted between the position b and the position c is always a parallel light flux, there is no restriction on the length of the distance d3, and the second convex lens 130 is set to whatever value the distance d3 is set to. The function of condensing the incident parallel light beam at a predetermined condensing point can be achieved. Therefore, for example, when the position of the viewpoint E is to be moved further to the right by δ from the illustrated position d, the second convex lens 130 is moved to the right by δ, and the distance between the two sets of lenses is d3 + δ. You only have to set it. Thus, if the lens arrangement of the above example is taken, the position of the condensing point can be set freely, and the degree of freedom of the position of the viewpoint E can be increased.

  Note that the spatial light modulator 80 shown in FIGS. 18 and 19 is used for the light condensing effect by adding one set of convex lenses 110 and the light condensing effect by adding two sets of convex lenses 120 and 130. The present invention is not limited to application to the embodiment, and is also effective when applied to an embodiment using a display hologram recording medium 75 as shown in FIG. In addition, the optical system for obtaining such a light collecting effect is not limited to a convex lens, and a holographic optical element (HOE) or a diffractive optical element (DOE) may be used.

<<< §7. Elimination of zero-order diffracted light >>>
An object of the present invention is to efficiently and sufficiently suppress the generation of speckles when a stereoscopic image recorded as a hologram is reproduced using coherent light and displayed. This object is achieved by introducing a technique of scanning a light beam made of coherent light on the illumination hologram recording medium 45 on which the image of the scattering plate is recorded. This is because the incident angle of the reproduction illumination light incident on the display hologram recording medium 75 or the spatial light modulator 80 is temporally fluctuated by light beam scanning, and speckle generation factors are temporally dispersed. is there.

  However, the speckles observed from the viewpoint E include not only speckles generated on the surface of the display hologram recording medium 75 or the spatial light modulator 80 but also speckles (light source) originally present in the reproduction illumination light. Speckle on the side) is also included.

  For example, consider the optical path shown in FIG. FIG. 25 is a diagram showing the incident position of the 0th-order diffracted light near the viewpoint in the modification shown in FIG. 23 (an example in which one set of convex lenses 110 is inserted), and shows the light path at a certain time t0. ing. That is, the light beam L50 generated by the coherent light source 50 is bent into the light beam L60 (t0) by the light beam scanning device 60 at the time t0, and is centered on the illumination hologram recording medium 45 (on the optical axis Z). The irradiation point P (t0) located is irradiated. The diffracted light L45 (t0) emitted from the irradiation point P (t0) spreads in a conical shape with the optical axis Z as the central axis and enters the convex lens 110 as shown in the figure. When the light is condensed by the convex lens 110 and is not diffracted by the spatial light modulator 80, the light converges to the light condensing point E0 as indicated by a one-dot chain line in the figure. This condensing point E0 is nothing but the position of the viewpoint E on the optical axis Z-axis.

  In the end, the optical path indicated by the alternate long and short dash line in FIG. 25 means that the 0th-order diffracted light ( That is, the light traveling straight without being diffracted by the spatial light modulator 80 is condensed at the position of the viewpoint E (the condensing point E0). This means that if the observer is observing with the pupil at the position of the viewpoint E, the 0th-order diffracted light from the spatial light modulator 80 is incident on the inside of the pupil. , Which means that 0th-order diffracted light is visible. In other words, the observer looks into the light source from the front and sees speckles originally contained in the light source.

  On the other hand, as shown in FIG. 23, at time t1, in a state where the light beam L60 (t1) is scanning the position of the irradiation point P (t1), the 0th-order diffracted light is condensed at the condensing point E1, and time t2 In the state where the light beam L60 (t2) is scanning the position of the irradiation point P (t2), the 0th-order diffracted light is condensed at the condensing point E2. In the example shown in the figure, these condensing points E1 and E2 are slightly deviated from the viewpoint E. Therefore, when the observer observes with the pupil placed at the position of the viewpoint E, the light from the spatial light modulator 80 Zero-order diffracted light does not enter the interior of the pupil. In FIG. 25, in order to avoid the figure from becoming complicated, the optical paths from the irradiation points P (t1) and P (t2) are not shown, and only the positions of the condensing points E1 and E2 are shown.

  Eventually, in FIG. 25, if the light beam L60 is being applied to the irradiation points P (t1) and P (t2), the condensing points E1 and E2 deviate from the viewpoint E. You won't see it, and you won't see the speckles contained in the light source. However, when the irradiation point P (t0) is being irradiated, the condensing point E0 is at the position of the viewpoint E, so that the 0th-order diffracted light enters the eyes of the observer and speckles included in the light source are present. You will see it. Therefore, in order to prevent the speckle on the light source side from entering the eyes of the observer, it is only necessary to prevent the 0th-order diffracted light from the spatial light modulator 80 from entering the observer's pupil. For this purpose, the light beam may be scanned while avoiding the irradiation point P (t0) where the 0th-order diffracted light enters the inside of the observer's pupil.

  FIG. 26 is a diagram showing the relationship between the irradiation point of the light beam L60 on the illumination hologram recording medium 45 shown in FIG. 26A is a plan view of the illuminating hologram recording medium 45 shown in FIG. 25, and X indicates the position of each irradiation point. On the other hand, FIG. 26B shows a plan view of the light receiving surface when a light receiving surface perpendicular to the paper surface is defined at the position c shown in FIG. 25, and the circle EE is placed on the light receiving surface. A virtual pupil contour is shown. When the condensing point of the 0th-order diffracted light by the convex lens 110 is located inside the pupil contour EE, the 0th-order diffracted light enters the pupil and reaches the retina so that the speckles on the light source side can be seen by the observer's eyes. Become.

  Each irradiation point P (t0), P (t1), P (t2), P (t11), P (t12), P (t13), and P (t14) shown in FIG. b) correspond to the respective condensing points E0, E1, E2, E11, E12, E13, E14. That is, when the light beam L60 is applied to the irradiation points P (t0) to P (t14) on the illumination hologram recording medium 45, the 0th-order diffracted light is condensed at the corresponding condensing points E0 to E14. To do. Here, on the premise that such a correspondence is obtained between the position of each irradiation point and the position of each condensing point, light is emitted so that the irradiation point draws a circle on the illumination hologram recording medium 45. Consider the case where the beam scanning device 60 scans the light beam L60 along a conical surface.

  For example, when the light beam L60 is scanned along the circular scanning trajectory T indicated by the broken line in FIG. 26A, the 0th-order diffracted light moves along the pupil contour EE shown in FIG. Become. Therefore, in order to avoid the 0th-order diffracted light from entering the inside of the pupil, when scanning the light beam L60 on the illumination hologram recording medium 45, the circular scanning trajectory T indicated by the broken line in FIG. In this case, the inner area may be determined as a scanning prohibition area, and the light beam may be scanned while avoiding the scanning prohibition area.

  Here, considering only the point of “avoiding the 0th-order diffracted light from entering the inside of the pupil”, the scanning trajectory of the light beam L60 on the illumination hologram recording medium 45 may be set as far as possible. For example, in the example shown in FIG. 26 (a), when the light beam L60 is scanned along a circular scanning trajectory T indicated by a broken line, it is considered that the spot of the light beam has a predetermined area. There is a possibility that part of the next-order diffracted light enters the inside of the pupil. Therefore, if the diameter of the circular scanning trajectory T is set larger, and a circular scanning trajectory passing through points located outside such as the irradiation points P (t1) and P (t2) is set, for example, the next time. It is possible to completely prevent the folding light from entering the inside of the pupil.

  However, when scanning is performed along the outer scanning trajectory in this way, there is a possibility that the reproduced image is adversely affected. The reason is that, as described above, the spatial light modulator 80 such as a liquid crystal display has a limited diffraction capability, and thus a sufficient diffraction angle cannot be secured. Hereinafter, this point will be described in detail.

  FIG. 27 is a plan view showing the condensing position of the 0th-order diffracted light and the incident range of the 1st-order diffracted light in the stereoscopic image display device shown in FIG. This plan view shows a plan view of the light receiving surface when a light receiving surface perpendicular to the paper surface is defined at a position c shown in FIG. 25, and a point Z drawn at the center corresponds to the optical axis Z. A solid circle EE indicates the outline of a virtual pupil placed on the light receiving surface, and a broken circle G1 indicates the locus of the condensing point of the 0th-order diffracted light.

  As described above, when the light beam is scanned along the scanning trajectory T indicated by the broken-line circle in FIG. 26A, the condensing points E11 to E14 of the 0th-order diffracted light are pupils indicated by the solid-line circle in FIG. Move along the contour EE. Therefore, the trajectory G1 indicated by the broken circle in FIG. 27 is obtained when the beam is scanned on the medium 45 along the scanning trajectory having a diameter larger than the circular scanning trajectory T shown in FIG. This is the locus of the light collecting point. Since the condensing points E11 to E14 on the locus G1 are sufficiently separated from the contour EE of the pupil, the 0th-order diffracted light does not enter the inside of the pupil.

  However, considering the incident position of the 1st-order diffracted light that plays a role in forming the hologram reproduction image, the 1st-order diffracted light enters the inside of the pupil as the locus G1 of the focusing point of the 0th-order diffracted light is further away from the contour EE of the pupil. It turns out that it becomes difficult. First-order diffracted light is light obtained by bending zero-order diffracted light in a predetermined diffraction direction by a predetermined diffraction angle, and the diffraction direction and diffraction angle are determined by a hologram (interference fringe pattern) on the spatial light modulator 80. . However, as described above, the upper limit of the diffraction angle depends on the resolution of the hologram (interference fringe pattern), and when a liquid crystal display or the like is used as the spatial light modulator 80, a sufficient diffraction angle should be secured from the limitation of the resolution. I can't.

  A circle indicated by an alternate long and short dash line in FIG. 27 indicates a diffractable region of the first-order diffracted light, and the diameter thereof is determined based on the resolution of the spatial light modulator 80. For example, the region C11 is a circle centered on the condensing point E11 of the 0th-order diffracted light, which is the time when the light beam scanning is performed such that the 0th-order diffracted light is condensed on the condensing point E11. 3 shows the reachable range of the first-order diffracted light bent by the spatial light modulator 80. Of course, the actual arrival point of the first-order diffracted light is determined by the hologram (interference fringe pattern) formed on the spatial light modulator 80. However, since the resolution of the spatial light modulator 80 is limited, it is out of the range of the region C11. The first-order diffracted light does not reach the center. In other words, the spatial light modulator 80 does not have the ability to diffract the light traveling toward the condensing point E11 to the outside of the region C11.

  In the example shown in FIG. 27, the diffractive region C11 of the first-order diffracted light cannot completely cover the inside of the pupil contour EE, and a part that cannot be completely covered is generated. This means that a region where the 1st-order diffracted light does not reach the inside of the pupil is generated at the time when the light beam scanning is performed such that the 0th-order diffracted light is collected at the condensing point E11. The same applies to the diffractable regions C12, C13, and C14 shown in the figure. In either case, a region where the first-order diffracted light does not reach the inside of the pupil is generated. This means that the reproduced image formed on the retina is missing. Of course, the missing portion of the reproduced image also varies with time due to the scanning of the light beam, so if averaged over time, a reproduced image having no defect can be observed, but a partial luminance difference occurs in the reproduced image. Inevitable.

  From the viewpoint of preventing such a lack of a reproduced image, the scanning trajectory of the light beam L60 on the illumination hologram recording medium 45 may be set as much as possible inside. For example, consider the example shown in FIG. This FIG. 28 is also a plan view showing the condensing position of the 0th-order diffracted light and the incident range of the 1st-order diffracted light, as in FIG. G2 indicates the locus of the condensing point of the 0th-order diffracted light. Here, the locus G2 shown in FIG. 28 is a circle having a smaller diameter than the locus G1 shown in FIG. In order to obtain such a locus G2, the diameter of the circular scanning orbit of the light beam L60 on the illumination hologram recording medium 45 may be made smaller.

  Dotted line circles C11 to C14 shown in FIG. 28 indicate diffractable regions of the first-order diffracted light as in FIG. Since the resolution of the spatial light modulator 80 remains unchanged, the diameters of the circles C11 to C14 shown in FIG. 28 are naturally equal to the diameters of the circles C11 to C14 shown in FIG. However, since the diameter of the locus G2 of the condensing points E11 to E14 is reduced, the diffractable regions C11 to C14 sufficiently cover the inside of the pupil contour EE. This means that the first-order diffracted light can be delivered to the entire area inside the pupil by the diffraction capability of the spatial light modulator 80. Therefore, in the example shown in FIG. 28, the reproduced image is not chipped, and a partial luminance difference is not generated in the reproduced image.

  In the end, the scanning trajectory of the light beam L60 on the illumination hologram recording medium 45 may be set as far as possible from the viewpoint of “avoiding the 0th-order diffracted light from entering the inside of the pupil”. From the viewpoint of “delivering to an arbitrary position inside the pupil and preventing a missing portion of the reproduced image”, it should be set as much as possible inside. Therefore, in practice, an appropriate scanning trajectory may be set by balancing the two. The diffracted light includes multi-order diffracted light such as −1st order, 2nd order, and −2nd order. However, since these diffracted lights have lower intensity than the 0th order and 1st order diffracted light, practically, There is no problem even if the behavior of these multi-order diffracted lights is ignored.

  FIG. 29 is a plan view showing an ideal scanning trajectory T ′ of the light beam L60 with respect to the illumination hologram recording medium 45. FIG. As described above, in order to avoid speckle generation on the light source side during observation, it is necessary to prevent the 0th-order diffracted light from entering the inside of the pupil. For this purpose, it is assumed that a stereoscopic image is observed. When the virtual pupil is arranged at the position of the viewpoint E, the condition that “the 0th-order diffracted light from the spatial light modulator 80 (the same applies to the display hologram recording medium 75) is incident on the inside of the pupil”. The “irradiation range of the light beam L60 on the illuminating hologram recording medium 45” that satisfies the above condition is determined as a scanning prohibited area, and the light beam scanning device 60 scans the light beam while avoiding the scanning prohibited area. . Note that there are individual differences in the size of the pupil, and the open / close state of the pupil changes depending on the surrounding lighting environment. Therefore, the average pupil diameter (for example, diameter 4) of the average person is used as the virtual pupil diameter. It is sufficient to adopt about .5 mm).

  The irradiation point P (t0) shown in FIG. 29 is a point on the optical axis Z-axis, and the circular scanning trajectory T drawn with a broken line around the irradiation point P (t0) is the scanning trajectory T in FIG. is there. Therefore, the area inside the scanning trajectory T is a scanning prohibited area. In other words, when the light beam L60 is irradiated into this scanning prohibited area, the 0th-order diffracted light enters the inside of the pupil. However, since the light beam L60 is not a geometric line but a beam having a width, when the illumination hologram recording medium 45 is irradiated, a spot A having a certain area around the irradiation point P is formed. Is done. Therefore, in the example shown in FIG. 29, a circular scanning trajectory T ′ positioned outside the scanning trajectory T by a distance corresponding to the radius of the spot A is set, and the irradiation point moves along the scanning trajectory T ′. In this way, the light beam L60 is scanned.

  Of course, beam scanning may be performed along a trajectory passing further outside the scanning trajectory T ′, and the scanning trajectory is not necessarily a circular trajectory. From the viewpoint of “delivering to an arbitrary position inside the pupil and preventing the lack of a reproduced image”, it is preferable to set the scanning trajectory as inside as possible. Therefore, in practice, the light beam scanning device 60 has a circular shape outside the scanning prohibited area so that the spot A of the light beam L60 does not enter the scanning prohibited area (inside the circle T shown in FIG. 29) during scanning. It is preferable to set the scanning trajectory T ′ and perform scanning so that the central axis of the light beam L60 moves around the scanning trajectory T ′.

  The beam scanning along the scanning trajectory T ′ may be continuous scanning (scanning in which the spot A continuously moves on the trajectory at a constant speed), or intermittent scanning (where the spot A is on the trajectory). (Scanning repeatedly moving and stationary). The example shown in FIG. 29 is an example in which twelve irradiation points P (t1) to P (t12) are set at equal intervals on a circular scanning trajectory T ′ and intermittent scanning is performed. That is, the light beam L60 is irradiated to the irradiation point P (t1) at time t1, stays for a while in a state where the spot A (t1) is formed, moves to the irradiation point P (t2) at time t2, and the spot A ( The operation is stopped for a while with t2) formed, then moved to the irradiation point P (t12) at time t12, and stopped for a while with the spot A (t12) formed. Therefore, the spot A of the light beam L60 moves while jumping sequentially from 1 o'clock to 12 o'clock on the dial of the watch.

  As described in §5, in the case of a practical embodiment using the spatial light modulator 80, the image data applied to the spatial light modulator 80 is switched in synchronization with the scanning of the light beam L60. For example, in the stereoscopic image display apparatus shown in FIG. 23, if the intermittent scanning shown in FIG. 29 is performed, 12 sets of image data PIC (t1) to PIC (t12) are prepared in the image data storage unit 250. The control device 200 may perform control to synchronize scanning by the light beam scanning device 60 and provision of image data to the spatial light modulator 80.

  FIG. 30 is a table for explaining such synchronization control. The display such as “t1” in the period column indicates each period of beam scanning. For example, “t1” in the first line indicates a period from time t1 to immediately before time t2, and the 12th line. “T12˜” indicates a period from time t12 to immediately before time t1. The operations shown in the first to twelfth rows of this table correspond to one cycle of beam scanning, and in practice, such periodic operations are repeatedly executed. In addition, the display such as “P (t1)” in the irradiation point column indicates each irradiation point shown in FIG. 29, and the display such as “A (t1)” in the spot column indicates each spot shown in FIG. Show. On the other hand, the display such as “PIC (t1)” in the image data column indicates image data provided to the spatial light modulator 80 during the period. As described above, these image data can be created in advance by computer simulation.

  The operation of the apparatus based on the table shown in FIG. 30 is as follows. First, at time t1, the light beam L60 is irradiated to the irradiation point P (t1), and is in a stationary state until just before time t2 with the spot A (t1) formed. During this period, the image data PIC (t1) is provided to the spatial light modulator 80. When a liquid crystal display is used as the spatial light modulator 80, a hologram (interference fringe pattern) corresponding to the image data PIC (t1) is displayed on the screen. The hologram is such that a correct reproduced image FF can be obtained when the light beam L60 is irradiated to the position of the irradiation point P (t1), that is, the 1 o'clock position of the dial of the watch in FIG. Yes.

  Subsequently, at time t2, the irradiation position of the light beam L60 moves to the irradiation point P (t2) and remains stationary until just before time t3 with the spot A (t2) formed. During this period, the image data PIC (t2) is provided to the spatial light modulator 80. This image data PIC (t2) is such that a correct reproduced image FF can be obtained when the light beam L60 is irradiated to the position of the irradiation point P (t2), that is, the 2 o'clock position of the clock face in FIG. This is image data for forming a simple hologram.

  Even if the shape and position of the reproduction image FF are the same, if the irradiation point of the light beam L60 is different, the incident angle of the reproduction illumination light applied to the spatial light modulator 80 is different. It will be slightly different. In the example shown in FIG. 30, different image data (holograms) are prepared for each irradiation point set at 12 locations, and control is performed to synchronize the irradiation point and image data. A correct reproduced image FF can be obtained, and blurring of the reproduced image can be prevented. In addition, since the incident angle of the reproduction illumination light irradiated on the spatial light modulator 80 varies with time, speckle noise generated on the surface of the spatial light modulator 80 can be suppressed. In addition, since light beam scanning is performed while avoiding the inside of the circle T (scan prohibited region) shown in FIG. 29, it is possible to prevent the 0th-order diffracted light from entering the inside of the pupil, and speckle noise on the light source side is reduced. It can also be prevented from being observed.

  FIG. 31 is a table showing experimental results in which the speckle reduction effect is obtained by performing the control operation as described above. In general, a method of using a numerical value called speckle contrast (unit%) as a parameter indicating the degree of speckle generated on an image to be observed has been proposed. This speckle contrast is the value obtained by dividing the standard deviation of the luminance variation that occurs on the actually observed image when the test pattern image that should have a uniform luminance distribution is displayed, by the average luminance value. A defined amount. The larger the speckle contrast value, the greater the degree of speckle occurrence on the observed image, and the spotted brightness unevenness pattern is more prominently presented to the observer. become.

  The table in FIG. 31 shows an environment in which a test pattern image that should originally have a uniform luminance distribution is observed using the stereoscopic image display device shown in FIG. 23 or a conventional stereoscopic image display device for comparison. Shows the result of measuring the speckle contrast. Measurement examples 1 to 3 are all results of using the same DPSS laser apparatus capable of emitting green laser light as the coherent light source 50. Note that the diffusion angle of the illumination hologram recording medium 45 used in Measurement Examples 2 and 3 (the maximum angle at which the reproduced image 35 of the scattering plate is desired from a point on the hologram recording medium) is set to 20 ° in any case. .

  First, as a measurement result shown as Measurement Example 1, the light beam scanning device 60 and the illumination hologram recording medium 45 in the stereoscopic image display device shown in FIG. 23 are omitted, and the light beam L50 from the coherent light source 50 is expanded by a beam expander. This is a result obtained by using a measurement system in which the parallel light flux (laser parallel light) is condensed by the convex lens 110 and irradiated to the spatial light modulator 80. More specifically, this measurement example 1 is a measurement result of speckle contrast of the plain test pattern projected on the screen by setting a screen at the position of the spatial light modulator 80. This corresponds to the speckle contrast of the illumination light incident on. In this case, as shown in the table, a result of speckle contrast of 20.1% was obtained. This is a state in which a spot-like luminance unevenness pattern can be observed quite remarkably when observed from the viewpoint E, and is an inappropriate level for appreciating a practical reproduction image.

  On the other hand, the measurement results shown as measurement examples 2 and 3 are the results of illumination using the stereoscopic image display device shown in FIG. 23 (installed at the position of the spatial light modulator 80 as in measurement example 1). Shows the speckle contrast on the screen). Here, measurement example 2 is a result of using a volume hologram produced by an optical method as illumination hologram recording medium 45, and measurement example 3 is a surface relief type as illumination hologram recording medium 45. This is a result of using CGH. In all cases, speckle contrast of less than 4% was obtained, which is a very good state in which uneven brightness patterns are hardly observable with the naked eye (generally, speckle contrast value is 5% or less). It is said that there will be no discomfort for the observer). Therefore, a practically sufficient stereoscopic image display apparatus is configured both when a volume hologram created by an optical method is used as the illumination hologram recording medium 45 and when a surface relief type CGH is used. Can do. The reason why the result of measurement example 2 (3.0%) is better than the result of measurement example 3 (3.7%) is that the resolution of the actual scattering plate 30 that is the original image is a virtual scattering plate. This is considered to be because the resolution is higher than 30 ′ (a collection of point light sources shown in FIG. 22).

  The measurement result shown as the last measurement example 4 is a result obtained by using a measurement system in which light from a green LED light source is collected by the convex lens 110 and irradiated to the spatial light modulator 80 (also this measurement result). Similarly to measurement example 1, the speckle contrast on the screen placed at the position of the spatial light modulator 80 is shown). In the first place, since the LED light source is not a coherent light source, it is not necessary to consider the problem of speckle generation. As shown in the table, a good result of speckle contrast of 4.0% was obtained. The reason why the result of Measurement Example 4 using non-coherent light is inferior to the results of Measurement Examples 2 and 3 using coherent light is considered to be due to uneven brightness in the light emitted from the LED light source.

<<< §8. Other variations >>
Here, some further modifications will be described with respect to the various embodiments and modifications described so far.

<§8-1: Modification with added half mirror>
FIG. 32 is a side view showing a modification in which a half mirror 150 is added to the modification shown in FIG. In FIG. 32, only the main optical components are shown for convenience of explanation, but actually, in addition to the illustrated components, the coherent light source 50, the control device 200, and the image data storage unit 250 are included. Provided.

  As illustrated, in this modification, a half mirror 150 having a reflecting surface inclined with respect to the optical axis Z of the convex lens 110 is disposed between the position of the viewpoint E and the spatial light modulator 80. When the half mirror 150 is arranged in this way, a part of the light that should originally reach the vicinity of the viewpoint E is reflected by the half mirror 150 and guided to the vicinity of another viewpoint E ′. In the figure, for reference, the optical path of the 0th-order diffracted light emitted from the irradiation point P (t1) is indicated by a one-dot chain line, and the optical path of the 0th-order diffracted light emitted from the irradiation point P (t2) is indicated by a two-dot chain line. is there. A part of the 0th-order diffracted light passes through the half mirror 150 and converges to the condensing points E1 and E2 near the viewpoint E, but another part is reflected by the half mirror 150 and near another viewpoint E ′. It converges to the condensing points E1 ′ and E2 ′.

  In this modification, the observer can observe from another viewpoint E ′. In this case, the observer sees the reproduced image FF ′ instead of the reproduced image FF. In addition, the reproduced image FF ′ is observed in a state where the reproduced image FF ′ overlaps the background Bk existing in a direction different from the direction in which the illumination hologram recording medium 45 is arranged. Therefore, it is possible to obtain a special effect that a stereoscopic image reproduction image FF ′ is formed on a desired background Bk.

  Note that the modification example in which the half mirror 150 is added can be applied to the embodiment using the display hologram recording medium 75 instead of the spatial light modulator 80.

<§8-2: Modified example of displaying color image>
Each of the embodiments described so far is an example of a stereoscopic image display apparatus using a monochromatic laser light source as the coherent light source 50, and a reproduced image FF displayed to an observer is a monochrome image corresponding to the color of the laser. It will be an image. However, it is desirable that a general stereoscopic image display apparatus can display a color image. Therefore, here, a configuration example of a stereoscopic image display apparatus capable of displaying a color image will be described.

(1) First Configuration Example In order to display a color image, three primary colors R (red), G (green), and B (blue) may be determined, and individual images of these primary colors may be combined and displayed. In the first configuration example shown here, a light source that generates a combined light beam obtained by time-division combining the components of the three primary colors of R, G, and B is used as the coherent light source 50 in the reproduction illumination light generation unit 100 shown in FIG. Then, a method of irradiating the spatial light modulator 80 with the reproduction illumination light including the three primary color components is adopted.

  FIG. 33 is a configuration diagram showing an example of such a coherent light source 50. This apparatus has a function of generating a white light beam by combining three primary colors of red, green, and blue. That is, the red laser beam L (R) generated by the red laser light source 50R and the green laser beam L (G) generated by the green laser light source 50G are synthesized by the dichroic prism 15, and further the blue laser light source 50B is generated. By synthesizing the blue laser beam L (B) to be generated by the dichroic prism 16, a white combined light beam L (R, G, B) can be generated. However, as will be described later, since the laser light sources 50R, 50G, and 50B perform time-sharing operations, when a certain point in time is captured, the combined light beam L (R, G, B) is not white but red, green, It becomes a light beam of one color of blue.

  On the other hand, the light beam scanning device 60 shown in FIG. 23 may scan the hologram recording medium 45 by bending the combined light beam L (R, G, B) thus generated. The hologram recording medium 45 is preliminarily provided with light having the same wavelength (or approximate wavelength) as the laser beams L (R), L (G), and L (B) generated by the three laser light sources 50R, 50G, and 50B. Each is used to record the image 35 of the scattering plate 30 as three types of holograms. Then, diffracted light is obtained for each of the R, G, and B color components from the hologram recording medium 45, and a reproduced image 35 for each of the R, G, and B color components is generated at the same position. A white reproduced image is obtained.

  In order to create a hologram recording medium on which an image of the scattering plate 30 is recorded using light of three colors R, G, and B, for example, a dye sensitive to R light and a light sensitive to G light are used. A hologram recording medium using a hologram photosensitive medium in which a dye to be dyed and a dye sensitive to B-color light are uniformly distributed and the above-described combined light beam L (R, G, B) may be used. Further, a hologram photosensitive film having a three-layer structure in which a first photosensitive layer sensitive to R light, a second photosensitive layer sensitive to G light, and a third photosensitive layer sensitive to B light are laminated. A medium may be used. Alternatively, the above three photosensitive layers are prepared as separate media, respectively, and hologram recording is performed separately using light of the corresponding colors, and finally, the three layers are bonded to form a three-layer structure. You may comprise the hologram recording medium which has.

  Eventually, illumination light including R, G, and B color components is supplied to the spatial light modulator 80 shown in FIG. 23 in a time-division manner. Therefore, image data for each of the R, G, and B color components is prepared in the image data storage unit 250, and the control device 200 supplies these image data to the spatial light modulator 80 in a time-division manner. To perform the control action. In addition, the control device 200 performs scanning control for the light beam scanning device 60 and performs synchronous control such that the laser light sources 50R, 50G, and 50B perform time-division operations.

  FIG. 34 is a table for explaining such synchronization control. Similarly to the table shown in FIG. 30, the display such as “t1” in the period column indicates each period of beam scanning. For example, “t1” indicates a period from time t1 to immediately before time t2. Show. However, this period is further divided into three equal parts of “t1R˜”, “t1G˜”, and “t1B˜”. Here, the small period “t1R˜” is a period from time t1R (= time t1) to just before time t1G, and the small period “t1G˜” is a period from time t1G to just before time t1B, The small period “t1B˜” is a period from time t1B to immediately before time t2R (= time t2).

  Similarly to the table shown in FIG. 30, the display such as “P (t1)” in the irradiation point column indicates each irradiation point shown in FIG. 29, and the display such as “A (t1)” in the spot column. Shows each spot shown in FIG. In the table of FIG. 34, a laser light source column is newly added, and time division operations of the laser light sources 50R, 50G, and 50B are shown. The period described as “ON” in the laser light source column indicates a period during which the laser light source is ON and operating. A period in which the laser light source column is blank indicates that the laser light source is in an OFF state, and laser light is not irradiated during the period.

  On the other hand, “PIC (t1R)”, “PIC (t1G)”, “PIC (t1B)”, and the like in the image data column indicate image data provided to the spatial light modulator 80 in each period. Here, the image data with R at the end is image data for forming a hologram for reproducing the red component of the color stereoscopic image, and the image data with G at the end is the green color of the color stereoscopic image. This is image data for forming a hologram for reproducing a component, and image data having B at the end is image data for forming a hologram for reproducing a blue component of a color stereoscopic image. These image data can also be created in advance by computer simulation.

  The operation of the apparatus based on the table shown in FIG. 34 is as follows. First, during the period “t1”, the light beam L60 is irradiated onto the irradiation point P (t1) to form a spot A (t1). However, this period “t1” is divided into small periods “t1R˜”, “t1G˜”, “t1B˜”, and only the laser light source 50R is turned on during the small period “t1R˜”. . Accordingly, the spatial light modulator 80 is irradiated with only red reproduction illumination light. At this time, image data PIC (t1R) is given to the spatial light modulator 80, and the red component of the color stereoscopic image is reproduced. During the subsequent small period “t1G˜”, only the laser light source 50G is turned ON, and the spatial light modulator 80 is irradiated with only green reproduction illumination light. At this time, image data PIC (t1G) is given to the spatial light modulator 80, and the green component of the color stereoscopic image is reproduced. Further, only the laser light source 50B is turned ON during the small period “t1B˜”, and the spatial light modulator 80 is irradiated with only the blue reproduction illumination light. At this time, image data PIC (t1B) is given to the spatial light modulator 80, and the blue component of the color stereoscopic image is reproduced.

  As described above, a time division method is adopted in which the period “t1” during which the light beam L60 stays at the irradiation point P (t1) is divided into three sub-periods, and the reproduction images of the respective color components are sequentially reproduced in each sub-period. This makes it possible to present a color stereoscopic image to the observer.

  After all, in the first configuration example, the coherent light source 50 includes three laser light sources 50R, 50G, and 50B that generate monochromatic light beams having respective wavelengths of the three primary colors, and these three laser light sources. The light beam scanner 60 synthesizes the combined light beam generated by the light combiner 15 on the illumination hologram recording medium 45. A configuration for scanning is adopted. In addition, the image of the scattering plate 30 is recorded as three types of holograms on the illumination hologram recording medium 45 so that reproduced images can be obtained by the respective laser beams generated by the three laser light sources.

  In addition, the image data storage unit 250 stores a total of (3 × N) single-color image data for each of the three primary colors corresponding to a plurality of N irradiation points (in the above example, N = 12). The j-th (1 ≦ j ≦ 3) monochromatic image data stored and corresponding to the i-th (1 ≦ i ≦ N) irradiation point is the j-th single color from the i-th irradiation point. When the illumination light for light reproduction is applied to the spatial light modulator 80, the hologram image data forms a hologram reproduction image for the jth primary color of the stereoscopic image to be displayed at a predetermined position. .

  Then, the control device 200 gives a scanning control signal to the light beam scanning device 60 so that the light beams L60 are sequentially irradiated to a plurality of N irradiation points, and also corresponds to each of the plurality of N irradiation points. When the monochromatic image data is supplied to the spatial light modulator 80 and the light beam scanning device 60 performs scanning to irradiate the i-th irradiation point with the light beam L60, each i-th monochromatic image data is Only the laser light source that generates the j-th monochromatic light is selected when the spatial light modulator 80 is provided with the j-th monochromatic image data in order. Thus, synchronous control is performed so that an operation control signal is given to each laser light source so as to operate in the same manner.

(2) Second Configuration Example In the second configuration example for displaying a color image, three sets of single-color stereoscopic image display devices described so far are prepared, and a reproduction image of each primary color is formed. These are synthesized and presented to the observer.

  FIG. 35 is a layout diagram showing this second configuration example. As shown in the figure, this apparatus includes three sets of three-dimensional image display devices, a red unit 500R, a green unit 500G, and a blue unit 500B, and a combined optical system 550 that combines the reproduced images formed by these three sets of three-dimensional image display devices. And. Here, the j-th (1 ≦ j ≦ 3) stereoscopic image display device uses a coherent light source that generates a monochromatic laser beam having the wavelength of the j-th primary color among the three primary colors. It has a function of forming a reconstructed image of a j-th primary color stereoscopic image. On the other hand, the combining optical system 550 is constituted by an optical system such as a cross dichroic prism, for example, and has a function of forming a reproduction image of a color stereoscopic image by combining the reproduction images of the three primary colors.

  The observer can observe the reproduced image of the color stereoscopic image synthesized by the synthesis optical system 550 at the position of the viewpoint E.

<§8-3: Modification of Light Beam Scanning Device>
In the embodiments described so far, the light beam scanning device 60 in the reproduction illumination light generation unit 100 bends the light beam at a predetermined scanning base point B, and this bending mode (the direction of bending and the size of the bending angle). However, the scanning method of the light beam scanning device 60 is not limited to the method of bending the light beam at the scanning base point B. Absent.

  For example, it is possible to adopt a scanning method in which the light beam is translated. However, in that case, it is also necessary to change the recording method of the scattering plate 30 with respect to the illumination hologram recording medium 45. That is, the reference light Lref composed of a parallel light beam is irradiated onto the photosensitive medium 40, and information on interference fringes with the object light Lobj from the scattering plate 30 is recorded. FIG. 36 is a side view of the reproduction illumination light generation unit 100A using the illumination hologram recording medium 46 created by such a method. As shown in the figure, the reproduction illumination light generation unit 100A includes an illumination hologram recording medium 46, a coherent light source 50, and a light beam scanning device 65.

  Here, as described above, the image 35 of the scattering plate 30 is recorded on the illumination hologram recording medium 46 as a hologram using the reference light Lref composed of a parallel light flux. The coherent light source 50 is a coherent light having the same wavelength as the light (object light Lobj and reference light Lref) used when creating the illumination hologram recording medium 46 (or an approximate wavelength capable of reproducing the hologram). It is a light source that generates a light beam L50.

  On the other hand, the light beam scanning device 65 has a function of irradiating the illumination hologram recording medium 46 with the light beam L50 generated by the coherent light source 50. At this time, the light beam scanning device 65 is parallel to the reference light Lref used in the hologram recording process. Scanning is performed so that the light beam L65 is irradiated onto the illumination hologram recording medium 46 from the direction. More specifically, by irradiating the illumination hologram recording medium 46 while moving the light beam L65 in parallel, scanning is performed so that the irradiation position of the light beam L65 on the illumination hologram recording medium 46 changes with time.

  The light beam scanning device 65 that performs such scanning can be constituted by, for example, a movable reflecting mirror 66 and a drive mechanism that drives the movable reflecting mirror 66. That is, as shown in FIG. 36, the movable reflecting mirror 66 is disposed at a position where the light beam L50 generated by the coherent light source 50 can be received, and the movable reflecting mirror 66 is slid along the optical axis of the light beam L50. A drive mechanism may be provided. In practice, the light beam scanning device 65 having a function equivalent to the above function can be configured by a micromirror device using MEMS. Alternatively, the light beam L60 bent at the position of the scanning base point B by the light beam scanning device 60 shown in FIG. 13 is passed through a convex lens having a focal point at the scanning base point B, thereby generating a light beam that moves in parallel. Can do.

  In the case of the example shown in FIG. 36, the illuminating hologram recording medium 46 that has been irradiated with the light beam L65 reflected by the movable reflecting mirror 66 generates diffracted light based on the recorded interference fringes, and is scattered by this diffracted light. A reproduced image 35 of the plate 30 is generated. The reproduction illumination light generation unit 100A performs illumination using the reproduction light of the reproduction image 35 thus obtained as reproduction illumination light.

  In FIG. 36, for convenience of explanation, the position of the light beam at time t1 is indicated by a one-dot chain line, and the position of the light beam at time t2 is indicated by a two-dot chain line. That is, at time t1, the light beam L50 is reflected at the position of the movable reflecting mirror 66 (t1), and is applied to the irradiation point P (t1) of the illumination hologram recording medium 46 as the light beam L65 (t1). At time t2, the light beam L50 is reflected at the position of the movable reflecting mirror 66 (t2) (the movable reflecting mirror 66 (t2) shown in FIG. 2 is the one in which the movable reflecting mirror 66 (t1) is moved), and the light beam is reflected. The irradiation point P (t2) of the illumination hologram recording medium 46 is irradiated as L65 (t2).

  In the drawing, for convenience, only the scanning mode at two points in time t1 and t2 is shown. The irradiation position of the L65 on the illumination hologram recording medium 46 gradually moves from the irradiation points P (t1) to P (t2) in the figure. That is, during the period from time t1 to time t2, the irradiation position of the light beam L65 is scanned to the irradiation points P (t1) to P (t2) on the illumination hologram recording medium 46. Here, an example has been described in which the light beam L65 is translated in the one-dimensional direction (the left-right direction in the figure). If a mechanism (with a reflecting mirror disposed thereon) is provided, it can be translated in a two-dimensional direction.

  Here, since the light beam L65 is scanned so as to be always parallel to the reference light Lref used in the hologram recording process, the light beam L65 is recorded there at each irradiation position of the illumination hologram recording medium 46. It functions as the correct reproduction illumination light Lrep for reproducing the hologram being reproduced.

  For example, at time t1, a reproduced image 35 of the scattering plate 30 is generated by the diffracted light L46 (t1) from the irradiation point P (t1), and at time t2, the diffracted light L46 (t2) from the irradiation point P (t2) is generated. ), A reproduced image 35 of the scattering plate 30 is generated. Of course, also during the period from time t1 to t2, the reproduced image 35 of the scattering plate 30 is similarly generated by the diffracted light from each position irradiated with the light beam L65. That is, as long as the light beam L65 is subjected to parallel scanning, the same reproduced image 35 is diffracted from the irradiated position by the diffracted light from the irradiated position regardless of the position on the illumination hologram recording medium 46. Will be generated.

  After all, in the reproduction illumination light generator 100A shown in FIG. 36, the light beam scanning device 65 irradiates the illumination hologram recording medium 46 while moving the light beam L65 in parallel, thereby illuminating the hologram of the light beam L65. The function of changing the irradiation position on the recording medium 46 with time is achieved. In addition, an image of the scattering plate 30 is recorded as a hologram on the illumination hologram recording medium 46 using reference light composed of parallel light beams, and the light beam scanning device 65 emits light from a direction parallel to the reference light. The beam L65 is irradiated onto the illumination hologram recording medium 46, and the light beam is scanned. As a result, the same reproduced image 35 can always be generated at the same position, and the display hologram recording medium 75 and the spatial light modulator 80 can be generated by the reproduced image 35 in the same manner as the reproducing illumination light generating unit 100 shown in FIG. Can be illuminated. Of course, it is also possible to perform parallel light beam scanning along a circular scanning trajectory as in the example shown in FIG. In this case, for example, an optical system that bends the light beam scanned conically with a convex lens or the like, or a mechanism for two-dimensionally driving the movable reflecting mirror 66 in the light beam scanning device 65 shown in FIG. 36 is prepared. You can do it.

  In short, in the present invention, an image of the scattering plate is recorded as a hologram on the illuminating hologram recording medium using reference light irradiated along a predetermined optical path, and the light with respect to the hologram recording medium is recorded by a light beam scanning device. The light beam may be scanned so that the irradiation direction of the beam is a direction along the optical path of the reference light (an optically conjugate direction). In addition, as the light beam scanning device, a scanning mirror device, a total reflection prism, a refraction prism, an electro-optic crystal, or the like can be used.

<§8-4: Modification using microlens array>
In the embodiments described so far, illumination hologram recording media 45 and 46 on which the hologram image of the scattering plate 30 is recorded are prepared, and the illumination hologram recording media 45 and 46 are scanned with coherent light. The diffracted light produced is used as illumination light for reproduction. Here, a modified example using a microlens array instead of the illumination hologram recording medium will be described.

  FIG. 37 is a side view of a modification of the reproduction illumination light generation unit using the microlens array. The reproduction illumination light generation unit 100B according to this modification includes a microlens array 48, a coherent light source 50, and a light beam scanning device 60. The coherent light source 50 is a light source that generates a coherent light beam L50 as in the above-described embodiments. Specifically, a laser light source can be used.

  The light beam scanning device 60 is a device that scans the light beam L50 generated by the coherent light source 50, as in the above-described embodiments. More specifically, it has a function of irradiating the microlens array 48 with the light beam bent at the scanning base point B. Further, by changing the bending mode of the light beam L50 with time, the microlens of the light beam L60 is changed. Scanning is performed so that the irradiation position on the lens array 48 changes with time.

  On the other hand, the microlens array 48 is an optical element composed of an assembly of a large number of individual lenses. Each of the individual lenses constituting the microlens array 48 refracts the light incident from the scanning base point B and is on a light receiving surface (referred to as a reference surface R here) of the illumination object 90 arranged at a predetermined position. It has a function of forming a predetermined irradiation region I. Moreover, the irradiation area I formed by any individual lens is configured to be the same common area on the reference plane R. As a microlens array having such a function, for example, a so-called “fly eye lens” is commercially available.

  FIG. 38 is a side view showing the operation principle of the reproduction illumination light generation unit 100B shown in FIG. Also here, for convenience of explanation, the bending mode at the time t1 of the light beam L60 is indicated by a one-dot chain line, and the bending mode at the time t2 is indicated by a two-dot chain line. That is, at time t1, the light beam L50 bends at the scanning base point B and enters the individual lens 48-1 positioned below the microlens array 48 as the light beam L60 (t1). The individual lens 48-1 has a function of expanding the light beam incident from the scanning base point B and irradiating the two-dimensional irradiation region I on the reference plane R of the illumination object 90. Therefore, an irradiation region I is formed on the reference plane R of the illumination object 90 as illustrated.

  At time t2, the light beam L50 is bent at the scanning base point B, and enters the individual lens 48-2 positioned above the microlens array 48 as the light beam L60 (t2). The individual lens 48-2 has a function of expanding the light beam incident from the scanning base point B and irradiating the two-dimensional irradiation region I on the reference plane R of the illumination object 90. Accordingly, even at time t2, the irradiation region I is formed on the reference plane R of the illumination object 90 as illustrated.

  In the figure, for the sake of convenience, only the operating states at two points in time t1 and t2 are shown, but actually, the bending direction of the light beam changes smoothly during the period from time t1 to t2, and the light beam L60. The irradiation position with respect to the microlens array 48 gradually moves from the lower side to the upper side in the figure. That is, the irradiation position of the light beam L60 is scanned up and down on the microlens array 48 during the period from time t1 to time t2. Of course, when a microlens array 48 in which a large number of individual lenses are arranged two-dimensionally is used, the light beam can be scanned on the two-dimensional array by the light beam scanning device 60. Good.

  Due to the property of the microlens array 48 described above, the two-dimensional irradiation region I formed on the reference plane R is common no matter which individual lens the light beam L60 is incident on. That is, the same irradiation region I is always formed on the reference plane R regardless of the scanning state of the light beam. Therefore, the display hologram recording medium 75 and the spatial light modulator 80 (liquid crystal display) are arranged as the illumination object 90, and the light modulation surface (hologram recording surface) is located in the irradiation region I of the reference surface R. If it does in this way, the illumination light for reproduction | regeneration will always be irradiated to the light modulation surface, and the three-dimensional image recorded as a hologram can be reproduced | regenerated. That is, the display hologram recording medium 75 and the spatial light modulator 80 arranged as the illumination object 90 can form a reconstructed image of a stereoscopic image using the refracted light obtained from the microlens array 48 as reproduction illumination light. it can.

  In practice, even if the irradiation area I generated by the individual lenses is not completely the same and is slightly shifted, at least the area of the light modulation surface is always irradiated with the reproduction illumination light. If so, there is no problem in reproducing the stereoscopic image. Further, instead of arranging the display hologram recording medium 75 and the spatial light modulator 80 at the position of the illumination object 90 in the figure, the reproduction illumination light irradiated in the irradiation region I is collected by an optical system such as a convex lens. After that, it is possible to irradiate the display hologram recording medium 75 and the spatial light modulator 80 with the reproduction illumination light passing through the optical system.

  After all, in the case of the reproduction illumination light generation unit 100B shown here, the light beam scanning device 60 irradiates the microlens array 48 with the light beam L60, and the irradiation position of the light beam L60 with respect to the microlens array 48 is temporal. It has a function to scan to change. On the other hand, each of the individual lenses constituting the microlens array 48 has a function of refracting light irradiated from the light beam scanning device 60 to form a predetermined irradiation region I on the reference plane R of the illumination object 90. The reproduction image can be obtained by reproducing the hologram on the display hologram recording medium 75 or the spatial light modulator 80 using the reproduction illumination light irradiated in the irradiation region I. Become. Therefore, each irradiation region I formed by the refracted light L48 from each individual lens constituting the microlens array 48 is a reproduction necessary for reproducing the hologram on the display hologram recording medium 75 or the spatial light modulator 80. It suffices if the position and size are set so that the illumination light can be obtained. Of course, if the illumination light for reproduction necessary for hologram reproduction can be obtained, the irradiation areas I formed by the individual lenses do not need to be completely the same common area, and a slight shift occurs between them. However, the greater the deviation, the less energy is used, which is not preferable. Therefore, in practical use, the irradiation area I formed by any individual lens can be efficiently illuminated on the same common area (the display hologram recording medium 75 and the spatial light modulator 80) on the reference plane R. It is preferable that the regions overlap each other as much as possible.

  Even when the reproduction illumination light generation unit 100B is used, the incidence angle of the reproduction illumination light is multiplexed in time as in the above-described embodiments, and speckles are generated. Be suppressed.

<§8-5: Modification using light diffusing element>
So far, an example in which the reproduction illumination light generation units 100 and 100A are configured using the illumination hologram recording media 45 and 46 on which the hologram image of the scattering plate 30 is recorded will be described. The example in which the reproduction illumination light generation unit 100B is configured using the microlens array 48 instead of the illumination hologram recording media 45 and 46 has been described. In these reproduction illumination light generation units, the illumination hologram recording medium and the microlens array ultimately have the function of diffusing the incident light beam to form a predetermined irradiation area on a predetermined reference plane. It plays the role of a diffusing element. In addition, the light diffusing element has a feature that the formed irradiation region is the same common region on the reference surface regardless of the incident position of the light beam.

  Therefore, it is not always necessary to use the above-described illumination hologram recording medium or microlens array in order to configure the reproduction illumination light generation unit used in the stereoscopic image display apparatus according to the present invention. The light diffusing element can be used.

  In short, the reproduction illumination light generation unit used in the stereoscopic image display apparatus according to the present invention essentially controls a coherent light source that generates a coherent light beam and the direction and / or position of the light beam. Thus, the light beam scanning device that performs the beam scanning and the light diffusion element that diffuses and emits the incident light beam can be used.

  Here, the light beam scanning device emits the light beam generated by the coherent light source toward the light diffusing element, and scans so that the incident position of the light beam with respect to the light diffusing element changes with time. As long as it has. The light diffusing element has a function of diffusing an incident light beam to form a predetermined irradiation region on a predetermined reference surface, and the irradiation region to be formed is independent of the incident position of the light beam. On the reference plane, it is only necessary to be configured so that they are substantially the same common area (areas that overlap each other to such an extent that efficient illumination can be performed on the display hologram recording medium 75 and the spatial light modulator 80). Diffused light obtained from such a light diffusing element is given as reproduction illumination light to a display hologram recording medium or a spatial light modulator, and a three-dimensional reproduction image is formed.

  Of course, when a reconstructed image is formed using the spatial light modulator 80, a plurality of N images corresponding to a plurality of N irradiation points are stored in the image data storage unit 250, as in the above-described embodiments. Data is stored, and control for providing corresponding image data to the spatial light modulator 80 is performed in synchronization with the operation of scanning a plurality of N irradiation points by the light beam scanning device 60.

<<< §9. Stereoscopic image display method according to the present invention >>
Finally, the present invention is regarded as a stereoscopic image display method for reproducing and displaying a stereoscopic image recorded as a hologram, and an outline thereof will be briefly described.

  First, in the case of an embodiment using an illumination hologram recording medium as a means for generating reproduction illumination light, the stereoscopic image display method according to the present invention records an image of a scattering plate on a recording medium as a hologram. An illumination hologram preparation stage for creating an illumination hologram recording medium, and reproducing light of a scattering plate image obtained from the illumination hologram recording medium as reproduction illumination light, thereby reproducing a stereoscopic image to be displayed Display hologram recording medium having a function or a spatial light modulator having a diffraction function equivalent to this display hologram preparation stage, and a coherent light beam suitable for obtaining a reproduced image of the scattering plate is illuminated. The hologram recording medium is irradiated from a direction suitable for obtaining a reproduced image of the scattering plate, and the optical position is changed so that the irradiation position changes with time. A hologram reproducing step of scanning the beam on the illumination hologram recording medium, constituted by.

  Further, in the case of an embodiment using a microlens array as a means for generating illumination light for reproduction, the stereoscopic image display method according to the present invention refracts a light beam irradiated from a specific direction, respectively, on a predetermined reference plane. And a plurality of individual lenses having a function of forming a predetermined irradiation area, and the irradiation areas formed by any of the individual lenses are configured to be substantially the same common area on the reference plane. A microlens array preparation stage for preparing a microlens array, and a display hologram having a function of reproducing a stereoscopic image to be displayed by providing refracted light obtained from the microlens array as illumination light for reproduction A display hologram preparation stage in which a recording medium or a spatial light modulator having a diffraction function equivalent thereto is arranged; A hologram that irradiates a microlens array from a specific direction with a coherent light beam having a wavelength suitable for reproducing an image, and scans the irradiation position of the light beam with respect to the microlens array in a temporal manner. And a reproduction stage.

  Further, in the case of an embodiment using a light diffusing element as a means for generating illumination light for reproduction, the stereoscopic image display method according to the present invention diffuses a light beam incident from a specific direction to a predetermined reference plane. A light diffusing element having a function of forming an irradiation region of the light source and configured so that the formed irradiation region is substantially the same common region on the reference surface regardless of the incident position of the light beam. Preparation stage of light diffusing element to be prepared, and display hologram recording medium having a function of reproducing a stereoscopic image to be displayed by giving diffused light obtained from the light diffusing element as reproduction illumination light, or equivalent to this The display hologram preparation stage where the spatial light modulator having the diffraction function of the above is arranged, and the light diffusing element is irradiated with a coherent light beam having a wavelength suitable for reproducing a stereoscopic image And configured and hologram reproducing step of irradiating position with respect to the light diffusion element of the optical beam is scanned so as to vary temporally, by.

  In the above-described stereoscopic image display method, a spatial light modulator that forms a hologram reproduction image corresponding to the image data by providing a plurality of N types of hologram image data and reproduction illumination light in the display hologram preparation stage. When prepared, at the hologram reproduction stage, scanning is performed so that a plurality of N irradiation points are sequentially irradiated with the light beam, and the i-th (1 ≦ i ≦ N) irradiation point is irradiated with the light beam. The spatial light modulator forms a hologram reproduction image corresponding to the i-th image data, and the illumination light for reproduction from the i-th irradiation point is spatial light as the i-th image data. What is necessary is just to use the image data of the hologram which forms the hologram reproduction image of the stereo image used as a display object in a predetermined position, when given to a modulator.

  In order to avoid the observation of speckles on the light source side when the 0th-order diffracted light is incident on the inside of the pupil, a virtual pupil is placed at the position of the viewpoint assumed to observe the stereoscopic image. And an irradiation range of the light beam that satisfies the condition that “the 0th-order diffracted light from the display hologram recording medium or the spatial light modulator is incident on the inside of the pupil” is defined as a scan-prohibited region. The light beam may be scanned while avoiding the scanning prohibited area.

  Further, reproduction illumination light condensed by an optical system having a function of condensing light in the vicinity of a viewpoint assumed to observe a stereoscopic image is given to a display hologram recording medium or a spatial light modulator. By doing so, it becomes easy to collect the diffracted light contributing to the reproduction of the stereoscopic image at the viewpoint position, and a sufficient viewing angle can be secured at the time of observation.

10: Coherent light source 11: Reflector 12: Beam expander 15, 16: Dichroic prism 20: Beam splitter 21: Reflector 22: Beam expander 23: Convex lens 30: Scattering plate 30 ': Virtual scattering plate 35: Hologram of scattering plate Reconstructed image 40: Photosensitive medium 40 ': Recording surface 45: Illumination hologram recording medium 46: Illumination hologram recording medium 48: Microlens arrays 48-1, 48-2: Individual lenses 50, 50R constituting the microlens array 50G, 50B: coherent light source 60: light beam scanning device 65: light beam scanning device 66: movable reflecting mirror 70: photosensitive medium 75: display hologram recording medium 80: spatial light modulator (liquid crystal display)
90: Illumination object 100, 100A, 100B: Reproduction illumination light generation unit 110, 120, 130: Convex lens 150: Half mirror 200: Control device 250: Image data storage unit 500R: Red unit 500G: Green unit 500B: Blue unit 550: Synthetic optical system (dichroic prism)
A, A1, A2: Light beam cross section (spot)
a: Arrangement position of each component B: Scanning base point Bk: Background b: Arrangement position of each component C: Lens focus / convergence points C11 to C14: Diffraction region of first-order diffracted light c: Arrangement position of each component D: Point light source d: Arrangement position d1 to d3 of each component: Distance E, E ′: Viewpoints E0 to E14: Condensing point E1 ′ of 0th order diffracted light, E2 ′: Condensing point of 0th order diffracted light EE: Virtual Outline F of pupil: original image / object FF, FF ′: reproduced image f, f1, f2: focal length G1, G2 of convex lens: locus of condensing point of zero-order diffracted light H: hologram recording medium I: irradiation area K: object point / representative point L10, L11: light beam L12: parallel light beam L20, L21: light beam L22: parallel light beam L23: irradiated light L30: scattered light L31 to L33: object light L45: diffracted light L46: diffracted light L48 : Refraction light L50: Light beam L60: Light L61, L62: light beam L65: light beams L71, L72: diffracted light L110: 0th order diffracted light L120: parallel light beam L130: 0th order diffracted light L (R): red laser beam L (R, G): red green composition Light beam L (R, G, B): Three primary colors combined light beam Ldif: Diffracted light Lobj: Object light Lref: Reference light Lrep: Reproduction illumination light Ls: Light beam M: Photosensitive media P, P1, P2: On the medium Point / light beam irradiation points Pa, Pb: Pitch of point light source D PIC: Image data Q: Points of interest Q1-Q3: Object point R: Reference plane S: Coherent light sources S1, S2: Cross sections T, T ′ of reference light : Circular scanning trajectory t0 to t14: Time V: Rotation axis (axis perpendicular to the drawing sheet)
W: Rotating axis X: Beam expander Z: Optical axis

Claims (2)

A stereoscopic image display device that reproduces and displays a stereoscopic image recorded as a hologram,
A coherent light source that generates a coherent light beam;
A microlens array consisting of a collection of many individual lenses;
A light beam scanning device that irradiates the microlens array with the light beam and scans so that an irradiation position of the light beam with respect to the microlens array changes with time;
A spatial light modulator that, based on image data indicating modulation characteristics for individual positions on the modulation plane, emits light that is incident on the modulation plane according to an incident position, and
An image data storage unit storing a hologram for reproducing a stereoscopic image to be displayed as image data;
A control device that provides the spatial light modulator with the image data read from the image data storage unit;
With
Each of the individual lenses constituting the microlens array refracts light irradiated from the light beam scanning device, and forms a predetermined irradiation region on a reference plane defined in the modulation plane of the spatial light modulator. The irradiation region formed by any individual lens has a function to form, and is configured to be substantially the same common region on the reference surface,
The coherent light source generates a light beam having a wavelength capable of reproducing the stereoscopic image;
The spatial light modulator uses the refracted light obtained from the microlens array as reproduction illumination light to form a reproduction image of the stereoscopic image based on given image data ,
The light beam scanning device has a function of performing scanning so that a plurality of N irradiation points on the microlens array are sequentially irradiated with a light beam,
The image data storage unit stores a plurality of N image data corresponding to the plurality of N irradiation points, and the i-th (1 ≦ i ≦ N) image data is the i-th image data. When the illumination light for reproduction from the irradiation point is given to the spatial light modulator, hologram image data for forming a hologram reproduction image of a stereoscopic image to be displayed at a predetermined position,
The control device gives a scanning control signal to the light beam scanning device so that the light beams are sequentially irradiated to the plurality of N irradiation points, and the spatial light modulation is performed on the plurality of N image data. And the i-th image data is given to the spatial light modulator when the light beam scanning device is performing a scan to irradiate the i-th irradiation point with the light beam. A stereoscopic image display device characterized by performing control. A stereoscopic image display method for reproducing and displaying a stereoscopic image recorded as a hologram,
Irradiation consisting of an assembly of a large number of individual lenses each having a function of refracting a light beam irradiated from a specific direction and forming a predetermined irradiation area on a predetermined reference plane, and formed by any individual lens A microlens array preparation step of preparing a microlens array configured so that the area is also substantially the same common area on the reference plane;
A spatial light modulator having a diffraction function equivalent to that of a display hologram recording medium having a function of reproducing a stereoscopic image to be displayed is provided by providing refracted light obtained from the microlens array as reproduction illumination light. A hologram preparation stage for display,
The microlens array is irradiated with a coherent light beam having a wavelength suitable for reproducing the stereoscopic image from the specific direction, and the irradiation position of the light beam with respect to the microlens array changes with time. A hologram reproduction stage that scans to
Have
In the display hologram preparation step, the spatial light modulator is arranged so that a light modulation surface of the spatial light modulator is located on the reference surface,
In the display hologram preparation stage, a plurality of N types of hologram image data and a spatial light modulator that forms a hologram reproduction image according to the image data by providing reproduction illumination light,
In the hologram reproduction stage, scanning is performed so that a plurality of N irradiation points are sequentially irradiated with the light beam, and when the i-th (1 ≦ i ≦ N) irradiation point is irradiated with the light beam, The spatial light modulator forms a hologram reproduction image corresponding to the i-th image data;
Hologram that forms a hologram reproduction image of a stereoscopic image to be displayed in a predetermined position when reproduction illumination light from the i-th irradiation point is given to the spatial light modulator as the i-th image data A stereoscopic image display method characterized by using the image data.

Images