JP2013104964A - Holographic display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To propose a mounting method as a realistic holographic display by taking an approach that compensates for insufficient performance of an SLM from the viewpoint of an optical system.
According to an embodiment, a holographic display device including a light source, a condensing optical element, a spatial light modulator, a condensing position switching device, and a light shielding unit is provided. The condensing optical element condenses the reference light output from the light source. The spatial light modulator has a two-dimensional array structure, and modulates at least one of the intensity and the phase of the reference light output from the condensing optical element for each pixel. The switching device switches the condensing position of the reference light output from the condensing optical element to any one of a plurality of condensing positions. The light shielding unit is arranged to remove unnecessary light at a plurality of light collecting positions.
[Selection] Figure 1

Description

  Embodiments described herein relate generally to a holographic display device.

  Although the holographic display has been studied for several decades since the principle of the hologram was devised in the 1940s, there are several obstacles to its realization. Unfortunately, until today, rewritable CGH (Computer Generated Hologram) displays have not been provided in practical form.

  The reason is that the amount of calculation required for displaying interference fringes is enormous, and it is difficult to enlarge the screen size of a spatial light modulator for hologram display (hereinafter referred to as “SLM (Spatial Light Modulator)”). In addition, the reproducible image observation range (viewing zone) is extremely narrow. Here, it is known that the required calculation amount is proportional to the total number of pixels of the SLM, the screen size is defined by the pixel pitch and the number of pixels of the SLM, and the viewing area has a negative correlation with the pixel pitch. Yes.

Special table 2010-513964 gazette Special table 2007-518113 gazette

  Some of the above problems are expected to be improved to some extent by improving the SLM performance (reducing the pixel pitch and increasing the number of pixels). However, in order to achieve the same level of performance as that of a general display in terms of the range in which the reproduced image can be observed and the screen size, the pixel size is set to 1 [μm] or less and the total number of pixels is several tens. It is necessary to set it to 100 million to several tens of billion pixels or more. For this reason, the actual situation is that the difference between the required specification and the current specification is too large to solve the problem by mainly improving the performance of the SLM.

  Therefore, it is desired to take an approach to compensate for the lack of performance of the SLM from the viewpoint of the optical system, and to propose a mounting method as a realistic holographic display.

  According to the embodiment, a holographic display device including a light source, a condensing optical element, a spatial light modulator, a condensing position switching device, and a light shielding unit is provided. The condensing optical element condenses the reference light output from the light source. The spatial light modulator has a two-dimensional array structure, and modulates at least one of the intensity and the phase of the reference light output from the condensing optical element for each pixel. The switching device switches the condensing position of the reference light output from the condensing optical element to any one of a plurality of condensing positions. The light shielding unit is arranged to remove unnecessary light at a plurality of light collecting positions.

The figure which shows the holographic display apparatus which concerns on embodiment The figure which shows the case where a specific example of a switching device is a variable angle mirror The figure which shows the case where the concrete example of a switching device is made into several light-shielding shutters The figure for demonstrating the viewing area of reproduction | regeneration reference light The figure for demonstrating condensing of reproduction | regeneration reference light The figure for demonstrating switching of a reproduction | regeneration reference light condensing position The figure for demonstrating arrangement | positioning of the light-shielding part to the reproduction | regeneration reference light condensing position Diagram showing the case where a half mirror is applied to the optical system Diagram for explaining the design conditions of the light-shielding part The figure for explaining the case where the area of the shading part is secured widely The figure which shows the case where a light-shielding part is formed in the frame shape of glasses

  In the present embodiment, an approach to compensate for the lack of performance of the SLM is also taken from the viewpoint of the optical system, and a mounting method as a realistic holographic display is proposed. Specifically, the present embodiment relates to enlargement of the screen size in a holographic display, improvement of the viewing zone, and removal of unnecessary light associated therewith.

  In the holographic display, the screen size is simply defined by the pixel pitch of the SLM for the interference fringe display × the number of pixels. The size of the viewing zone corresponds to the diffraction angle from the SLM. If the pixel pitch of the SLM is reduced, the diffraction angle, that is, the viewing zone range is enlarged. In the current SLM, the viewing area is extremely narrow, so to increase the apparent screen size seen by the observer, the pixel pitch is reduced to widen the viewing area, and at the same time the screen pitch is reduced by the number of pixels. It is necessary to compensate. In this case, the number of pixels required for the SLM increases dramatically, and depending on the size of the screen, the number of SLM pixels of several hundreds k × several hundreds may be required. Therefore, it is difficult to increase the actual screen size.

  The enlargement of the screen size viewed from the observer without an extreme increase in the number of pixels can be achieved by reproducing the hologram with reproduction reference light that is condensed at or near the observer position. That is, this is a technique of reproducing a hologram using reproduction reference light such that the reference light for reproduction is condensed toward the observer's pupil position or the vicinity thereof. When this method is adopted, the area (viewing area) where the reproduction light from the hologram can be observed is limited to the vicinity of the observer's pupil, but the screen size can be enlarged while the pixel pitch of the SLM is large. . As a result, this contributes to a reduction in the number of necessary pixels.

  With this method alone, the screen size seen by the observer is large, but observation outside the vicinity of the condensing position is impossible. Further, when the reproduction reference light is irradiated in the vicinity of the observer, it is easily assumed that the zero-order light that is unnecessary light jumps into the eyes of the observer and it becomes difficult to observe the reproduction image. For unnecessary zeroth-order light, if a phase SLM or the like is used, ideal light should not be generated. However, in reality, a phase shift may occur due to wavefront disturbance or wavelength shift between the light source wavelengths. In many cases, it is difficult to completely remove unnecessary light.

  Therefore, in the present embodiment, enlargement of the screen size viewed from the observer is achieved while avoiding an extreme increase in the number of pixels, so that the narrow viewing zone associated therewith can be compensated and unnecessary zero-order light can be easily removed. Holographic display device is provided.

  In order to expand the narrow viewing zone, it is effective to perform a time-division playback that switches the collection position of the playback reference light in time, thereby increasing the region where the playback image can be observed, that is, the viewing zone range. . In this embodiment, the irradiation position of the reproduction reference light is determined in advance at a plurality of positions fixed in space, and the viewing zone is expanded by switching the irradiation position by time division. At the same time, by forming a light-shielding portion that reflects, absorbs, or scatters light at a predetermined irradiation position of the reproduction reference light, unnecessary zero-order light can be easily removed.

  Hereinafter, the hologram display device according to the present embodiment will be described in detail with reference to the drawings.

  FIG. 1 is a view of the hologram display device according to the present embodiment as viewed from above. As shown in the figure, in the hologram display device according to the present embodiment, a light source 1, a reference light condensing device 2, a reference light condensing position switching device 3, a spatial light modulator (SLM) 5, and a light shielding unit 6. Are arranged in this order along the optical axis.

  Depending on the configuration of the display device, a plurality of light sources 1, a reference light condensing device 2, a reference light condensing position switching device 3, a spatial light modulator 5, and a light shielding unit 6 may be provided. May be replaced.

  In addition to the components shown in FIG. 1, the hologram display device according to the present embodiment includes a control unit (not shown) for performing control so that they interlock with each other at appropriate timing. This control unit performs appropriate control such as matching the switching cycle between the SLM 5 and the condensing position switching device 3 so as to output the SLM display image corresponding to the selected reference light condensing position. .

  As the light source 1 that outputs the reference light, light having a narrow wavelength width and good coherence is basically used, that is, various laser light sources typified by a He-Ne laser and a semiconductor laser (LD), based on hologram reproduction conditions. Although it is preferable, it is possible to use LEDs for the purpose of reducing the price and suppressing speckles, and it is also possible to use broadband light such as halogen lamps as the light source 1 by adding a dichroic mirror or the like as a color filter. It is.

  Examples of the condensing device 2 that condenses the reference light include a condensing optical element having a general condensing function such as a convex lens or a Fresnel lens, a prism, a liquid crystal GRIN (Graded Index or Gradient Index) lens, and the like. .

  As the reference light condensing position switching device 3, for example, a configuration example in which a plurality of mirrors and liquid crystal shutters are combined can be assumed. The switching device 3 switches the condensing position of the reference light output from the condensing device 2 to any condensing position in a plurality of condensing positions.

  In the configuration example shown in FIG. 2, the reproduction reference light that has passed through a lens or the like and has become convergent light is reflected by the mirror 4 with a variable angle, thereby shifting the condensing position to an arbitrary position. This has the advantage that the number of condensing optical elements such as lenses can be reduced.

  In the configuration example shown in FIG. 3, an optical system in which a plurality of reproduction reference beams are incident on the SLM 5 at different incident angles is constructed in advance, and a target reference is made using a mechanical shutter or a liquid crystal shutter. The reference light condensing position is selected by shielding light other than light. The light from the light source 1a is condensed by the reference light condensing device 2a and enters the reference light condensing position switching device 3a (first light shielding shutter). The light from the light source 1b is condensed by the reference light condensing device 2b and enters the reference light condensing position switching device 3b (second light shielding shutter). The light from the light source 1c is condensed by the reference light condensing device 2c and enters the reference light condensing position switching device 3c (third light-shielding shutter). The reproduction reference light from the reference light condensing position switching devices 3a to 3c is incident on the SLM 5 at different incident angles. In this case, particularly when a liquid crystal shutter is used, a long life and stable operation can be expected since the mechanical drive unit can be reduced.

  The SLM 5 is a spatial light modulator that has a two-dimensional array structure and modulates at least one of the intensity and the phase of the reference light output from the light collecting device 2 for each pixel. The light shielding unit 6 is provided to remove unnecessary light at a plurality of condensing positions.

  Hereinafter, it will be described in detail how the light-shielding unit 6 solves the problem of unnecessary light expansion due to the expansion of the viewing zone by the collection of the reproduction reference light.

  FIG. 4 shows the relationship between the reproduction reference light and the observable region. The object light reproduced from each point of the SLM 5 can be observed only within a certain angular range spanned with respect to the optical axis direction of the reproduction reference light at each point, that is, within a diffraction angle by the SLM 5. In FIG. 4, a solid line indicates the optical axis direction of the reproduction reference light, and a broken line indicates a range in which the reproduction light from each point can be observed.

  That is, it is possible that the reproduction light emitted from a certain point is visible to the observer 1 but cannot be observed from the observer 2. The diffraction angle is a parameter defined by the wavelength of the light source and the pixel pitch of the SLM 5. When reproduction is performed using parallel light, the observer must observe from a position sufficiently away from the SLM 5 to cover the entire surface of the SLM 5. The reproduced image cannot be observed across. Due to this property, under a condition where the pixel pitch is constant, the larger the screen size of the SLM 5 is, the more the observer is required to move away from the SLM 5, and the apparent screen size of the SLM 5 viewed from the observer. It is difficult to increase.

  As a technique for solving this problem, as shown in FIG. 5, the reproduction reference light is deflected to the vicinity of the observer by the reference light condensing device 2, so that an observer located at a short distance from the SLM 5 can also apply to the entire surface of the SLM 5. It is possible to observe a reconstructed image that passes.

  In this case, the viewing area is limited to the vicinity of the reference light condensing position, but the viewing area can be expanded by switching the condensing position of the reference light using the reference light condensing position switching device 3. It is. In this case, it is necessary to switch the interference fringe image displayed on the SLM 5 to an appropriate one in accordance with the change in the light collection position. By performing time-division reproduction that repeatedly switches between the condensing position and the display image of the SLM 5 in a short time, it becomes possible to observe a large size reproduction image simultaneously from a plurality of viewpoints as shown in FIG.

  The reference light condensing position is a plurality of discrete fixed points on a space that is appropriately set in advance. This facilitates the removal of 0th-order light, which will be described later, and the observer's viewpoint position is determined first. Therefore, the interference fringes of the reproduced image corresponding to the required viewpoint position are calculated in advance and read as necessary. In other words, an effect that the calculation processing of the display image (interference fringes) of the SLM 5 in real time according to the observer position is not required can be expected.

  At this time, the observer position and the number of people are not detected, and the images are reproduced in a time-sharing manner at a plurality of condensing positions so that the observer can always observe the reproduced image from a plurality of pre-set condensing positions. It is assumed that the reference light is continuously irradiated. As will be described later, since the focusing position of the reference light in this disclosure is required to be controlled with several millimeters of accuracy, it is difficult to determine the reference light focusing position by detecting the observer's pupil position with the same accuracy. It is expected to accompany. For this reason, there are many merits to surely enlarge the viewing zone without using the detection of the observer position. Specifically, it is possible to prevent a state in which a reproduced image cannot be observed due to a failure in detecting the observer position, and to expect simplification of the apparatus configuration and control method.

  In the following, explanation on zero order light and countermeasures will be described. The reference light for reproduction itself collected in the vicinity of the observer is generally called “0th-order light” and is a component different from the target reproduced image, and thus becomes unnecessary noise for the observer. In order to solve this problem, as shown in FIG. 7, a light-shielding portion 6 for reflecting, scattering, or absorbing the zero-order light is installed at a predetermined reference light condensing position so that the zero-order light is reliably transmitted. After the removal, the observer observes the reproduced image from the vicinity of the reference light condensing position.

  Materials that can be used as the light shielding part 6 include various metal films (aluminum vapor deposition film, chromium vapor deposition film, etc.), dielectric multilayer film, opaque metal plate or resin plate, diffusion plate having sufficient diffusion effect, liquid state Alternatively, a solid opaque object, a polymer film with a transparent electrode used for light control glass, and the like can be used as candidates. In particular, when the light control glass method is used, it is possible to form the light shielding portion 6 that can electrically switch between shielding and transmitting the reference light. Note that the use of the light-shielding portion 6 that can be electrically switched between light-shielding and transmission is not limited to the light control glass system, and the fusion of the real space such as AR (Augmented Reality) and the reproduced image is more natural. There is a possibility that can be done.

  Assuming an optical system using the half mirror 7 as shown in FIG. 8, when the light shield 6 is in the transmissive state, the reproduction reference light is not irradiated, and the entire real space image can be directly observed without being shielded. it can.

  On the contrary, when the reproduction reference light is irradiated, the light shielding unit 6 is switched to the light shielding state, and the three-dimensional reproduction image is displayed superimposed on the real space background. By switching this in a short time and performing time-division display, the entire real space image can be observed at all times even when the light-shielding portion 6 partially covers the observer's field of view. Such a holographic display optical system that can realize superposition with a real space with little discomfort can be applied to a head-mounted display or the like.

  Further, as shown in FIG. 9, the viewing zone is formed around the light collection position, that is, the position corresponding to the light shielding portion 6. When the distance between the reference light irradiation position and the observer pupil position is increased, the viewing zone 8 needs to be wider. The viewing zone range 8 corresponds to the diffraction angle of the SLM5 and has a negative correlation with the pixel pitch of the SLM5. Therefore, the pixel pitch of the SLM5 is kept large, that is, the screen size is kept large under the condition that the number of pixels is constant. Therefore, it is necessary that the light shielding unit 6 is appropriately arranged or designed according to each optical system so that the position of the light shielding unit 6 corresponding to the reference light irradiation position is as close as possible to the pupil of the observer. .

  In other words, the pixel pitch needs to be reduced when the focusing accuracy of the focusing position is not sufficient or when the focusing spot diameter increases due to lens aberration or the like, but the area of the light-shielding portion 6 as shown in FIG. It is also effective to more reliably shield the zero-order light by securing a large distance and by charging and separating the distance between the condensing position and the pupil position.

  As for the shape of the light-shielding part 6, the observer's pupil position needs to be located in the vicinity of the condensing position, and since the diameter of the human pupil is about 7 [mm], the human visual field is not disturbed as much as possible. In order to make the viewable area wide, it is preferable that the interval between the adjacent light shielding portions 6 is close to the pupil diameter and the size thereof is as small as possible. Therefore, if the line segment direction connecting the centers of both eyes is defined as the horizontal direction, the horizontal length of the light shielding portion 6 is preferably 7 mm or less so that at least the entire visual field is not shielded.

  These light shielding portions 6 are formed by a method of forming a metal film or a dielectric film by vapor deposition on a transparent glass plate or a transparent resin plate, a method of directly installing a light control glass, an opaque metal A method of manufacturing a light-shielding plate having an opening by processing a plate, a resin plate, or the like, or a method of forming it as a part on an existing instrument or device such as an eyepiece lens or glasses for a microscope can be considered. In that case, the position in the space of the light shielding part 6 formed on the eyepiece, glasses or the like is also fixed and does not change depending on the position of the observer.

  An example of a specific usage situation is to watch or observe a 3D reproduction image by wearing pre-installed glasses or goggle-like equipment under conditions where the observer position is relatively fixed, such as in a movie theater. Such a situation is assumed. For example, in the case of FIG. 11, the light shielding portion 6 is formed in a frame shape of glasses. Since the viewing zone range is reduced to about the pupil diameter on one side of the observer, an effect that the screen size can be sufficiently enlarged while stably blocking the zero-order light is expected. In addition, in the example of FIG. 11, when the positioning accuracy of the reference light condensing position is not sufficient, it is desirable to increase the area of the light shielding unit 6 as described above. That is, it is possible to take measures such as increasing the width of the frame that is the light-shielding portion 6 to fully separate the distance between the condensing position and the observer pupil.

  According to the present embodiment described above, the condensing position of the reproduction reference light, that is, the unnecessary zero-order light can be easily matched with the position of the light shielding unit 6, and the observer can detect the unnecessary zero-order from the vicinity of the condensing position. It becomes possible to observe the reproduced image from which the light has been removed.

  Therefore, the screen size is enlarged by the reference light condensing device 2 as in the present disclosure, the viewing zone is expanded by time-division reproduction using the reference light condensing position switching device 3, and the reference light condensing position According to the present embodiment that employs the method of using the fixed point and providing the light shielding portion as described above, it is possible to realize a holographic display device that can reliably and easily remove the zero-order light.

[Modification of Embodiment]
(When the reproduction reference light condensing device 2 and the switching device 3 are the same)
In the above-described embodiment, it is assumed that the reference light condensing device 2 and the reference light condensing position switching device 3 are separate devices. However, in the above embodiment, a liquid crystal GRIN lens or an electrowetting cell is used. As in the case of a condensing device having a structure, an element having a function for the reference light condensing device 2 itself to switch the reference light condensing position may be used. As a result, various effects such as downsizing of the entire device, cost reduction effect, simplification of the device by a mechanism-less mechanism and the like can be expected.

(Head tracking mechanism)
The irradiation region is switched by selecting the reference light condensing position closest to the pupil position of the observer by a sensor or a camera for detecting the observer position. Thereby, it is possible to suppress reproduction light irradiation to a position where there is no observer, and light utilization efficiency is improved.

(Size of light shielding part 6)
In the above-described embodiment, the reference light irradiation position is described as “near the observer”. Specifically, the reference light may be condensed at a position of about 1 [mm] from the pupil end of the observer. . In this case, it is possible to shield light by providing a circular light shielding part 6 having a diameter of about 2 [mm] with the condensing position as the center. Since there is a negative correlation between the distance between the observer's pupil position and the reference light condensing position and the required pixel pitch of the SLM5, it is possible from the viewpoint of maintaining the screen size without changing the number of pixels of the SLM5. As much as possible, it is required to shorten the distance between the observer's pupil position and the focusing position.

  In addition, as a shape of the light-shielding part 6, not only circular but the polygonal shape represented by the rectangle, or strip | belt shape may be sufficient.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

1 ... light source;
2 ... Condensing device for reference light (condensing optical element);
3 ... reference light condensing position switching device;
4 ... Angle variable mirror;
5 ... Spatial light modulator (SLM);
6 ... light shielding part;
7 ... Half mirror;
8 ... View zone range

Claims (8)

A light source that outputs a reference light;
A condensing optical element for condensing the reference light;
A spatial light modulator that has a two-dimensional array structure and modulates at least one of the intensity and the phase of the reference light output from the condensing optical element for each pixel;
A switching device for switching the condensing position of the reference light output from the condensing optical element to any condensing position in a plurality of condensing positions;
A light shielding portion for removing unnecessary light at the plurality of light collecting positions;
A holographic display device comprising:   The apparatus according to claim 1, wherein the light shielding unit is configured to be able to electrically switch between transmission and light shielding of the reference light.   The apparatus according to claim 1, wherein the light shielding portion is a metal film, a dielectric multilayer film, or an opaque metal plate or resin plate.   The apparatus according to claim 1, wherein the shape of the light shielding portion is a circle, a polygon represented by a rectangle, or a band.   The apparatus according to claim 1, wherein when the line segment direction connecting the binocular centers of the observer is defined as a horizontal direction, a length in a horizontal direction of the light shielding portion is 7 [mm] or less.   The apparatus according to claim 1, wherein one or a plurality of the light shielding units are arranged as fixed and discrete points in space so as to have an appropriate observable region.   The apparatus according to claim 6, wherein when a plurality of the light shielding parts are arranged, a distance between adjacent light shielding parts is determined based on a diameter of an observer pupil. It further comprises detection means for detecting the observer position,
The apparatus according to claim 1, wherein the switching device performs switching to a condensing position closest to the detected position of the observer.

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