JP2000122588A - Video projecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small video projecting device having a very thin optical system before eyes. SOLUTION: This video projecting device is comprised of a light-transmissive substrate 9, an optical waveguide 3 which is arranged on the light-transmissive substrate 9 and guides light, a hologram optical element 4 which is formed on the optical waveguide 3 and diffracts the incident light, and a spatial converter 5 which is located on the side opposite to the optical waveguide of the light-transmissive substrate 9 and receives the light diffracted by the hologram optical element and makes it exit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a head mounted video projector which projects and displays a high-definition image at a wide angle of view on a retina.

[0002]

2. Description of the Related Art A head mounted display (HMD) is a small image display device which is mounted on a head to observe an image. The HMD is an image forming unit including a display element typified by a liquid crystal display (LCD), a lens,
An image transmission unit consisting of a mirror is arranged in front of the eyes, and is fixed to the head with a belt or other mounting mechanism. The image displayed on the display element of the image forming unit is displayed by forming a large virtual screen in a place that is easy to see by the aberration correction and enlargement functions by the lens and the mirror of the image transmission unit.

[0003] Taking advantage of this feature, HMD is a device for displaying flight information such as altitude and speed for aircraft, personal movies,
It has been developed and commercialized to realize video games and artificial reality. Recently, Wearable
Research as a computer display is also being conducted.

[0004] Such HMDs are classified into a type that can see the outside world (see-through type) and a type that cannot see the outside world (closed type). In some cases, a closed type rather than a see-through type such as artificial reality is preferable, but in many cases, a see-through type that allows simultaneous observation of the outside world is more convenient for portable use. In this see-through HMD,
In addition to the above-described image forming unit and image transmitting unit, a beam combiner is required as an element for realizing the see-through function.

The beam combiner is, for example, a CRT or LC
The display image D is enlarged and displayed, and at the same time, incident light from the outside can be observed. As a typical method, there is a method using a half mirror, a prism, or a hologram. Half mirrors and prisms are based on the principle that the sum of the amount of image light and the amount of external light is 100%. Therefore, if a high reflectance is set to obtain a bright image, the amount of external light decreases and the see-through performance may decrease. Inevitable. On the other hand, the hologram method has a sharp wavelength selectivity with respect to a specific wavelength and can reflect and diffract only that wavelength, so that 100% of the image display light of the specific wavelength and 100% of the external world excluding that wavelength are displayed. You can see the light overlaid. This function is a method in which a display image is displayed by the beam combiner and 100% of light from the outside can be taken in at the same time, and a high see-through property can be realized.

The HMD is excellent in portability because it can display a screen virtually larger than the entire apparatus size. An ideal form of the portable display device is a glasses-type display. In order to realize a small size and light weight like a glasses-type display, it is necessary to reduce the size of a display element (display) and also the size of an image transmission unit and a combiner. Half mirrors, prisms, and ordinary asymmetric optics (Small-off axis: SOA) holograms all require a large device size in front of their eyes due to restrictions due to their principle, and the thickness must be reduced to a shape like glasses. It is difficult. In contrast, by using a large asymmetric optical system (Large-off axis: LOA) hologram for the combiner, it is possible to greatly reduce the thickness of the member in front of the eyes.

[0007]

It has been proposed to manufacture a small head-mounted image display device using such an LOA hologram optical element. In this device, a light beam from a light source is focused through a condenser lens and focused by a spatial filter. This focal point is a secondary point light source, which is a light source image, and acts as a new light source. The divergent spherical wave from the secondary point light source is diffracted by the illumination hologram optical element serving as an aspherical convex lens, and is converted into focused light. The focused light illuminates a transmission type spatial modulator (display element) arranged near the hologram optical element for illumination. As a result, the image light from the spatial modulator is focused at the pupil, and a geometric image is formed on the retina.

When a secondary point light source is used as in this device,
High resolution images can be observed with a large angle of view. Also, L
By using the OA hologram, the thickness of the anterior optics system can be extremely reduced to about 5 mm. However, in this device, a certain degree of space is required because the light with enhanced coherence from the secondary point light source is diffracted by the LOA hologram optical element to illuminate the spatial modulator. For this reason,
In this method, there is a problem that it is more difficult to reduce the size of the device.

Accordingly, it is an object of the present invention to provide a small-sized image projection device having an extremely thin anterior ocular optical system.

[0010]

Means for Solving the Problems The present inventor has made intensive studies on a method of thinning the anterior optics of an image projection apparatus. As a result, a glass substrate needs to have a certain thickness to transmit light with enhanced coherence from a secondary point light source while reflecting the light inside the glass substrate. It was found that the standardization of the lightwave mode was carried out within the above, and that a conventional thickness was not required, leading to the present invention.

That is, an image projection apparatus according to the present invention comprises a light-transmitting substrate, a waveguide disposed on the light-transmitting substrate, for introducing light, and a light formed on the waveguide and incident on the waveguide. A hologram optical element for diffracting, and a spatial modulator arranged on the opposite side of the light-transmitting substrate from the side on which the waveguide is arranged, the spatial modulator configured to receive diffracted light by the hologram optical element and emit image light. It is composed.

Here, a prism can be used to introduce light into the waveguide. The hologram optical element is disposed on the side of the waveguide opposite to the side where light is introduced or on the side opposite to the side of the light-transmitting substrate. The spatial modulator used here is composed of a liquid crystal cell and a polarizing means. As the polarizing means, any one of a polarizing plate, a polarizing film, and a diffractive optical element having a polarizing action can be used.

According to another aspect of the present invention, there is provided an image projection apparatus comprising: a light emitting source; a waveguide including a waveguide layer for introducing light from the light emitting source; a hologram layer for diffracting light introduced into the waveguide layer; And a spatial modulator that illuminates with the diffracted light and emits image light. Here, the waveguide can have a two-layer structure of a waveguide layer and a hologram layer.

Further, in the image projection method according to the present invention, the light from the light emitting light source is condensed and incident on a waveguide provided on a translucent substrate, and the incident light is reflected on the hologram formed on the waveguide. The image of the spatial modulator is projected on the retina by irradiating the diffracted light with the diffractive optical element and illuminating the transmissive spatial modulator arranged near or in close contact with the translucent substrate with the diffracted light.

With such a configuration, the thickness of the anterior optics system conventionally needs to be the sum of the thickness of the spatial modulator and the thickness of the illumination glass substrate. The sum of the thickness and the thickness of the illumination waveguide is sufficient. And since this waveguide can be used in the form closely contacted with the spatial light modulator, the anterior ocular optical system can be made extremely thin.

[0016]

(Embodiment 1) FIG. 1 is a view showing one embodiment of a head mounted video projection apparatus according to the present invention.
As shown in the figure, the present apparatus comprises a light emitting light source 1, a light collecting means 2,
It comprises a waveguide 3, a hologram optical element 4 formed in the waveguide, a translucent substrate 9, a spatial modulator composed of a liquid crystal cell 5 and a polarizing plate 6. Here, for example, a laser diode (LD) is used as the light emitting light source 1, and a ball lens is used as the light collecting means 2.

In this embodiment, as shown, light from the LD 1 is incident on the end face of the waveguide 3 via the ball lens 2. Here, the waveguide 3 is made of, for example, a light-transmitting material such as a silver halide film, gelatin dichromate, and photopolymer. Light incident from the end face of the waveguide 3 travels while diverging in the waveguide, and is diffracted by the hologram optical element 4 formed in the waveguide. This light is diffracted into a converged light, illuminates the monochrome liquid crystal cell 5 constituting the spatial modulator arranged in close contact with the translucent substrate 9, and after passing through the polarizing plate 6, acts as spatially modulated light. Here, the polarizing plate 6 must be arranged so as to be orthogonal to the polarized light of the LD entering the liquid crystal cell. The spatially modulated light focuses on the pupil 7 (the focal point of the hologram optical element lens: the Fraunhofer diffraction image plane / Fourier transform plane). Then, a geometric image is formed on the retina 8. An observer recognizes a viewing angle corresponding to the aperture of the hologram optical element.

The conventional LOA hologram optical element is installed at an inclination of about 10 degrees from the direction perpendicular to the line of sight. Let L be the length of the spatial modulator. The thickness of the anterior eye optical system is determined by the thickness t of the LOA hologram optical element and L · sin (10 · π / 18).
0) and the thickness d of the spatial modulator. For example, L is 40 to 50 mm, t is about 2 mm, and L · sin (10 · π
/ 180) is about 9 mm and d is 2-3 mm, the total thickness of the anterior ocular optical system is about 14 mm. As described above, conventionally, the thickness of the anterior ocular optical system is set to L · sin (10 · π / 18).
0) It could not be thinned below. However, if a waveguide is used as in the present invention, the thickness of the anterior ocular optical system is only the thickness d of the spatial modulator, and can be extremely thin.

Here, in addition to the above-mentioned LD, a light-emitting element such as a fluorescent lamp, LED or EL can be used as the light-emitting light source 1, and their polarization directions are aligned. Light can be incident on the waveguide using a condensing means such as a ball lens, but the light source may be directly adhered to the waveguide. Here, a commercially available objective lens or a refractive index distribution lens can be used as the light collecting means, in addition to the ball lens. The waveguide is formed of a hologram photosensitive material (film), and a hologram optical element is formed in a part thereof. A hologram photosensitive material (photopolymer) can be used as a waveguide since scattering is small depending on the material. For example, the refractive index (n) of a photopolymer
Is 1.50, quartz 146 (n = 1.45) can be considered as the hologram film holding substrate. When the substrate of the liquid crystal cell is quartz, the waveguide may be formed directly on quartz. Assuming that the thickness of the waveguide is, for example, 20 μm, the waveguide is a spatial filter (pinhole) in addition to optical transmission.
At the same time.

The hologram optical element is manufactured in a reflection type arrangement or a transmission type arrangement. 2 is a diagram illustrating an example of a method of manufacturing a hologram optical element in a case of a transmission type arrangement (for example, T. Suhara et al, "Wa").
Vegide Holograms: A New A
pproach to Hologram integra
The optical arrangement is produced by interference between a divergent spherical wave and a focused spherical wave. A hologram is produced, for example, using a YAGSHHG laser 10. One laser beam is composed of 2 laser beams.
The beam is split by the beam splitter 11 into two beams. One of the beams acts as the object light 12 and the other acts as the reference light 13. The object light 12 is the mirror 1
After the optical path is changed in 4, the light is converted into parallel light through an objective lens 15, a spatial filter 16, and a collimator lens 17, then focused by a condenser lens 18, and
Is irradiated on the hologram optical element photosensitive material 20 from the normal line direction. On the other hand, the reference light 13 changes the optical path by the mirror 21, passes through the objective lens 22 and the spatial filter 23, and thereafter, as a divergent spherical wave, for example, an incident angle of −70 degrees from the normal to the glass substrate 19. Is applied to the hologram optical element photosensitive material 20. The hologram optical element photosensitive material 20 is exposed by the interference of these two light waves,
By performing the heat treatment, the transmission type hologram optical element is completed.

(Embodiment 2) FIG. 3 is a view showing another embodiment of a head mounted image projection apparatus according to the present invention. As shown in the figure, the apparatus includes a light emitting light source 31, a light condensing means 32, a waveguide 33, a thin film hologram optical element (for example, a film thickness of 10 microns) 34 formed in close contact with the waveguide, It comprises a light-transmitting substrate 9 and a spatial modulator composed of a liquid crystal cell 35 and a polarizing plate 36. This embodiment is different from the first embodiment in that the waveguide 33 and the hologram optical element 34
The point is that a layer structure is used. Here, the waveguide can be viewed as a two-layer structure of the waveguide layer (33) and the hologram layer (34). This is because, when the hologram material is a material with much scattering, it is better to separate the layer that guides the light and the layer that diffracts the hologram.
In this embodiment, the image light is focused on the pupil 37 in this manner, and a geometric image is formed on the retina 38.

(Embodiment 3) FIG. 4 is a view showing another embodiment of a head mounted video projector according to the present invention. As shown in the figure, the apparatus includes a light emitting light source 41, a condensing means 42, a prism 43, a waveguide 44, and a hologram optical element of a thin film formed in close contact with the waveguide (for example, a film having a thickness of 10 μm). ) 45, a translucent substrate 9, and a spatial modulator including a liquid crystal cell 46 and a polarizing plate 47. This embodiment is different from the second embodiment in that a prism 43 is used to introduce light into a waveguide. When the prism is used as described above, light can be easily introduced into the waveguide through the end face. In the present embodiment, the pupil 48
Focus on the image light to form a geometric image on the retina 49.

As described above, according to the present invention, the light from the minute light source is made incident on the waveguide via the condensing means, and the light diverged in the waveguide is diffracted and condensed by the hologram forming section, and is displayed by this converged light. By illuminating a liquid crystal cell as an element and focusing on the pupil (eyeball lens surface), the image of the display element is projected on the retina. As a result, the anterior optics system can be made extremely thin, and a small-sized head-mounted image projection device with excellent wearability can be obtained.

[0024]

【The invention's effect】 According to the invention, an extremely thin preocular optical system
And a small video projection device having

[Detailed description of drawings]

FIG. 1 is a diagram showing one embodiment of a head mounted video projection device according to the present invention.

FIG. 2 is a diagram illustrating an example of a method for manufacturing a hologram optical element.

FIG. 3 is a diagram showing another embodiment of the head mounted video projector according to the present invention.

FIG. 4 is a diagram showing another embodiment of the head mounted video projection device according to the present invention.

[Explanation of symbols]

 1,31,41 Light-emitting light source 2,32,42 Condensing means 3,33,44 Waveguide 4,34,45 Hologram optical element 5,35,46 Liquid crystal cell 6,36,47 Polarizer 7,37,48 Pupil 8, 38, 49 Retina 9 Transparent substrate 43 Prism

Claims (9)

[Claims] 1. A light-transmitting substrate, a waveguide disposed on the light-transmitting substrate for introducing light, a hologram optical element formed on the waveguide and diffracting light incident on the waveguide, A spatial modulator disposed on the side opposite to the side on which the waveguide of the light-transmitting substrate is arranged and configured to receive image light diffracted by the hologram optical element and emit image light. Video projection device. 2. The image projection device according to claim 1, further comprising a prism for introducing light into said waveguide. 3. The image projection apparatus according to claim 1, wherein the hologram optical element is arranged on a side of the waveguide opposite to a side where light is introduced. 4. The image projection device according to claim 1, wherein the hologram optical element is arranged on a side of the waveguide opposite to the light-transmitting substrate. 5. An image projection apparatus according to claim 1, wherein said spatial modulator comprises a liquid crystal cell and a polarizing means. 6. An image projection apparatus according to claim 5, wherein said polarizing means is constituted by one of a polarizing plate, a polarizing film and a diffractive optical element having a polarizing action. 7. A light-emitting light source, a waveguide including a waveguide layer for introducing light from the light-emitting light source, a hologram layer for diffracting the light introduced to the waveguide layer, and illumination with the diffracted light from the hologram layer. And a spatial modulator that emits image light. 8. The image projection device according to claim 7, wherein said waveguide layer and said hologram layer are formed in a two-layer structure. 9. A light condensing light from a light emitting light source is incident on a waveguide provided on a light transmitting substrate, and the incident light is diffracted by a hologram optical element formed in the waveguide, and An image projection method, wherein an image of the spatial modulator is projected on a retina by illuminating the spatial modulator, which is disposed near or in close contact with a light-transmitting substrate, with the diffracted light.