JP2862019B2 - Video superimposition device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] A video superimposing apparatus for superimposing and displaying second video information on a scene in a visual field, a video, and the like. An optical element for converting an information image from the display means into parallel light, a first diffraction element for diffracting the parallel light at an end of a transparent parallel plate for changing the propagation direction by reflection or diffraction, and the transparent parallel light Deflecting means forming a second diffraction element for diffracting and diffracting the diffracted light of the first diffraction element propagated on the flat plate, wherein the second diffraction element is provided together with the transparent parallel flat plate. An image superimposition sandwiched by a converging means for converging the light flux of the background image, and a diverging means for superimposing and extracting the information image extracted from the second diffraction element and the background image from the focusing means. In the apparatus, both the first and second diffraction elements are Constituting the recording hologram or a reflection hologram.

[Industrial applications]

The present invention relates to a video superimposing device that superimposes and displays second video information on a scene, a video, or the like in a visual field.

Superimposing the second video information on the scenery, video, etc. in the field of view is a store that can recognize more information almost simultaneously without a large movement of the field of view. It has been put to practical use as a head-up display for aircraft and aircraft cockpits. Also, recently, when maneuvering or driving, it is possible to visually obtain maneuvering, driving information etc. without leaving the eyes from the field of view, and it is also applied to automobiles for the purpose of improving mobility, safety and convenience. Are being considered.

[Conventional technology]

As a conventionally proposed method of superimposing an image, an optical element (referred to as an image combiner) on a flat plate or a curved plate whose reflectance and transmittance are appropriately set is used. For example, as shown in FIG. 15, a background image and a display image are superimposed at an appropriate intensity ratio using a reflective element image combiner such as a half mirror 1, or a wavelength selectivity (not shown). There is a combination of a certain reflection hologram and a display device having a narrow wavelength band. The former is simple but has a drawback that the reflectivity of the combiner needs to be increased in order to make the display easier to see, resulting in a decrease in transmittance and a dark background. The latter is an excellent method in terms of light intensity, but has a narrow wavelength band,
It is assumed that a display device with high brightness is used, otherwise there is no merit in terms of display brightness. However, a display device having a narrow wavelength band and a high luminance is generally expensive, and is not acceptable in a car or a consumer product even if there is no problem in price in a fighter or an aircraft.

In head-up displays for fighters and aircraft,
With respect to the displayed image, it is required to minimize distortion, and strict accuracy conditions are required for a lens system and a combiner therefor. However, depending on the use of the video superimposing device, there is also a device that does not require such high accuracy and some distortion is allowed. So come here,
There has been a need for the development of a simple and inexpensive image combiner and video superimposing device.

An example of such a simple image superposition device (J. Apatnieks,
SPIE Proc. Vol. 883, pp. 171-176, 1988) is shown in FIG. As shown in FIG. 17, transmission holograms 2A and 2B that diffract incident light beyond a critical angle (hologram medium 2
a) is formed on each of both sides of the transparent parallel plate 3. The image of the CRT 4 is converted into parallel light by the collimator lens 5, the image is totally reflected and propagated in the transparent parallel plate 3 via the first hologram 2A, and the image is taken out by the second hologram 2B. The background light is the second hologram 2B
Most of the light except for the light having the incident angle near the black angle is transmitted. Diffraction elements such as holograms have a wavelength analysis.
When A and 2B are formed as a pair, as shown in FIG. 18, the difference in diffraction angle due to the difference in wavelength is compensated by the second hologram 2B, and finally the light beam before entering the hologram system The direction is exactly the same, and no chromatic aberration occurs.

[Problems to be solved by the invention]

As a problem in the conventional example shown in FIGS. 16 to 18, since the beam incident on the observer's eye is parallel light, the position of the virtual image is limited to infinity, and the The position (range) is limited to an extremely small area, and a collimator lens 5 and holograms 2A and 2B with a diameter equal to or greater than the distance between at least two eyes are required to make images visible with both eyes The position of the eye is more severely limited as the position of the eye is farther from the combiner (parallel plate 3). If these shortcomings are solved, the application of the method will be further opened.

Therefore, the applicant of the present application has proposed a grating (hologram) for diffracting at least two incident lights at a critical angle or more.
In an apparatus for superimposing images using a transparent parallel plate 3 formed with 2A 'and 2B', a region where a grating (second grating 2B ') for extracting light from the parallel plate is formed by a concave lens. Means having a function (observer side) 6 and means having a convex lens function (opposite side) 7
(Fig. 8). With such a configuration, a superimposed image (virtual image) can be displayed at a point Q at a finite distance from the observer, and light traveling toward the observer is a divergent wave. The range of the position of the eye where the user can see the image can be expanded. The background is transmitted through both the concave and convex lenses 6 and 7, so by selecting the focal length of both lenses appropriately, the virtual power is negated and it looks just like seen through a transparent flat plate Can be done.

 Reference numeral 8 denotes an antireflection film.

As described above, the drawbacks of the conventional method can be improved. However, the transmission hologram has a problem in that the display area (the vertical display area of the CRT 4 in FIG. 8) is widened.
Limited by the sharp angle selectivity of 2A ', 2B'. The angle selectivity of the total reflection hologram as shown in FIG. 17 depends on the film pressure of the hologram and the degree of modulation of the refractive index.
As shown in the figure, the full width at half maximum is about 2 degrees. That is, when the display surface is viewed from the center of the collimator lens 5, only display at a height of 2 degrees can be used. Therefore, when a large area is required, the present video superimposing apparatus is not useful.

An object of the present invention is to increase the display angle width in the above-described video superimposing apparatus.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, an optical element for converting an information image from a display means into parallel light, and the parallel light is diffracted to an end of a transparent parallel plate that changes the propagation direction by reflection. A first diffractive element to be diffracted, and a second diffracted light for diffracting the diffracted light of the first diffractive element propagated through the transparent parallel plate.
Deflecting means having a diffractive element formed therein, wherein the second diffractive element together with the transparent parallel plate is converged by the converging means for converging the light flux of the background image, and the light is extracted from the second diffractive element. The information image and the background image from the converging means are sandwiched by a diverging means for superimposing and extracting the background image from the converging means. In the image superimposing apparatus for taking out a light flux of an information image transmitted through one of the means and the diverging means, the first and second diffraction elements are both formed by a hologram in which a plurality of plane diffraction gratings are multiplex-recorded. An image superimposing device characterized by the following is provided.

According to the second aspect of the present invention, there is provided an optical element for converting an information image from a display means into parallel light, and a first means for diffracting the parallel light at an end of a transparent parallel plate which changes a propagation direction by reflection. A diffractive element, and deflecting means forming a second diffractive element for diffracting and diffracting the diffracted light of the first diffractive element propagated through the transparent parallel plate, and A focusing means for focusing the light flux of the background image on the second diffraction element, and a divergence for extracting the information image extracted from the second diffraction element and the background image from the focusing means in a superimposed manner. Means, and the deflecting means and the converging means extract the luminous flux of the background image transmitted through both the oscillating means and the deflecting means and the luminous flux of the information image transmitted through one of the converging means and the diverging means. In the video superimposing device, the first and second Both diffraction elements are formed by reflection holograms.

(Operation)

As shown in FIG. 1A, the information image on the display means 4 is converted into parallel light by a conversion means (such as a collimator lens) 5, and the parallel light is diffracted by a first diffraction element 12A to form a transparent parallel plate. 3 is incident. In the transparent parallel plate 3, the propagation direction changes due to reflection, and the light is diffracted and emitted by the second diffraction element 12B. The emitted light (information image) at this time is parallel light, but is diverged to the observer 9 by the diverging means 6. Therefore, the information image has a finite virtual image position Q (Q ₁ , Q
₂ ) is confirmed. Further, the background video is recognized at the same magnification through the focusing means 17 and the diverging means 18, and the information video is superimposed on the background video.

Each of the first and second diffraction elements 12A and 12B is configured by an element in which a transmission type total reflection hologram is multiplexed and recorded. Therefore, the luminous flux of the information image emitted from the point P ₁ (FIG. 1A, FIG. 1B) on the display surface of the display means 4 is the multiple recording hologram 12A, 12
It proceeds as a solid line by the hologram H ₁ for example a first B,
To the point Q _1, also the luminous flux of information images from the point P ₂ advances the dotted path by the second hologram H _2, a virtual image is formed respectively on the point Q _2. In this way, since the superimposed image is divergent light for the observer, the range of the position of the eyes can be increased to increase the degree of freedom, that is, the display angle range can be increased.

That is, as shown in FIG. 10, a plane grating hologram (H ₁ ) that diffracts a light beam at an incident angle θ ₁ (in air) at an angle θ ₂ (in a transparent substrate), and an incident angle θ ₁ ′ (in air) The holograms (12A, 12B) in which a plane grating hologram (H ₂ ) for diffracting the light flux of ( ₂ ) at an angle θ ₂ ′ (in the transparent substrate) is multiplexed are
"Gratings" 2A ', 2B' of the optical system shown in FIG.
Use as By properly choosing the angles θ ₁ and θ ₁ ′, the multiplexed recorded planar grid functions independently,
The display of the height of 2 degrees can be performed in two lines, that is, the display of 4 degrees.
By increasing the number of grids to be multiplexed, the display area can be expanded.

In the second invention, a reflection hologram element is used in place of the transmission type total reflection hologram as a means for solving the problem that the display angle width is narrow. Third
As shown in the figure, the collimator means 5 on the transparent flat plate 3 is provided on the reflection side with a first diffraction element 22 for guiding light into the transparent flat plate.
A (reflection type hologram) is formed and the propagating light is
A second diffraction element 22B (reflection type hologram) for taking out from the transparent flat plate 3 is formed on any one surface of the transparent flat plate 3. Thereby, the light beam emitted from the point P on the display surface of the display means 4 is extracted from the transparent flat plate as a parallel light beam. next,
The parallel beam is converted into a divergent wave by the diverging means 18 having a concave lens function, and a virtual image is formed on the opposite side Q of the transparent flat plate.

Since the reflection hologram has a weaker angle selection than the transmission hologram, light in a wide display area can be propagated using a transparent flat plate. Incidentally, in the case of a transmission hologram, the angle range at which light is diffracted is about 2 degrees (full width at half maximum) as described above.
Wide 10-15 degrees. Focusing means 17 having a convex lens function,
As described above, between the diverging means 18 having a concave lens function,
Placed to offset power.

The reflection hologram has wavelength selectivity as shown in FIG. It has a high reflectivity only in a specific wavelength range, and is almost transparent in other wavelength ranges (the figure shows data including surface reflection). Therefore, it can be said that only wavelengths having a width of 20 to 30 nm can be used as display light. The general display means has a wide emission band compared to 20 to 30 nm, so it is difficult to use display light effectively.However, even if there is some light loss, as long as the display is sufficiently bright, it can be used as a display device. Useful enough. The feature of the second invention is that the display area is enlarged by utilizing the weak angle selectivity of the reflection hologram.

〔Example〕

 First, a first embodiment of the present invention will be described.

In the multiple recording hologram shown in FIG. 10, the angle selectivity of the diffraction efficiency is such that when the difference in Bragg angle between the diffraction gratings is about 4 degrees or more, the individual gratings function almost independently, The characteristics shown in Fig. 11 (R. Alferness and SK
Case, J.opt. Soc. Am, Vol. 65, No. 6, P. 730 (1975)). The solid line is the first hologram H ₁ and the broken line is the second hologram.
It represents the diffraction caused by H _2. Each curve has almost the same characteristics as the curve of the single diffraction grating shown in FIG. FIG. 12 shows that the divergent waves emitted from vertically different positions P ₁ and P ₂ on the display surface of the display means 4 are converted into parallel light beams by the collimator means 5 and the multiplexed hologram 12A is used to convert the divergent waves in the transparent flat plate 3. (Shown only the optical axis). Actually, P ₁ and P ₂ are lines extending in a direction perpendicular to the paper surface (FIG. 18). Therefore, when the information video is a character, it corresponds to a line.

If the difference between the Bragg angles in the multiple recording hologram is smaller than 4 degrees, an effect of diffracting the incident light by both gratings occurs (cross coupling effect). No.
Fig. 13 shows the situation. θ ₁ is the Bragg angle of H ₁ , but is also partially diffracted by H ₂ . Θ ₁ ′ is the Bragg angle of H ₂ , but is also partially diffracted by H ₁ . In such a case, a ghost occurs. As shown in FIG. 14, light emitted from one point on the display surface is split into light beams propagating in two directions by the first multiplex recording hologram 12A, and the second multiplex recording hologram 12B at the portion where light is extracted from the transparent flat plate 3 As a result, each light beam is further divided into two. When a virtual image is formed by the diverging means 18 having a concave lens function (FIG. 1A), these do not converge at one point. Therefore, when clear video superimposition is desired, it is preferable to design a plurality of holograms to be multiplexed to be recorded so that the Bragg angles thereof are different from each other by 4 degrees or more.

FIG. 1A shows the overall configuration of the optical system of the video superimposing device according to the present invention. As means 18 having a concave lens function and means 17 having a convex lens function, for example, Fresnel concave lens,
Fresnel concave lenses can be used. The light from the display 4 is collimated by the collimator lens 5, then diffracted by the first multiplex recording hologram 12A (H ₁ ) to a critical angle or more, propagates through the parallel plate 3 by total reflection, and By the multiple recording hologram 12B (H ₂ ). The traveling direction of the light beam at this time is the same as that immediately before the light beam enters the first multiplex recording hologram 12A. Next, the light beam is converted into a divergent wave by the concave lens 18, and virtual images Q ₁ and Q ₂ are formed on the reflection side of the parallel plate with respect to the light traveling direction, and the observer (shown by the eyeball 9) displays the image. The image of the container 4 can be seen in the field of view. Because it is a diverging wave, the image can be viewed even if the position of the eye is slightly changed. Light from the background is transmitted through a transparent curved plate having the same thickness due to the canceling effect of the combination of the concave and convex lenses 18 and 17, and has almost no optical power. Therefore, a normal field of view can be obtained without changing the magnification. The side surface of the parallel plate 3 is provided with an anti-reflection means 8 so that part of the total reflection propagation light is reflected or scattered by the side surface and does not become nozzle light. Specifically, a known technique such as applying a light absorbing substance may be used.

FIG. 2 shows the appearance of an image superimposing apparatus prepared by using the optical system shown in FIG. 12. The display 4 and the collimator system 5 are housed in a lower box (main body) 50. First,
The pair of the transparent parallel plate 3 on which the second holograms H ₁ and H ₂ are formed and the concave and convex Fresnel lenses 18 and 17 are in an upright shape.

In the above embodiment, the first multiple recording hologram
Although the case where 12A (H ₁ ) and the second multiplex recording hologram 12B (H ₂ ) are formed on different surfaces of the parallel substrate is shown, by forming them on the same side, the display 4 and the collimator system 5 become the image combiner. 3 can be arranged on the same side as the observer.

As the display means 4, a fluorescent display tube with a high luminance, a light emitting diode (LED) or the like is advantageous in addition to the CRT.
It is also possible to use a liquid crystal display or the like.

As the collimator 5, a lens or a lens system having good off-axis performance is preferable. The display on the display surface near the optical axis of the lens system forms an image without distortion, but when the off-axis performance of the lens system is poor, distortion occurs at the periphery of the display. The collimator lens is selected according to the quality required for the image to be displayed.

 Next, a second embodiment of the present invention will be described.

As described above, according to the second aspect of the present invention, the most characteristic feature is that the reflection type holograms 22A and 22B are used as the first and second diffraction means.

The method of producing a reflection hologram is well known. If the wavelength band used for display is a long wavelength (red), it can be created by irradiating a short wavelength laser from both sides of the hologram recording medium 12a at an appropriate angle and causing interference. However, when green or blue display is performed, a hologram in which diffracted light propagates in the transparent flat plate 3 by total reflection cannot be created by the above method. Actually, in consideration of human visibility, the display color is preferably green because it has a maximum value around 540 nm (green). Therefore, when forming a reflection hologram, the prism may be brought into optical close contact with the substrate surface, and one of the hologram forming lights may be irradiated at a large incident angle.
The technique itself is a known technique, and thus will not be described in detail. The reflection type hologram may be formed directly on the transparent flat plate 3 used for light propagation, but a separate hologram formed on a thin substrate 12b (FIG. 8) is adhered to the transparent flat plate (photocurable adhesive). A method may be adopted. The same applies to the second reflection type hologram for taking out the light beam outside the transparent flat plate 3.

As specific examples of the elements 17 and 18 having the concave and convex lens functions, plano-concave and plano-convex lenses may be used.However, if the thickness of the lens impairs the compactness and lightness of the device, the lens is made of plastic as described above. Fresnel concave and convex lenses (FIG. 5) may be used. Concentric lines exist in the Fresnel lens, but they are not on the focal plane of the person who observes the image, and thus are often not bothered. The concave and convex lenses 17 and 18 may be bonded to the transparent flat plate 3. However, before the light beam that is totally reflected and propagated in the transparent flat plate is diffracted by the second reflection hologram 22B, the concave and convex lenses 17 and 18 are bonded. In the case where a part of the light is emitted into the air by the convex lens, a method of providing a slight air layer with a spacer or the like and fixing the concave and convex lenses without obstructing total reflection is adopted.

In FIG. 3, the light from the display 4 is collimated by the collimator lens 5 and then taken into the transparent flat plate 3 by the first reflection hologram 22A, and propagates through the total reflection.
The light is taken out of the transparent flat plate by the second reflection type hologram 22B. Next, the same light beam is converted into a divergent wave by the concave lens 18, and a virtual image Q is formed on the side opposite to the light traveling direction with respect to the parallel plate 3, and the observer (shown by the eye 9) Can be seen in the field of view. Because it is a diverging wave,
You can see the video even if you change the position of your eyes slightly. Light from the background is transmitted through a transparent curved plate having the same thickness due to the canceling effect of the combination of the concave and convex lenses 17 and 18, and has almost no optical power. Therefore, a normal field of view can be obtained without changing the magnification.
The brightness of the background is such that light having a wavelength bandwidth of 20 to 30 nm is lost due to the reflection hologram, and there is a slight tint (complementary color), but the brightness hardly changes in appearance. The side surface of the parallel plate 3 is provided with an antireflection means 8 as in the case of FIG. 1A so that a part of the total reflection propagation light is reflected or scattered by the side surface and does not become noise light.

Note that the appearance of the video superimposing device created using the optical system shown in FIG. 3 is exactly the same as that of FIG.

In the above embodiment, the case where the first hologram 22A and the second hologram 22B are formed on different surfaces of the parallel substrate 3 is shown. However, by forming them on the same side, the display and the collimator system can be used as an image combiner. Can be arranged on the viewer side.

Further, the holograms 22A and 22B can be multiplexed holograms as in the case of FIG. 1A.

 In that case, color display can be performed.

FIG. 4 shows the wavelength selectivity of the reflection type hologram, as described above. The value of the wavelength band (peak wavelength) where the reflectivity is high depends on how the reflection type hologram is formed, as is well known. Can be changed. Therefore, for example, a reflection hologram having a maximum reflectance at 530 nm as shown in FIG. 4 is multiplexed with a reflection hologram having a maximum reflectance at 630 nm, or two types of reflection holograms are bonded. By using the resulting holograms as the reflection holograms 22A and 22B shown in FIG. 3, green and red light can be displayed. Furthermore, color display (RGB display) becomes possible by multiplex-recording the reflection hologram having the maximum reflectance at 450 nm (blue).

6 and 7 show two colors (585 nm and 655 nm),
It is a graph which shows the wavelength selection characteristic of the reflection type hologram created for three colors (445 nm, 530 nm, 630 nm) display.

In the present invention, the “multiple recording hologram” means not only a case where a plurality of holograms are recorded in the same hologram medium layer, but also a hologram medium in which holograms are separately formed in each hologram medium. Including things.

〔The invention's effect〕

With the configuration described above, the degree of freedom regarding the position of the eye increases. Even in the case of binocular vision, since the light emitted from the virtual image is divergent light, it is easy to place both eyes in the virtual cone. It is also possible to display an image at a finite distance from the observer. Concave and convex lens elements are added, but if a Fresnel lens made of plastic is used, an inexpensive device can be obtained. The display area can be expanded by using a multiplexed hologram or a reflection hologram.

[Brief description of the drawings]

1A is a diagram showing a basic configuration of a video superimposing device according to the present invention, FIG. 1B is a diagram showing a display position on a display surface of a display, FIG. 2 is an external view of the video superimposing device shown in FIG. Third
FIG. 4 is a diagram showing a basic configuration of the second invention, FIG. 4 is a diagram showing efficiency characteristics of a reflection hologram, FIG. 5 is a diagram showing an embodiment using a Fresnel convex-concave lens, FIGS. FIG. 7 is a diagram showing the efficiency characteristics of the reflection type hologram in the case of displaying two colors and three colors, respectively. FIG. 8 is a diagram showing a schematic configuration of a video superposition apparatus proposed by the applicant of the present invention in the prior application. The figure is a diagram showing the incident angle dependence of the diffraction efficiency in a transmission hologram,
FIG. 10 is a diagram for explaining the expansion of the selected incident angle by the multiple recording hologram, FIG. 11 is a diagram showing the incident angle dependence of the diffraction efficiency in the multiple recording hologram, and FIG. 12 is a case where the multiple recording hologram is used. FIG. 13 is a diagram for explaining the enlargement of the display area of FIG. 13, and FIG. 13 is a diagram for explaining the effect when the Bragg angle of each hologram in the multiplexed hologram is too close,
FIG. 14 is a diagram for explaining the occurrence of a ghost due to cross coupling, FIG. 15 is a diagram for explaining a conventional video superposition method, and FIG.
FIG. 16 is a diagram showing an example of another conventional image superimposing apparatus, FIG. 17 is a diagram for explaining characteristics of a transmission hologram, and FIG. 18 is a diagram for explaining compensation of chromatic dispersion by a hologram pair. 3 ... Transparent parallel flat plate, 4 ... Display, 12A, 12B ... Diffraction grating, 17 ... Converging means 18 ... Diffusion means.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-297516 (JP, A) JP-A-2-241841 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 27/02 B60K 35/00

Claims (5)

(57) [Claims] An optical element for converting an information image from a display means (4) into parallel light, and a first means for diffracting the parallel light at an end of a transparent parallel plate (3) for changing the propagation direction by reflection. Diffraction element (12A), and a second diffraction element (12B) for diffracting and diffracting the diffraction light of the first diffraction element (12A) propagated by the transparent parallel plate (3). Deflecting means, and the second diffraction element (12) together with the transparent parallel plate (3).
B) as focusing means (1) for focusing the light flux of the background image.
7) and the diverging means (18) for superimposing and extracting the information image taken out from the second diffraction element (12B) and the background image from the focusing means (17). The image superimposing device for extracting the light flux of the background image passing through both the means and the focusing means and the diverging means together with the light flux of the information image passing through one of the deflecting means and the focusing means and the diverging means. image superimposition device which is characterized in that both a plurality of plane gratings 2nd析素Ko formed by multiple recorded hologram (H _1, H _2). 2. An optical element for converting an information image from a display means (4) into parallel light, and a first element for diffracting the parallel light at an end of a transparent parallel plate (3) for changing the propagation direction by reflection. Diffraction element (12A), and a second diffraction element (12B) for diffracting and diffracting the diffraction light of the first diffraction element (12A) propagated by the transparent parallel plate (3). Deflecting means, and the second diffraction element (12) together with the transparent parallel plate (3).
B) as focusing means (1) for focusing the light flux of the background image.
7) and the diverging means (18) for superimposing and extracting the information image taken out from the second diffraction element (12B) and the background image from the focusing means (17). The image superimposing device for extracting the light flux of the background image passing through both the means and the focusing means and the diverging means together with the light flux of the information image passing through one of the deflecting means and the focusing means and the diverging means. An image superimposing apparatus, wherein both of the second diffraction elements are formed by reflection holograms. 3. An image superimposing apparatus according to claim 1, wherein said diverging means is formed by a concave lens made of glass or plastic. 4. An image superimposing apparatus according to claim 1, wherein said focusing means is formed by a convex lens made of glass or plastic. 5. An image superposition apparatus according to claim 2, wherein said first and second diffraction elements are both formed by holograms obtained by multiplex-recording a plurality of reflection holograms.