JPS5953805A - Method and device for transmission of image - Google Patents

Abstract

PURPOSE:To enable high speed transmission with ease by transmitting the positional information of the image directly to the waveguide mode excited in a specific waveguide so that the information on the image position can be transmitted, drawn out and reproduced without conversion processing. CONSTITUTION:An optical sheet (solid line) perpendicular to the plane of the figure enters the base of a prism 2 where the light is propagated by forming a mode in a waveguide 1. This light is emitted symmetrically from a prism 3 and forms a linear image on a screen 5. The transmission mode is formed within the angle at which the incident light can advance while making total reflection in the waveguide 1 and the number thereof is determined by the thickness of the waveguide 1. A substrate 0 in the device is quartz glass, the waveguide 1 is a thin film of borosilicate glass, a buffer layer 11 is a vinyl acetate layer, the primsms 2, 3 are SF glass. The thickness and the number of mode of the waveguide 1 have a linear relation when the refractive indices of said prisms for He-Ne laser light are respectively 1.457, 1.523, 1.47, 1.736. The total number of mode is increased if the thickness of the waveguide 1 is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for transmitting images. More specifically, the present invention relates to a method of transmitting and reproducing image information as it is via an optical waveguide without converting it into a time-series signal or the like, and an apparatus for carrying out the method.

When transmitting image information consisting of the brightness and color of a two-dimensional screen, most of the methods currently in practical use involve converting the image signal into an electrical signal as a time-series signal and processing it. On the other hand, although optical information processing methods have the great feature of being able to directly process images in parallel, they are not satisfactory in terms of input elements, memory elements, input methods to computers, etc. Further, conventional optical information processing systems are generally large and difficult to handle, and have the disadvantage of being difficult to incorporate into equipment.

Optical waveguides are a method that solves some of these problems and allows parallel processing of image information in a relatively compact, integrated system. Image information transmission methods using this optical waveguide include a method of using a fiber bundle or a gradient index fiber, and a method of forming an image at each location where the phase of propagating waves in the thin film waveguide matches (R. Ulr.
ich, G. Aukele; Appl. Phys. Le
tt. , 27, 337). However, none of these methods is necessarily suitable for performing image processing in a waveguide.

The present invention relates to a novel method and device for transmitting image information that eliminates the drawbacks of these conventional techniques, and allows image position information to be transmitted directly to a waveguide mode excited in a specific waveguide. It is. According to this method, image transmission processing can be facilitated, and the transmission device can be made smaller and simpler, eliminating the need for complicated image information conversion equipment.
It can be easily incorporated into various devices and applied as an optical integrated circuit or an image recording element.

That is, the present invention inputs optical image information into a waveguide made of a transparent body in the form of a thin film or a thin polygonal column. The present invention relates to an image transmission method characterized by forming a waveguide mode and transmitting through the waveguide, and an apparatus for carrying out the method.

The method of the invention will be explained in more detail below by means of illustrated embodiments.

FIG. 1 shows an embodiment of an image transmission device for carrying out the method of the present invention, in which a flat waveguide 1 is a thin film perpendicular to the drawing, and a low refractive index buffer layer 11 is disposed on a substrate 0. It is pasted through. A triangular prism 2 is attached to one end of the waveguide 1 with its slope facing outward as an input device for optical information, and another prism 3 is attached at a symmetrical position as an output device.

Reference numeral 4 is a cylindrical lens. For example, when a planar light sheet perpendicular to the plane of the paper shown by the solid line in the figure is incident on the bottom surface of the input prism 2 at an appropriate angle, it forms one mode in the waveguide 1 and propagates to the output prism 3. The light exits at symmetrical angles, forming a perfectly symmetrical light sheet. Therefore, the light sheet coming out of the prism 3 forms a linear image on the screen 5.

The light sheet entering the waveguide 1 from the prism 2 repeats total internal reflection within the waveguide 1 and moves forward, but the light sheet enters the waveguide 1 from the prism 2.
If the position that crosses the bottom surface of the optical sheet ends from the edge 21 of the prism 2, the optical sheet will return to the prism 2 without undergoing total internal reflection on the upper surface of the waveguide 1. is made incident through a fine linear region on the bottom surface near the edge 21 of the prism 2.

Furthermore, the angle between the light sheet entering the bottom surface of the input prism 2 and the bottom surface is called the synchronous angle, and the angle within the waveguide that corresponds to the synchronous angle is called the mode angle. It takes discrete values determined by the parameters of each element that makes up the wavepath. Therefore, light sheets incident at different angles (eg, the dashed lines in FIG. 1) will form different transmission modes. As shown in FIG. 1, when a wedge-shaped light wave is made incident using the cylindrical lens 4, a unique mode is excited in the waveguide 1, and a number of light sheets corresponding to the number of modes are emitted, and a number of light sheets are emitted from the rear screen 5. A large number of linear images are formed thereon. That is, if a film image or the like is inserted into the aperture on the entrance side (between the cylindrical lens 4 and the light source (not shown)), a corresponding image consisting of the number of lines corresponding to the number of modes is formed on the screen 5 on the exit side. Ru.

The transmission mode is formed within the range of angles at which the incident light can travel within the waveguide 1 while undergoing total internal reflection, and the number of transmission modes differs depending on the thickness of the waveguide.

That is, in the apparatus shown in FIG. 1, the substrate 0 is made of quartz glass, the waveguide 1 is made of a borosilicate glass thin film, the buffer layer 11 is a vinyl acetate layer, and the prisms 2 and 3 are made of SF13 glass.
The refractive index for Hc-Ne laser light is 1.4, respectively.
57, 1.523, 1.47, and 1.736, the relationship between the thickness of the waveguide 1 and the number of modes is as shown in FIG. As can be seen from the figure, by increasing the thickness of the waveguide, the total number of modes can be increased, and the resolution of the transmitted image can be improved.

FIG. 3 is a photograph of an image obtained using the apparatus shown in FIG. 1, and the test conditions are as follows.

Substrate 0 Fused silica glass Refractive index n=1.457 Waveguide 1 Borosilicate glass
Refractive index n=1.523 Buffer layer 11 Vinyl acetate Refractive index n=1.47 Prism 2
, 3 double flint glass SF-13 refractive index n=1.7
36 Light source Distance between He-Ne laser prisms (from input edge 21 to output edge 31
) 40 mm, and the thickness of the waveguide 1 is 75 μm.

Furthermore, in this case, the light waves are confined in their respective modes in the horizontal direction, but are transmitted in free space in the vertical direction, so a diffraction phenomenon is observed in the vertical direction. For this purpose, an imaging lens is inserted between the exit prism 3 and the screen 5 to form an image. In the image transmission shown in FIG. 3, as the waveguide 1 becomes thicker and the number of modes increases, the resulting image becomes clearer.

As described above, by using the device shown in Fig. 1 to input and output image information to and from the waveguide 1 using a prism, the position information of the image is transmitted as is without any conversion processing, and is extracted. Since the data can be reproduced after being recorded, simple and high-speed transmission becomes possible.

FIG. 4 shows a second embodiment of the present invention, in which the device is almost the same as the device shown in FIG. This is when it is illuminated. In this case, although light is emitted from the transmission object 6 in all directions, only the light in the direction exactly corresponding to the synchronization angle forms a mode in the waveguide 1 and is transmitted. This transmitted reproduced image is shown in FIG. Figure 5 shows the thickness t of the waveguide 1.
is 75 μm, and no input cylindrical lens is used.

FIG. 6 shows the optical system shown in FIG. 4 in which the transmission target 6 is illuminated with white light. The one-to-one correspondence between the incident light sheet and the output light sheet is established regardless of the wavelength of the incident light, and therefore, even when illuminated with white light, transmission is possible without chromatic aberration. In Figure 7, waveguide 1
The relationship between the mode angle and the wavelength at which a mode can be formed is shown when the thickness t is 5 μm. In the figure, m is the number of modes.

When illuminated with light of a single wavelength, the mode angles were discrete, but when illuminated with white light, the mode angles overlapped with those of other wavelengths and became continuous, as shown in Figure 6. As shown in Figure 2, the transmitted image is much more continuous than illumination with a single wavelength of light. However, since the wavelengths forming the transmission mode at each mode angle are discrete, the thickness t of the waveguide 1
If it is 5 μm, the color tone will differ depending on the location. However, in the case of t = 75 μm, the number of transmitted modes becomes very large, so not only are the mode angles continuous, but the intervals between the wavelengths transmitted at a certain mode angle are also dense, and the color spreads over the entire surface. A clear image without unevenness can be formed.

As described above, according to the method of the present invention, not only the shape but also the color of a two-dimensional image can be directly transmitted using white light.

Next, transmission of images of three-dimensional objects will be explained.

Transmitted object 6 of the optical system shown in Fig. 4 (diffusion plate and transparent image)
Instead, a toy about 10 cm in length was placed, illuminated with white light, and an image information transmission test was conducted.

The resulting image is shown in FIG. In this case, since the difference in refractive index between the substrate 0 and the waveguide 1 was small, the field of view was narrow, but a fairly clear transmission image was obtained.

Although the waveguide 1 in the above embodiment is of a refractive index step type, it can also be applied to a refractive index gradient type waveguide. For example, by configuring the lower part of the waveguide 1 shown in FIGS. 1 and 4 so that the refractive index gradually decreases, the optical sheet can be refracted near the lower surface of the waveguide 1 even without the buffer layer 11. and forms a waveguide mode.

Furthermore, by making the waveguide 1 into a thin polygonal prism, for example, a square prism, independent modes that are perpendicular to each other between opposing planes can be formed in the waveguide, allowing multiple optical information to be transmitted simultaneously. You can also do that.

Although the embodiment of the image transmission device described above uses a flat waveguide 1, an entrance prism 2, and an exit prism 3, the same effect can be obtained by using only a flat waveguide.

An example thereof is shown in FIG. 9 as a third embodiment. Waveguide 1'
is a transparent body with a trapezoidal cross section in the longitudinal direction.

Reference numeral 6 is a transmission target, 5 is a screen, and 7 is an imaging lens. An injector and an emitter are not provided at the ends of the waveguide 1', but an entrance surface 8 and an exit surface 9 having an inclination angle θ are formed on both end faces of the waveguide 1'.

The number of modes that serve as a guideline for resolution in the above embodiments, and
Thickness t and material of waveguide 1' (glass n=1.52,
The relationship for sapphire (n=1.76) is shown in FIG. As can be seen from this figure, when the transmitted object 6 is illuminated with monochromatic light, the thickness of the waveguide 1' is t=100 μm, and when it is illuminated with white light, the thickness of the waveguide 1' is about several tens of μm. By using , image information can be transmitted fairly well.

Further, the relationship between the angles of view α_1 and α_2 with respect to the inclination angle θ of the entrance surface 8 is shown in FIG. That is, at the inclination angle θ,
A mode is formed between angles of view α_1 and α_2,
transmission becomes possible. As can be seen from the figure, if θ is set to 50° or less, the direction facing the waveguide can be covered within a range of about 70° to 100°.

According to this configuration, since an input/output prism and a substrate are not required, the transmission element can be further downsized, and can be easily manufactured and used by directly attaching it to other equipment.

It has long been known to condense and diverge guided light by changing the mechanical shape of a waveguide, but conventional technology has focused on research as a one-dimensional lens that operates only within a plane.

In the image transmission method using the mode of the present invention as a carrier, it can act as a two-dimensional lens to form a two-dimensional image or a three-dimensional image.

This will be explained using the fourth embodiment shown in FIG.

The same reference numerals in FIG. 12 as in the previous embodiment indicate the same members. Reference numeral 5' indicates the obtained image, and 10 indicates a waveguide lens. As the thickness changes in this waveguide, the propagation constant changes. If we interpret this as a change in the effective refractive index (equivalent refractive index) at that part, we get
It can be considered that the refractive index distribution changes locally in a waveguide having a uniform thickness, and this causes the guided light to be refracted. The equivalent refractive index with respect to the thickness of the waveguide 1 changes depending on the mode, and an example thereof is shown in FIG. 13.

In other words, the cylindrical lens 10 portion of the device shown in FIG. 12 acts as a lens having a different focal length for each mode. The focal length of such a lens is expressed by the following equation.

However, n_m is the equivalent refractive index of each mode in the waveguide section, z
_2-z_1=d is the width of the lens, and ■(y, z) is the equivalent refractive index distribution. For example, the thickness of waveguide 1 is 100 μm.
, the height of the thickest part of the lens is 50 μm, d = 5 mm
, the focal length when the lens length is 10 mm is the first
Shown in Figure 4.

As can be seen from the figure, the focal length becomes large in the low-order mode, but if you use the high-order mode, the image portion transmitted in the higher-order mode will be imaged closer to the lens within the waveguide. An image 5' is formed. It is also possible to form an image in space by placing an exit prism immediately after the lens.

The method and apparatus for transmitting image information according to the present invention have been described above, but the present invention can also record image information and reproduce it at any time.

An example of this is shown in FIG. 15 as a fifth embodiment. Code 0 in the diagram
, 1, 2, 3, etc. are the same as those in the previous embodiments. As the substrate 0, for example, a slide glass is used, and a buffer layer 11 of a low refractive index polymer (polymethyl methacrylate, fluororesin, vinyl acetate, etc.) with a thickness of 80 μm to 150 μm is interposed thereon. A waveguide (glass sheet) 1 is provided. Reference numeral 12 is a photosensitive material, such as a photoresist such as dichromate gelatin.

In the same manner as in the previous embodiment, image information of the object to be transmitted 6 is transmitted through the prism 2 into the waveguide 1 to form a mode of the image information. On the other hand, a reference plane wave 13 is irradiated from the outside to form interference fringes between the mode of the transmitted image and the reference plane wave 13, and this is recorded on the photosensitive material 12, thereby forming a waveguide hologram.

Next, when reproducing an image, when the reference plane wave 13 is irradiated again to the hologram recorded as described above, a mode of the image information recorded in the waveguide is formed, and this is transmitted to the output prism, for example. 3 and form an image on the screen.

The waveguide hologram recorded in this way can be used as an image recording element, an input element, etc. Also, since the recording density is very high and the recorded information can be easily retrieved and reproduced, it can be used in optical integrated circuits or It is useful as an optical integrated functional element.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a side view of the first embodiment of the image transmission device of the present invention;
Figure 2 is a graph showing the relationship between waveguide thickness and total number of modes; Figures 3, 5, 6 and 8 are photographs of transmission images obtained by the device of the present invention; The figure is a side view of the second embodiment, Figure 7 is a graph showing the relationship between the mode angle and the wavelength that can form a mode, Figure 9 is a perspective view of the third embodiment, and Figure 10 is the thickness of the waveguide. Figure 11 is a graph showing the relationship between the total number of modes and the refractive index of the waveguide, Figure 11 is a graph showing the relationship between the inclination angle of the incident surface and the angle of view, Figure 12 is a perspective view of the fourth embodiment, and Figure 13. 14 is a graph showing the relationship between the thickness of the waveguide, the number of modes, and the equivalent refractive index, FIG. 14 is a graph showing the relationship between the focal length and mode order of the cylindrical lens of the fourth example, and FIG. It is a side view of 5th Example. 0... Substrate 1, 1'... Waveguide 2... Input prism 3... Output prism 4...
Cylindrical lens 5...Screen 6...Transmission object 7
...Imaging lens 8...Incidence surface 9...Output surface 10...Waveguide lens 11...Buffer layer 12.
...Photosensitive material 13...Reference wave 21, 31...Edge part of prism

Claims (16)

[Claims] (1) Optical image information is input into a transparent thin-film plate-like or polygonal columnar waveguide using an input element, and a waveguide mode is formed for each positional information of the image, thereby transmitting the information through the waveguide. An image transmission method characterized by: (2) The image transmission method according to claim 1, wherein a triangular prism-shaped transparent body is used as an image information input element and/or output element to the waveguide. (3) Connect the inclined end face of the waveguide to the image information input section and/or
Alternatively, the image transmission method according to claim 1 or 2, which is used as an output unit. (4) Image transmission according to any one of claims 1 to 3, which uses a grating coupling element formed on the waveguide surface as an image information input element and/or output element to the waveguide. Method. (5) The image transmission method according to any one of claims 1 to 4, wherein a stepped refractive index flat plate element is used as the waveguide. (6) The image transmission method according to any one of claims 1 to 4, wherein a flat plate element of a gradient index type is used as the waveguide. (7) The image transmission method according to any one of claims 1 to 6, wherein an optical waveguide lens using an additional film thickness or a change in the film thickness of the waveguide itself is used as an image information processor. (8) applying a photosensitive material on the surface of the waveguide and recording a pattern of mode image information as a hologram;
Claims 1 to 6 used as an image memory
The image transmission method according to any of paragraphs. (9) An image transmission device comprising a thin film plate-like or polygonal columnar waveguide made of a transparent material, an input section provided at one end of the waveguide, and an output section provided at the other end of the waveguide. (10) The image transmission device according to claim 9, wherein the input section and/or the output section comprises a triangular prism-shaped transparent body provided at an end of the waveguide. (11) The image transmission device according to claim 9, wherein the inclined end face of the waveguide is an input/output section for image information. (12) The image transmission device according to any one of claims 9 to 11, wherein the waveguide is a stepped refractive index flat plate element. (13) The image transmission device according to any one of claims 9 to 11, wherein the waveguide is a flat plate element with a gradient index of refraction. (14) The image transmission device according to any one of claims 9 to 11, wherein the waveguide is a polygonal columnar waveguide such as a triangular prism or a quadrangular prism. (15) The image transmission device according to any one of claims 9 to 14, wherein an optical waveguide lens is attached to the rear of the input section of the waveguide. (16) The image transmission device according to any one of claims 9 to 15, wherein an image processing hologram is provided on the surface of the waveguide.