JPH04354076A - Optical pattern recognition element - Google Patents

Abstract

PURPOSE:To miniaturize an optical pattern recognition device by forming a three-dimensional waveguide optical system by arranging flat optical elements consisting of a diffraction grating, a Fourier transformation lens, a mirror, and a light modulation layer on the surfaces opposite to each other of a transparent base board. CONSTITUTION:Diffraction grating holographic gratings (HG) 2,6, polarized beam splitters 3,5, and the holographic Fourier transformation lens 4 are arranged on the upper surface of the transparent base board 1. The light modulation layers 7,8 and a dielectric multilayer film mirror 9 are arranged on the lower surface of the transparent base board 1. In an input picture write-in process (a), input picture write-in light 10a irradiates the light modulation layer 7. In a joint Fourier transformation write-in process (b), coherent light 11 irradiates the HG 2. In a correlation function write-in process (c), the coherent light 12 irradiates the HG 6. In a correlation function read-out process (d) the correlation function recorded on the light modulation layer 7 is read out by irradiating it with correlation read-out light 13.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention applies optical correlation processing to two-dimensional images obtained from an imaging device such as a CCD camera or images directly input from an object in the fields of optical information processing and optical measurement. The present invention relates to an optical element that automatically performs pattern recognition and measurement when applied.

0002

2. Description of the Related Art Conventionally, as an optical pattern recognition device using Fourier correlation optics, a VanderLugt correlator (VanderLugt Correlator) has been used.
(hereinafter abbreviated as VLC) and joint transform correlator (Join
tTransform Correlator (hereinafter abbreviated as JTC) is well known. FIG. 5 shows an example of these correlators. FIG. 5(a) is an example of a conventional JTC. In this method, the input image 34 is an image in which a reference image serving as a reference for recognition and a correlated image serving as a recognition target are placed adjacent to each other at the same time. The beam emitted from the laser 31 is expanded by a beam expander 32 and then split into two beams by a beam splitter 33. The light beam transmitted through the beam splitter 33 illuminates the input image 34, converting the input image 34 into a coherent image. This coherent image is Fourier transformed using the first Fourier transform lens 35, and the light intensity distribution of the joint Fourier transform image of the reference image and the correlated image is displayed on the optical writing type liquid crystal light valve 36 placed on the transform surface. let

Next, the light beam reflected by the beam splitter 33 passes through mirrors 40 and 41 and a polarizing beam splitter 37.
The light is reflected by the optical writing type liquid crystal light valve 36, and the light intensity distribution of the stored joint Fourier transform image is converted into a coherent image. This coherent image is generated by a polarizing beam splitter 37 which acts as an analyzer.
The light is read out as a negative or positive image by passing through the light, subjected to Fourier transformation by a second Fourier transformation lens 38, and received by a CCD camera 39 disposed on the transformation surface. In this way, a correlation peak representing a two-dimensional correlation coefficient between the reference image and the correlated image can be obtained.

FIG. 5(b) is a diagram showing an example of a conventional VLC. In this method, only the correlated image to be recognized is used as the input image 34. The light beam emitted from the laser 31 is expanded by a beam expander 32 and then illuminates an input image 34 to convert the correlated image into a coherent image. This coherent image is subjected to Fourier transformation using the first Fourier transformation lens 35, and a matched filter 42 placed on the transformation surface is irradiated. The matched filter 42 is generally formed as a holographic image containing a complex conjugate component of the Fourier transform of a reference image and a predetermined carrier wave component on a photosensitive medium such as a silver salt photographic plate or a photoresist dry plate. This manufacturing method includes forming a hologram on a photosensitive medium using a two-beam interference method using a reference plane wave and a reference image, or using a computer generated hologram calculated by a computer.
ed hologram (CGH) on a photoresist using electron beam exposure or the like to form a hologram. The thus formed matched filter is irradiated with the Fourier transform of the coherent correlated image as described above, and the diffracted light is then Fourier transformed again by the second Fourier transform lens 38.
A CCD camera 39 placed on the Fourier transform plane detects the correlation peaks between the correlated image and the reference image and their convolution. Therefore, by measuring the intensity of the correlation peak, it is possible to know how similar the correlated image and the reference image are.

As the matched filter 42 in the VLC, a high-resolution optical writing type spatial light modulator such as a ferroelectric liquid crystal light valve or thermoplastic can be used. FIG. 6 shows an example of an input image in the JTC, and FIG. 7 shows a pair of correlation peaks representing a two-dimensional correlation coefficient between the correlated image and the reference image obtained from the CCD camera 39.

FIG. 8 shows an example of the correlation peak and convolution between the correlated image obtained from the CCD camera 39 and the reference image when the alphabet A is used as an input image in VLC.

[0007]

[Problem to be solved by the invention] As explained above,
JTC and VLC, which are optical pattern recognition devices using Fourier correlation optics, have the advantage of processing image information in parallel and easily obtaining a correlation peak corresponding to the correlation coefficient between the correlated image and the correlated image. This is an optical pattern recognition device. However, since conventional JTCs and VLCs use bulk lenses and prism components as their constituent optical components, it is difficult to miniaturize these optical pattern recognition devices by making the optical components more precise. This has the disadvantage that it requires extremely difficult work because adjustments must be made.

[0008]

[Means for Solving the Problems] The optical pattern recognition element of the present invention includes a diffraction grating or prism for introducing external light and a required target on at least one surface of a transparent substrate having surfaces parallel to each other. a first optical writing type light modulation layer for recording and displaying external image information including at least one reference image and at least one newly input correlated image; a planar Fourier transform lens; a second optical writing type light modulation layer for recording and displaying Fourier transform of external image information recorded in the first optical writing type light modulation layer; and recording on the second optical writing type light modulation layer. The Fourier transform of the displayed image information from the outside,
a third optical writing type light modulation layer for recording and displaying a correlation image representing a correlation function between the reference image and the correlated image obtained by Fourier transformation again; a polarizing beam splitter made of an optical multilayer film; By creating an optical pattern recognition element structure characterized by comprising a light reflection layer that optically couples all of these planar optical elements, microfabrication can be achieved using microfabrication technology typified by semiconductor processing. The above-mentioned problems regarding JTC have been solved by realizing a compact optical pattern recognition device that can adjust the optical system with an accuracy of .

[0009]

[Function] The diffraction grating in the optical element used in the optical pattern recognition element of the present invention has the function of bending the optical path of coherent light used in optical pattern recognition and guiding the coherent light to a predetermined optical element. The planar Fourier transformation lens has the function of Fourier transforming coherent light containing target image information onto a predetermined optical element. These diffraction gratings and planar Fourier transform lenses are
It is created by scanning and recording an interference pattern calculated in advance on a computer with an electron beam on a photosensitive material such as a photoresist or a silver salt photosensitive film, or by performing two-beam interference exposure using coherent light with a predetermined wavefront. Since it is a holographic optical element, the position at which it is manufactured can be controlled extremely precisely, and it is also thin.

[0010] Furthermore, the first optical writing type light modulation layer is
The second optical writing type light has the function of optically writing and displaying external image information including at least one reference image including a desired target and at least one newly input correlated image. The modulation layer has a function of optically writing and displaying the Fourier transform of image information from the outside, and the third optical writing type light modulation layer is written in the second optical writing type light modulation layer. It has the function of recording and displaying a correlation image representing a correlation function between the reference image and the correlated image obtained by Fourier transforming the image information from the outside.

Furthermore, since these planar optical elements are formed on transparent substrates with extremely good surface precision and parallelism,
The optical axis can be easily adjusted by simply moving these planar optical elements on a plane.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the optical pattern recognition device of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an example of the optical pattern recognition element of the present invention (FIG. 1(a) is a plan view,
FIG. 1(b) is a side sectional view), in which 1 is a transparent substrate, 2 is a first holographic grating (hereinafter HG: H
(abbreviated as holographic grating), 3 is the first polarizing beam splitter, and 4 is the holographic grating.
Fourier transform lens (HFL: Holograph)
ic Fourier Transform Lens
), 5 is the second polarizing beam splitter, and 6 is the second polarizing beam splitter.
HG, 7 is the first light modulation layer, 8 is the second light modulation layer, 9
is a dielectric multilayer mirror. The transparent substrate with surfaces parallel to each other is a transparent substrate 1, the diffraction gratings for introducing external light are a first HG and a second HG, and at least one reference image including a desired target is newly inputted. The first optical writing type light modulation layer that records and displays image information from the outside including at least one correlated image is the first light modulation layer 7, the planar Fourier transform lens is HFL4, and the A second optical writing type light modulation layer that records and displays the Fourier transform of external image information recorded in the first optical writing type light modulation layer is the second optical modulation layer 8; recording a correlation image representing a correlation function between the reference image and the correlated image obtained by performing Fourier transform again on the Fourier transform of the external image information recorded and displayed on the optical writing type light modulation layer; The third optical writing type light modulation layer to be displayed is the first light modulation layer 7, the polarization beam splitters made of optical multilayer films are the first polarization beam splitter 3 and the second polarization beam splitter 5, A light reflecting layer that optically couples all these planar optical elements is a dielectric multilayer mirror 9. In order to facilitate the explanation below, the surface on which the first HG2, first polarizing beam splitter 3, HFL4, second polarizing beam splitter 5, and second HG6 of the transparent substrate 1 are formed is referred to as the upper surface, and 1
The surface on which the light modulating layer 7, the second light modulating layer 8, and the dielectric multilayer mirror 9 are formed will be referred to as the lower surface.

As can be seen from FIG. 1, the first HG 2, the first polarizing beam splitter 3, the HFL 4, the second polarizing beam splitter 5, the second HG 6, the first light modulating layer 7,
Planar optical elements such as the second light modulation layer 8 and the dielectric multilayer mirror 9 are arranged on the surface of the transparent substrate 1 at symmetrical positions with the HFL 4 at the center. 1st HG2, HFL4
, the second HG6 coats a resist on the transparent substrate 1,
Each predetermined diffraction grating was written and formed using an electron beam drawing exposure device. Of course, these may be formed by optical interference exposure.

The transparent substrate 1 has a thickness of 10 to 30 mm.
A piece of quartz glass polished to an accuracy of parallelism of 5 seconds or less and flatness of λ/10 or more was used. Of course, as the material for the transparent substrate 1, optical glass such as flint glass or crown glass may be used, or in special cases, transparent plastic may be used. Furthermore, the first polarizing beam splitter 3, the second polarizing beam splitter 5, and the dielectric multilayer mirror 9 are made of TiO2 or ZrO2 having a large refractive index.
2, Si, SiO2 and MgF2 with small refractive index, Al2O3 and Y2O3 with intermediate refractive index, etc.
It is constructed by periodically laminating layers with predetermined film thicknesses and combinations.

As the light modulation layers 7 and 8, the transparent substrate 1
An optical writing type liquid crystal light valve or BS formed on the photoconductive layer, a liquid crystal alignment layer, a liquid crystal layer, and a voltage application means.
An optical writing type electro-optic crystal spatial light modulator having a structure in which an O (Bi12SiO20) single crystal is sandwiched between transparent electrodes with an insulating film interposed therebetween can be used. In this example, an optical writing type ferroelectric liquid crystal light valve using a ferroelectric liquid crystal layer having a bistable memory property between light reflectance and applied voltage was used as the light modulation layer as the liquid crystal layer. .

Next, the operation of the optical pattern recognition element of the present invention shown in FIG. 1 will be explained using FIG. 2. FIG. 2 is a process diagram showing the operation steps of the optical pattern recognition element of the present invention,
10a and 10b are input image writing lights, 11 is a first coherent light, 12 is a second coherent light, and 13 is a correlation function reading light. 2(a) shows the input image writing process, (b) shows the joint Fourier transform writing process, (
c) is a correlation function writing step, and (d) is a correlation function reading step. Note that the same components as in FIG. 1 are given the same numbers and their explanations will be omitted.

In the input image writing step (a), the first
After uniformly erasing the light modulation layer 7 and the second light modulation layer 8,
An input image is formed on the first light modulation layer 7 by an imaging optical system outside the element. The direction in which the input image is formed may be determined by irradiating the input image writing light 10a from the bottom surface of the element.
The input image writing light 10b may be irradiated from the top surface of the element. The input image thus formed on the first light modulation layer 7 is optically recorded on the first light modulation layer 7. The input image recorded at this time is an image in which a correlated image and a reference image are placed adjacent to each other at the same time, as shown in FIG.

Joint Fourier transform writing process (b
), first, the first coherent light 11 is transmitted to the first HG
2 is irradiated from a predetermined direction with a predetermined beam spread angle. The first coherent light 11 irradiated onto the first HG 2 is diffracted by the first HG 2 and becomes a parallel readout beam, which is irradiated onto the first light modulation layer 7 and written in the input image writing step (a). The input image is read out, reflected according to Snell's law, and irradiated onto the first polarizing beam splitter 3. The readout light flux irradiated at this time is preliminarily arranged so that it becomes p-polarized light (or s-polarized light) with respect to the first light modulating layer 7.
Let us determine the polarization direction of . Many light modulation layers, such as optical writing type liquid crystal light valves and spatial light modulation elements using BSO crystals, spatially modulate the polarization plane of light. When such a spatial light modulation element is used as the first light modulation layer 7, the readout light beam just before being irradiated onto the first polarization beam splitter 3 has a spatial polarization plane reflecting the information of the input image. Since it is modulated, the readout light beam after being reflected by the first polarizing beam splitter 3 contains the input image as a positive image (or negative image). The readout light beam containing this input image as a positive image (or negative image) is reflected by the dielectric multilayer mirror 9, and then reflected by the HFL 4.
The light is focused by the dielectric multilayer mirror 9 and the second polarizing beam splitter 5, and is Fourier transformed onto the second light modulating layer 8 to form a joint Fourier transformed image of the correlated image and the reference image. form. This joint Fourier transform image is optically recorded on the second light modulating layer 8. Thereafter, the input image recorded on the first light modulation layer 7 is erased.

The correlation function writing step (c) is similar to the joint Fourier transform image writing step. First, the second coherent light 12 is irradiated onto the second HG 6 from a predetermined direction with a predetermined beam spread angle. The second coherent light 12 irradiated to the second HG 6 is
It is diffracted by the second HG 6 and becomes a parallel readout light beam, which is irradiated onto the second light modulation layer 8, reads out the joint Fourier transform image written in the joint Fourier transform image writing step (b), and is reflected according to Snell's law. The second polarizing beam splitter 5 is irradiated. The polarization direction of the second coherent light 12 is determined in advance so that the readout beam irradiated at this time becomes p-polarized light (or s-polarized light) with respect to the second light modulation layer 8 . When the above-described spatial light modulation element that spatially modulates the plane of polarization is used as the second light modulation layer 8, the second
The readout beam just before being irradiated onto the second polarizing beam splitter 5 has its plane of polarization spatially modulated reflecting the information of the joint Fourier transform image. The readout light beam includes the joint Fourier transform image as a positive image (or negative image). The readout light beam containing this joint Fourier transform image as a positive image (or negative image) is
After being reflected by the dielectric multilayer mirror 9, the light is focused by the HFL 4, reflected one after another by the dielectric multilayer mirror 9 and the first polarizing beam splitter 3, and then Fourier transformed onto the first light modulation layer 7. A correlation function including a correlation peak representing a correlation coefficient between the correlated image and the reference image is formed. A correlated image as a correlation function including a correlation peak representing a correlation coefficient between the correlated image and the reference image is optically recorded on the first light modulation layer 7. Thereafter, the joint Fourier transform image recorded on the second light modulation layer 8 is erased.

In the correlation function readout step (d), the correlation function readout light 13 is irradiated from the top surface of the element to read out the correlation function recorded in the first light modulation layer 7. This read correlation function is converted into an intensity distribution image via a polarizer set in an optical system outside the element, and detected by a photodetector or an imaging device. Input image writing light 1
0a, 10b and the correlation function readout light 13,
Although it is preferable to use incoherent light, it goes without saying that coherent light may also be used.

Next, in the optical pattern recognition element of the present invention shown in FIG.
An example in which an optical writing type ferroelectric liquid crystal light valve is used will be described. FIG. 3 is a cross-sectional view showing the configuration of the optical pattern recognition element of the present invention using an optical writing type ferroelectric liquid crystal light valve in the light modulation section, and (a)
(b) is an enlarged sectional view of the light modulation section. In FIG. 3, 14 is a first light modulation section, 15 is a second light modulation section, 16a and 16b are transparent electrode layers, 1
7a and 17b are alignment film layers; 18 is a ferroelectric liquid crystal layer; 19
20 is a dielectric mirror, 20 is a photoconductive layer, 21 is a second transparent substrate, 22 is a spacer, and 23 is a non-reflective coating. Note that the same components as in FIG. 1 are given the same numbers and their explanations will be omitted.

The first light modulation section 14 and the second light modulation section 15 in FIG. 3A correspond to the first light modulation layer 7 and the second light modulation layer 8 in FIG. 1, respectively. The structure and operation of an optical writing type ferroelectric liquid crystal light valve as a light modulating section will be explained using FIG. 3(b). First, the configuration will be explained. A transparent substrate 1 and a second transparent substrate 21 made of glass or plastic, which sandwich liquid crystal molecules, have transparent electrode layers 16a and 16b on their surfaces, and are formed at an angle of 75 degrees to 85 degrees from the normal direction of each transparent substrate. Alignment film layers 17a and 17b formed by obliquely vapor-depositing silicon monoxide are provided.

Furthermore, a photoconductive layer 20 and a dielectric mirror 19 are laminated on the transparent electrode layer 16a on the second transparent substrate 21 side between the alignment film layer 17a and the cells of the second transparent substrate 21. A non-reflective coating 23 is formed on the outer surface. As the photoconductive layer 20, a chalcogenide-based semiconductor thin film, an organic photoconductive film, or a silicon-based semiconductor thin film can be used, but it is preferable to use hydrogenated amorphous silicon, which is excellent in various characteristics such as photosensitivity and wavelength of use. preferable. Furthermore, as the dielectric mirror 19, a dielectric multilayer mirror in which a plurality of dielectrics having different refractive indexes or thin films of high-resistance semiconductor materials are periodically laminated at a predetermined thickness is often used. The light transmittance is designed so that a predetermined amount of light reaches the photoconductive layer 20 from the ferroelectric liquid crystal layer 18 side. The dielectric mirror 19 may be omitted if an optical image with sufficient intensity can be read out even without the dielectric mirror 19.

Next, a method for initializing the light modulation section having the above structure will be described. The first method is to irradiate the entire reading surface (or writing surface) of an optically writable ferroelectric liquid crystal light valve with light, and apply a pulse voltage or DC bias voltage sufficiently higher than the operating threshold voltage during the bright state, or
Applying a DC bias voltage superimposed with an AC voltage of 00Hz to 50kHz between the transparent electrode layers 16a and 16b,
This method aligns ferroelectric liquid crystal molecules into a stable state in one direction and stores that state in memory. The second method is to apply a pulse voltage or DC bias voltage sufficiently higher than the operating threshold voltage in the dark, regardless of whether there is light irradiation or not.
In this method, a DC bias voltage superimposed with an AC voltage of Hz to 50 kHz is applied between the transparent electrode layers 16a and 16b to align the ferroelectric liquid crystal molecules in a stable state in one direction, and to store this state in memory.

Furthermore, the operation of the optically written ferroelectric liquid crystal light valve after initialization as described above will be described. A pulse voltage or DC bias voltage of the opposite polarity to that at initialization, lower than the operating threshold voltage in the dark and higher than the operating threshold voltage during light irradiation, or 100 Hz to 5
While applying a DC bias voltage superimposed with an AC voltage of 0 kHz between the transparent electrode layers 16a and 16b, the input image writing lights 10a and 10b, the first coherent light 11, and the second coherent light 12 shown in FIG. Write by irradiating. When hydrogenated amorphous silicon is used as the photoconductive layer 20, the wavelength of the irradiated writing light is 9.
00 nm or less, carriers are generated in the photoconductive layer in the area irradiated with the write light, and the generated carriers drift in the direction of the electric field due to the applied voltage.As a result, the operating threshold voltage decreases, and the read light irradiation A bias voltage with a polarity opposite to that during initialization is applied to the region above the operating threshold voltage, and the ferroelectric liquid crystal molecules undergo molecular inversion due to the reversal of spontaneous polarization, and shift to the other stable state. Therefore, the image is binarized and stored. This stored image remains stored even when the drive voltage goes to zero.

The binarized and stored image is generated by irradiation with linearly polarized readout light whose polarization axis is aligned with the alignment direction of the ferroelectric liquid crystal molecules aligned through initialization (or in a direction perpendicular thereto), and , by passing the reflected light through an analyzer arranged so that the polarization axis is perpendicular (or parallel) to the polarization direction of the light reflected by the dielectric mirror 19 (or the photoconductive layer 20 if there is no dielectric mirror). Can be read in positive or negative state.

The optical pattern recognition element of the present invention using an optical writing type ferroelectric liquid crystal light valve in the light modulation section shown in FIG. It works. At this time, the input image and the joint Fourier transform image are recorded and read out to the first light modulator 14 and the second light modulator 15 according to the method for driving the optical writing type ferroelectric liquid crystal light valve described above. .

Next, an embodiment of a method for forming correlation peak detection means included in a correlation image in the optical pattern recognition element of the present invention will be described. FIG. 4 is a cross-sectional view showing the configuration of an optical pattern recognition element of the present invention having a correlation function readout optical system, in which 24 is a polarizing beam splitter, 25 is a protective transparent substrate, 26 is a third transparent substrate, and 27 is a coupling element. Image holographic lens (hereinafter referred to as HL)
28 is a fourth transparent substrate, 29 is a photodiode array, and 30 is an adhesive layer. Note that the same components as in FIG. 1 are given the same numbers and their explanations will be omitted. The polarizing beam splitter 24, the protective transparent substrate 25, the third transparent substrate 26, the imaging HL 27, the fourth transparent substrate 28, and the photodiode array 29 are connected to each other via an adhesive layer 30 as shown in FIG. 1 or 3. It is glued onto the optical pattern recognition element. Further, although not shown in FIG. 4, optical components indicated by numbers 24 to 30 are also bonded to each other with adhesive. polarizing beam splitter 24, protective transparent substrate 25, third transparent substrate 26,
The imaging HL 27, the fourth transparent substrate 28, and the photodiode array 29 form a correlation coefficient reading optical system, which, together with the protective transparent substrate 25, is formed on the optical pattern recognition element of the present invention. Protects planar optics,
It also has the role of reducing noise generated from dirt and dust.

The correlation function readout light 13 passes through the polarization beam splitter 24, and only its p-polarized light component illuminates the first light modulation layer 7. The polarization direction of the correlation function readout light 13 that irradiates the first light modulation layer 7 can be set arbitrarily by attaching the polarization beam splitter 24 in a position rotated by an appropriate angle around the optical axis of the correlation function readout light. can be decided. It is assumed that a correlated image corresponding to the correlation function between the correlated image and the reference image is recorded on the first light modulation layer 7 in the same manner as described in the previous embodiments. This correlation image is read out by the correlation function reading light and reaches the polarization beam splitter 24 again. As described above, the light from which this correlation image has been read has its plane of polarization rotated with a spatial distribution corresponding to the correlation image, and enters the polarization beam splitter 24 with an s-polarized component.

The correlation image thus converted into a light amplitude image is sent to the photodiode array 2 at the imaging HL 27.
The image is formed on 9. The photodiode array 29 photoelectrically converts the correlation peak included in the correlation function between the formed correlated image and the reference image, and transmits it to an external electrical processing system. This photodiode array 29 must have at least half the number of photoelectric conversion surfaces as the number of correlation peaks included in the correlation function. For example, if one correlated image and one reference image are each input to the first light modulation layer 7 as input images, two correlation peaks appear in the corresponding correlated image, so the photodiode array 29 uses a photodiode with a single photoelectric conversion surface or a two-split photodiode. However, in general, a plurality of correlated images or reference images are often used, and in that case, a plurality of correlation peaks are included in the correlated images corresponding to the correlation functions therefor. Of course, instead of the photodiode array 29, a CCD (Charge Coupled Dev)
ice) to detect a correlation image corresponding to the correlation function, convert it into a video signal and observe it on a CRT or video monitor, or convert the correlation image into a digital signal and perform digital processing using a computer, etc. Needless to say, it may also be used for image processing.

Furthermore, it goes without saying that a Selfoc lens or a small spherical lens may be used in place of the imaging HL 27. By the way, in the embodiments of the optical pattern recognition element of the present invention described so far, the light modulation layer is formed separately, so if you try to configure this using liquid crystal, it will be difficult to prepare a liquid crystal cell or inject liquid crystal. It was difficult to do. Therefore, one example of an embodiment for solving this problem will be described. FIG. 9 is a cross-sectional view showing the configuration of an optical pattern recognition element of the present invention in which a planar optical element is formed on the read-out side substrate of an optical writing type ferroelectric liquid crystal light valve, and 16c
17c is an alignment film layer, and 18a and 18b are ferroelectric liquid crystal layers. Note that the same components as in FIG. 1 are given the same numbers and their explanations will be omitted.

The structure of this element differs from the conventional optical writing type ferroelectric liquid crystal light valve in that the transparent electrode formed on the second transparent substrate 21 side is divided into two parts, and the dielectric The multilayer film mirror 19 is formed only in the center of the device, the area where the thickness of the ferroelectric liquid crystal layer is controlled is divided into two, and the surface of the transparent substrate 1 has the structure shown in FIG. The point is that the planar optical element shown in is formed. Although it is not necessary to divide the dielectric multilayer mirror 19, if a dielectric multilayer mirror with a high reflectivity is formed without dividing it, it becomes impossible to write a joint Fourier transform image or a correlation function from the transparent substrate 1 side. This is because, in the binarization joint transform correlator, it is rare that a readout light strong enough to require a dielectric multilayer mirror in the light modulation region is required.

[0033] By adopting such a structure, the injection and alignment process of the ferroelectric liquid crystal can be simplified, and the first light modulation layer and the second light modulation layer can be manufactured at the same time. became. In order to operate the first light modulation layer and the second light modulation layer independently, the transparent electrode layer 16b is grounded, and driving voltages are applied to each of the transparent electrode layers 16a and 16b independently. , ferroelectric liquid crystal layers 18a, 18
This is carried out by independently exciting each of b.

Of course, it goes without saying that a correlation function reading optical system as shown in FIG. 4 may be formed in the configuration shown in FIG. It goes without saying that the operating method of the optical pattern recognition device shown in FIG. 9 is the same as the operating method of the optical pattern recognition element in the embodiments described in FIGS. 2 and 3.

Note that in the embodiments described so far, either the first polarizing beam splitter 3 or the second polarizing beam splitter 5 formed on the upper surface of the transparent substrate 1 may be a simple mirror. Needless to say. When pattern recognition of alphabetic characters was performed using the optical pattern recognition element described above, it was confirmed that recognition could be performed at an operating speed higher than the video rate. It has also been found that accurate character recognition can be achieved even when six or fewer alphabetic characters are placed adjacent to each other and used as a reference image. The pattern recognition ability of the optical pattern recognition element of the present invention varies depending on the spatial frequency distribution of the image to be recognized, and is better able to identify correlated images included in medical images, landscape photographs, etc. than when performing character recognition. In this case, the pattern recognition ability deteriorates, so in this case, it is preferable to use one correlated image and one reference image.

[0036]

As explained above, the optical pattern recognition element of the present invention has a diffraction grating or prism for introducing external light on at least one surface of a transparent substrate having surfaces parallel to each other, and a required amount of light. a first optical writing type light modulation layer for recording and displaying external image information including at least one reference image including a target and at least one newly input correlated image; a planar Fourier transform lens; a second optical writing type optical modulation layer for recording and displaying a Fourier transform of the external image information recorded and displayed on the first optical writing type optical modulation layer; and a second optical writing type optical modulation layer. third optical writing for recording and displaying a correlated image representing a correlation function between the reference image and the correlated image obtained by Fourier transforming the external image information recorded and displayed on the layer; The structure includes a light modulation layer of the type, a polarizing beam splitter made of an optical multilayer film, and a light reflection layer that optically couples all of these planar optical elements. By using an optically written ferroelectric liquid crystal light valve structure as the light modulation layer and the second optically written light modulation layer, the optical system can be miniaturized, the optical system can be easily adjusted, and the video rate can be increased. The above-described high-speed pattern recognition can be achieved, and the present invention has great effects on machine vision used in automatic assembly machines, medical image diagnosis systems, and various other pattern recognition systems.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an example of an optical pattern recognition element of the present invention, in which (a) is a plan view and (b) is a cross-sectional view.

FIG. 2 is a process diagram showing the operation steps of the optical pattern recognition element of the present invention, in which (a) is an input image writing step, (b) is a joint Fourier transform writing step, (c) is a correlation function writing step, ( d) is a correlation function reading step.

FIG. 3 is a cross-sectional view showing the configuration of an optical pattern recognition element of the present invention using an optical writing type ferroelectric liquid crystal light valve in the light modulation section, (a) is a cross-sectional view of the overall configuration, and (b) is a cross-sectional view of the overall configuration. FIG. 3 is an enlarged cross-sectional view of the light modulation section.

FIG. 4 is a cross-sectional view showing the configuration of an optical pattern recognition element of the present invention having a correlation function reading optical system.

FIG. 5 is a configuration diagram showing an example of a conventional optical correlator;
FIG. 2A is a configuration diagram showing an example of a joint transform correlator, and FIG. 1B is a configuration diagram showing an example of a Vander Lucht type optical correlator.

FIG. 6 is a diagram showing an example of an input image in a joint transform correlator.

[Figure 7] One of the correlation peaks in the joint transform correlator
It is a figure which shows an example.

FIG. 8 is a diagram showing an example of a correlation peak in a Vander Lucht type correlator.

FIG. 9 is a cross-sectional view showing the structure of an example of an optical pattern recognition element of the present invention in which a planar optical element is formed on the readout side substrate of an optical writing type ferroelectric liquid crystal light valve.

[Explanation of symbols]

1 Transparent substrate 2 First HG 3 First polarizing beam splitter 4 HFL 5 Second polarizing beam splitter 6 Second HG 7 First light modulating layer 8 Second light modulating layer 9 Dielectric multilayer mirror 10a , 10b Input image writing light 11 First coherent light 12 Second coherent light 13 Correlation function reading light 14 First light modulator 15 Second light modulator 16a, 16b, 16c Transparent electrode layers 17a, 17b
, 17c alignment film layers 18, 18a, 18b ferroelectric liquid crystal layer 19 dielectric mirror 20 photoconductive layer 21 second transparent substrate 22 spacer 23 anti-reflection coating 24 polarizing beam splitter 25 protective transparent substrate 26 third transparent substrate 27 Imaging HL 28 Fourth transparent substrate 29 Photodiode array 30 Adhesive layer 31 Laser 32 Beam expander 33 Beam splitter 34 Input image 35 First Fourier transform image 36 Optically written liquid crystal light valve 37 Polarizing beam splitter 38 Second Fourier transform lens 39 CCD camera 40, 41 Mirror 42 Matched filter 43 DC component 44 Correlation peak 45 Convolution

Claims (6)

[Claims] 1. A diffraction grating or prism for introducing external light, at least one reference image including a desired target, and at least one newly inputted image on at least one surface of a transparent substrate having surfaces parallel to each other. a first optical writing type light modulation layer for recording and displaying external image information including two correlated images; a planar Fourier transform lens; A second device that records and displays the Fourier transform of the image information from the outside.
The reference image obtained by Fourier transforming the external image information recorded and displayed on the second optical writing type light modulation layer and the second optical writing type optical modulation layer is A third optical writing type light modulation layer that records and displays a correlation image representing a correlation function with the correlation image, a polarizing beam splitter made of an optical multilayer film, and a light reflection that optically couples all these planar optical elements. An optical pattern recognition element characterized by comprising a layer. 2. The first optically writable light modulating layer and the third optically writable light modulating layer are the same light modulating layer, and all the planar optical elements have one planar Fourier transform. 2. The optical pattern recognition element according to claim 1, wherein the optical pattern recognition element is arranged at symmetrical positions with respect to the lens. 3. All of the planar optical elements include a transparent substrate, a photoconductive layer, a liquid crystal alignment layer, a ferroelectric liquid crystal layer having bistable memory property between light reflectance and applied voltage, and voltage application means. 3. The optical pattern recognition element according to claim 1, wherein the optical pattern recognition element is formed on a surface of a read-out side substrate of an optical writing type liquid crystal light valve. 4. The first to third optically writable light modulation layers include a transparent substrate, a photoconductive layer, a liquid crystal alignment layer, and a ferroelectric material having bistable memory property between light reflectance and applied voltage. 3. The optical pattern recognition element according to claim 1, wherein the optical pattern recognition element is an optical writing type liquid crystal light valve comprising a liquid crystal layer and voltage applying means. 5. A means for detecting a correlation peak included in the correlation image, which includes at least a polarizing beam splitter, an imaging lens, and a photodetector, is adhesively formed on the transparent substrate having surfaces parallel to each other. The optical pattern recognition element according to claim 3 or 4. 6. The optical device according to claim 1, wherein the surface of the transparent substrate on which the planar optical element is formed is protected by adhering another transparent substrate. Optical pattern recognition element.