JP2811468B2 - Optical writing type liquid crystal light valve and liquid crystal ride valve device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical writing type liquid crystal light valve used for an optical pattern recognition device and an optical associative device.

[Summary of the Invention]

The present invention relates to a writing means using light such as a laser beam or an LED, and an optical writing type liquid crystal light valve formed of a photoconductive layer, a light reflecting layer, a liquid crystal alignment layer, a liquid crystal layer, a voltage applying means, and a transparent substrate. Of the voltage applying means, the voltage applying means sandwiched between the transparent substrate and the photoconductive film is a transparent electrode, and the transparent electrode is divided into at least two or more parts to which voltage can be independently applied. Is divided into a ring shape or a matrix shape centered on the center of the substrate surface, so that the magnitude of the spatial frequency component of the information to be optically written can be arbitrarily controlled or the information to be optically written can be arbitrarily divided. By enabling recording, the liquid crystal layer used in the present liquid crystal light valve is made of a ferroelectric liquid crystal having a bistable memory, thereby facilitating binary recording of information to be optically written, and providing high sensitivity light. putter This provides a means that can realize the recognition of the user.

[Conventional technology]

Conventionally, there have been many proposals and attempts to recognize an optical pattern by applying an optical writing type liquid crystal light valve having high resolution and contrast to correlated optics. Also, in optical pattern recognition using a joint transform correlator, the binarization processing is performed on the Fourier transform plane, so that the SN for the cross-correlation peak is obtained.
There have been proposals to improve R [B. Javidi, CJ Kuo, Applied Optics, 27, 663 (1
988): B.Jabidi and CJKuo.Appl.Opt.27,663 (198
8)].

[Problems to be solved by the invention]

However, the conventional optical writing type liquid crystal light valve is TN
Most of them use liquid crystal.In order to record a binarized Fourier transform image, the Fourier transform image is read into an electric system using a CCD or the like, and then binarized. Recording must be performed on an optical writing type liquid crystal light valve using a scanning optical system such as a scanner. Further, even if an optical writing type liquid crystal light valve using a ferroelectric liquid crystal having a bistable memory property as seen in the present invention is used, the light intensity distribution of the Fourier transform image is abruptly changed in the central symmetry. If you want to binarize recording up to a high spatial frequency, you must create a Fourier transform image using extremely intense light or perform long-time exposure, and conversely, the Fourier transform image in the low spatial frequency region will be destroyed There was a problem that.

[Means for solving the problem]

The liquid crystal light valve of the present invention divides a transparent electrode as a voltage applying means sandwiched between a transparent substrate and a photoconductive film layer into at least two or more portions to which a voltage can be independently applied. Of the Fourier-transformed image in the liquid crystal light valve of the present invention, or the optical writing sensitivity for an arbitrary portion of the information to be optically written. The above problem was solved by making it controllable.

[Action]

The liquid crystal light valve of the present invention irradiates the entire writing surface of the liquid crystal light valve once with light, and a DC bias voltage sufficiently higher than the bright threshold voltage of the photoconductive layer or 100 Hz to 5 Hz.
Apply a DC bias voltage superimposed with an AC voltage of 0 kHz to all divided voltage applying means to align the ferroelectric liquid crystal to a stable state in one direction and memorize the state, or in the dark without light irradiation, Applying a DC bias voltage sufficiently higher than the threshold value or a DC bias voltage superimposed with an AC voltage of 100 Hz to 50 kHz to all voltage applying means to align the ferroelectric liquid crystal to a unidirectional stable state, A DC bias voltage of the opposite polarity which is equal to or lower than the threshold voltage of the photoconductive layer at the time of darkness and equal to or higher than the threshold voltage of the photoconductive layer at the time of light irradiation without light irradiation. Optical writing of an image or a Fourier transform image is performed by using a laser beam or the like while applying a DC bias voltage on which an AC voltage of 50 kHz is superimposed to a divided voltage application unit with a predetermined magnitude. Performing the second step. In the second step, carriers are generated in the photoconductive layer in the region irradiated with the laser, and the generated carriers drift in the direction of the electric field due to the DC bias voltage. As a result, the threshold voltage of the photoconductive layer decreases, A bias voltage having a reverse polarity equal to or higher than the threshold voltage is applied to the irradiated region, and the molecules of the ferroelectric liquid crystal are inverted with the inversion of spontaneous polarization, and the liquid crystal shifts to the other stable state and the image or The Fourier transform image is stored. At this time, even if the information to be optically written has a centrally symmetric light intensity distribution in which the central light intensity is large, such as a Fourier transform image, the voltage applying means is provided in a ring shape or a matrix centered on the in-plane center. By applying a higher voltage to the outer electrode than the in-plane center of the divided ring-shaped or matrix-shaped electrode, the surface of the divided ring-shaped or matrix-shaped electrode is substantially more illuminated than the light applied to the in-plane center. Since the optical writing sensitivity to the light irradiated inside and outside can be improved, the Fourier spectrum in a wide spatial frequency region can be clearly stored. The image or Fourier transform image formed in this manner is irradiated with light of linearly polarized projection light whose polarization axis is aligned with the direction of alignment of liquid crystal molecules aligned in the first step (or a direction perpendicular thereto), and light reflection. It can be read out on a screen by projection through an analyzer arranged so that the polarization axis is perpendicular (or parallel) to the polarization direction of the light reflected by the layer. After the completion of the second step, the polarity is inverted again, and a DC bias voltage that is equal to or less than the dark threshold voltage and equal to or greater than the bright threshold voltage is applied to all the electrodes or a specific electrode. By irradiating light, partial erasing (partial writing) can be performed.

〔Example〕

Hereinafter, embodiments of the liquid crystal light valve of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing the structure of a liquid crystal light valve according to the present invention. The part having a different structure from the conventional liquid crystal light valve uses a ferroelectric liquid crystal having a clear bistability between light transmittance or light reflectance and an applied voltage as a liquid crystal layer, and has at least a transparent electrode as a voltage applying means. That is, it is divided into two or more portions to which a voltage can be independently applied.

Transparent substrates 1a and 1b, such as glass or plastic, for holding liquid crystal molecules are composed of a transparent electrode layer 2a, a lead wire 12, and an insulating film layer 13 divided so that at least two or more voltages can be independently applied to the surface. The transparent electrode layer 2b, which is not divided at all, and the alignment film layers 3a and 3b on which silicon monoxide is obliquely deposited at an angle in the range of 75 to 85 degrees from the normal direction of the transparent substrate are provided. The transparent substrates 1a and 1b have their alignment film layers 3a and 3b side,
The ferroelectric liquid crystal layer 4 is sandwiched between the spacers 9 by controlling the gap therebetween.

Further, a photoconductive layer 5, a light shielding layer 6, and a dielectric mirror 7 are formed on the transparent electrode layer 2a on the writing side by light between the alignment film 3a and the transparent substrate 1a on the writing side and the reading side. Transparent substrate
On the outside of the cell 1b, anti-reflection coating layers 8a and 8b are formed.

Next, a method of dividing the transparent electrode layer 2a will be described in more detail. FIG. 2 is a plan view showing one embodiment of the transparent electrode division. FIG. 2 (a) shows a case where the transparent electrode layer 2a is divided into a ring shape, and FIG. It shows the case of dividing into a shape. In either case, the divided transparent electrode layer 2a is electrically connected to a lead wire 12 for connection to an external power supply, and the lead wire 12 is short-circuited with another transparent electrode layer. It is configured to be insulated by the insulating film layer 13 in order to prevent this. The transparent electrode layer 2a and the lead wire are electrically connected by through holes as shown in FIG. Therefore, the lead wire 12 and the transparent electrode layer 2a are not electrically coupled to each other except at the through holes, and no short circuit occurs between the divided transparent electrode layers. The material for the transparent electrode layer was ITO, which was 1600 mm thick, formed by vapor deposition, sputtering, or CVD.
A thin film was used. The insulating film 13 was made of SiO ₂ having a thickness of 1000 Å, and the lead wire 12 was made of Cr having a line width of 100 μm and a thickness of 500 Å. Au / Cr, A which is a material other than Cr as the lead wire 12
It goes without saying that l, Al-Si, Ti, Mo, Ti-Si, Cr-Si or the like may be used. In addition, the lead wire 12 and the transparent electrode layer 2a are not bonded using the insulating film layer 13 and the through hole as shown in the embodiment of FIGS. 12 and transparent electrode 2a directly connected
The lead wire 12 may be led out to the outer periphery of the transparent substrate 1a through a gap appropriately provided in 1a.

In one embodiment of the transparent electrode division in the case of the ring division shown in FIG. 2 (a), the transparent electrode layer 2a has a line width of 2 m.
m and a ring width of 0.2 mm, and the number of divisions was 6. By dividing the transparent electrode layer 2a in this way,
For example, when a centrally symmetric optical pattern such as a Fourier transform image is recorded in the liquid crystal light valve of the present invention, an arbitrary centrally symmetric weight can be given to the recorded optical pattern. Of course, the line width of the transparent electrode layer 2a in FIG. 2A is several tens μm or more, the gap width is several μm or more,
Can be easily formed without using a special fine processing technique if the line width is several μm or more.

Further, in one embodiment of the transparent electrode division in the case of the matrix division shown in FIG. 2 (b), the transparent electrode layer 2a is divided into a matrix having a size of 3 mm square and a gap of 0.2 mm, and the number of divisions is eight. × 8. The lead wire 12 may be arbitrarily taken out other than the way shown in FIG. 2B. Thus, the transparent electrode layer 2a
By dividing, for example, in the case of performing a matrix recording of an image using a microlens array, each of the recorded matrix-shaped optical patterns can be arbitrarily weighted, or any of the matrix-shaped optical patterns An optical pattern can be selected and recorded. Of course, if the size of the transparent electrode layer 2a in FIG. 2B is several μm square or more, the gap width is several μm or more, and the lead wire width is several μm or more, as in the case of ring-shaped electrode division, special Matrix-shaped electrode division can be easily formed without using fine processing. However, there is a drawback that as the number of divisions increases, it becomes more difficult to take out the lead wire than the ring-shaped electrode division.

Next, a method for manufacturing the liquid crystal light valve of the present invention will be briefly described. First, a transparent glass substrate is prepared as the transparent substrates 1a and 1b, and a Cr thin film is coated on the glass substrate 1a for 500 minutes.
(4) After formation, a lead wire 12 having a line width of 100 μm was formed by photolithography. Further, after forming SiO ₂ thereon by 1000 mm, a through hole is formed by photolithography to form an insulating film layer 13, an ITO transparent electrode layer is formed on the insulating film layer 13 as a transparent electrode layer 2 a, and photolithography is performed again. The ITO transparent electrode layer was divided into rings or matrices. On the other hand, an ITO transparent electrode layer was also formed as a transparent electrode layer 2b on the surface of the transparent glass substrate 1b. On the optical writing side transparent electrode layer 2a, a gas mainly composed of SiF ₄ was subjected to discharge decomposition to form intrinsic hydrogenated amorphous silicon having a thickness of 3 μm, thereby forming a photoconductive layer 5. A light-shielding layer 6 is provided on the photoconductive layer 5 thus manufactured,
And the SiO ₂ are stacked 15 layers dielectric mirror 7 as a light reflective layer
Was formed. When the visible light reflectance of the dielectric mirror 7 is sufficiently large and the influence of the read light on the photoconductive layer 5 is extremely small, the light shielding layer 6 can be omitted. Further, silicon monoxide (SiO) was set on the dielectric mirror 7 and the transparent electrode 2b on the read side such that the straight line connecting the substrate and the evaporation source had an angle of 82 degrees with respect to the normal direction of the substrate. While observing the film thickness with a liquid crystal oscillator type film thickness meter set in the normal direction of vapor deposition, the liquid crystal alignment layer
3a and 3b were formed. The transparent substrates 1a and 1b have their alignment film layers 3a and 3b
Are opposed to each other to control and form a gap through a spacer 9 made of an adhesive to which glass fiber having a diameter of 1.5 μm is added.
The ferroelectric liquid crystal layer 4 was sandwiched. The encapsulated ferroelectric composition is a ferroelectric liquid crystal composition obtained by adding an optically active substance to an ester-based SmC liquid crystal mixture. As the ester-based SmC liquid crystal mixture, 4-((4′-octyl) phenyl ) Benzoic acid (3 "-fluoro, 4" -octyloxy) phenyl ester and 4-((4'-octyloxy) phenyl) benzoic acid (3 "-fluoro, 4"-)
A 1: 1 mixture of octyloxy) phenyl ester and 25% by weight of 5-octyloxynaphthalenecarboxylic acid, 1′-cyanoethyl ester as an optically active substance were added to obtain a ferroelectric composition. Using.
Also, as shown in FIG. 3, the surface of the transparent electrode layer 2a of the liquid crystal light valve of the present invention has irregularities due to through holes provided in the lead wire 12 and the insulating film 13, and the influence of the dielectric mirror 7 is reduced. It reaches the surface and adversely affects the read image. Therefore, it is desirable to perform the surface smoothing treatment of the photoconductive layer 5 by a method such as forming the photoconductive layer 5 by the above-described method, spin-coating the resist, and ion-etching the surface until the resist disappears.

An example of light pattern recognition performed using the liquid crystal light valve manufactured as described above will be described. FIG. 4 is a diagram showing the principle of the configuration of an optical pattern recognition device using the liquid crystal light valve of the present invention. In FIG. 4, a first laser light source
The coherent light emitted from 14 is expanded to a predetermined beam diameter by a first beam expander 15 and then applied to a photographic film 16 on which a reference image and a correlated layer are recorded side by side, and subjected to a first Fourier transform. The light is Fourier-transformed by the lens 17 and is applied to the writing surface of the liquid crystal light valve 18 of the present invention. The liquid crystal light valve of the present invention is uniformly erased in advance by applying a voltage higher than the dark threshold voltage or higher than the light threshold voltage. However, when erasing is performed by applying a voltage equal to or higher than the threshold voltage at the time of light, uniform writing light is irradiated on the surface simultaneously with the application of the voltage.

Then, when the Fourier-transformed laser light is applied to the writing surface of the liquid crystal light valve 18 of the present invention, the liquid crystal light valve 18 of the present invention causes the liquid crystal light valve 18 to have a threshold voltage lower than or equal to the threshold voltage at the time of darkness. DC bias voltage of reverse polarity or
A DC bias voltage on which an AC voltage of 100 Hz to 50 kHz is superimposed is applied for a predetermined time to record a Fourier transform image of the reference image and the correlated image recorded on the photographic film 16. Since the optical writing sensitivity to the liquid crystal light valve of the present invention increases as the bias voltage applied at this time becomes larger than the threshold voltage at the time of light, an appropriate voltage is applied to each of the divided transparent electrode layers independently. By applying a bias voltage, a desired image can be recorded on the liquid crystal light valve of the present invention. Needless to say, at this time, the liquid crystal light valve 18 of the present invention has a DC bias voltage having a reverse characteristic of a DC bias voltage lower than the dark threshold voltage and higher than the bright threshold voltage, or a DC bias voltage superimposed with a current voltage of 100 Hz to 50 kHz. With the voltage applied, the first laser light source 14 is turned on for a predetermined time, or an optical shutter disposed at a predetermined position in an optical path between the first laser light source 14 and the liquid crystal light valve 18 of the present invention is activated. Optical writing may be performed by turning ON only for a predetermined time. By applying a bias voltage only to a specific transparent electrode among the divided transparent electrodes, optical writing can be performed only in a specific area to which the bias voltage has been applied, or only a specific area of a recorded image can be erased. can do.

Next, after emitting a coherent image from the second laser light source 19, the light beam is expanded to a desired diameter by the second beam expander 20, and the optical path is switched by the polarizing beam splitter 21 to switch the liquid crystal light valve 18 of the present invention. Irradiate the reading surface of At this time, the above-described Fourier transform image of the reference image and the correlated image is recorded in the liquid crystal light valve of the present invention, and no bias voltage is applied. Accordingly, in the light from the second laser light source 19 applied to the reading surface, the light applied to the area where the Fourier transform image is recorded is read by rotating the polarization plane by 90 degrees, and is read by the polarization beam splitter. Light that has passed through 21 and applied to the area where the Fourier transform image has not been recorded is reflected by the polarization beam splitter 21 again because it is not affected by its polarization plane. That is, the light immediately after passing through the polarization beam splitter 21 becomes intensity information of the Fourier transform of the reference image and the correlated image recorded on the photographic film 16. Of course, at this time, even if a normal beam splitter is used instead of the polarizing beam splitter 21 and a polarizer such as a polarizing film or a Glan-Thompson prism is arranged between the beam splitter and the liquid crystal light valve 18 of the present invention, the above-described reading is performed. The same operation as the stock operation can be performed. The intensity information of the Fourier transform of the reference image and the correlated image read out in this way is again Fourier transformed by the second Fourier transform lens 22 and the CCD camera 2
Read in 3. The information read out by the CCD camera 23 can be observed on the video monitor 24, and the observed information is the autocorrelation peak and the cross-correlation peak of the reference image and the correlated image. Note that the photographic film 16 and the liquid crystal light valve 18 of the present invention are each provided with a first Fourier transform lens 17.
The liquid crystal light valve 18 and the CCD camera 23 of the present invention are arranged on the front focal plane and the rear focal plane of the second Fourier transform lens 22, respectively. Further, when the size of the Fourier transform image recorded in the liquid crystal light valve 18 of the present invention is not appropriate, or when the size of the autocorrelation peak and the cross-correlation peak input to the CCD camera 23 are not appropriate, A magnifying lens system may be inserted between the rear focal plane of the first Pulley transform lens 17 and the liquid crystal light valve 18 of the present invention, or a magnifying lens system may be inserted between the rear focal plane of the second Fourier transform lens 22 and the CCD camera 23. To enlarge the image to the desired size. It is considered that the greater the intensity of the cross-correlation peak among the correlation peaks thus obtained, and the smaller the half-width of the cross-correlation peak, the more accurately the similarity between the reference image and the correlated image can be identified. .

One embodiment of the reference image and the correlated image input to the photographic film 16 in FIG. 4 is shown in FIG. The input image shown in FIG. 5 is a negative image in which Chinese characters “light” are arranged side by side.

The pattern shown in FIG. 5 is applied to the photographic film 16 shown in FIG.
The liquid crystal light valve having a transparent electrode divided into a ring shape shown in FIG. 2A and used as the liquid crystal light valve 18 of the present invention shown in FIG. The resulting cross-correlation peak was observed. As a result, it was found that the intensity and half width of the cross-correlation peak obtained by the magnitude and distribution of the bias voltage applied to each divided electrode of the liquid crystal light valve of the present invention having the transparent electrode divided into a ring shape changed. When a voltage having a distribution as shown in FIG. 6 is applied between the transparent electrode layer 2a and the photoconductive layer 5 in FIG. 1, a cross-correlation peak having the strongest intensity and the narrowest half width is obtained. all right. At this time, it was also found that it was necessary to increase the difference between the maximum value and the minimum value of the applied bias voltage for a more complicated pattern.

Next, the pattern shown in FIG. 5 is recorded on the photographic film 16 shown in FIG. 4, and the liquid crystal light valve having the transparent electrodes divided into a matrix shown in FIG. The liquid crystal light valve of FIG.
The image of the photographic film 16 can be changed to the liquid crystal light valve of the present invention by replacing the Fourier transform lens with a lens having a short focal length.
An image recorded on the liquid crystal light valve of the present invention is arranged at an image forming position where the image is formed on the writing surface of the CCD camera 2 by using a lens having a short focal length due to the structure of the second Fourier transform lens 22.
The recording characteristics of the liquid crystal light valve of the present invention were observed using the optical pattern recognition device shown in FIG. At this time, it was found that various images as shown in FIG. 7 could be recorded by applying various bias voltages to the transparent electrode layers divided in a matrix.

〔The invention's effect〕

As described above, the liquid crystal light valve of the present invention is formed by writing means using light such as a laser beam or an LED, and a photoconductive layer, a light reflecting layer, a liquid crystal alignment layer, a liquid crystal layer, a voltage applying means, and a transparent substrate. In the optical writing type liquid crystal light valve, the voltage applying means sandwiched between the transparent substrate and the photoconductive film is a transparent electrode, and at least two or more independent voltages are applied to the transparent electrodes. By dividing the transparent electrode into rings or a matrix around the center of the substrate, the size of the spatial frequency component of the optically written information can be arbitrarily controlled, It is possible to divide the information to be written arbitrarily and record the binary information of the optically written information by using a ferroelectric liquid crystal having a bistable memory for the liquid crystal layer used in the present liquid crystal light valve. Since it is easy to record and can realize highly sensitive optical pattern recognition, machine vision, character / graphic recognition and associative memory using optical pattern recognition, as well as optical arithmetic processing and copying using optical images The effect on high performance of office equipment such as a projector and a projector is great.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of a liquid crystal light valve according to the present invention, and FIG. 2 is a plan view showing one embodiment of a transparent electrode division of the liquid crystal light valve according to the present invention.
FIG. 2B shows the case of matrix division, while FIG. 2B shows the case of matrix division. FIG. 3 is a view showing a sectional structure of a voltage applying means of the liquid crystal light valve of the present invention, and FIG. 4 is a view showing a principle configuration of an optical pattern recognition device using the liquid crystal light valve of the present invention. FIG. 6 is a diagram showing an embodiment of inputting an image to a photographic film in FIG. 4, FIG. 6 is a diagram showing an embodiment of voltage application to a liquid crystal light valve of the present invention, and FIG. It is a figure which shows the example of recording of the pattern to the liquid crystal light valve of this invention. 1a, 1b ... transparent substrate 2a, 2b ... transparent electrode layer 3a, 3b ... alignment film layer 4 ... ferroelectric liquid crystal layer 5 ... photoconductive layer 6 ... light shielding layer 7 ... dielectric mirror 8a, 8b … Non-reflective coating 9… Spacer 10… Write light 11… Read light 12… Lead wire 13… Insulating film layer 14… First laser light source 15… First beam expander 16 ... Photographic film 17 First Fourier transform lens 18 Liquid crystal light valve of the present invention 19 Second laser light source 20 Second beam expander 21 Polarizing beam splitter 22 Second Fourier transform lens 23 ... CCD camera 24 ... Video monitor

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-2-131218 (JP, A) JP-A-1-116527 (JP, A) JP-A-1-74529 (JP, A) JP-A-61- 198119 (JP, A) JP-A-56-89714 (JP, A) JP-A-50-81497 (JP, A) Japanese Utility Model Laid-Open No. 57-14123 (JP, U) (58) Fields investigated (Int. ⁶ , DB name) G02F 1/135

Claims (4)

(57) [Claims] 1. An optical writing type liquid crystal light valve comprising a transparent substrate on which a transparent electrode and a photoconductive layer are formed, wherein the transparent electrode is divided into a plurality of portions to which voltage can be independently applied, and is divided. An optical writing liquid crystal light valve, wherein an applied voltage applied to the transparent electrode is a voltage having a centrally symmetric distribution. 2. The applied voltage according to claim 1, wherein the applied voltage has a distribution such that the voltage is higher in a divided electrode outside the central divided electrode than in the central divided electrode.
3. An optical writing type liquid crystal light valve according to claim 1. 3. The optical device according to claim 1, wherein the liquid crystal layer used in the liquid crystal light valve is a ferroelectric liquid crystal having a bistable memory between a light reflectance and an applied voltage. Built-in liquid crystal light valve. 4. An image writing unit using light such as a laser beam or an LED, an optical writing type liquid crystal light valve including a transparent substrate on which a transparent electrode and a photoconductive layer are formed, the image writing unit and the light And a Fourier transform lens provided between the write-type liquid crystal light valves, wherein the transparent electrode is divided into a plurality of portions to which a voltage can be independently applied, and an application voltage is applied to the divided transparent electrodes. A liquid crystal light valve device, wherein the voltage has a distribution according to the position of the transparent electrode.