JP2610031B2 - Bistable spatial light modulator and light modulation method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spatial light modulator and a light modulation method, and particularly to binarization, amplification, recording, and analogization of optical two-dimensional information such as an image and a data pattern. The present invention relates to a bistable spatial light modulator having various functions such as digital conversion, digital logical operation, and display, and a light modulation method using the spatial light modulator.

SUMMARY OF THE INVENTION The present invention relates to a spatial light modulator and a light modulation method for controlling amplitude or phase of light and spatially processing and displaying two-dimensional information such as an image and a data pattern.
Between a photoconductive layer that converts optical two-dimensional information into electrical two-dimensional information and an electro-optical layer that converts electrical information into optical properties of the material such as refractive index and optical rotation, polyvinyl alcohol ( (Hereinafter referred to as PVA) A polarizing film mainly composed of a material is inserted, these three layers are adhered to each other, and transparent electrodes are attached to both end surfaces thereof.
By injecting two-dimensional information or further injecting two-dimensional bias light or signal light from the photoconductive layer side, for a certain intensity of the incident light, the light emitted from this element becomes two stable lights. It realizes the so-called optical bistability characteristic that has a state and settles in one of the states according to the history of the incident light, and the differential gain characteristic in which the output light intensity is binarized using a certain incident light intensity as a threshold. It can execute two-dimensional optical signal binarization, amplification, recording, analog / digital conversion, digital logic operation between two-dimensional information, display, and the like.

[Prior Art] As a conventional bistable spatial light modulator, there are the following elements.

(1) As shown in FIG. 20, the liquid crystal light valve 12, the polarizer 13, the mirror 14, the semi-transmissive mirror 17, and the lens 16 driven by the AC power supply 8 are combined to make the input light 9 from the entire surface of the liquid crystal light valve. (Ref.1, UHGerlach, UKSengupta and S.A. Collins,
Jr.:Optical Engineering, Vol.19, No.4 (1980) P.452 ~
See page 455).

(2) As shown in FIG. 21, a liquid crystal cell is inserted between two polarizers 13 (polaroid films), the photoconductive element is connected to the transparent electrode 2 of the liquid crystal cell, and the input light 9 is modulated. An element that obtains output light 10 (Reference 2, AAVasiliev, INKompanets a
nd AVParfenov: Mikroelektronika Vol.9 No.1 (198
0) P.87-P.89, or Reference 3, AAVasiliev, INKompan
ets and AVParfenov: Optik, Vol. 67, No. 3 (1984) P. 22
3 to P.236).

(3) As shown in FIG. 22, an element in which the liquid crystal layer 6 and the photoconductive layer 3 are in close contact with each other and the transparent electrodes 2 are attached to both end surfaces thereof (Reference 4, IN
Kompanets, AVParfenov and Yu.M.Popov: Optics Commu
nications, Vol. 36 No. 5, (1981) P. 415 to P. 416).

(4) Dielectric mirrors 18 are provided on both sides of the liquid crystal layer 6 as shown in FIG.
Fabry-Perot resonator (eg JAJenk)
ins and HEWhite: Fundamentals of Optics P.301-P.
302) is adhered to the photoconductive layer 3 and the transparent electrodes 2
Attached element. (Ref. 5, INKompanets, AVParfenov
and Yu.M.Popov: Optics Communications, Vol.36, No5
(1981) pp. 417-418).

[Problems to be Solved by the Invention] The conventional bistable spatial light modulator has the following disadvantages. That is, the device shown in FIG. 20 has drawbacks such as a large-scale configuration, weakness to mechanical vibration, and difficulty in optical position adjustment because optical feedback is performed using a mirror and a lens. Was.

In the device shown in FIG. 21, the liquid crystal cell and the photoconductive device are electrically connected, so that the photoconductive device is spatially arranged and an enormous amount of wiring is required to process two-dimensional information. It has disadvantages such as.

Since the device shown in FIG. 22 uses a guest-host type liquid crystal, the difference between these two emitted light intensities in a so-called bistable characteristic having two emitted light intensities with respect to a certain incident light intensity is small ( (Small contrast) and slow response speed.

Since the element shown in Fig. 23 has the same structure as the Fabry-Perot resonator, only light of a specific wavelength can be used, and the thickness of the liquid crystal must be uniform on the order of the wavelength of the light. It had drawbacks such as difficulty in device fabrication.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned drawbacks of the related art, and binarizes two-dimensional optical information such as images and data patterns, amplifies and records, analog-digital conversion, and two-dimensional information. It is an object of the present invention to provide a spatial light modulator capable of performing digital logic operation and display of two-dimensional optical information among each other.

[Means for Solving the Problems] In order to achieve such an object, the optical modulator of the present invention has a liquid crystal layer whose optical characteristics change due to an electric field between two transparent electrodes, and a liquid crystal layer equivalent to the liquid crystal layer. Or a transparent dielectric layer with a larger dielectric constant and a polarizing layer with the same or larger dielectric constant and resistivity as the liquid crystal layer and the ability to select linearly polarized light in a specific polarization direction, and a transparent oil And a transparent photoconductive layer whose resistivity is reduced by light irradiation.

The light modulation method of the present invention comprises a transparent photoconductive layer whose resistivity changes by light irradiation, a liquid crystal layer whose optical properties change by an electric field, and a transparent dielectric layer having a dielectric constant and resistivity equal to or larger than that of the liquid crystal layer. A bistable type in which a polarizing layer having the same or larger relative permittivity and resistivity as the body layer and the liquid crystal layer and capable of selecting linearly polarized light in a specific polarization direction and a transparent oil are sequentially arranged. An AC drive voltage is applied between two transparent electrodes of the spatial light modulator, a two-dimensional optical signal is incident from the liquid crystal layer side, and a two-dimensional optical signal is emitted from the photoconductive layer side. I do.

[Operation] The bistable optical modulator of the present invention performs feedback without using a mirror or a lens, and therefore solves the problems of the conventional element shown in FIGS. In this structure, the voltage change of the layer is efficiently transmitted to the liquid crystal layer. Therefore, the problem of the conventional device shown in FIG. 21 can be solved, and the problem of the device shown in FIG. 22 can be solved because the response speed is high and the contrast is high. Further, since the usable wavelength range of light is wide and element fabrication is easy, it has a feature that the conventional disadvantage shown in FIG. 23 can be solved.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of an embodiment of a bistable spatial light modulator according to the present invention. In this example, a glass substrate having a transparent electrode 2 attached thereto, a transparent photoconductive layer 3 having a transparent electrode 2 attached thereto, a transparent oil layer 4 having a high dielectric constant and resistivity, and a linearly polarized light having a specific polarization direction are selected. It includes a polarizing layer 5, a transparent dielectric layer 19 to which an alignment layer 7 is attached, a liquid crystal layer 6, and an alignment layer 7 and a glass substrate 1 to which a transparent electrode 2 is attached.

As a liquid crystal material, a nematic liquid crystal or a cholesteric liquid crystal is used, and a bistable light modulation operation is performed by utilizing a change in birefringence or optical rotation caused by a change in the molecular arrangement of the liquid crystal due to an applied electric field. Do.

Photoconductive layer, CdS, (hereinafter referred to as BSO) CdSe, Se, SeTe, amorphous silicon film, B _i12 S _i O _20, made of a material that resistivity varies greatly by light irradiation such as B _i12 GeO _20.

The polarizing layer is made of a material having a dielectric constant and a resistivity equal to or larger than that of the liquid crystal (for example, a polarizing film mainly composed of PVA). As the transparent dielectric layer, a material having a high light transmittance, a high dielectric constant and a high resistivity, and a uniform refractive index in the XY plane when the light travels in the Z direction as shown in FIG. 1 is suitable. ing. For example, ferroelectric crystals such as SrTiO ₃ , LiTaO ₃ , LiNbO ₃ , and KD ₂ PO ₄ whose Z direction in FIG. 1 coincides with the c-axis of the crystal are suitable. Glass has a smaller dielectric constant than these materials, but can be used if its thickness is sufficiently reduced so as to satisfy the following expression (13). As the transparent oil, an insulating oil having a high light transmittance, a high relative dielectric constant and a high resistivity (for example, castor oil or fly oil) is suitable. The transparent oil has a role of preventing the formation of an air layer between the photoconductive layer and the polarizing film when they are in close contact with each other, and has a thickness of several μm or less. Here, as shown in FIG. 1, photoconductive layer 3, oil layer 4, polarizing film
5, Thickness (t _i ) of liquid crystal layer 6, alignment layer 7 and transparent dielectric layer 19
And the relative permittivity (ε _i ) are t ₁ , ε ₁ , t ₂ , ε ₂ , t ₃ ,
Assuming that ε ₃ , t ₄ , ε ₄ , t ₅ , ε ₅ , t ₆ , ε ₆ , the following relationship is established in the present invention.

t ₁ / ε ₁ >> t _i / ε _i > t _j / ε _j (1) where i = 3,4,6 and j = 2,5 By giving such a relationship to the thickness and relative dielectric constant of each layer, When light does not enter the device according to the present invention, a sufficient voltage can be applied only to the photoconductive layer.

Next, the operation of the optical modulator shown in FIG. 1 will be described. As an example, Table 1 shows the parameters (relative permittivity ε _i , thickness t _i , and resistivity ρ _i ) of the materials of each layer excluding the glass substrate and the transparent electrode constituting the present element. Obtaining these materials is easy. These materials have parameters suitable for the construction of the device. Since the liquid crystal layer, which is a main element of the present device, requires AC driving, the operation of the device when an AC voltage is applied to the transparent electrode will be described in the future.

In this optical modulator, there are six types of layers between the two transparent electrodes. In the case of AC driving, the impedance of the transparent dielectric layer 19, the alignment layer 7, and the transparent oil layer 4 is extremely small. The layers will be omitted, and the operation and operation of the optical modulator will be described assuming a three-layer structure element including the liquid crystal layer 6, the polarizing film 5, and the photoconductive layer 3.

The equivalent circuit of this three-layer structure is given in FIG. Wherein C ₁ is the capacitance of the photoconductive layer (BSO), resistance when R ₁ is not irradiated with light to BSO, R _P is P _j mw / cm ² of monochromatic light to BSO (wavelength: 442 nm) when irradiated with Resistance, R and C are BS
The resistance and capacitance determined by the average carrier (electron) capture time τ generated when a voltage is applied to O, C ₃ and R ₃ are the polarization film capacitance and resistance, and C ₄ and R ₄ are the liquid crystal layer capacitance and resistance. And each is represented by the following equation.

C ₁ = ε ₁ ε ₀ S / t ₁ (2) R ₁ = ρ ₁ t ₁ / S (3) R _P = ρ _P t ₁ / S (4) RC = τ (5) C ₃ = ε ₃ ε ₀ S / t ₃ (6) R ₃ = ρ ₃ t ₃ / S (7) C ₄ = ε ₄ ε ₀ S / t ₄ (8) R ₄ = ρ ₄ t ₄ / S (9) where ε ₀ is Vacuum permittivity, S is the cross-sectional area of the device, ρ
_P is the resistivity when the BSO is irradiated with light.

Reference 6 (P. Aubourg, JP Huignard, M. Hareng and RA
Mullen, Applied Optics, Vol. 21, No. 20, (1982), P. 3706
For illumination light R = 6MΩ of -P.3712) from P _k = 14mw / cm ² (wavelength 442 nm), and it found to be a C = 1.2nF, changing the irradiation intensity P _j from the document 6 Is given as shown in FIG.

Here, a voltage frequency suitable for driving the present device will be clarified. The parameters in Table 1, R and C obtained from FIG.
Is substituted into the equations (2) to (9), and the impedances of the BSO, the polarizing film and the liquid crystal layer are calculated assuming that S = 1 cm ² , and the applied voltage V _{0 of the} entire device as shown in FIG. The irradiation light intensity (P _j ) dependence of the ratio of the voltage _VLC applied to the layer is obtained. From this, it is understood that when the frequency f of the driving voltage is 100 Hz or more, the voltage applied to the liquid crystal layer and the intensity of the irradiation light have a substantially linear relationship, which is suitable for driving the element.

Next, the fact that the present optical modulator exhibits a bistable characteristic will be described.
As shown in FIG. 5A, when a linearly polarized light 9 is incident in the same direction as the polarizing film 5 from the 90 ° twisted nematic liquid crystal layer having a 90 ° twisted orientation, a two-layer structure composed of a liquid crystal layer and a polarizing film is formed. The device has a function equivalent to that of a generally well-known 90 ° twisted nematic liquid crystal cell, and exhibits, for example, a transmittance (T) vs. applied voltage (V _LC ) characteristic given in FIG. 5B. However, the current for driving the liquid crystal cell is an alternating current, and the horizontal axis is the effective value of the amplitude. Incident light 9
Is preferably blue or green light according to the sensitivity characteristics of BSO. Here, assuming that _Pi and _Pj are the intensities of the incident light and the outgoing light of the liquid crystal cell, the above characteristic is given by T = _Pj / _Pi = F ( _VLC ) (10).

Next, the light (P _j ) passing through the polarizing film is applied to the photoconductive layer (BS).
For changing the resistance R _P enters the O), the applied voltage V _LC applied to the liquid crystal layer is changed. As a result, the light amount P _j is changed entering the BSO, again the voltage of the liquid crystal layer is changed. By this series of feedback operations, the present device exhibits bistable characteristics.

Voltage V _LC applied to the liquid crystal layer in the range of frequencies of the above-mentioned drive voltage is expressed by approximately _{V LC = V D + αP j} (11). Here V _D is the voltage applied to the liquid crystal layer when no irradiation of light, alpha is a proportionality constant determined by the frequency f of the driving voltage. Equation (11) can be rewritten as T = P _j / P _i = (V _LC −V _D ) / αP _i (12), and P _{i is} a solution that satisfies equations (10) and (12) simultaneously. And P _j are given. This is
As shown in Fig. 5C, it can be easily known from the intersection of both equations. Optical bistable characteristics can be obtained at points A, B, C or
As shown in D and E, it is limited to the case where at least two or more intersections exist between the equations (10) and (12). That is, as shown in FIG. 5C, the applied voltage corresponding to the inflection point H of T = F (V _LC ) is V _H , and the impedance of the liquid crystal layer between the two transparent electrodes in FIG. _L and the total impedance of materials other than the liquid crystal layer and photoconductive layer is Z _M
And, when the minimum impedance of the photoconductive layer at the time of light irradiation is Z _ON , and the impedance at the time of no light irradiation is Z _OFF , at least the following conditions must be satisfied in order to obtain optical bistable characteristics. is there.

When the absorption coefficient at this time BSO and gamma, intensity P ₀ of the output light 10 of the present device to the intensity P _i of the input light 9 is given by _{P 0 = P j exp (-γt} 1) (14).

As an example, this element having the parameters in Table 1 is represented by f =
Driving with a voltage of 400 Hz (amplitude V ₀ = 30 V expressed in effective value)
490 n with the intensity P _c of light incident from the photoconductive layer as zero
FIG. 6 shows input / output characteristics (calculated values) when light _Pi having a wavelength of m is incident from the liquid crystal layer side. However, from γ = 3.4 cm ⁻¹ and t ₁ = 2 mm, exp (−γt ₁ ) = 0.5. In P _i <P _t when increasing the P _i from 0 in the figure, P ₀ vs. P _i characteristic is represented by a line connecting the points A, B. When P _i is further increased and P _t ≦ P _i , the P ₀ vs. P _i characteristic is represented by a line connecting points B, C, and D. Thereafter, when P _i is decreased, the P ₀ vs. P _i characteristic is represented by a line connecting points D, E, F, and A. As described above, the figure shows the incident light intensity P _i and the output light intensity
This indicates that P ₀ is in a bistable relationship.

By utilizing the characteristics shown in FIG. 6, it is possible to control a light pulse having a large power with a weak light pulse. For example, elements having the P ₀ -P _i characteristics such as FIG. 7 (a) (a characteristic of FIG. 6 and is equivalent), the incident light P _B of large power, such as shown in FIG. 7 (b) Then, the output light P _O is as shown in FIG.
At the point B. Next, the weak light pulse
When P _A enters the element, the value of the output light P ₀ becomes the value indicated by point A. And even finished incidence of the light pulse P _A, output light P ₀ is almost the same level as the point A as long as the P _B is sustained C
Keep point values. As a result, as shown in temporal changes FIG intensity P ₀ of the output light (c). That is, a light pulse having a large power can be controlled by a weak light pulse. The results are optical amplification, optical memory, wavelength and polarization conversion, conversion from incoherent light to coherent light,
Alternatively, various applications such as the inverse transform are possible.

Further, since V _D and α Changing the f is changed, P ₀ vs. P _i characteristic no hysteresis can be obtained. F = 370 Hz as an example, the amplitude of the drive voltage (effective value) V ₀ = 30 V, the light intensity P _c entering from the photoconductive layer side as zero, when entering from the liquid crystal layer side light P _i of a wavelength of 490nm FIG. 8 shows the P ₀ vs. P ₁ characteristics (calculated values) of the above. By utilizing the P ₀ vs. P _i characteristic of FIG. 8, a two-dimensional photodiode (only in the forward direction) can be constructed.

Furthermore, it is possible to control the transmittance of the element (T) changing the f by a constant P _i. As an example, P _i = 14
_{^{mw / cm 2, V 0 =}} 30V and as ^{_{P c = 0mW / cm 2,}} , shows T vs. f characteristics when incident P _i from the liquid crystal layer side (calculated) in Figure 9. Using the T vs. f characteristic of FIG.
The reset can be controlled by the frequency f.

Further, as shown in FIG. 1, by irradiating a control light 11 having a short wavelength of the incident light 9 at the same time as the intensity P _C of the intensity P _i from the photoconductive layer side, to control the intensity P ₀ of the emitted light 10 It is also possible. As an example, FIG. 10 shows T vs. _Pc characteristics (calculated values) when P _i = 14 mw / cm ² , V ₀ = 30 V, and f = 500 Hz. Utilizing T vs. P _C characteristic of FIG. 10, it is possible to control the output light P ₀ nonlinearly by P _C, it is possible to construct a two-dimensional optical transistor. For example FIG. 11 (a) and (b) 2 two optical images or data as shown in the pattern P _A and P _B of the incident light 9 and the control light 11 in FIG. 1
If incident on the element as can be done P _A, the optical logic operations such as AND or OR of P _B two-dimensionally.

It is also possible to control the P _i, P _c, the transmittance by adjusting the f (T) versus driving voltage (V ₀₎ characteristics. As an example, when f = 400 Hz, P _i = 14 mw / cm ² and P _c = 0 mw / cm ² ,
V ₀ characteristics (calculated values) are shown in FIG. 12, and f = 400 Hz, P _i = 14
mw / cm ^2, respectively T versus V ₀ characteristics when P _c = 10mw / cm ² (calculated value) in FIG. 13 shows. Utilizing T versus V ₀ characteristic of Figure 12, it is possible to construct a two-dimensional shutter having a memory function. That is, even if the transparent electrodes shown in FIG. 1 are formed into a simple matrix structure and the magnitude of the matrix is increased as in the case of an active matrix structure liquid crystal display comprising a thin film transistor array simply by controlling the magnitude of the driving voltage. A high definition display with high contrast can be constructed. This element has a simpler electrode structure than an element having an active matrix structure, and is suitable for high definition display.

Further, by adjusting the intensity of the frequency input light or control light of the drive voltage as shown in FIG. 13, it can be changed easily T versus V ₀ characteristics. That is, by controlling these parameters, the γ curve of the display can be changed, and a display with a variable γ curve can be configured.

When blue light or green light linearly polarized in the direction perpendicular to the polarizing film is incident on the device, the transmittance versus applied voltage characteristic of the two-layer structure device including the liquid crystal layer and the polarizing film is shown in FIG. 14, for example. 14 and (12) to be given
From the equation, the input / output characteristics of this element are limiter characteristics as shown in FIG. In addition, BSO, which is a photoconductive layer, can control long-wavelength light with short-wavelength light by utilizing the property that the photoconductive effect on long-wavelength light such as red light and infrared light is very small. The characteristics relating to the long wavelength are similar to those of FIGS. 6, 8, 10, 12, 13 and 15, which are the characteristics of the short wavelength. However, the parameters P _i and P _c in the figure are the values of short-wavelength light. In this case, γ << ₁ cm ⁻¹ , and the absorption loss in BSO can be ignored (exp (−γr ₁ ) 1).

Although a 90 ° twisted nematic liquid crystal has been described above, the same effect can be obtained by using a nematic liquid crystal having a twist angle other than 90 °.

Further, the same effect can be obtained by using the electric field control birefringence mode of the liquid crystal. In this case the transmittance of the liquid crystal corresponding to the (10) equation _{^{T = cos 2 (φ 1 -φ}} 2) -sin2 φ 1 sin2 φ 2 sin 2 {[πΔn (V) t 4 / λ + θ 0/2]} ( 15) given by Here, φ ₁ and φ ₂ are angles between the optical axis of the liquid crystal at the time of initial alignment (drive voltage is 0 V) and the polarization directions of the incident light and the polarizing film, and Δn (V) is the voltage (V) applied to the liquid crystal. birefringence which depends on (the difference between the refractive index of ordinary light and extraordinary light), theta ₀ is the optical phase difference based on birefringence when V = 0, lambda is the incident wavelength. Since the equation (15) has a repetitive transmittance (T) versus voltage (V) characteristic as shown in FIG. 16, the device according to the present invention combining this liquid crystal layer and the photoconductive layer has V ₀ , f , P _i , P _c , and by controlling φ ₁ , φ _2, and θ ₀ in addition to the parameters already described, P ₀ vs. P _i
Characteristic, it is possible to obtain P _o versus P _c characteristics, T vs. f characteristics, a variety of multi-stability in various properties such as T versus V _o characteristics. As an _{example, V 0 = 23V, f =} 400Hz, P C = 0mw / cm 2, φ 1 = φ 2 = 2
2.5 °, P ₀ vs. P _i characteristic (calculated value) at θ ₀ = 0
Shown in the figure. Using the multi-stable P ₀ vs. P _i characteristic in FIG. 17,
Various signal processing such as multi-valued logic operation, analog / digital conversion, multi-valued memory, and multi-value display can be performed two-dimensionally.

The characteristic of Fig. 17 obtained by using the birefringence of liquid crystal is
This is a characteristic corresponding to FIG. 6 obtained by using the optical rotation of the liquid crystal, and from this correspondence, P ₀ vs. P _i using the optical rotation of the liquid crystal
It can be seen that the characteristics (FIG. 8) and the T vs. V ₀ characteristics (FIGS. 12 and 13) show multi-stable characteristics when the birefringence of the liquid crystal is used.

Until now, an optical modulator in which a liquid crystal layer, an alignment layer, a transparent dielectric layer, a transparent oil layer, a polarizing layer, and a photoconductive layer are sequentially arranged between two transparent electrodes as shown in FIG. 1 has been described. Also, as shown in FIG. 18, an element excluding the transparent dielectric layer can exhibit the same function and effect as the optical modulator shown in FIG. This element has the feature that it can be driven at a lower voltage than the element shown in FIG. In addition, if a polarizing layer having orientation (for example, a PVA film) is used, the first
As shown in FIG. 9, not only the transparent dielectric layer but also a part of the alignment layer can be omitted. Even if this element is used, functions and effects equivalent to those of the element shown in FIG. 1 can be exhibited.

[Effects of the Invention] Since a bistable spatial light modulator can digitally process a two-dimensional optical signal such as an image, the signal processing is performed as an element that performs logical operation of an image, recording of an image, analog / digital conversion, and the like. -There are a wide range of applications in fields such as arithmetic processing and displays.

The optical modulator according to the present invention does not require electrical wiring in units of mirrors, lenses and cells, is compact, has no optical resonator structure, is easy to manufacture, and has the optical rotation and birefringence of liquid crystal. Therefore, it has higher contrast and faster response speed than before.

By using the optical modulator of the present invention, not only two-dimensional light modulation is possible, but also optical amplification, optical memory, conversion of wavelength and polarization direction, conversion from incoherent light to coherent light, or the inverse conversion thereof. Is possible.

In addition, a two-dimensional photodiode (only in the forward direction) can be configured. Further, the set / reset of the element can be controlled by the frequency.

In addition, a two-dimensional optical transistor can be formed by using the element of the present invention. If an optical image or a data pattern is incident on the element as control light, optical logic operations such as AND or OR can be performed two-dimensionally. Can be.

Further, a two-dimensional shutter having a memory function can be configured using the optical modulator according to the present invention. That is, the transparent electrodes shown in FIG. 1 are made to have a simple matrix structure, and only by controlling the magnitude of the driving voltage, the arrangement of the matrix is increased similarly to a liquid crystal display having an active matrix structure comprising a thin film transistor array. Thus, a high-definition display having a high contrast can be formed.

Further, by controlling parameters such as the frequency input light of the drive voltage or the intensity of the control light, the gamma curve of the display can be changed, and a gamma curve variable display can be configured.

Further, using the element according to the present invention, a multi-valued logical operation,
Various signal processing such as analog-to-digital conversion and multi-value memory and multi-value display can be performed two-dimensionally.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a bistable spatial light modulator of the present invention, FIG. 2 is an equivalent circuit diagram of the bistable spatial light modulator of the present invention, and FIG. FIG. 4 is a graph showing the irradiation light intensity (P _j ) dependence of the capacitance determined by the average capture time of the carriers of _{Bi 12} S _i O ₂₀ used in the layer. FIG. 4 shows the voltage (V _LC ) applied to the liquid crystal layer and the device. FIG. 5A is a diagram showing the irradiation light intensity (P _j ) dependence of the ratio to the voltage (V ₀ ) applied to the whole, FIG. 5A is a diagram showing the structure of a 90 ° twisted nematic liquid crystal cell, and FIG. 5B is a diagram showing a 90 ° twist FIG. 5C is a graph showing the dependence of the transmittance (T) of the nematic liquid crystal cell on the applied voltage (V _LC ). FIG. 5C is a graph analysis method for obtaining the input light versus output light characteristics of the bistable spatial light modulator of the present invention. FIG. 6 is a diagram showing an example of light input / output characteristics of the optical modulator of the present invention. FIG. 7 is a diagram showing optical amplification and monostable characteristics of the optical modulator of the present invention. FIG. 8 is a diagram showing an example of optical input / output characteristics of an optical modulator, and FIG. 9 is a diagram showing the frequency dependence of the drive voltage of the transmittance (T) of the optical modulator. FIG. 10 is a diagram showing the control light (P _c ) dependence of the transmittance of the optical modulator of the present invention; FIG. 11 is a diagram showing the application of the optical modulator of the present invention to optical logic operation; 13 is a diagram showing the amplitude dependence of the drive voltage of the transmittance of the optical modulator of the present invention, FIG. 14 is a diagram showing the drive voltage dependence of a 90 ° twisted nematic liquid crystal cell, and FIG. 15 is FIG. Fig. 16 shows the light input / output characteristics of an optical modulator with a liquid crystal layer having the characteristics shown in Fig. 16 as a component. Fig. 16 shows the drive voltage dependence of the transmittance of a liquid crystal cell using an electric field controlled birefringence mode. FIG. 17 is a diagram showing light input / output characteristics of an optical modulator having a liquid crystal layer having the characteristics shown in FIG. 16 as a part of its constituent elements. FIGS. 18 and 19 show another embodiment of the bistable spatial light modulator of the present invention. FIGS. 20 to 23 show the configuration of a conventional bistable spatial light modulator, respectively. FIG. DESCRIPTION OF SYMBOLS 1 ... Glass substrate, 2 ... Transparent electrode, 3 ... Transparent photoconductive layer, 4 ... Transparent oil layer, 5 ... Polarizing layer, 6 ... Liquid crystal layer, 7 ... Alignment layer, 8 ... AC power supply , 11 ...... control light (P _C), 19 ...... transparent dielectric layer.

Claims (10)

(57) [Claims] 1. A liquid crystal layer whose optical characteristics are changed by an electric field between two transparent electrodes, a liquid crystal layer having a dielectric constant and a resistivity higher than that of the liquid crystal layer, and a liquid crystal layer having a liquid crystal alignment on its surface. A transparent dielectric layer provided with an alignment layer,
A polarizing layer having a dielectric constant and resistivity equal to or larger than that of the liquid crystal layer, and having the ability to select linearly polarized light having a specific polarization direction, a transparent oil layer, and a transparent material whose resistivity is reduced by light irradiation. A bi-stable spatial light modulator, comprising: 2. The photoconductive layer has an impedance at the time of light irradiation of Z _ON , an impedance at the time of non-irradiation at Z _OFF , an impedance of the liquid crystal layer at Z _L , and is provided between two transparent electrodes. The total impedance excluding the layer is Z _M , the voltage applied to the transparent electrode is V ₀ , and the characteristic curve showing the relationship between the transmittance of the liquid crystal cell composed of the liquid crystal layer and the polarizing layer and the voltage applied to the liquid crystal is changed. when the applied voltage corresponding to the inflection point and V _H, less than _{Z L / (Z L + Z} M + Z OFF) is _{V H / V 0, Z L} / (Z L
+ Z _M + Z _ON ) has Z _L , Z _M , Z _ON , and Z _OFF greater than V _H / V ₀ , and the thickness and relative permittivity of the photoconductive layer are t ₁ and ε ₁ , respectively. The thickness and relative permittivity of the oil layer are t ₂ and ε ₂ , respectively, the thickness and relative permittivity of the polarizing layer are t ₃ and ε ₃ , respectively, and the thickness and relative permittivity of the liquid crystal layer are t ₄ , respectively. And ε ₄ , the thickness and relative dielectric constant of the alignment layer are t ₅ and ε ₅ , respectively, and the thickness and relative dielectric constant of the transparent dielectric layer provided with the alignment layer are t ₆ and ε ₆ , respectively. Then, t ₁ / ε ₁ becomes t _i / ε _i (i =
2,3,4,5,6), t ₂ / ε ₂ and t ₅ / ε ₅ are t _i /
2. The bistable spatial light modulator according to claim 1, wherein the value is smaller than [epsilon] _i (i = 1, 3, 4, 6). Wherein the liquid crystal layer comprises a nematic liquid crystal or cholesteric liquid crystal, the photoconductive layer B _i12 S _i O _20,
B _i12 G _e O ₂₀ , C _d S, C _d S _e , Se, S _e T _e or one of amorphous silicon films, wherein the polarizing layer is made of a polarizing film mainly composed of polyvinyl alcohol, The oil layer is made of an insulating oil having a large relative dielectric constant and resistivity, and the transparent dielectric layer provided with the alignment layer has a ferroelectricity of SrTiO ₃ , LiTaO ₃ , LiNbO ₃ or KD ₂ PO ₄ . The bistable spatial light modulator according to claim 1, comprising a crystal. 4. A liquid crystal layer whose optical characteristics are changed by an electric field between two transparent electrodes, and having a dielectric constant and a resistivity equal to or larger than that of the liquid crystal layer, and a linear polarization of a specific polarization direction. A polarizing layer having the ability to select wave light, a transparent oil layer, and a transparent photoconductive layer whose resistivity is reduced by light irradiation are sequentially disposed, and the liquid crystal layer is provided on at least one surface of the liquid crystal layer. A bistable spatial light modulator, comprising an alignment layer for aligning liquid crystal. 5. The bistable spatial light modulator according to claim 1, wherein an AC drive voltage is applied between the two transparent electrodes, and the amplitude of the drive voltage and its amplitude are controlled. A light modulation method, wherein a light input / output characteristic is controlled using a frequency or light irradiated from the photoconductive layer side as a parameter. 6. The bistable spatial light modulator according to claim 1, wherein an AC drive voltage is applied between the two transparent electrodes, and a voltage is applied from the liquid crystal layer side. A two-dimensional optical signal is incident, and a two-dimensional optical signal is emitted from the photoconductive layer side. The light incident from the liquid crystal layer side, the light incident from the photoconductive layer side, and the amplitude of the driving voltage are changed. An optical modulation method comprising controlling, as a parameter, the dependence of transmittance on the frequency of the drive voltage. 7. The bistable spatial light modulator according to claim 1, wherein an AC drive voltage is applied between said two transparent electrodes, and said liquid crystal layer side and said liquid crystal layer side are connected to each other. A two-dimensional optical signal is incident from the photoconductive layer side, and a two-dimensional optical signal is emitted from the photoconductive layer side. The light incident from the liquid crystal layer side, the amplitude of the driving voltage and the frequency thereof are changed. A light modulation method comprising controlling, as a parameter, dependence of transmittance on incident light from the photoconductive layer side. 8. The bistable spatial light modulator according to claim 1, wherein an AC drive voltage is applied between the two transparent electrodes, and the liquid crystal layer is connected with an AC drive voltage. A two-dimensional optical signal is incident, and a two-dimensional optical signal is emitted from the photoconductive layer side. The frequency of the drive voltage and the light incident from the liquid crystal layer side and the photoconductive layer side are used as parameters. Controlling the dependence of transmittance on the amplitude of the drive voltage. 9. A transparent electrode of the bistable spatial light modulator according to claim 1, wherein the transparent electrode has a simple matrix structure, and an AC drive voltage is applied between the two transparent electrodes. ,
In addition, it is preferable that a two-dimensional optical signal is incident from the liquid crystal layer side, a two-dimensional optical signal is emitted from the photoconductive layer side, a driving voltage is stored, and voltage dependency of transmittance is controlled. Characteristic light modulation method. 10. The bistable spatial light modulator according to claim 1, wherein an AC drive voltage is applied between said two transparent electrodes, and said liquid crystal layer side and said liquid crystal layer side are connected to each other. A two-dimensional optical signal is incident from the photoconductive layer side, and a two-dimensional optical signal is emitted from the photoconductive layer side. The amplitude or frequency of the driving voltage, the liquid crystal layer and the photoconductive layer side And the angle between the optical axis of the liquid crystal at the time of the initial alignment and the polarization direction of the incident light from the polarizing layer and the liquid crystal layer side, and the liquid crystal at the time of the initial alignment. By controlling the optical phase difference based on the birefringence, the light input / output characteristics, the dependence of the transmittance on the frequency of the drive voltage, the dependence of the transmittance on the incident light from the photoconductive layer side, and the transmittance Controls the dependence of drive voltage on amplitude. Light modulation method according to.