JPH0318829A - Space optical modulation element - Google Patents

Abstract

PURPOSE:To realize a stable and satisfactory input/output characteristic even when the intensity of a read-out light is high by using a metallic film for executing the reflection and the interruption of the read-out light. CONSTITUTION:As for a reflecting film for constituting a space optical modulation element 20, a dielectric mirror 5 is used or a metallic film 11 arranged like as island is used instead of the dielectric mirror 5. This metallic film 11 arranged like an island prevents the electric conduction in the in-plane direction so that the write of a two-dimensional pattern can be executed by the prescribed resolution at the time of write, and reflects a read-out light, and also, interrupts the read-out light against a photoconductive layer 4 to be sensitized by a write light at the time of read-out. In such a manner, even when the intensity of the read-out light is high, a stable and satisfactory input/output characteristic can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spatial light modulation element having a function of spatially modulating light in parallel and storing it.

[Prior Art] The function of a spatial light modulator (hereinafter abbreviated as SLM) is to write a two-dimensional pattern (for example, an image) with a writing light, and read out the written two-dimensional pattern with another light (reading light). It is something to read out. by this,
Processing such as amplification of image light, threshold processing, inversion, incoherent tocoherent conversion between read light and write light, wavelength conversion, etc. can be performed.

The structure of a conventional SLM was disclosed in Japanese Patent Application No. 1-45716 previously filed by the present applicant, as shown in the configuration diagram of the conventional example seen from the side in FIG. There are some in the city that have uniform reflective coatings. 1 is one glass substrate, and 2 is the other glass substrate. A transparent electrode 3 is formed on one glass substrate l, and a photoconductive layer 4. Dielectric mirror5. Orientation @6 is deposited, respectively.

Further, on the other glass substrate 2, a transparent electrode 7 and an alignment film 8 are formed thereon. The glass substrate I and the glass substrate 2 configured in this way are arranged with a spacer 9 in between so that the alignment films 6.8 face each other, and a ferroelectric liquid crystal (FLC) 10 is placed in the gap. ing. In this conventional structure, the photosensitive layer is amorphous.
A photoconductive layer 4 made of a silicon (a-8i) film is used, and a ferroelectric liquid crystal (hereinafter referred to as FLC) 10 is placed thereon via a dielectric mirror 5 made of a dielectric multilayer film as a reflective film. The writing light is irradiated from one side of the glass substrate 1, but in the area irradiated with the writing light, the voltage applied to the FLC 10 increases due to its photoconductivity and exceeds the threshold voltage of FLClO, so that the liquid crystal axis It rotates about 45 degrees based on the OFF state. The readout light is irradiated from the glass substrate 2 side via a polarizer (not shown), modulated and reflected by the SLM, further reflected by a half mirror (not shown), and read out through an analyzer (not shown).

In the above, for example, if the liquid crystal axis and the polarizer are arranged so that they match in the polarization direction in the off state, the polarization direction of the readout light will rotate only in the portion irradiated with the writing light.

On the other hand, in areas where the writing light is not irradiated, the liquid crystal axis remains off, so the polarization does not rotate. Therefore, the pattern read through the analyzer corresponds to the written pattern.

[Problems to be Solved by the Invention] However, in the spatial light modulator according to the above-mentioned conventional technology, when creating the dielectric mirror 5, the optical lengths of the high refractive index dielectric and the low refractive index dielectric are read out alternately. Approximately 20 layers of Iθ~20 are laminated with a thickness of 1/4 wavelength of light, but it has been difficult to produce a mirror with a thickness of over 99% due to problems with the accuracy of the film formation. Therefore, when the readout light intensity is high, a portion of the readout light is transmitted to the dielectric mirror 5.
Since the light reaches the photoconductive layer 4 without being reflected by the light, there is a problem that the input/output characteristics change depending on the readout light intensity. FIGS. 5(a) and 5(b) are input/output characteristic diagrams of a conventional SLM showing the above-mentioned problems. In each figure, the horizontal axis is the writing light intensity, and the vertical axis is the readout reflectance after passing through the analyzer. ) shows a measurement example in the case of parallel Nicols (the state in which the polarization axes of the polarizer and analyzer are parallel). The solid line in the figure (
+) indicates the change characteristics of the read reflectance when the read light intensity is low, and the dotted line (2) indicates the change characteristics of the read reflectance when the read light intensity is high. (a)
, (b) both show that the polarization plane of the readout light rotates 90 degrees at a writing state with a certain write intensity, but when the readout intensity is high, a portion of the readout light mentioned above reaches the photoconductive layer. By reaching this point, the writing intensity at the boundary changes, and the input/output characteristics change.

The present invention was devised to solve the above-mentioned problems, and an object of the present invention is to provide a spatial light modulation element that can realize stable and good input/output characteristics even when the intensity of readout light is high.

[Means for Solving the Problems] The configuration of the spatial light modulator of the present invention for achieving the above object is as follows: A photoconductive layer is provided on one transparent substrate having a transparent electrode, and a dielectric mirror or a dielectric mirror is provided on one transparent substrate. A metal film arranged in an island shape and a liquid crystal alignment film are arranged in place of the mirror, and the liquid crystal alignment film is arranged on the other transparent substrate having a transparent electrode, and both the one transparent substrate and the other transparent substrate are connected with a spacer. It is characterized by a structure in which the liquid crystals are placed facing each other with a ferroelectric liquid crystal in between, and the gap is filled with ferroelectric liquid crystal.

[Function] The present invention uses an island-like array of metal films together with or in place of a dielectric mirror as a reflective film constituting a spatial light modulator. This island-shaped metal film prevents electrical conduction in the in-plane direction during writing, making it possible to write a two-dimensional pattern with a predetermined resolution, and reflects the reading light and is sensitive to the writing light during reading. The photoconductive layer blocks readout light to achieve stable and good input/output characteristics even when the intensity of readout light is high.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIGS. 1(a) and 1(b) are structural diagrams of a spatial light modulator (SLM) showing one embodiment of the present invention, in which (a) is a side view and (b) is a pattern of electrodes and metal films. FIG. In this embodiment, members equivalent to those of the conventional example shown in FIG. 4 are given the same reference numerals. In the figure, ■ is one glass substrate, and 2 is the other glass substrate. Formed on one glass substrate l are 3 a transparent electrode, 4 a photoconductive layer formed on the transparent electrode l and sensitive to writing light, and 5 a dielectric formed on the photoconductive layer 4. mirror 1
1 is a metal light shielding film formed on the dielectric mirror 5 to reflect readout light and block light from the photoconductive layer 4; 6 is formed to cover the metal light shielding film 11 together with the dielectric mirror 5; It is an alignment film with As those formed on the other glass substrate 2, 7 is a transparent electrode, 8 is a transparent electrode 7
This is an alignment film formed on top. One glass substrate 1 and the other glass substrate 2 configured in this manner are arranged with spacers 9 in between so that their respective alignment films 6.8 face each other. 10 is a ferroelectric liquid crystal (hereinafter referred to as FLC) filled in a gap of a certain thickness created by the spacer 9;
2 is a transparent electrode formed separately from the transparent electrode 3 on the side of one glass substrate l, and I3 is this transparent electrode 12.
and the transparent electrode 7 on the other glass substrate 2; 14 is a sealing material for sealing and fixing the whole; 15 is a silver paste layer on one glass substrate Fi, I; The lead electrode I6 is connected to the transparent electrode 12 which is electrically connected to the transparent electrode 7 on the other glass substrate 2. A predetermined drive voltage for writing is applied to the FLCIO from the lead electrodes 15 and 16. As the transparent electrodes 3, 7.12, indium-
A model of tin oxide (ITO) is used. The following structure constitutes the spatial light modulation element 20 of this embodiment as a whole.

Next, the structure of each part of the spatial light modulator of the above embodiment will be explained. The FLCI O used has a tilt angle close to 22.5 degrees and has good self-holding properties.

In order to improve self-retention properties, it is preferable to have a small spontaneous polarization, preferably 20 nC/cm'' or less.

The alignment film 6.8 on the glass substrate 1.2 (for example, a polyimide or polyvinyl alcohol film with a thickness of about 5000 Å or less) is aligned in the longitudinal direction
On the other hand, both the upper and lower glass substrates 1.2 are weakly aligned in the 225 degree direction (rubbing direction) A. At this time, FLC
Depending on the direction of the electric field, the lo liquid crystal molecules are aligned in the same direction as the longitudinal direction of the element (up state) or in a direction at 45 degrees with respect to it (down state). In the up state, light that is incident on the FLCIO layer through the polarizer and reflected returns back in its original polarization state. On the other hand, d
In the own state, the plane of polarization of the returning light is rotated due to the refractive index anisotropy of FLCl 2 O. At this time, the thickness d of FLClO determined by the spacer 9 is d=m・λ/(4・Δn) (m=1.3.5..., λ: wavelength of readout light, Δ
n: refractive index difference in the long and short directions of the FLC molecule),
The polarization of the returning light will be rotated by 90 degrees. However, in order to improve the self-holding property of FLCI O and increase the response speed, the thinner the liquid crystal layer is, the better, and from this point of view, it is desirable to set d to m=l. Usually d is 2μ
m, and in order to control the thickness uniformly, a structure is used in which spherical particles of uniform diameter are dispersed in the liquid crystal layer as spacers 9.

As the photoconductive layer 4, a photoresist film such as amorphous silicon (aSi) is used. Generally, it is formed on the glass substrate 1 by a plasma CVD method or the like as a highly sensitive hydrogen-doped model. In this structure, the photoconductive layer 4 has a uniform structure,
Configured to operate on positive and negative bipolar pulses. The thickness of the aSi film is determined by the balance between its capacitance and resistance, and is preferably about 2-7 μm.

The dielectric mirror 5 is formed by alternately laminating two types of dielectric films, and each of these dielectric films is preferably made of a material with a high dielectric constant, such as Tidy.

When formed by alternately stacking 17 layers of SIO, the reflectance is 9.
A mirror of 8% can be obtained.

The metal light shielding film 11 has a thickness of about 2000 mm, for example.
7 aluminum membrane can be used. When introducing the metal light-shielding film 11, the aluminum film is etched in a mesh pattern so that it remains in the form of islands in order to avoid electrical conduction in the in-plane direction. That is, after uniformly depositing aluminum on the entire surface, photolithography is performed to form a pattern of, for example, 18x18μ.
A pattern is formed in the form of m islands with an interval of 2 μm between each island.

If the number of pixels of SLM is about 250,000 per cm',
The above dimensions provide sufficient resolution.

In addition to aluminum, materials for the metal light shielding film 11 include:
Titanium, gold, etc. can be used.

The operation and effect of the embodiment configured as above will be described.

FIGS. 2(a), (b), (c), and (d) are explanatory diagrams of the operation of the spatial light modulation element of this example. 20 in each figure
is a spatial light modulator,! 2 is a glass substrate which is one transparent substrate, and 2 is a glass substrate which is the other transparent substrate, which have been described above. This will be explained below with reference to FIG. FLC10 filled in spatial light modulator (SLM) 20
is the product of the voltage Vf applied to this FLCI O layer and the pulse width τ of the applied voltage, vf・τ, when it exceeds a certain threshold C, the orientation direction is changed by the electric field, and the voltage does not reach the threshold. In this case, the previous orientation direction is maintained. SLM2
0, the applied voltage is applied to the photoconductive layer 4, the dielectric mirror 5. F
By setting the voltage/pulse width product Vf·τ applied to the SLM 20 to be larger than the threshold value C, the optical characteristics of the SLM 20 can be improved by the photoelectric conduction effect of the photoconductive film 4. can be controlled by writing light (or erasing light) Lw. Figure 2(a)
is a case where the writing light (or erasing light) Lw is irradiated onto one surface of the glass substrate of the SLM 20 and a voltage of +■ is applied, and Fl and CIO are tilted at 45 degrees from the vertical direction (in the down state). ), the glass substrate 2
The polarization direction of the linearly polarized readout light LRI irradiated onto the surface is rotated by 90 degrees and reflected as lf. on the other hand,
In the case of FIG. 2(b) where no write light is irradiated and a voltage of +V is applied, the FLCIO does not show any change in state, and the reflected read light LRx maintains its previous state. Next, when the writing light is irradiated and a voltage of -■ is applied as shown in FIG. 2(c),
Since a voltage exceeding the negative threshold is applied to FLCI O, FLCI O goes into the up state, and the read linearly polarized light LR+ is read out with the same polarization. Figure 2 (
d) is a case where no write light is irradiated and a voltage of -V is applied, and the reflected read light Lllt maintains its previous state as in the case of FIG. 2(b).

When reading out based on the above principle, the readout light LRI is polarized by the polarizer, and the readout light L□ modulated by s L M 20 and reflected is read out through the analyzer. Based on the above principle, the polarizer,
With the analyzer orthogonal (orthogonal Nicols), FLC
The readout light becomes dark in the up state (corresponding to the state in which a negative voltage is applied), and becomes bright in the down state (corresponding to the state in which a positive voltage is applied). In a state where the polarizer and analyzer are parallel (parallel Nicol), the brightness and darkness are opposite to the above case.

In the above, in this embodiment, at the time of reading, the metal reflective film It reflects the reading light LR+ and blocks the light to the photoconductive layer 4. That is, in this embodiment, the reflectance of the dielectric mirror 5 is compensated for by utilizing the metal film having good light blocking properties, and the readout light reaches the photoconductive layer 4 when the readout light intensity is high. Block the light to prevent it from happening.

This makes the read reflectance stable and good with respect to the write light intensity, regardless of the magnitude of the read light intensity. On the other hand, at the time of writing, since the metal light shielding film 11 is arranged in an island-like (mesh-like insulated state) arrangement, the potential of the pattern exposed to the photoconductive layer 4 is adjusted to F at a predetermined resolution.
It can be applied to LC10, making writing possible.

FIGS. 3(a) and 3(b) are input/output characteristic diagrams showing the above-described effects in this embodiment. In each figure, the horizontal axis is the writing light intensity, and the vertical axis is the readout reflectance after passing through the analyzer. (b) shows a measurement example in the case of parallel Nicols (the state in which the polarization axes of the polarizer and analyzer are parallel), and the solid line (1) shows the change characteristics of the readout reflectance when the readout light intensity is small. The dotted line (2) shows the change characteristics of the readout reflectance when the readout light intensity is high. Both (λ) and (b) show that the polarization plane of the read light rotates 90 degrees at a writing state with a certain write intensity. The writing strength at the boundary hardly changes. That is, the input/output characteristics are stable and good.

In fact, regarding an SLM fabricated with an effective surface area of 1 cm,
White light (0.5 mW/cm") was used as the writing light, and Ar laser light (100 mW/cm") was used as the read light.
), and applied pulses to the SLM at a voltage of 15 V and a width of 0.
, 2 ms, and the pattern could be read out with a contrast of 20:1 or more and a pixel count of 500 x 500. This is a metal light-shielding film! By using l,
This shows that even when reading light with an intensity 200 times stronger than the writing light is used, a portion of the reading light does not reach the photoconductive layer 4. The writing interval at this time could be up to 30 minutes or more.

Note that in the above embodiment, the dielectric mirror 5 can be omitted by increasing the thickness of the metal light shield *11 to improve its reflectance. In this case, the manufacturing process is simplified. In addition, by changing the lamination order of the dielectric mirror and the metal light-shielding film, the transparent electrode 3, the photoconductive layer 4,
Metal light shielding film II.

A structure in which the dielectric mirror 5 and the alignment film 6 are stacked in this order is also possible. As described above, the present invention can be applied in various ways and can take various embodiments in accordance with its gist.

[Effects of the Invention] As is clear from the above description, the spatial light modulator of the present invention uses gold W4 which reflects and blocks the readout light, so even if strong readout light is applied manually, Light to the photoconductive layer is blocked, normal input/output characteristics can be obtained, and images can be converted and displayed.

It can be used for optical memory, etc.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are structural diagrams showing an embodiment of the present invention, FIGS. 3(a) and 3(b) are input/output characteristic diagrams showing the operation of this embodiment, FIG. 4 is a configuration diagram of the conventional example, and FIG. 5 (
Figures a) and (b) are input/output characteristic diagrams showing problems in the conventional example. G...One glass substrate, 2...The other glass substrate,
3... Transparent electrode, 4... Photoconductive layer, 5... Dielectric mirror 6... Alignment film, 7... Transparent electrode, 8... Alignment film, 9 Yui spare, lO. ...Ferroelectric liquid crystal, 11.
...Metal light-shielding film, 20...Spatial light modulation element. Figure 2

Claims (1)

[Claims] (1) On one transparent substrate having a transparent electrode, a photoconductive layer, a metal film arranged in an island-like arrangement together with or in place of a dielectric mirror, and a liquid crystal alignment film are arranged, and the other having a transparent electrode. A space characterized by having a structure in which a liquid crystal alignment film is arranged on a transparent substrate, the one and the other transparent substrates are arranged facing each other with a spacer interposed therebetween, and the gap is filled with ferroelectric liquid crystal. Light modulation element.