JPS5913609Y2 - liquid crystal spatial modulator - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a liquid crystal spatial modulator for matrix-type display used in the production of Fourier transform holograms.

Fourier transform holograms are attracting attention as large-capacity memories because of their high-density recording and redundancy.

A Fourier transform hologram of a matrix-like binary displayed pattern is produced using a spatial modulator that displays a matrix-like pattern.

However, since the Fourier transform pattern of the pattern displayed in binary form in a matrix has locally steep intensity peaks due to its periodic arrangement, it cannot be faithfully recorded as is on a photosensitive material.

Therefore, a method is used in which a phase plate having the same pitch as the display pattern and giving a random optical phase difference is used, and this is superimposed on the display pattern to suppress the steep intensity peak of the Fourier transform pattern.

Various spatial modulators that display patterns in a matrix have been devised, including those using mechanical shutter arrays, liquid crystals, electro-optic crystals, etc., but none of them have sufficient S/N, writing speed, and size. is a liquid crystal spatial modulator.

When a phase plate is stacked on a liquid crystal spatial modulator, the pattern display portion is separated from the phase plate by the thickness of the glass substrate constituting the liquid crystal cell.

In producing a Fourier transform hologram that can be reproduced without a lens, light enters the spatial modulator obliquely, and the angle of incidence changes as the lens moves.

For this reason, the pattern of the phase plate and the pattern of the spatial modulator become misaligned, which destroys the effect of the phase plate.

To solve this problem, it would be possible to make the glass substrate of the liquid crystal spatial modulator thinner, but this is difficult due to problems with the strength and flatness of the glass.

For this reason, in the past, an optical system configuration was used in which the light incident on the liquid crystal and the spatial modulator was perpendicularly incident, and a lens was required for reproduction.

The object of this invention is to provide a liquid crystal spatial modulator which eliminates the above-mentioned drawbacks and has a random phase effect even for obliquely incident light.

According to this invention, a transparent substrate with a transparent electrode attached on the inside, a transparent electrode on the inside, and a film thickness such that the transparent electrodes are spatially randomly arranged and give an optical retardation (nl-nz) d of λ/2 are used. A liquid crystal spatial modulator can be obtained in which a liquid crystal having a display function is filled between a transparent substrate and a thin film attached thereto.

Something similar to each component of the present invention is published in Japanese Patent Application Laid-open No. 47-1
1737, Proceedings of the 21st Applied Physics Association Conference 1. P167 (hereinafter abbreviated as Proceedings of the Japan Society of Applied Physics), JP-A-48-96141.

However, JP-A No. 47-11737 is concerned with optical cells using liquid crystals, especially those used for hologram storage, and the Proceedings of the Japan Society of Applied Physics describes liquid crystal cells, which are one of the IC-conversion elements necessary for creating holograms. This invention relates to a photoconductor element.

Further, Japanese Patent Application Laid-open No. 48-96141 relates to a method of recording a hologram by installing a phase plate whose phase component changes stepwise on the object plane.

These documents do not describe a spatial modulator for holography that uses liquid crystal, which is a component of the present invention, and is equipped with a phase plate that imparts a phase difference to a binary pattern.

The configuration obtained by combining the techniques described in these documents is to overlap a phase plate and a liquid crystal spatial modulator.

However, the phase plate and liquid crystal spatial modulator are overlapped.

Alternatively, if the two are glued together, the pattern display part and the phase plate will be separated by the thickness of the glass substrate of the liquid crystal spatial modulator, and if light enters the spatial modulator obliquely, the patterns of both will shift, causing the phase plate to become separated. The effect will be reduced.

Therefore, it is necessary to place the phase plate and the pattern display section of the liquid crystal spatial modulator as close as possible.

For this reason, it is impossible to make the glass substrate of the spatial modulator thinner because of its strength.

This invention was developed in this respect, and a phase plate is constructed below the pattern display inside the liquid crystal spatial modulator.

In other words, by randomly arranging phase films with different refractive indexes under transparent electrodes for driving the display pattern by liquid crystal, a phase plate is formed adjacent to the pattern display area (liquid crystal), so that the pattern produced by obliquely incident light is created. The problem of misalignment disappears.

In addition, it is undesirable for the transparent electrode part to have a step difference depending on the presence or absence of a phase film at the bottom. Therefore, an insulating film with a low refractive index is uniformly applied to cover the phase film with a high refractive index. It is designed to obtain a phase difference, and has a different structure from conventional random phase plates.

Therefore, the present invention is different from the technical idea of the above-mentioned document.

This invention will be explained in detail below with reference to the drawings.

FIG. 1 shows a method for producing a Fourier transform hologram that can be reproduced without a lens.

The coherent light 1 is turned into convergent light by a lens 2, passes through a phase plate 3 and a liquid crystal spatial modulator 4, and then is focused onto a recording medium 6.

Reference light 5 emitted from the same light source as coherent light 1 is incident on recording medium 6, interference fringes with coherent light 1 are recorded on recording medium 6, and Fourier transform hologram 7 is created.

Next, the lens 2 and the reference beam 5 are moved in the y direction, and the recording medium 6 is
Create a hologram in a different position than before.

In the reproduction process for extracting information from the hologram, if the reproduction light 5' is incident on the hologram 7 in a direction conjugate with the reference beam 5, a reproduced image is formed at the spatial modulator 4.

FIG. 2 is an enlarged view of the phase plate 3 and liquid crystal spatial modulator 4 in FIG. 1.

The phase plate 3 consists of a glass substrate 8 and a thin film 9 that provides a phase difference.

The liquid crystal spatial modulator 4 has transparent electrodes 11 and 13 on glass substrates 10 and 14, respectively.

In such a conventional device, the pitch of the pattern of the phase plate thin film 9 and the pattern of the transparent electrode 11 is the same, but when the light 1 is obliquely incident, the thickness of the glass substrate 10 causes the two patterns to become optically different. do not overlap.

This means that one bit displayed on the liquid crystal spatial modulator 4 is divided into two in terms of phase, and it is well known that the reproduced one-bit image is greatly degraded.

Therefore, in the conventional configuration, it is not possible to place the liquid crystal spatial modulator 4 behind the lens 2 as shown in FIG.

Next, one embodiment of this invention will be described.

3 and 4 are a schematic cross-sectional view and a top view, respectively, of the structure of the liquid crystal spatial modulator according to this embodiment.

This liquid crystal spatial modulator consists of a transparent upper substrate 20 made of glass or the like with a striped transparent electrode thin film 19 made of tin oxide or indium oxide having a width of several mm, and a ZnO thin film 1 for a phase plate.
6 and a transparent lower substrate 15 on which a stripe-shaped transparent electrode thin film 18 is attached via an insulating thin film 17, and a structure in which, for example, nematic liquid crystal MBBA (methoxybenzylene butyl aniline) is filled is used. have.

The thickness of the liquid crystal layer is 10 to 30 μm, and is maintained at a constant thickness by a spacer such as a Mylar film (not shown).

How to attach the phase plate 16 and the transparent electrode thin film 18 to the lower substrate 15 will be described.

First, a phase plate thin film 16 is attached to the lower substrate 15.

This material is a dielectric with a high refractive index, such as ZnO, CeO2,
ZnS, Tie, etc. are preferred.

These dielectric thin films are applied to the lower substrate 15 by sputtering, vapor deposition, or the like.

A pattern is created on this thin film by photo-etching,
A phase plate thin film 16 is completed.

Where in the matrix the thin film will remain is randomly determined.

Next, an insulating thin film 17 is uniformly applied on the phase plate thin film 16 using a sputtering method or a low-temperature oxidation method.

On top of that, a thin film 1 for phase plate 1 is disposed perpendicularly to the transparent electrode 19.
A striped transparent electrode 18 is applied with tin oxide or indium oxide by sputtering or the like so that the pitch matches the pattern 6.

Here, the thickness d of the phase plate thin film 16 is determined by (
n7-n2) d=λ/2 (λ is the wavelength of coherent light in FIG. 1).

Furthermore, since the insulating thin film 17 is sufficiently thin, the position of the pattern does not shift due to obliquely incident light, so this liquid crystal spatial modulator can be placed behind the lens 1 in FIG.

FIG. 5 is a schematic diagram showing a method of driving the liquid crystal spatial modulator according to this embodiment.

When a liquid crystal drive voltage is applied to a general X-Y matrix type liquid crystal spatial modulator using a normal application method,
The half-selective voltage appearing at the Y electrode base intersection is shown.

The display selection point is now X2. Y2, a driving voltage ■ is applied to this point, and the selection point X2. Y2 causes strong light scattering.

At other points, since the voltage is lower than the threshold voltage, no scattering occurs, and a binary pattern is displayed in a matrix.

The liquid crystal spatial modulator described above with reference to FIGS. 4, 5, and 6 is not limited to the dimensions, materials, and structure described above in terms of implementing this invention.

As described above, the liquid crystal spatial modulator in which the phase plate according to this invention is provided in the liquid crystal cell can eliminate the phase shift between the phase plate pattern and the display pattern with respect to obliquely incident light.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a method for manufacturing a Fourier transform hologram that can be reproduced without a lens, Figure 2 is a diagram showing details of a phase plate and a liquid crystal spatial modulator, and Figures 3 and 4 are an example of an embodiment of the present invention. FIG. 5 is a schematic cross-sectional view and a top view showing the structure of a liquid crystal spatial modulator according to the present invention. 1.5,5'... Coherent light, 2...
... Lens, 3 ... Phase plate, 4 ... Liquid crystal spatial modulator, 6 ... Recording medium, 7 ...
・Fourier transform hologram, 8, 10° 14, 15.2
0...Glass substrate, 9,16...Thin film for phase plate, 11.13.18.19...Transparent electrode, 12.21...Liquid crystal , 17...Insulating thin film.

Claims (1)

[Scope of utility model registration request] A transparent substrate with a transparent electrode on the inside, a transparent electrode on the inside, and a spatially randomly arranged optical retardation (nt
n2) A liquid crystal spatial modulator characterized in that a liquid crystal having a display function is filled between a transparent substrate having a thin film having a thickness such that d is λ/2.