JPS6030948B2 - porogram recording device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hologram recording device that records two-dimensional optical information as a hologram.

In particular, the present invention relates to a hologram recording device using a two-dimensional spatial modulator that includes an optical spatial modulator for the column direction of two-dimensional optical information and a row-direction mirror deflector. Figure 1 shows a conventional multiple exposure type (time series recording type) hologram recording device using an amplitude modulation type optical spatial modulator made of a strong electrolyte whose polarization direction can be electrically reversed. .

In Fig. 1, 3 to 9 are optical spatial modulators;
is a polarizing plate, and 5 and 8 are 1/4 skin long plates. 4 and 7 are optical spatial modulation elements for configuring information in the row direction and column direction.

A transparent NESA electrode is attached to the back surface of this element, and long strip-shaped insulating portions and transparent NESA electrode portions are alternately arranged on the front surface in the row direction (or column direction).

By applying the voltage necessary to invert the polarization of the strong electrolyte to the front and back NESA electrodes, input electrical information in a row (or column) is converted into optical information. 4 and 7 are 1/umbrella long slopes, and their crystal axis directions match the crystal axis directions of the 1'4 skin long slopes of 5 and 8, and the polarization direction of the polarizing plates of 3, 6, and 9 is the same as that of 45o. They are arranged with great care.

Parts 3 to 6 constitute information in the row direction, and parts 6 to 9 constitute information in the column direction.

These parts that configure information in the row or column direction are both called a row-wise information configuration type optical spatial modulator.

The information light transmitted through 9 is hologram 1 from Shins 101.
The light is focused on 1.

A hologram is created by superimposing this information light and a variable reference light on the information light condensing section. To record two-dimensional information on a hologram, set only the first line to “1” in sections 3 to 6.
and forms an information light that sets the other rows to “0”, and at the same time turns 6
The column-direction information formation units from to 9 apply an input voltage to 7 according to the information on the first row, thereby forming optical information on the first row. After recording the optical information of the first row, the second and subsequent rows are sequentially recorded on the hologram in the same manner. When information is recorded on a hologram using the above method, when focusing on the information on the first line, light leaks from the portion corresponding to the first line while writing the information on the second line and subsequent lines.

Since this light leakage always occurs until the last row is written, the noise due to the leakage is accumulated. That is, the signal-to-noise ratio of the row-by-row information configuration type spatial modulator is (S/N). If a hologram recording device is created by exposing M rows of information M times, the signal-to-noise ratio (S/N) r of the reproduced hologram image is (S
/N)r=吏kus/N). becomes.

Therefore, even if (S/N)D is 1000, (S/N)
In order to make r 20 or more, M cannot be 8 or more. Therefore, it is very difficult to construct a spatial modulator that forms eight or more rows of information using the conventional method. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a hologram recording device that creates a hologram that can obtain reproduced image quality with a high signal-to-noise ratio even when the multiplicity is increased.

In order to achieve the above objective, the (S/N) o of the portion that forms the basis of information in the row or column direction is made sufficiently large.

That is, for example, if the signal-to-noise ratio (S/N) oc of the part that provides information in the column direction is sufficiently large. (S/
N) r is the signal-to-noise ratio (S
/N)o, is approximately equal to. (S/N). In order to make c sufficiently large, light is irradiated only on the lines to be written, and lines that are not written are not irradiated with light at all. In this case, (S/N). It is easily possible to set c to 1 pi or more. In order to form such irradiation light, an illumination hologram as shown in FIG. 2 and a mirror deflector are used.

This illumination hologram forms one or more rows of light strips. This band-shaped light is a collection of small circles arranged in a band-like shape. The light reproduced by this illumination hologram is focused on a mirror deflector as shown in FIG. 3, and the mirror deflector is arranged so that the center of rotation of the mirror deflector and the focused area almost coincide. When such an arrangement is adopted, when a hologram is created using this two-dimensional optical spatial modulator, it is possible to prevent deterioration of the hologram image quality due to noise vibrations due to rotation of the mirror. The present invention will be explained in detail below with reference to Examples.

FIG. 2 shows a hologram recording device which is an embodiment of the present invention. 14 is a Caesar light source, 17 is an illumination hologram, 18 is a mirror deflector, 19 and 2
0 is an imaging optical system, 21 is a polarizing plate, 22 is a 1' paternal skin long slope,
23 is a light spatial modulation element made of gadolinium molybdate crystal consisting of a 1' long plate, and 24 is an analyzer.

21 to 24 are optical spatial modulators 25 of row-by-row information configuration type.

The illumination hologram 17 is made as follows.

At position 23, a plate with a strip pattern consisting of one or more rows of small circular holes arranged in a strip is placed, and a parallel light beam is irradiated onto this plate.

This transmitted light is passed through lenses 19 and 20, and mirror 18
, 28 is placed at the position 17 in FIG. 2, and a reference beam is irradiated from the direction opposite to that of the laser beam 29. The rotation axis of the mirror deflector 18 is located at the focal point of the lens 20, and this focal point is imaged onto the illumination hologram surface by the lens 19.

Therefore, the Fourier transform pattern of the strip-shaped pattern plate placed at 23 is imaged on the hologram. Therefore, after the first-order diffracted light 30 of the illumination hologram 17 created by the above-mentioned optical system passes through the lens 19, the beam is focused on the rotation axis on the mirror deflector 18. Since the center of rotation of this east-centered beam coincides with the east-focus point, the virtual image of the east-focus point created by this mirror does not move even if the mirror rotates. That is, the lens 20
Light entering from the mirror deflector side as seen from the mirror is always reflected from the same point, regardless of the deflection angle of the mirror. The first-order diffracted light 30 of the illumination hologram 17 is irradiated onto the optical spatial modulator 25 with information configuration in row units by the mirror deflector 18 at different locations, forming information in the column direction each time, and the information is transferred to the hologram medium 27 with the lens 26. Concentrate and create a Fourier transform hologram.
FIG. 3 is a diagram in which the focusing point of the lens 19 of the light beam 30 described above is aligned with the rotation axis C of the mirror deflector 18.

FIG. 4 is a diagram illustrating the effect of this coincidence. If the first-order diffracted light of the illumination hologram that has passed through the lens 19 in FIG. Light is emitted from virtual image B.

If the mirror 18 does not stand completely still but rotates by Δ and reaches 18', a virtual image of B becomes B'. Therefore, the light parallelized by the two collimator lenses is irradiated onto the row-by-row information configuration type optical spatial modulator 25, and the position B where the light is focused on the hologram medium 27 by the lens 26 is changed to B by the rotation of the mirror by △. ’. If there is such movement of the diffracted light, the interference fringes of the hologram created by overlapping the diffracted light and the reference light will move during the exposure process, making it impossible to record the interference lines. However, when the light passing through the lens 19 in FIG. 4 coincides with the rotation axis C of the mirror deflector 18, the mirror deflector 18
The light is always focused on a fixed point on the hologram medium 27 (the backward point of the lens 26), regardless of the rotation of the light.

Therefore, no movement of interference fringes occurs on the hologram medium during the exposure time. In Figure 4, the distance between B and C is 1, and lens 2
6 and the ratio of the V point distance of lenses 20 is Rf,
BB' of 21Δ=21RfΔ, whereas CC'iCC'=.

becomes.

When Δ is 10-4, in order to suppress BB to one-tenth of the wavelength, when Rf=1, it is necessary to make 1<250 μm (the wavelength is set to 5000 A).

As is clear from the above calculations, it is only possible to record a high-quality hologram by concentrating the light that has passed through the lens 19 in the very vicinity of the rotation axis of the mirror deflector 18. In FIG. 2, although the amount of light from other than the band-shaped portion of the illumination hologram 17 is very small, it irradiates light to areas other than the rows that constitute the information, resulting in noise.

Therefore, by blocking light other than this band-shaped portion with the slit 31, (S/N) Dc can be further increased, and high-quality hologram recording becomes possible. The above-mentioned illumination hologram is formed by interference fringes between a diffracted light obtained by amplitude Fourier transformation of light transmitted through a strip-patterned plate used in creating the illumination hologram, and a reference light.

However, the light is extremely concentrated in the center of this diffracted light, making it impossible to create a high-quality illumination hologram. Therefore, if an illumination hologram is created by adding random phase modulation to the strip pattern, an illumination hologram with less noise and high diffraction efficiency will be obtained.

That is, it is sufficient to create an illumination hologram consisting of a collection of small circles arranged in a band shape, each having a constant phase within each small circle and a random phase independent of their positions. By creating the illumination hologram in this manner, it is easy to increase the diffraction efficiency of the illumination hologram from 10% to 20%. Since all of this diffracted light is used to constitute two-dimensional information, the power of the light source is used much more effectively than in the secondary method shown in FIG. In other words, in conventional methods, the amount of light is reduced by about 50% in order to make the light beam uniform, and since only a portion of that uniform light is used, the actual light usage efficiency is about 1%. . Therefore, by using the illumination hologram of the present invention, it becomes possible to use one digit of light more effectively than before. The row-by-row information configuration type optical spatial modulation element is not limited to gadolinium molybdate crystal, and other strong current materials or liquid crystals may be used.

As explained above, it has become possible to significantly increase the signal-to-noise ratio of a hologram created using the hologram recording device of the present invention compared to the conventional one.

In addition, the illumination hologram generates light consisting of a collection of small circular lights distributed with a random phase in the column direction, and irradiates it to the spatial modulation element that constitutes the information in the row direction, thereby constructing two-dimensional information. The amount of light can be used effectively.

Furthermore, by concentrating the elongated light beam made up of a collection of small circular lights reproduced by the illumination hologram using a lens, and by aligning the focus point with the rotation axis of the mirror deflector, we can prevent noise-like rotational vibrations of the mirror. It is now possible to create holograms with less impact.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a hologram device using a subordinate optical spatial modulator, Fig. 1 is a block diagram of a hologram device showing an embodiment of the present invention, and Fig. 3 is a reproduction of an illumination hologram used in the present invention. FIG. 4 is a diagram showing the relationship between light and a mirror deflector, and is a diagram illustrating how the positional relationship between the reproduction light of the illumination hologram used in the present invention and the mirror deflector has an effect on hologram creation due to the noisy rotational vibration of the mirror. 12 is an object light carrying information, 13 is a reference light, 14 is a laser light source, 15 is a mechanical shirt, 16 is an electrical shirt (15 and 16 are not necessarily necessary), 1
7 is an illumination hologram, 18 is a mirror deflector, 19 is an imaging lens, and 20 is a collimator lens. 21 is a polarizer, 22 is a 1'4 long skin plate, 23 is a cadrinium molybdate 1/4 skin long plate spatial modulation element, and 24 is an analyzer. 21 to 24 are row-by-row information optical spatial modulators 25. 26 is a condenser lens, 27 is a hologram medium, 28, 28
', 28'' is a mirror. Figure O1 Soup 2 Crab Next Figure O4 Figure

Claims (1)

[Claims] 1. A laser beam is divided into a first and a second beam, and the first beam is spatially modulated by a two-dimensional spatial modulator, and the second beam is caused to interfere with the light beam. In a hologram recording device that multiplexes holograms on a recording medium, the secondary spatial modulators are arranged in parallel in the same plane and have elongated light control areas, and the light irradiated onto the areas is It consists of a plurality of light modulation means for modulating the light, and a means for simultaneously sending a desired modulation signal to each of the light modulation means, and has a constant phase internally as the first light beam, and is mutually has an illumination hologram that generates an elongated light beam consisting of a collection of small circular lights with randomly distributed phases, an optical element that focuses the elongated light beam, and a mirror deflector placed near the focusing point. and simultaneously projecting the narrow beam reflected by the mirror deflector onto each light modulating means so that its longitudinal direction is orthogonal to the longitudinal direction of the light modulating means, and changing the deflection angle of the mirror deflector. a light projection device that moves the irradiation position of the elongated light beam onto the light modulation means in the longitudinal direction of the light modulation means; A hologram recording device characterized in that it is configured to send a signal to each optical modulation means to form multiple holograms on a recording medium. 2. The hologram recording device according to claim 1, further comprising a band-shaped slit for blocking noise-induced light beams other than the elongated light beam formed by the illumination hologram.