JP2766906B2 - Hologram storage device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a storage device for recording and reproducing information.

[Conventional technology]

FIG. 2 shows the principle of storage of a volume hologram. Hologram storage is performed by spatially recording the density of interference fringes generated by the signal wave and the reference wave. Assuming that both the signal wave and the reference wave intersect as a plane wave at an angle θ, an interference fringe occurs in a direction that bisects the traveling direction of each wave, and the pitch p is Becomes λ is the wavelength of light. By placing the hologram photosensitive material on the portion where the interference fringes have occurred, the density is recorded. Reproduction is performed using Bragg reflection by interference fringes. The condition of Bragg reflection is m is an integer, and φ is the incident angle of the reproduction light with respect to the interference fringes (see FIG. 3), and a signal is detected as diffracted light only when this condition is satisfied.

Therefore, by changing the angle θ between the signal wave and the reference wave, the space between interference fringes and the direction of the fringes can be changed to spatially multiplex recording. This is called volume multiplexed hologram storage.

FIG. 4 shows a conventional configuration for performing this type of multiplex recording. In FIG. 4, M1, M2, M3,... Mi are mirrors. To change the angle of the reference light with respect to the signal light, the following is performed. In order to perform the operation with one mirror, one mirror is moved to the position of each mirror in FIG.
The angle (θ) of the mirror is also changed to match the position of the signal light with the position of the reference light with respect to the hologram medium. There is also a method in which mirrors are placed at the positions shown in FIG. 4 from the beginning by the number of multiplicity, and only necessary light is selected by attaching a shutter mechanism to the mirrors.

[Problems to be solved by the invention]

Each of the above methods has a disadvantage that the configuration is complicated, and the control of the light position at high speed and accurately requires a large scale as well as a high cost.

An object of the present invention is to provide a high-speed, high-accuracy, low-cost volume multiplexed hologram storage device.

[Means for solving the problem]

In general, the present invention relates to a hologram storage device, which includes a laser light source for recording and reproducing a hologram, a deflector for oscillating a light beam at an arbitrary angle, and a light beam emitted from one focal point to another focal point. Reflector for converging light, spatial light modulator for information input, holographic optical system for holographically recording light emitted from the laser light source, volume hologram storage medium, and two-dimensional optical information It is characterized by comprising a photodetector for detection.

The present invention is characterized by using an optical deflector and an elliptical reflector so that the angle of the reference light with respect to the signal light is arbitrarily changed and the light intersects in the same space in order to eliminate the conventional disadvantage. A mechanically movable part can be eliminated, and a high-speed, high-accuracy, low-cost volume multiplexed hologram storage device can be realized.

 Hereinafter, the present invention will be specifically described with reference to the drawings.

FIG. 1 is a schematic diagram showing one embodiment of the device of the present invention. In FIG. 1, reference numeral 4.1 is a laser, 4.2 is a light beam, 4.3 is a light beam passed without being deflected by the deflector 4.6, 4.4 is a light beam deflected by the deflector 4.6, 4.
5 is an elliptical reflector, 4.6 is a deflector, 4.7 is a beam expander lens, 4.8 is a condenser lens, 4.9 is a spatial light modulator, 4.10 is a volume hologram storage medium, 4.11 is a photodetector array, 4.12 is an optical shutter . The principle of operation is as follows.

Light beam 4.2 from laser 4.1 is deflector 4.6
Into a light beam 4.3 that travels straight without being deflected, and a light 4.4 that is deflected and bent in a certain direction. Light beam 4.4 is reflected by the surface of elliptical reflector 4.5. By placing the position of the deflector 4.6 at one focal position of the elliptical reflector 4.5, the deflected light 4.4 passes through the other focal position. By placing the volume hologram storage medium at the other focal position, the deflection light 4.4 always irradiates the volume hologram storage medium regardless of the deflection angle.
The deflected light 4.4 is used as reference light when storing a hologram.

On the other hand, the light 4.3 that is not deflected passes through the shutter 4.12 (the shutter 4.12 is initially opened) and then passes through the beam expander lens 4.7, whereby the beam diameter is enlarged. As an example, a light beam of 0.5 mm diameter is expanded to a diameter of 10 mm by a 20-fold beam expander. After expansion, the light passes through a spatial light modulator. 10 m for spatial light modulator 4.9
It is about m square and divided into 200-500 μm square cells, and each cell has a function of transmitting or not transmitting light. After passing through this, the light 4.3 has information spatially and becomes signal light. The signal light is narrowed down by the lens 4.8 and spatially intersects with the reference light to form an interference fringe as a hologram. Hologram recording is performed by recording this interference fringe on a volume hologram medium. When multiplexing information, as shown by the dotted line in FIG.
By changing the deflection angle by 6 and by changing the angle of the reference light incident on the medium 4.10.

Reproduction is performed by closing the optical shutter 4.12 and irradiating the polarized light 4.4 as reproduction light to the volume hologram medium 4.10.
The signal light is reproduced. Receiving it at the photodetector array results in two-dimensional batch signal reproduction.

In the present invention, the content is not limited to individual components, and various lasers (HeNe laser, HeCd laser,
Semiconductor laser, SHG, etc.), various deflectors (mechanical deflector, acousto-optic deflector, etc.), various spatial light modulators (ferroelectric, magnetic material, semiconductor, etc.), various volume hologram media (silver halide, photopolymer, It is obvious that the hologram storage device of the present invention is constituted by a combination of photochromics, photorefractive material, magnetic material, and the like, and in this case, the present invention is also applied.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples.

Example 1 As a laser light source, an Ar laser having a wavelength of 50 mW and a wavelength of 514 nm was used. Electro-optical deflector, mechanical shutter, 20x beam expander, CC as deflector
We recorded 20 multiplexed holograms using an electric input type spatial light modulator combining D and liquid crystal, a BSO (2 mm diameter, 5 mm length) as a volume hologram medium, and a CCD array as a light receiver. The positioning accuracy of the reference light and the signal light on the volume hologram was 50 μm. One recording was performed at 50 msec.

〔The invention's effect〕

As described above, the volume multiplexed hologram storage device according to the present invention can accurately and quickly change the incident angle of the reference light beam, which is indispensable for multiplexing, by using comparatively small components. And cost / performance is greatly improved. Therefore, the future
In the ISDN society, it is indispensable to make a great contribution by using it as an information storage device in a field handling a large amount of information.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing one embodiment of the apparatus of the present invention, FIG. 2 is a diagram showing the principle of volume hologram storage, FIG. 3 is a diagram showing Bragg reflection conditions, and FIG. FIG. 4.1: laser, 4.2: light beam, 4.3: undeflected light beam, 4.4: deflected light beam, 4.5: elliptical reflector,
4.6: Deflector, 4.7: Lens for beam expander, 4.8: Condensing lens, 4.9: Spatial light modulator, 4.10: Volume hologram storage medium, 4.11: Photodetector array, 4.12: Optical shutter

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-55-45004 (JP, A) JP-A-1-78057 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11C 13/04 G03H 1/00

Claims (1)

(57) [Claims] 1. A laser light source for recording and reproducing a hologram, a deflector for oscillating a light beam at an arbitrary angle, an elliptical reflector for condensing light from one focal point to another focal point, and spatial light for information input. A holographic optical system for holographically recording light emitted from the laser light source, a volume hologram storage medium, and a photodetector for detecting two-dimensional optical information collectively. Hologram storage device.