JPS5953554B2 - One-dimensional hologram writing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a hologram memory writing device.

In a hologram memory device in which a hologram plate consisting of a large number of holograms is irradiated with a readout laser beam and a reproduced bit image is detected by a photoelectric conversion element array, increasing the capacity is the most important goal.

To this end, it is essential to establish high-density recording technology, high-speed recording technology, and high-speed multi-bit read technology. Fourier transform holograms, which display digital information two-dimensionally and then Fourier transform it into a hologram, are an excellent method that allows high-density, high-speed recording, but require a two-dimensional photoelectric conversion element array. Hologram memory using this method has not been put into practical use because it requires two-dimensional alignment with the reproduced bit image, and high-speed readout is difficult. On the other hand, since a one-dimensional photoelectric conversion element array is easy to obtain and easy to align and operate at high speed, it is said to be a good idea to build a system around such devices. A hologram for obtaining a one-dimensional reproduced bit image may be obtained by performing Fourier transformation of one-dimensionally displayed information (one-dimensional Fourier transform hologram) and recording interference fringes with reference light. It is well known that this method enables high-density recording comparable to that of a two-dimensional Fourier transform hologram. However, since the number of bits recorded simultaneously is substantially smaller than in the two-dimensional case, the recording speed decreases. This means that increasing the capacity requires a long writing time, and there is a risk that the original goal of the hologram memory may not be achieved in real time.
An object of the present invention is to make a large-capacity, high-density hologram memory practical by providing a writing device that simultaneously records a plurality of one-dimensional Fourier transform holograms.

According to the present invention, a plurality of one-dimensional spatial modulators that express digital information transparently or opaquely and convert it into a one-dimensional pattern sequence are arranged in another dimension, and a pattern sequence of one-dimensional spatial modulators is provided. By using a group of prisms having different inclinations for each one-dimensional spatial modulator in the vertical direction, and a Fourier transform lens, the Fourier transform image of each one-dimensional spatial modulator is transferred to different positions of the photosensitive material. By forming a plurality of one-dimensional Fourier transform holograms, a writing device that simultaneously records a plurality of one-dimensional Fourier transform holograms can be obtained.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a conventional one-dimensional Fourier transform hologram writing device, which includes a one-dimensional spatial modulator 1 made of liquid crystal or PLZT crystal, and a Fourier transform lens 2.
and a photosensitive material 3.

The one-dimensional spatial modulator 1 and the photosensitive material 3 are placed at the front and rear focal lengths of the Fourier transform lens 2, respectively. Now, if the spatial pattern size of one digital information of the spatial modulator 1 is Axb (a is the size in the one-dimensional pattern row direction), the size of the Fourier transform hologram is (
2fλ/a)×(2fλ/b).

Here, f is the focal length of the Fourier transform lens 2, and λ is the wavelength of the writing light. If lined up, f=100mm1λ=0.
5 μM. a=250 μM. If b=10 mm, the hologram size will be 400 μm×10 μm. Therefore, in order to record a Fourier transform hologram with another one-dimensional pattern separated by 10 μm, the photosensitive material 3 must be moved 10 μm in the direction of arrow 4 to change the pattern of the spatial modulator and record in time series. Must be. Note that if the number n of bits reproduced from a one-dimensional Fourier transform hologram is 100 bits, the one-dimensional spatial modulator size is Na=25.
mm, and the effective diameter of the Fourier transform lens is 30 to 40 mm.
mm is enough. FIG. 2 is a diagram showing an embodiment of the writing device of the present invention, and 1a, 1b, and 1c are the same as in FIG. 1, respectively. It is the same one-dimensional spatial modulator, but it is made up of multiple arrays (
The one-dimensional pattern row direction is perpendicular to the paper surface).

2 is a Fourier transform lens, and 3 is a photosensitive material.

One-dimensional spatial modulator] A, lb, lc and the photosensitive material 3 have the front and rear focal lengths of the Fourier transform lens 2, respectively. It is installed in a remote location. 10a, 10b, and 10c are prism groups that give a different angle change to the parallel light 8 incident on the one-dimensional spatial modulators 1a, 1b, and 1c for each spatial modulator, and closely contact the spatial modulators 1a, 1b, and 1C. be placed.

If the angle change due to the prism 10a directed to the prism 10b is θ, then the Fourier transformed images of the spatial modulators 1a and 1b are shifted by f·θ on the photosensitive material 3. Similarly, if the angle change due to the prism 10C is 1 θ, there is a deviation of −f·θ. By interfering these three object beams 5 and reference beam 6, three one-dimensional Fourier transform holograms can be recorded simultaneously. Now, in order to record at a pitch of 101 tm according to the above example, when f=100 mm, it is sufficient to tilt the lens by θ=0.1 mrad. Such a prism group can be made by sputtering SiO2 or etching glass. Furthermore, in order to record a group of holograms, the photosensitive material may be moved in the direction of arrow 4 to rewrite and record the information on the spatial modulators 1a, 1b, 1c. In the above example, 30μm
If you move, you can record the following three holograms. In order to read out the hologram group written on the photosensitive material using the above method, a one-dimensional photoelectric conversion element array is provided at the position of the spatial modulator 16, and is brought into close contact with the lens 2 to have a light condensing effect in the X direction. After providing a cylindrical lens where is approximately equal to f, the photosensitive material 3 is moved in the direction of the arrow 4, and the readout light 7 approximately equal to the size of one hologram is irradiated from the direction opposite to the direction of the reference light 6 during fabrication. The reproduced bit images from each hologram can be focused in time series on the photoelectric conversion element array by the lens 2 and the cylindrical lens.

FIG. 3 is a diagram showing another embodiment of the writing device of the present invention, which operates in the same manner as the embodiment shown in FIG. 2, except that the lens 2 is not required during reading.

In this case, the spatial modulators 1a, 1b, 1c and the prism 10
It is not necessary that the prisms 10a, 10b, and 10c are in close contact with each other, and even if the prisms 10a, 10b, and 10c are provided within the parallel beam 8 on the left side of the lens 2, the substantial effect will be the same. Also, the images of the prisms 10a, 10b, 10C are transferred to the spatial modulators 1a, 1
Similar effects can be obtained by forming images on b and 1c.
In the above embodiments, the number of one-dimensional pulley transformation holograms recorded simultaneously is three, but the number is not limited to this. The number of holograms that can be recorded simultaneously is determined by (effective diameter of lens)/(spatial modulator size b), so if a lens with an F number of 2 is used in the above embodiment, five holograms can be recorded simultaneously. According to the present invention, it takes 100 hours (=4 days) to write a large-capacity hologram memory, which would require 500 hours (=21 days) using conventional methods, which is a practically important time reduction. I understand that. In the above explanation, a prism was used as a means to give a certain inclination to the parallel light that passed through each spatial modulator, but the same effect can also be obtained by using the primary light using a diffraction grating. .

Furthermore, although the above explanation deals with digital information,
It is clear that the present invention can also be applied to analog information.

Further, in the above description, the operation of forming a plurality of holograms in the direction perpendicular to the one-dimensional spatial modulator has been described, but it is also possible to simultaneously record a plurality of holograms in the same direction as the one-dimensional spatial modulator.

To achieve this, it is sufficient to tilt each prism of the prism group toward the spatial modulator. As described above in detail, according to the present invention, a hologram writing device can be obtained that can achieve a large capacity, high density memory, which is the original goal of a hologram memory.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional writing device, and FIGS. 2 and 3 are diagrams showing an embodiment of the writing device of the present invention, in which 1 is a one-dimensional spatial modulator, 2 is a Fourier transform lens, and 3 is a photosensitive 5 and 8 are object beams, 6 is a reference beam, and 7 is a readout beam.

Claims (1)

[Claims] 1. A plurality of one-dimensional spatial modulators arranged in parallel to display information in a spatial pattern, and means for separating the light passing through each of the plurality of one-dimensional spatial modulators into different directions in the one-dimensional direction. and a lens for producing a Fourier transformed image of the information pattern displayed on the plurality of one-dimensional spatial modulators on a photosensitive material, the information pattern displayed on each of the plurality of one-dimensional spatial modulators. A one-dimensional hologram writing device characterized by simultaneously forming information patterns at different positions on a photosensitive material.