Only-readable three-dimensional optical storage device

• US 6,738,337 B2
• Filed: 06/08/2001
• Issued: 05/18/2004
• Est. Priority Date: 07/20/2000
• Status: Expired due to Fees

• Current Assignee: Nankai University
• Original Assignee: Nankai University
• Inventors: Wu, Qiang, Sun, Qian, Huang, Hui, Sha, Zuojin, Tang, Baiquan, Xu, Jingjun, Zhang, Guangyin, Zhang, Xinzheng, Qiao, Haijun
• Primary Examiner(s): Hindi, Nabil
• Application Number:
  US09/875,947
• Publication Number:
  US 20020018429A1
• Time in Patent Office: 1,075 Days
• Field of Search: 369/103, 369/275.3, 369/112.01, 369/112.22
• US Class Current: 369/103
• CPC Class Codes: G03H 1/265 Angle multiplexing; Multichannel holograms G03H1/268 takes precedence
• CPC Class Codes: G03H 2260/54 Photorefractive reactivity wherein light induces photo-generation, redistribution and trapping of charges then a modification of refractive index, e.g. photorefractive polymer
• CPC Class Codes: G11B 7/0065 Recording, reproducing or erasing by using optical interference patterns, e.g. holograms
• CPC Class Codes: G11B 7/127 Lasers; Multiple laser arrays lasers per se H01S
• CPC Class Codes: G11B 7/128 Modulators G11B7/1245 takes precedence
• CPC Class Codes: G11B 7/135 Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
• CPC Class Codes: G11B 7/1362 Mirrors
• CPC Class Codes: G11B 7/2433 Metals or elements of Groups 13, 14, 15 or 16 of the Periodic Table, e.g. B, Si, Ge, As, Sb, Bi, Se or Te

Abstract

The invention relates to the information storage. It consists of a computer, a precise rotary table, a writing laser source, a readout laser source, a spatial filter, a spatial light modulator, lens, mirrors, photorefractive crystals (such as doubly doped lithium niobate), and a phase-mismatch adjustor; Due to used a green light (532 nm) as the writing light, and a red light (670 nm) as the readout light, the signal-to-noise ratio is improved greatly and the problem of fixing the stored information is solved. The transmission configuration is used to realize the high-density digital storage in which the irregular lens is designed to work as a phase-mismatch adjustor and read out the whole stored image with no distortion and loss. The dynamically differential encoding and decoding technique is used to suppress the bit-error-rate to lower than 10⁻⁶.

Claims

1. A only-readable three-dimensional optical storage, wherein said storage consists of two systems:

A writing system which includes a computer, a beam splitter, a precise rotary table, a writing light source, lenses, a spatial light modulator, a spatial filter, mirrors, a photorefractive crystal and a CCD; and

in which said spatial light modulator (104), precise rotary table (109), CCD (111) are connected to said computer (112);

said photorefractive crystal (107) is fixed on said precise rotary table (109);

said beam splitter (101) is placed in the front of said writing light source (100), and said spatial filter (102), lens (103), spatial light modulator (104) is placed in turn between said beam splitter (101) and said mirror (105);

said mirror (108) is placed between said beam splitter (101) and said photorefractive crystal (107);

said lens (106) is placed between said beam splitter (101) and said photorefractive crystal (107); and

said lens (110) and said CCD (111) is in turn placed behind said photorefractive crystal (107) and opposite to the lens (106), with a intersect angle 2θ

of two writing beam from the lens (106) and mirror (108) being within the range of 10°

˜

35°

;

a read-out system which includes a computer, a precise rotary table, a slit, a phase-mismatch adjustor, a readout light source, a photorefractive crystal, lenses and a CCD;

in which said precise rotary table (203) and CCD (205) are connected to said computer (206);

said photorefractive crystal (204) is fixed on said precise rotary table (203), and said slit (201), phase-mismatch adjustor (202), precise rotary table (203), photorefractive crystal (204), lens (207) and CCD (205) are in turn placed behind the readout light source (200), with a angle (180°

-2α

) between the light from the phase-mismatch adjustor (202) and the diffracted light to the lens (207) being a function of θ

as λ

_wsinθ

=λ

_rsinα

.

2. A only-readable three-dimensional optical storage according to claim 1, wherein said phase-mismatch adjustor (202) is an irregular double-convex lens, with the transverse focus length range of 50˜

400 mm and the longitudinal focus lens range of 300 mm˜

+∞

.

3. A only-readable three-dimensional optical storage according to claim 1, wherein one of the mirrors (105) and (108) can be selectively used, or a plurality of mirrors can be used.

4. An only-readable three-dimensional optical storage according to claim 1, wherein said photorefractive crystals are doped and doubly doped lithium niobate and LiTaO₃, and their composition is as follow:

Doped congruent lithium niobate;

Fe 0.02˜

0.05 wt. %

LiTaO₃;

Fe 0.02˜

0.05 wt. %

Doubly doped lithium niobate;

Fe 0.007˜

0.03 wt. %, Mg 1.0˜

5.5 mol. %;

Fe 0.01˜

0.05 wt. %, In 0.75˜

3.0 mol. %;

Fe 0.02˜

0.06 wt. %, Zn 1.5˜

6.5 mol. %;

and the [Li]/[Nb]=0.87˜

0.95.

5. A only-readable three-dimensional optical storage process, wherein said process include a writing procedure and a read-out procedure,

Said writing procedure includes following steps:

(1) A storage file being encoded under the control of a computer to form an encoded two-dimensional pattern, which is output to a spatial light modulator (104), and a coded image or a storage image is formed by way of the spatial light modulator (104);

(2) A beam of green light from the laser source for green light being divided into two beams through a beam slitter (101);

one beam 1 passing through the spatial filter (102) and being collimated by the lens (103) to pass through the spatial light modulator (104) where it is modulated and to carry the information of the encoded image, and then it being reflected by the mirror (105) and is focused by the lens (106) upon the crystal (107);

another beam 2 is reflected by the mirror (108) and incident on the sample crystal (107) as a reference light;

two writing beams interfering in the crystal (107) and recording the hologram in the crystal (107.);

(3) After the holographic recording is finished, the rotary table (109) being rotated to another angle, and the next image storage being started,

(4) Repeat the steps (1)-(3) mentioned above until the multi-page image could be stored;

Said readout procedure includes following steps;

(1) The sample being rotated to a needed angle by the rotary table controlled by a computer, and using a red light from the semiconductor laser as the read out light to pass the slit (201) first, and then through the phase-mismatch adjustor (202), to be incident on the crystal;

the diffracted light being collected by the lens (207) and imaged on to CCD;

the image information detected by the CCD being decoded to the original computer files by the computer;

(2) Rotating the sample to next angle, and obtaining more stored images.

6. A only-readable three-dimensional optical storage process according to the claim 5, wherein said green light have a wavelength of 532 nm.