Optical information storage system

• US 4,063,226 A
• Filed: 12/31/1975
• Issued: 12/13/1977
• Est. Priority Date: 03/18/1974
• Status: Expired due to Term

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Bardos, Andrew M., Vander Lugt, Anthony, Kozma, Adam
• Primary Examiner(s): Hecker, Stuart N.
• Application Number:
  US05/645,525
• Time in Patent Office: 713 Days
• Field of Search: 340/173 LM, 340/173 LT, 178/6.7 R, 178/6.6 R, 178/7.6, 179/100.3 B, 179/100.3 V
• US Class Current: 365/125
• CPC Class Codes: G03H 1/0486 Improving or monitoring the quality of the record, e.g. by compensating distortions, aberrations
• CPC Class Codes: G03H 2001/0489 by using phase stabilized beam
• CPC Class Codes: G11C 13/042 using information stored in the form of interference pattern

Abstract

A wideband holographic information storage system records Fourier holograms on film in rapid succession, each hologram storing 128 bits of data. The hologram fringe pattern is held stationary by varying the reference beam frequency to track the variations of frequency of the signal beam that are caused by acoustic-optic modulation of the signal beam. Holograms are successively recorded in adjacent positions by scanning a light beam across a photosensitive film with a rotating polygonal mirror, the recording light beam being wide enough to cover two facets of the mirror so as to achieve nearly 100% scanning duty cycle. During readout, a readout light beam is steered to compensate for prismatic deflection effects caused by variations in thickness of the film. The direction of the output beam is maintained constant despite a scanning motion of the incident readout beam, by reflecting the output beam a second time from a different facet of the polygonal mirror to compensate the rotational component of beam motion. Clocking of output data is self-synchronized, based upon modulation signals. Acoustically caused defocusing of the light beam is optically corrected. Methods are employed to reduce crosstalk.

Claims

1. An information storage system comprising a member bearing a spatially distributed record of information stored in a form adapted for readout by a scanning light beam, light source means for producing a beam of light propagating in a first direction along a first longitudinal segment of said beam, first light deflection means at the end of said first beam segment for deflecting said beam to propagate in a second general direction along a second longitudinal beam segment to said information bearing member, said member disposed in the light path for modulating the light beams by said information, said modulated beam that follows said member propagating along a third longitudinal beam segment, second light deflection means at the end of said third beam segment for deflecting said beam to propagate in another direction as a fourth beam segment, and means for rotatably moving said first light deflection means about an axis substantially perpendicular to the plane defined by said first and second beam segments for scanning said second beam segment across said member, and for rotatably moving said second deflection means about said axis so as to substantially eliminate any rotational component of motion from said fourth beam segment.

2. An information storage system as defined in claim 1 and wherein said first and second light deflection means comprise first and second mirrors respectively, and wherein said axis is spaced apart from the reflecting surfaces of said mirrors.

3. An information storage system as defined in claim 1 and further comprising convergent third light deflection means positioned on said second beam segment intermediate said first deflection means and said member for producing telecentric scanning of said member by the light beam.

4. An information storage system as defined in claim 1 and wherein said spatially distributed record comprises a hologram.

5. A method for use in an information storage system having a member bearing spatially distributed record of information comprising the steps of establishing a light beam from a light source, said beam having a plurality of longitudinally spaced beam segments, deflecting a first segment of the beam by means of a first light deflector to propagate along a second segment of the beam to the information-bearing member, moving said first light deflector about an axis which is substantially perpendicular to the plane defined by said first and second segments to scan said second beam segment across said information-bearing member, producing a modulated third beam segment by modulating said second segment with said information record, deflecting the third beam segment by a second light deflector to propagate along a fourth beam segment, and moving said second light deflector about said axis in synchronism with said first light deflector in a motion adapted to substantially eliminate any rotational component of motion from said fourth beam segment.

6. An information storage system comprising a light source means for providing a light beam propagating along a first longitudinal beam segment;

first and second light deflection means each receiving said first beam segment for producing by deflection a second beam segment and a third beam segment respectively;

actuation means for translating said first and second light deflection means successively into, across, and out of said first beam segment transversely to the direction of light propagation and for rotating said first and second deflection means to successively scannably move said second and third beam segments;

information storage member means for storing a spatially distributed record and for successively receiving said second and third beam segments upon the successive scanning by said first and second light deflection means; and

lens means interposed between said deflection means and said information storage member means for redirecting said second and third beam segments to shorten the respective arcs described by the scanning motion thereof at said information storage member means;

said light source means including means for providing said first beam segment so as to be wide enough transversely that said first deflection means is fully illuminated transversely by said first beam segment substantially until at least such time as said second deflection means is fully illuminated by said first beam segment.

7. An information storage system as defined in claim 6 and wherein said first and second deflection means comprise adjacent mirror facets of a rotating polygonal scanner.

8. A holographic information storage system as set forth in claim 6 wherein said light source means provides a coherent light beam and wherein said information storage member comprises holographic recording means.

9. A holographic information storage system as set forth in claim 8 wherein said light source means provides a coherent light beam resolvable into at least two transverse segments serving as reference and object beams, said second and third beams being similarly resolvable, and wherein said lens means serves to focus said reference and object beams at a common point moving scannably across said holographic recording means.

10. A method for use in an information storage system having a light beam divided into beam segments following one another along the direction of propagation of said light beam and having a member for storage of a spatially distributed information record across which a segment of said beam is to be scanned comprising the steps of translating a first light-deflection means transversely into, across, and out of a first segment of said beam while simultaneously rotating said first deflection means to scan a deflected second segment of said beam across said first beam segment far enough to achieve full transverse illumination thereof by said first beam segment while said first deflection means is also still substantially fully transversely illuminated by said first beam segment to transfer illumination scanning services from said first to said second deflection means substantially without interruption;

translating said second deflection means transversely across said first beam segment while simultaneously rotating said second deflection means to scannably move a third beam segment deflected therefrom across said storage member; and

refracting said second and third beam segments towards said storage member so that the portion of time that said storage member receives each of said second and third beams is enhanced, thereby increasing the duty cycle of said system.

11. A method for use in an information storage system as defined in claim 13 and wherein said step of translating a first light-deflection means into, across, and out of a first segment of said beam while simultaneously rotating said first deflection means to scan a deflected second segment of said beam across said storage member which comprises a step of revolving a first mirror about an axis spaced apart from the reflecting surface plane of said first mirror and wherein said step of translating and rotating said second deflection means comprises a step of revolving a second mirror about said axis, the reflecting surface of said second mirror being spaced apart from said axis.