Heterodyne readout holographic memory

Claim 2

In a holographic optical memory having a memory medium upon which a plurality of holograms are stored, a system for reading out a bit pattern stored in one of the holograms, comprising: light source means for providing a coherent light beam, beam splitter means for splitting the coherent beam into a first and a second beam, light beam directing means for directing the first beam to one of the plurality of holograms, a portion of the first beam being diffracted by the hologram to form at a reconstructed image plane a reconstructed image of the bit pattern stored in the hologram, light beam superimposing means for superimposing the second beam with the diffracted portion of the first beam, optical frequency translator means positioned in the path of one of the first and second beams to cause the one beam to have a different frequency from that of the other beam during readout, such that a beat frequency signal is produced when the first and second beams are superimposed, and an array of detectors positioned at the reconstructed image plane, each detector positioned to receive light representing one bit of the bit pattern and to provide an output signal indicative of the intensity of the beat frequency signal received.

Claim 3

The invention as described in claim 1 wherein the memory medium is a magnetic film.

Claim 4

The invention as described in claim 2 wherein the magnetic film is manganese bismuth.

Claim 5

A holographic optical memory comprising: light source means for providing a coherent light beam, beam splitter means for splitting the coherent light beam into a first and a second beam, a memory medium for the storage of a plurality of holograms, beam directing means for simultaneously directing the first and second beams to coincide at a selected region of the memory medium, page composer means positioned in the path of the second beam between the beam splitter means and the memory medium for creating a bit pattern in the second beam during the writing stage, optical frequency translator means positioned in the path of one of the first and second beams to cause the one beam to have a different frequency from that of the other beam, such that a beat frequency signal is produced when the first and second beams are superimposed, beam intensity control means for causing the combined intensity of the first and second beams to be sufficient to store the bit pattern as a hologram during the writing stage, and insufficient to alter the hologram during the reading stage, pivoting means positioned proximate the memory medium for pivoting, during the reading stage, superimposed beams comprising a diffracted portion of the first beam and an undiffracted portion of the second beam into a common reconstructed image plane, and an array of detectors positioned at the common reconstructed image plane, each detector positioned to receive the light representing one bit of a reconstructed bit pattern formed by the diffracted portion of the first beam and to provide an output signal indicative of the intensity of the beat frequency signal received.

Claim 6

A holographic optical memory comprising: light source means for providing a coherent light beam, beam splitter means for splitting the coherent light beam into a first and a second beam, a memory medium for the storage of a plurality of holograms, beam directing means for simultaneously directing the first and second beams to coincide at a selected region of the memory medium, page composer means positioned in the path of the second beam between the beam splitter means and the memory medium for creating a bit pattern in the second beam during the writing stage, optical frequency translator means positioned in the path of one of the first and second beams to cause the one beam to have a different frequency from that of the other beam, such that a beat frequency signal is produced when the first and second beams are superimposed, beam intensity control means for causing the combined intensity of the first and second beams to be sufficient to store the bit pattern as a hologram during the writing stage, and insufficient to alter the hologram during the reading stage, pivoting means positioned proximate the memory medium for pivoting, during the reading stage, superimposed beams comprising a diffracted portion of the first beam and an undiffracted portion of the second beam into a common reconstructed image plane, and an array of detectors positioned at the common reconstructed image plane, each detector positioned to receive the light representing one bit of a reconstructed bit pattern formed by the diffracted portion of the first beam and to provide an output signal indicative of the intensity of the beat frequency signal received.

Claim 7

The holographic optical memory of claim 4 wherein the beam directing means comprises: light beam deflector means positioned between the light source means and the beam splitter means for deflecting the first and second beams to a plurality of resolvable spots, mirror means positioned in the path of one of the first and second beams for changing the direction of propagation of the beam, inverting means positioned in the path of one of the first and second beams for inverting the angular direction of the beam, an array of individual lenses positioned in the path of the second beam, each lens being positioned at one of the plurality of resolvable spots, for reducing the beam diameter of the resolvable spots, and field lens means positioned in the path of the second beam between the array of individual lenses and the page composer means for pivoting the second beam at a first pivot plane.

Claim 8

The holographic optical memory of claim 5 wherein beam inverting means comprises first and second lenses.

Claim 9

The holographic optical memory of claim 5 wherein the beam inverting means is positioned in the path of the second beam.

Claim 10

The holographic optical memory of claim 7 wherein the beam inverting means is positioned essentially at the first pivot plane and wherein the beam inverting means further pivots the second beam at a second pivot plane.

Claim 11

The holographic optical memory of claim 8 wherein the page composer means is positioned proximate the second pivot plane.

Claim 12

The holographic optical memory of claim 5 wherein the page composer means is positioned essentially at the first pivot plane.

Claim 13

The holographic optical memory of claim 4 and further comprising Fourier transform lens means positioned in the path of the second beam proximate the page composer means for performing a Fourier transform of the bit pattern produced by the page composer meAns.

Claim 14

The holographic optical memory of claim 4 and wherein the pivoting means comprises pivoting lens means.

Claim 15

The holographic optical memory of claim 12 wherein the pivoting lens means comprises a lens having a substantially flat surface and a curved surface.

Claim 16

The holographic optical memory of claim 13 wherein the memory medium comprises a deposited layer on the substantially flat surface.

Claim 17

The holographic optical memory of claim 4 wherein the memory medium is a magnetic film.

Claim 18

The holographic optical memory of claim 15 wherein the diffracted portion of the first beam and the undiffracted portion of the second beam are transmitted through the magnetic film.

Claim 19

The holographic optical memory of claim 15 wherein the diffracted portion of the first beam and the undiffracted portion of the second beam are reflected by the magnetic film.

Claim 20

The holographic optical memory of claim 15 wherein the magnetic film is manganese bismuth.