HOLOGRAPHIC CORRELATOR WITH A FOLDED PATH ACOUSTIC CELL INPUT

• US 3,694,657 A
• Filed: 03/30/1971
• Issued: 09/26/1972
• Est. Priority Date: 03/30/1971
• Status: Expired due to Term

• Current Assignee: Robert E. Brooks
• Original Assignee: Robert E. Brooks
• Inventors: Brooks, Robert E.
• Primary Examiner(s): Schonberg, David
• Assistant Examiner(s): Stern, Ronald J.
• Application Number:
  US05/176,090
• Time in Patent Office: 546 Days
• Field of Search: 250/216 350/3.5,162SF,161 235/181 356/71
• US Class Current: 250/216
• CPC Class Codes: G02B 27/46 Systems using spatial filters
• CPC Class Codes: G06E 3/005 using electro-optical or opto-electronic means

Abstract

An optical signal processing system includes apparatus for identifying a complex signal by an optical matched filter. The matched filter consists of a hologram recorded by projecting coherent light through an acoustic delay line arranged to propagate an acoustic wave therein with multiple intersecting paths. This hologram is now used as the optical matched filter for identifying a signal which is impressed on the same acoustic delay line and projected on the hologram. The hologram may be so arranged as to focus the reference beam substantially in a point whenever the signal to be recorded matches the previously recorded signal.

Claims

1. In an optical signal processing system, apparatus for identifying a complex signal by an optical matched filter, said apparatus comprising:

a. an acoustic delay line arranged to propagate an acoustic wave therein along a folded acoustic path having a plurality of linear portions, each of the portions intersecting a plurality of other portions;

b. an electronic signal generator including means for impressing a signal to be identified on said acoustic cell;

c. a laser for generating a monochromatic light beam;

d. means for projecting said light beam through said acoustic cell, said cell being transparent to said light beam;

e. a hologram on which a signal to be identified has previously been recorded through said acoustic cell, said hologram being disposed in the path of the light beam having passed through said acoustic cell; and

f. means for detecting the light output of said hologram to determine the correlation between the signal originally recorded on said hologram and the signal to be identified.

2. Apparatus as defined in claim 1 wherein a stop is provided in the path of the light beam having passed said acoustic cell, said stop being positioned to stop substantially all light except the first order diffracted light.

3. Apparatus as defined in claim 1 wherein said means for detecting includes a photodetector and a lens for imaging the light having passed said hologram on said photodetector.

4. Apparatus as defined in claim 1 wherein said acoustic cell has a multiplicity of walls disposed at an angle, each wall reflecting the acoustic wave to create said plurality of linear portions.

5. Apparatus for recording a hologram suitable as an optical matched filter for signal correlation, said apparatus comprising:

a. an acoustic cell arranged to propagate therein an acoustic wave along a folded acoustic path having a plurality of linear portions, each of the portions intersecting a plurality of other portions;

b. a laser for generating a monochromatic light beam and projecting it through said acoustic cell, said cell being transparent to said light beam;

c. a recording medium disposed in the path of the light beam having passed said acoustic cell;

d. means for diverting a portion of said light beam and projecting it onto said recording medium to provide a reference beam; and

e. an electronic signal generator including means for impressing a signal to be recorded onto said acoustic cell.

6. Apparatus as defined in claim 1 wherein a stop is provided in the path of the light beam having passed said acoustic cell, said stop being positioned for intercepting substantially all light but the first order diffracted light.