Coherent optical correlator

• US 4,277,137 A
• Filed: 10/06/1978
• Issued: 07/07/1981
• Est. Priority Date: 10/06/1978
• Status: Expired due to Term

• Current Assignee: The United States Of America As Represented By The Secretary Of The Army
• Original Assignee: The United States Of America As Represented By The Secretary Of The Army
• Inventors: Upatnieks, Juris, Christensen, Charles R., Guenther, Bobby D.
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): ARNOLD, BRUCE
• Application Number:
  US05/949,325
• Time in Patent Office: 1,005 Days
• Field of Search: 350/162 SF, 340/146.3 Q, 244/3.17, 356/71
• US Class Current: 359/560
• CPC Class Codes: F41G 7/2226 comparing the observed data with stored target data, e.g. target configuration data
• CPC Class Codes: F41G 7/2246 Active homing systems, i.e. comprising both a transmitter and a receiver
• CPC Class Codes: F41G 7/2253 Passive homing systems, i.e. comprising a receiver and do not requiring an active illumination of the target
• CPC Class Codes: F41G 7/2293 using electromagnetic waves other than radio waves
• CPC Class Codes: F41G 7/343 comparing observed and stored data of target position or of distinctive marks along the path towards the target

Abstract

Reference scenes stored in a filter set containing an array of sets of suimposed, holographic, matched filters are optically correlated with input images displayed on an optically-addressed, liquid crystal, light modulator 34. In operation, a selected laser diode is energized to direct a polarized light beam through the collimating lens L1 to the reflecting surface of a polarizing beam splitter 35. After reflecting off the beamsplitter surface, the beam is expanded by positive lens L2 and passed to the liquid crystal modulator. There it is modulated by the input image and reflected; after which it is recollimated by positive lens L2, transmitted by the beamsplitter, and directed to a particular array location of the filter set dependent upon which particular laser diode is energized. The filter set is positioned to be in the back focal plane of lens L4 so that the Fourier-transform of the input image is incident on the particularly located, superimposed matched filter at 31. If the Fourier transformed input image corresponds to one of the superimposed matched filters the incident light beam is diffracted by that particular hologram matched filter to form a spot of light at a predetermined array location of a detector array. The optical correlator finds use as a terminal guidance system in guiding a missile to its target.

Claims

1. An optical correlator comprising an array of coherent light sources;

an imaging device having an input image thereon;

a filter set array having a plurality of filters therein;

first means selectively directing one of said light sources through said imaging device so as to form a Fourier transform of the image at a corresponding location in said filter set array;

a detector array having a plurality of detectors thereon;

said filter set array having stored reference images thereon such that if the input image illuminated by the selected light source corresponds to the reference image, then a correlation spot will appear in a corresponding field of the detector array;

said coherent light sources comprises a plurality of laser diodes; and

a polarizing beam splitter connected between said laser diodes and said imaging device so as to reflect light from said laser diodes through said imaging devices and to pass reflected light from said imaging device through said beam splitter to said filter set array.

2. An optical correlator as set forth in claim 1 further comprising lenses and reflecting devices for reflecting the light thru said lenses, polarizor beam splitter, filter set array and detector array so as to reduce the overall size of the correlator.