Frequency multiplexed joint transform correlator system

• US 4,357,676 A
• Filed: 09/08/1980
• Issued: 11/02/1982
• Est. Priority Date: 09/08/1980
• Status: Expired due to Term

• Current Assignee: Ampex Corporation (Delta Information Systems, Inc.)
• Original Assignee: Ampex Corporation (Delta Information Systems, Inc.)
• Inventors: Brown, Hugh B.
• Primary Examiner(s): Arnold, Bruce Y.
• Application Number:
  US06/185,053
• Time in Patent Office: 785 Days
• Field of Search: 356/349, 356/353, 356/354, 356/345, 356/347, 364/822, 350/162 SF
• US Class Current: 708/816
• CPC Class Codes: G06E 3/005 using electro-optical or opto-electronic means

Abstract

An improved joint transform correlator system frequency multiplexes two input signals to reduce the resolution along a single optical axis by one half, and uses full input transducer resolution in the other axis to provide a 20% increase in overall system performance. The two input channels are combined by summing baseband channel 1 information with reference channel 2 information which is frequency shifted using single sideband modulation techniques. The resultant signal is used to drive an input transducer of an optical system. The input transducer spatially modulates the light from a laser. A frequency plane is produced by the input optics, where the spatially separated channels may be observed. An interferometer is used to further process the signal information by combining the two channels at the joint transform plane. The combined signals are then written onto an optical-to-optical transducer where the joint transforms are multiplied together through a detection process. The output of this transducer is transformed by the output optics system to provide the cross correlation plane to an output transducer.

Claims

1. A joint transform correlator system including means for providing the joint transform and means for providing the cross correlation products of a first and second channel of information, comprising the combination of:

channel mixer means for carrier modulating and filtering one channel of information and for adding the carrier modulated and filtered information to the other channel of information;

electrical-to-optical input transducer means for receiving the summed channels of information and for providing spatially separated channels of information; and

interferometer means disposed to interfere said spatially separated channels of information to produce the joint transform at a joint transform plane.

2. The system of claim 1 including

optical-to-optical transducer means for storing the joint transform for readout of the cross correlation products.

3. The system of claim 2 wherein:

the interferometer means is a Michelson type interferometer having two adjustable mirrors; and

one of the adjustable mirrors is adjusted to provide an optical axis offset to the incoming light beam.

4. The system of claim 2 wherein:

the interferometer means includes a pair of optical wedges of selected optical refractive angle, said wedges disposed to receive the channels of information and to impart a selected angle between the channels at the transform plane.

5. The system of claim 2 wherein

the interferometer means includes a plurality of pairs of optical prisms disposed to receive the two channels and to re-direct the two light beams thereof;

and optical wedge means, including a pair of pivotable optical wedges, disposed to receive the re-directed light beams and to form an interference pattern between the beams which beams are incident at a selected angle at the transform plane.

6. The system of claim 2 wherein:

the electrical-to-optical input transducer means includes an input aperture;

a coherent light source illuminates the input aperture; and

there is provided input optic means, including spatial filters and transform lens means, for generating the joint transform plane.

7. The system of claim 6 further including:

readout electro-optical means, including a coherent light source, for spatially modulating the recording means and for generating a cross correlation plane; and

optical-to-electrical transducer means disposed at the cross correlation plane for detecting the cross correlation product.

8. A joint transform correlator system including means for providing the joint transform and means for providing the cross correlation products of a first and second channel of information comprising the combination of:

input electro-optical means including an electrical-to-optical transducer means having an optical input aperture for receiving each channel of information over the full input aperture, with each channel at 1/2 the total bandwidth, and for providing spatially separated channels of information; and

interferometer means disposed to interfere said spatially separated channels of information to produce the joint transform at a subsequent joint transform plane.