All optical nonlinear joint fourier transform correlator

• US 5,604,634 A
• Filed: 09/20/1993
• Issued: 02/18/1997
• Est. Priority Date: 09/20/1993
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Khoury, Jihad, Woods, Charles L.
• Primary Examiner(s): Dzierzynski, Paul M.
• Assistant Examiner(s): CHANG, AUDREY Y
• Application Number:
  US08/300,692
• Time in Patent Office: 1,247 Days
• Field of Search: 359/7, 359/29, 359/559, 359/560, 359/561
• US Class Current: 359/559
• CPC Class Codes: G02B 27/50 Optics for phase object visualisation
• CPC Class Codes: G03H 1/0248 Volume holograms
• CPC Class Codes: G06E 3/003 forming integrals of products, e.g. Fourier integrals, Laplace integrals, correlation integrals; for analysis or synthesis of functions using orthogonal functions

Abstract

A fully parallel, self-aligning, nonlinear and all optical joint transform correlator utilizes a photorefractive four wave mixer positioned to record the joint transform spectrum interfering with a reference beam together with a phase conjugator which directs a readout beam at the four wave mixer. The signal readout of the mixer is Fourier transformed and can be recorded upon an image sensor to detect the correlation spots indicating the degree of similarity of the two input images.

Claims

1. A nonlinear joint Fourier transform image correlator (JTC) comprising:

(a) joint image production means for producing a single signal beam having an intelligence bearing joint image of a reference image and a signal image;

(b) first Fourier transform means for producing a joint transform spectrum (JTS) of the single signal beam at a Fourier transform plane;

(c) a nonlinear holographic recording means positioned at the Fourier transform plane for receiving said JTS;

(d) reference input beam means illuminating said nonlinear holographic recording means with a reference beam for forming a hologram thereon having a grating associated therewith;

(e) phase conjugating means for forming a counter-propogating phase conjugate JTS in said nonlinear holographic recording means to produce an output beam therefrom; and

(f) a second Fourier transform means for inverse Fourier transforming the nonlinear holographic recording means output beam to produce a cross-correlation output signal from said JTC.

2. The JTC of claim 1 wherein said phase conjugator is a self pumped phase conjugator.

3. The JTC of claim 2 wherein said nonlinear holographic recording means is a four wave mixer.

4. The JTC of claim 3 wherein said nonlinear holographic recording means comprises a photorefractive material.

5. The JTC of claim 4 including means for adjusting the intensity of one or more beams directed at the nonlinear holographic recording means to obtain the desired output nonlinearity over a useful input dynamic range.

6. The JTC of claim 3 including means for adjusting the intensity of one or more beams directed at the nonlinear holographic recording means to obtain the desired output nonlinearity over a useful input dynamic range.

7. The JTC of claim 2 wherein said nonlinear holographic recording means comprises a photorefractive material.

8. The JTC of claim 1 wherein said nonlinear holographic recording means is a four wave mixer.

9. The JTC of claim 8 wherein said nonlinear holographic recording means comprises a photorefractive material.

10. The JTC of claim 8 including means for adjusting the intensity of one or more beams directed at the nonlinear holographic recording means to obtain the desired output nonlinearity over a useful input dynamic range.

11. The JTC of claim 1 wherein said nonlinear holographic recording means comprises a photorefractive material.

12. The JTC of claim 1 including means for adjusting the intensity of one or more beams directed at the nonlinear holographic recording means to obtain the desired output nonlinearity over a useful input dynamic range.

13. A nonlinear joint Fourier transform image correlator (JTC) comprising:

(a) joint image production means for producing a single signal beam having an intelligence bearing joint image of a reference image and a signal image;

(b) first Fourier transform means for producing a joint transform spectrum (JTS) of the single signal beam at a Fourier transform plane;

(c) a nonlinear four-wave mixing means positioned at the Fourier transform plane for receiving said JTS;

(d) reference input beam means illuminating said nonlinear four-wave mixing means with a reference beam;

(e) phase conjugating means for forming a counter-propogating phase conjugate JTS in said nonlinear four-wave mixing means to produce an output beam therefrom;

(f) optical means for optically coupling the four-wave mixing means and the phase conjugating means together;

and

(g) a second Fourier transform means for inverse Fourier transforming said output beam to produce a cross-correlation output signal from said JTC.

14. The JTC of claim 13 wherein said phase conjugator is a self pumped phase conjugator.

15. The JTC of claim 14 wherein said nonlinear four-wave mixing means is a nonlinear holographic recording means.

16. The JTC of claim 15 wherein said four-wave mixing means comprises a photorefractive material.

17. The JTC of claim 15 including means for adjusting the intensity of one or more beams directed at the nonlinear holographic recording medium to obtain the desired output nonlinearity over a useful input dynamic range.

18. The JTC of claim 14 wherein said four-wave mixing means comprises a photorefractive material.

19. The JTC of claim 13 wherein said nonlinear four-wave mixing means is a nonlinear holographic recording means.

20. The JTC of claim 19 wherein said four-wave mixing means comprises a photorefractive material.

21. The JTC of claim 13 wherein said four-wave mixing means comprises a photorefractive material.

22. The JTC of claim 13 including means for adjusting the intensity of one or more beams directed at the nonlinear holographic recording medium to obtain the desired output nonlinearity over a useful input dynamic range.

23. A nonlinear joint Fourier transform image correlator (JTC) comprising:

(a) joint image production means for producing a single signal beam having an intelligence bearing joint image of a reference image and a signal image;

(b) first Fourier transform means for producing a joint transform spectrum (JTS) of the single signal beam at a Fourier transform plane;

(c) a nonlinear optical wave coupling (NOWC) means positioned at the Fourier transform plane for receiving said JTS;

(d) reference input beam means illuminating said NOWC means with one or more reference beams;

(e) phase conjugating means for forming a counter-propagating phase conjugate JTS in said NOWC means to produce an output beam therefrom;

(f) optical means for optically coupling the NOWC means and the phase conjugating means together; and

(g) a second Fourier transform means for inverse Fourier transforming said output beam to produce a cross-correlation output signal from said JTC.

24. The JTC of claim 23 wherein said phase conjugator is a self pumped phase conjugator.

25. The JTC of claim 24 wherein said NOWC means is a nonlinear holographic recording means.

26. The JTC of claim 25 wherein said NOWC means comprises a photorefractive material.

27. The JTC of claim 24 wherein said NOWC means comprises a photorefractive material.

28. The JTC of claim 23 wherein said NOWC means is a nonlinear holographic recording means.

29. The JTC of claim 28 wherein said NOWC means comprises a photorefractive material.

30. The JTC of claim 23 wherein said NOWC means comprises a photorefractive material.