Multi-channel filter system

• US 5,005,946 A
• Filed: 04/06/1989
• Issued: 04/09/1991
• Est. Priority Date: 04/06/1989
• Status: Expired due to Fees

• Current Assignee: Grumman Aerospace Corporation Bethpage NY 11714
• Original Assignee: Grumman Aerospace Corporation (Northrop Grumman Corporation)
• Inventors: Brandstetter, Robert W.
• Primary Examiner(s): Arnold, Bruce Y.
• Assistant Examiner(s): PARSONS, DAVID
• Application Number:
  US07/334,593
• Time in Patent Office: 733 Days
• Field of Search: 350/162.12, 350/358, 350/169, 350/170, 350/173, 350/3.68, 350/3.82, 350/3.67, 350/384, 350/162.13, 350/162.14, 364/822, 364/825, 364/827, 356/347, 356/348, 356/349, 324/77 K
• US Class Current: 359/15
• CPC Class Codes: G01R 23/17 with optical or acoustical auxiliary devices
• CPC Class Codes: G06E 3/005 using electro-optical or opto-electronic means
• CPC Class Codes: Y10S 359/90 Methods

Abstract

A multi-channel filter which exploits the parallel processing advantages of an optical signal processor is used to sort, classify and remove noise or unwanted signals from signals of interest. This filter shall perform real time parallel signal processing to effectively channelize and remove unwanted spectra from the various signals of interest in a dense radio frequency environment. This would in effect transform a single channel that is corrupted with unwanted signals, interference and noise, to a number of discrete channels which are spectrally tailored to selected signals of interest. The filtering process is accomplished by modulating a laser carrier with the given signal of interest and performing all filtering functions optically and then down converting the filtered signal back into its original radio frequency for further use.

Claims

1. A multi-channel filter system comprising:

means for modulating a substantially coherent light beam with an input RF signal spectrum;

means for optically Fourier transforming and channelizing the modulated light beam to produce an input array of modulated light beams, each light beam in said input array being modulated by a spectral component of said input RF signal spectrum;

means for optically notching out noise in said input array of modulated light beams;

a holographic multi-channel spectrum filter, said spectrum filter selectively passing light beams from said input array having a correlation to preselected RF spectral components to produce a correlated output array;

means for illuminating said spectrum filter with said input array of modulated light beams to produce said correlated output array;

means for downconverting said correlated output array into an output array of noise excised and spectrum filtered RF signals; and

means for detecting and for respectively converting the signals passed by said holographic multi-channel spectrum filter into electrical output signal arrays.

3. The filter system of claims 1 or 2 wherein said illuminating means comprises a beam-splitting means for splitting said array of modulated light beams into a signal array and a corresponding self-derived reference array, and means for selectively blocking said reference array to permit said spectrum filter to be illuminated only by said signal array for producing said correlated output array.

4. The filter system of claim 3 wherein said beam-splitting means includes means for directing said signal and reference arrays to interfere optically at a predetermined plane and further including a photo-optical element positioned essentially at said plane to holographically record said multi-channel spectrum filter in situ.

5. The filter system of claim 4 wherein said beam-splitting means comprises an integrated cube.

6. The filter system of claims 1 or 2 wherein said spectrum filter comprises a plurality of self-derived holographic recordings.

7. The filter system of claim 6 wherein said plurality of holographic recordings are comprised of an array of unique fringe patterns which are generated by the optical interference of said input array of reference laser beams and an array of modulated light beams.

8. The filter system of claims 1 or 2 wherein said spectrum filter passes all of the light beams in said input array to produce an uncorrelated output array.

9. The filter system of claim 8 further including means for detecting said correlated and uncorrelated output arrays for producing a correlation function and for recording the correlated and uncorrelated spectrum.

10. The filter system of claim 9 further including a second beam splitting means for directing a portion of said correlated output array and said uncorrelated output array to said detecting means.

11. The filter system of claims 1 or 2 wherein said modulating means comprises an acousto-optical modulator.

12. The filter system of claim 11 further including a source of said substantially coherent light beam.

13. The filter system of claim 12 wherein said source of substantially coherent light is a laser.

14. The filter system of claim 12 wherein said Fourier transform means comprises a multiple holographic lens.

15. The filter system of claims 1 or 2 wherein said downconverting means comprises

means for performing an inverse Fourier transform of said correlated output array;

means for combining said inverse Fourier transformed array with a local oscillator light beam resulting in a combined array; and

photodetector array means for detecting said combined array and producing an array of noise excised and spectrum filtered RF signals.

16. The filter system of claim 15 wherein said inverse Fourier transforming means is single element holographic lens.

17. The filter system of claim 15 further including a multiple holographic lens for refracting said local oscillator beam into an array of local osciallator light beams.

18. The filter system of claim 15 further including a gradient density filter for shaping the local oscillator beam.

19. The filter system of claim 18 further including means for deriving said local oscillator beam from said substantially coherent light beam.

20. The filter system of claims 1 or 2 wherein said detector means comprises a charged-coupled device.

21. The filter system of claims 1 or 2 wherein said optical notching means comprises a liquid crystal light valve, said liquid crystal light valve responding as an intensity detector selectively blocking light beams above a preselected threshold intensity.

22. The filter system of claims 1 or 2 wherein said optical notching means comprises a programmable optical notching filter, said programmable optical notching filter selectively passing light beams based on a programmed filter pattern.

2. A multi-channel filter system comprising:

means for modulating a substantially coherent light beam with an input RF signal spectrum;

means for optically Fourier transforming and channelizing the modulated light beams to produce an input input array of modulated light beams, each light beam in said array being modulated by a spectral component of said input RF signal spectrum;

a holographic multi-channel spectrum filter, said spectrum filter selectively passing light beams in said input array having a correlation to preselected RF spectral components to produce a correlated output array;

means for illuminating said spectrum filter with said input array of modulated light beams to produce said correlated output array;

means for optically notching out noise in said correlated output array;

means for downconverting said correlated output array into an output array of noise excised and spectrum filtered RF signals; and

means for detecting and for respectively converting the signals passed by said holographic multi-channel spectrum filter into electrical output signal arrays.

23. A method of filtering incoming RF spectra comprising:

modulating a substantially coherent light beam with an input RF signal spectrum;

optically performing a Fourier transform and channelizing the modulated light beam to produce an input array of modulated light beams, each light beam in said array being modulated by a spectral component of said input RF signal spectrum;

optically notching out noise in said input array of modulated light beams;

filtering said input array be selectively passing light beam in said input array having a correlation to preselected RF spectral components to produce a correlated output array;

illuminating a power spectrum filter with said array of modulated light beams to produce said correlated output array;

downconverting said correlated output array into an output array of noise and spectrum filtered RF signals; and

detecting and converting the signals passed by said holographic multi-channel spectrum filter into electrical output signal arrays.

25. The method of claims 23 or 24 wherein said illuminating step comprises splitting said array of modulated light beams into a self-derived signal array and a corresponding self-derived reference array, and selectively blocking said self-derived signal array to permit said spectrum filter to be illuminated only by said reference array for producing said correlated output array.

26. The method of claim 25 wherein said splitting step includes directing said signal and reference arrays to interfere optically at a predetermined plane and positioning a photo-optical element essentially at said plane to holographically produce said multi-channel spectrum filter in situ.

27. The method of claims 23 or 24 wherein said filtering step includes passing all of the light beams in said input array to produce an uncorrelated output array.

28. The method of claim 27 further including detecting said correlated and uncorrelated output arrays for producing a correlation function and for recording a correlated and uncorrelated spectra.

29. The method of claim 28 further including directing a portion of said correlated output array and said uncorrelated output array to said detecting means.

30. The method of claims 23 or 24 wherein said downconverting step comprises:

performing an inverse Fourier transform of said correlated output array;

combining said inverse Fourier transformed array with a local oscillator light beam; and

detecting said combined array and producing an array of RF signals.

31. The method of claim 30 further including for shaping the local osciallator beam with a gradient density filter.

32. The method of claim 31 further including deriving said local oscillator beam from said substantially coherent light beam.

33. The method of claims 23 or 24 wherein said optical notching step comprises filtering said input array of modulated light beams by selectively varying an intensity threshold of a liquid crystal light valve.

34. The method of claims 23 or 24 wherein said optical notching step comprises filtering said input array of modulated light beams by programming a programmable optical notching filter to selectively notch out noise.

24. A method of filtering incoming RF spectra comprising:

modulating a substantially coherent light beam with an input RF signal spectrum;

optically performing a Fourier transform and channelizing the modulated light beam to produce an input array of modulated light beams, each light beam in said array being modulated by a spectral component of said input RF signal;

filtering said input array be selectively passing light beam in said input array having a correlation to preselected RF spectral components to produce a correlated output array;

illuminating a power spectrum filter with said array of modulated light beams to produce said correlated output array;

optically notching out noise in said correlated output array;

downconverting said correlated output array into an output array of noise and spectrum filtered RF signals; and

detecting and converting the signals passed by said holographic multi-channel spectrum filter into electrical output signal arrays.