Disk-based optical correlator and method

• US 5,339,305 A
• Filed: 08/14/1992
• Issued: 08/16/1994
• Est. Priority Date: 08/14/1992
• Status: Expired due to Fees

• Current Assignee: California Institute of Technology, Northrop Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Curtis, Kevin R., Psaltis, Demetri
• Primary Examiner(s): Dzierzynski, Paul M.
• Assistant Examiner(s): CHU, KIM KWOK
• Application Number:
  US07/930,095
• Time in Patent Office: 732 Days
• Field of Search: 369/112, 369/94, 369/100, 369/103, 369/102, 359/29, 359/22, 359/561, 359/59, 359/26, 359/900, 359/3, 359/19, 382/31, 382/42, 365/125
• US Class Current: 369/103
• CPC Class Codes: G03H 1/0406 Image plane or focused image holograms, i.e. an image of the object or holobject is formed on, in or across the recording plane
• CPC Class Codes: G03H 1/16 using Fourier transform G03H1/10, G03H1/12, G03H1/14 take precedence; analogue computers G06G, e.g. G06G7/19
• CPC Class Codes: G03H 1/26 Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique
• CPC Class Codes: G03H 2270/22 Disc shaped
• CPC Class Codes: G11B 7/0065 Recording, reproducing or erasing by using optical interference patterns, e.g. holograms

Abstract

The correlation speed and storage capacity of an optical disk-based correlator is enhanced by employing a thick (several hundred micron) photo- polymeric film (or other thick holographic media) on the disk as the recording media to permit volume holography and angular multiplexing of holograms in each spot on the disk. For example, if 100 holograms are multiplexed at one spot, 100 1-dimensional correlation functions can be read in parallel off of the disk while illuminating it with a single input image. The diffraction of the image beam by the recorded holographic patterns occurs at the holograms in the disk. The full 2-dimensional correlation function for each one of the holograms stored in a given spot on the disk is generated line-by-line a follows: By imaging in the along-track direction of the disk and Fourier transforming in the radial direction of the disk when both recording the template image hologram and presenting the input image to the recorded hologram, disk rotation generates the two-dimensional correlation functions between stored template images and the input image. All correlation functions for holograms angularly multiplexed at a given spot are generated line-by-line and detected in parallel along adjacent line detectors in the off-disk correlation plane.

Claims

1. An optical correlator comprising:

an optical recording medium said medium comprising an optical recording layer of a sufficient thickness for recording volume holographic information B

optical modulator means receiving an image signal representing one of (a) one of a set of template images or (b) an input image, and for modulating a coherent light beam to produce an image beam corresponding to said image signal;

means for imaging said image beam on a selected spot on said optical recording medium in a first direction while Fourier transforming said image beam in a second direction orthogonal to said first direction on said selected spot on said optical recording medium

recording reference beam source means, operable whenever said image signal represents successive respective ones of said set of template images, for projecting a reference beam onto said selected spot at successive respective angles relative to said optical recording medium, said reference beam being coherent with said coherent image beam, to form respective angularly multiplexed volume holograms in said optical recording layer at said spot;

correlation means comprising plural line detectors aligned in said second direction at a correlation plane, operable whenever said image signal represents said input image, for sensing at respective line detectors Fourier transformed versions of respective patterns of said image beam diffracted by respective volume holograms in said selected spot, each of said patterns corresponding to a one-dimensional slice of a two-dimensional correlation of said input image with a corresponding one of said template images; and

means for moving said optical recording medium in said first direction so as to scan said image beam across said spot, whereby to generate a two-dimensional correlation function for each one of said patterns.

2. The optical correlator of claim 1 wherein said recording medium comprises a rotatable optical disk, and wherein said first direction generally corresponds to a tangent along a circumference of said disk at a radius of said disk intersecting said spot, and said second direction corresponds to said radius of said disk intersecting said spot, and wherein said means for moving said optical recording medium comprises means for rotating said disk.

3. The optical correlator of claim 1 wherein said imaging and transforming means comprise a first pair of cylindrical lenses having their cylindrical axes oriented so as to cause said image beam to be imaged along said first direction at said spot on said optical recording medium and a middle cylindrical lens between said pair of cylindrical lenses having its cylindrical axis oriented so as to Fourier transform along said second direction said image beam at said spot.

4. The optical correlator of claim 1 wherein said correlation means further comprises a spherical lens between said disk and said correlation plane for generating said Fourier transformed version of said pattern of said image beam diffracted by said respective hologram.

5. The optical correlator of claim 1 further comprising phase diffuser means for uniformly distributing energy of said image beam across said spot.

6. The optical correlator of claim 1 wherein said recording reference beam source means comprises a rotatable mirror in a path of said reference beam and means for successively positioning said rotatable mirror at rotational positions corresponding to successive ones of said respective angles.

7. The optical correlator of claim 6 further comprising optical means in the path of said reference beam for maintaining said reference beam on said spot during rotation of said rotatable mirror.

8. An optical recording medium useful for performing optical correlations, comprising:

an optical recording layer of a thickness sufficient for recording volume holographic information throughout the volume of each of a plurality of spots therein;

a plurality of recorded spots in said medium spaced apart along a first direction, each of said spots including plural multiplexed volume holograms of template images imaged along said first direction and Fourier transformed along a second direction orthogonal to said first direction.

9. The optical recording medium of claim 8, wherein said optical recording layer comprises a rotatable disk, whereby said first direction corresponds to a rotation of said disk.

10. The optical recording medium of claim 8 wherein said multiplexed volume holograms are one of:

(a) angularly multiplexed or (b) frequency multiplexed.

11. Apparatus for optically storing information comprising:

an optical recording medium said medium comprising an optical recording layer of a sufficient thickness for recording volume holographic information throughout the volume of each of a plurality of spots therein;

optical modulator means for modulating a coherent light beam in response to an image signal representing a successive one of a set of template images, so as to produce an image beam corresponding to said image signal;

imaging and transforming means for imaging, in a first direction, said image beam on a selected spot on said optical recording medium while Fourier transforming, in a second direction orthogonal to said first direction, said image beam on said selected spot;

recording reference beam source means for projecting a reference beam onto said selected spot, said reference beam being coherent with said coherent light beam, whereby to generate a hologram of a respective template image through the volume in said spot;

means for multiplexing holograms of all of said set of template images in said spot;

means for moving said medium whereby said image beam is imaged onto a successive spots on said medium, whereby successive sets of multiplexed holograms are recorded in said successive spots.

12. The apparatus of claim 11 wherein said means for angularly multiplexing employs frequency multiplexing, and comprises:

means for changing the frequency of said light beam to successive respective frequencies corresponding to successive ones of said set of template images, whereby to form respective frequency multiplexed volume holograms in said optical recording layer.

13. The apparatus of claim 11 wherein said movable recording medium comprises a rotatable optical disk, and wherein said first direction generally corresponds to a tangent along a circumference of said disk at a radius of said disk intersecting said spot, and said second direction corresponds to said radius of said disk intersecting said spot, and wherein said means for moving said optical recording medium comprises means for rotating said disk.

14. The apparatus of claim 11 wherein said imaging and transforming means comprise a first pair of cylindrical lenses having their cylindrical axes oriented so as to cause said image beam to be imaged along said first direction at said spot on said optical recording medium and a middle cylindrical lens between said pair of cylindrical lenses having its cylindrical axis oriented so as to Fourier transform along said second direction said image beam at said spot.

15. The apparatus of claim 11 wherein said means for multiplexing employs angular multiplexing and comprises:

means for changing the angle of said reference beam to successive respective angles relative to said optical recording medium corresponding to successive ones of said set of template images, whereby to form respective angularly multiplexed volume holograms in said optical recording layer at said spot.

16. The apparatus of claim 15 wherein said recording reference beam source means comprises a rotatable mirror in a path of said reference beam and means for successively positioning s aid rotatable mirror a t rotational positions corresponding to successive ones of said respective angles.

17. The apparatus of claim 16 further comprising optical means in the path of said reference beam for maintaining said reference beam on said spot during rotation of said rotatable mirror.

18. A method of performing correlation in an optical recording medium said medium comprising an optical recording layer of a sufficient thickness for recording volume holographic information throughout the volume of each of a plurality of spots therein, said method comprising:

modulating a coherent light beam in response to an image signal representing one of (a) one of a set of template images or (b) an input image, so as to produce an image beam corresponding to said image signal;

imaging, in a first direction, said image beam on a selected spot on said optical recording medium while Fourier transforming, in a second direction orthogonal to said first direction, said image beam on said selected spot;

causing said image signal successively to represent respective ones of said set of template images, while successively projecting a reference beam onto said selected spot at respective angles relative to said optical recording medium, said reference beam being coherent with said coherent light beam, whereby to record respective angularly multiplexed volume holograms throughout the volume of said optical recording layer at said spot;

after recording of said holograms in said optical recording layer, causing said image beam to represent said input image while detecting at plural line detectors aligned in said second direction at a correlation plane Fourier transformed versions of respective patterns of said image beam diffracted by respective volume holograms in said selected spot, each of said patterns corresponding to a one-dimensional slice of a two-dimensional correlation of said input image with a corresponding one of said template images; and

, simultaneously,

moving said optical recording medium in said first direction so as to scan said image beam across said spot, whereby to generate a two-dimensional correlation function for each one of said patterns.

19. The method of claim 18 wherein said movable recording medium comprises a rotatable optical disk, and wherein said first direction generally corresponds to a tangent along a circumference of said disk at a radius of said disk intersecting said spot, and said second direction corresponds to said radius of said disk intersecting said spot, and wherein said moving said optical recording medium comprises rotating said disk.

20. The method of claim 18 further comprising generating with a spherical lens said Fourier transformed version of said pattern of said image beam diffracted by said respective hologram.

21. The method claim 18 further comprising maintaining said reference beam on said spot during the changing of the angle of said reference beam.

22. The method of claim 18 further comprising uniformly distributing energy of said image beam across said spot by a phase diffuser.

23. A method of producing an optical recording medium including an optical recording layer of a thickness sufficient for recording volume holographic information throughout the volume of each of a plurality of spots therein, comprising:

24. The method of claim 23 wherein said optical recording layer comprises a rotatable disk, whereby said first direction corresponds to a rotation of said disk.

25. The method of claim 23 wherein said recording comprises one of:

(a) angularly multiplexing the holograms recorded in each spot and (b) frequency multiplexing the holograms recorded in each spot.

26. A method of optically storing information in an optical recording medium said medium comprising an optical recording layer of a sufficient thickness for recording volume holographic information throughout the volume of each of a plurality of spots therein, comprising:

modulating a coherent light beam in response to an image signal representing a successive one of a set of template images, so as to produce an image beam corresponding to said image signal;

imaging, in a first direction, said image beam on a selected spot on said optical recording medium while Fourier transforming, in a second direction orthogonal to said first direction, said image beam on said selected spot;

projecting a reference beam onto said selected spot, said reference beam being coherent with said coherent light beam, whereby to generate a hologram of a respective template image in said spot;

multiplexing holograms of all of said set of template images in said spot;

moving said medium whereby said image beam is imaged onto a successive spots on said medium, whereby successive sets of multiplexed holograms are recorded in said successive spots.

27. The method of claim 26 wherein said multiplexing employs angular multiplexing and comprises:

changing the angle of said reference beam to successive respective angles relative to said optical recording medium corresponding to successive ones of said set of template images, whereby to form respective angularly multiplexed volume holograms in said optical recording layer at said spot.

28. The method of claim 26 wherein said multiplexing employs frequency multiplexing, and comprises:

changing the frequency of said light beam to successive respective frequencies corresponding to successive ones of said set of template images, whereby to form respective frequency multiplexed volume holograms in said optical recording layer.

29. The method of claim 26 wherein said movable recording medium comprises a rotatable optical disk, and wherein said first direction generally corresponds to a tangent along a circumference of said disk at a radius of said disk intersecting said spot, and said second direction corresponds to said radius of said disk intersecting said spot, and wherein said moving said optical recording medium comprises rotating said disk.

30. A method for optically recording and recovering information contained in a plurality of templates, comprising:

providing a recording medium distributed over a surface and having a sufficient thickness to provide a volume of said surface for recording volume holograms throughout the volume of each of a plurality of regions therein,

providing a first coherent light beam,

modulating a second coherent light beam which is coherent with said first beam with successive one of said templates to produce a succession of image beams,

imaging said modulated beam in a first direction,

Fourier transforming said modulated beam in a second direction orthogonal from said first direction,

forming a reference beam coherent with said first coherent light beam,

simultaneously imaging said modulated beam and said reference beam onto said region in said medium to form a volume hologram therein,

progressively changing the angle of impingement of said reference beam into the media so as to angularly multiplex the templates into said medium at said location, and

moving said medium so that said beams are imaged in successive regions in said medium while changing said templates.

31. A method of recovering the templates stored by the process of claim 30 further comprising:

illuminating the region with a reference beam to generated a diffracted beam containing the template information,

imaging said diffracted beam in a first direction,

Fourier transforming said diffracted beam in a second direction orthogonal to said first direction to reconstruct said template,

change the reference beam angle or location of the region to readout successive templates.

32. Apparatus for optical recording and recovering information contained in a plurality of templates, comprising

means for providing a recording medium distributed over a surface and having a sufficient thickness and provide a volume of said surface for recording optical holograms throughout the volume of each of a plurality of regions therein,

means for providing a first coherent light beam;

means for modulating said coherent light beam with an image of one Of said templates to produce an image beam,

means for imaging said modulated beam in a first direction

means for Fourier transforming said modulated beam in a second direction different from said first direction,

means for forming a reference beam coherent with said first coherent light beam,

means for imaging said modulated beam and said reference beam onto a region in said medium to form a volume hologram therein, and

means for moving said medium so that said beams are imaged in successive regions in said medium while changing said templates.

33. Apparatus for recovering the templates stored by the apparatus of claim 32 comprising:

means for illuminating the region with a reference beam to generated a diffracted beam containing the template information,

means for imaging said diffracted beam in a first direction,

means for Fourier transforming said diffracted beam in a second direction orthogonal to said first direction to reconstruct said template,

means for changing the reference beam angle or location of the region to readout successive templates.

34. A method for optically recording and recovering information contained in a plurality of templates, comprising:

providing a recording medium distributed over a surface and having a thickness to provide a volume for recording volume holograms throughout the volume of each of a plurality of regions therein,

providing a first coherent reference light beam and a second coherent light beam coherent with said first beam,

modulating said second coherent light beam with successive ones of said templates to produce a succession of image beams,

imaging said modulated beam in a first direction,

Fourier transforming said modulated beam in a second direction orthogonal from said first direction,

simultaneously illuminating said modulated beam and said reference beam into said region in said medium to form a volume hologram therein,

progressively changing the angle of said reference beam so as to angle multiplex the templates into said medium at said location,

moving said medium so that said beams are illuminated in successive regions in said medium, and subsequently

presenting a second coherent light beam with information from an unknown template,

moving the medium relative to that beam to generate correlation functions for said unknown template,

recovering a correlated template by

illuminating the region with an unmodulated, coherent readout beam to generate a diffracted beam containing the correlated template information,

imaging said diffracted beam in a first direction,

Fourier transforming said diffracted beam in a second direction orthogonal to said first direction to reconstruct said correlated template.