Spatially incoherent holographic correlator

• US 5,138,489 A
• Filed: 06/10/1991
• Issued: 08/11/1992
• Est. Priority Date: 06/10/1991
• Status: Expired due to Fees

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford University)
• Original Assignee: Bell Communications Research, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Paek, Eung-Gi
• Primary Examiner(s): Berman, Jack I.
• Application Number:
  US07/713,421
• Time in Patent Office: 428 Days
• Field of Search: 359/561, 359/29, 364/822, 382/31, 382/42
• US Class Current: 359/561
• 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
• CPC Class Codes: G06V 10/895 the filter being related to phase processing, e.g. phase-only filters

Abstract

An incoherent holographic correlator comprising a two-dimensional array of surface-emitting lasers which are selectable in an arbitrary pattern so as to emit a beam containing the pattern. The pattern is spatially incoherent because the lasers are not phase-locked but it is temporally coherent. The beams are collimated onto a recorded hologram, and each of the beams produces a diffracted beam from the recording. All the diffracted beams are focused onto an imaging plane. A high-intensity spot represents a strong correlation between the selected pattern on the laser array and the image previously recorded in the hologram.

Claims

1. An incoherent holographic correlator, comprising:

an array of individually activatable surface-emitting diode lasers, said diode lasers being optically non-coherent among themselves when more than one of said diode lasers are activated;

means for simultaneously activating a selected plurality of said diode lasers to form an emitting pattern;

a hologram impressed with at least one reference pattern and irradiated with said emitting pattern; and

a surface upon which images reconstructed through said hologram by all of said activated diodes lasers are overlapped.

2. An incoherent correlator as recited in claim 1, wherein said array of lasers are integrated in an optical integrated circuit.

3. An incoherent correlator as recited in claim 2, wherein said array of lasers are arranged in a two dimensional array on said optical integrated circuit.

4. An incoherent holographic correlator as recited in claim 2, further comprising a first optical system for collimating beams emanating from said activated diode lasers onto said hologram.

5. An incoherent correlator as recited in claim 4, further comprising a second optical system for focusing a beam diffracted from said hologram onto said surface.

6. An incoherent holographic correlator as recited in claim 4, further comprising at least one photodetector disposed at said surface.

7. An incoherent holographic correlator as recited in claim 6, where said at least one photodetector is an array of photodetectors arranged on said surface.

8. An incoherent holographic correlator as recited in claim 7, further comprising threshold circuits associated with each of said photodetectors.

9. An incoherent holographic correlator as recited in claim 7, further comprising an array of second surface-emitting diode lasers separately activatable in response to an output of a respective one of said photodetectors exceeding a predetermined threshold.

10. An incoherent correlator as recited in claim 9, wherein output beams of said second lasers irradiate said hologram.

11. An incoherent correlator as recited in claim 4, wherein said hologram is a reflective hologram and further comprising:

a beam splitter interposed between said laser array, said hologram, and said at least one photodetector.

12. An incoherent correlator as recited in claim 4, wherein said array of lasers, said first optical system, and said hologram as integrated into a rigid structure.

13. An integrated incoherent holographic correlator, comprising:

a spacer substantially transparent at a wavelength;

an array of surface-emitting lasers emitting at said wavelength and formed on a first side of said spacer;

at least one photodetector responsive to said wavelength and formed on said first side of said spacer;

a lens having a focal length, formed on a second side of said spacer and separated from said array of surface-emitting lasers by an optical distance equal to said focal length; and

a hologram integratedly attached to a side of said lens opposite from said spacer.

14. An integrated incoherent holographic correlator as recited in claim 13, further comprising a body in which a diffraction pattern of said hologram is impressed on a side of said body opposite from said lens.