COHERENT OPTICAL MULTICHANNEL CORRELATOR

• US 3,773,401 A
• Filed: 05/10/1972
• Issued: 11/20/1973
• Est. Priority Date: 05/13/1971
• Status: Expired due to Term

• Current Assignee: Gerhard Winzer, Nikolaos Douklias, Ulrich Wolff
• Original Assignee: Gerhard Winzer, Nikolaos Douklias, Ulrich Wolff
• Inventors: Winzer, Gerhard, Douklias, Nikolaos, Wolff, Ulrich
• Primary Examiner(s): Wibert, Ronald L.
• Application Number:
  US05/252,022
• Time in Patent Office: 559 Days
• Field of Search: 350/3.5,162SF,162R
• US Class Current: 359/19
• CPC Class Codes: G02B 5/32 Holograms used as optical elements
• 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

A coherent optical multichannel correlator for identifying an object by permeating an object with a beam of coherent light which is projected through a Fourier transformation lens onto a filter hologram which reconstructs a reference beam projected on a photo detector when the object to be identified corresponds to the filter hologram characterized by providing a plurality of filter holograms arranged on the focal plane of the lens, and a diffraction grating modulator to modulate the light beam to control the selection of the filter hologram on which the light is projected. Modulation can be either by changing the grating constant to vary the angle phi between the diffracted beam and original beam axis or by rotating the orientation of the diffracted beams through an angle theta. Preferably, the diffraction modulating varies both the angle phi and the angle theta either continuously to have the diffracted beam follow a spiral path along the filter holograms or in a step-like manner to have the diffracted beam follow a path of concentric circles along the filter holograms. The modulator can be a pair of rotatable diffraction gratings, a pair of rotatable diffraction gratings which are thin phase holograms, or a pair of diffraction gratings, one being a volume-phase hologram and the other a thin (phase) hologram. The modulator can also be a fixed grating of electro-optical material which has a grating pattern with a grating constant and orientation which are controlled by the application of an electrical or a magnetic field, or some other means that shifts the illuminating beam on an angle phi.

Claims

1. A coherent optical multichannel correlator for identifying an object corresponding to one of a plurality of filter holograms comprising:

means projecting a beam of coherent light for permeating an object to be identified, means for directionally modulating the beam of light by diffracting the beam to said one of said plurality of filter holograms, a Fourier transformation lens receiving the modulated light beam after permeating the object being identified, a plurality of filter holograms located on a focal plane of the lens, and photo detector means located in the focal plane of the filter holograms, said means for modulating serving to control the selection of the filter hologram used to identify the object.

2. A coherent optical multichannel correlator according to claim 1, wherein the photo detector means includes a plurality of individual photo detectors each having a threshold value with an individual photo detector arranged at the focal point of each of the filter holograms.

3. A coherent optical multichannel correlator according to claim 1, wherein the means for modulating comprises a rotatable diffraction grating.

4. A coherent optical multichannel correlator according to claim 1, wherein the means for modulating comprises a pair of rotatable diffraction gratings.

5. A coherent optical multichannel correlator according to claim 4, wherein the pair of diffraction gratings are gratings having ronchi gratings.

6. A coherent optical multichannel correlator according to claim 4, wherein the pair of rotatable diffraction gratings are thin phase holograms.

7. A coherent otpical multichannel correlator according to claim 4, wherein a pair of rotatable diffraction gratings include one grating being a volume-phase hologram and the other grating being a thin-phase hologram.

8. A coherent optical multchannel correlator according to claim 7, wherein the volume-phase hologram is arranged with the Bragg condition fulfilled at each angle by rotation of the grating.

9. A coherent optical multichannel correlator according to claim 4, which includes means for rotating the pair of gratings with the angle of orientation between the pair of gratings continually changing.

10. A coherent optical multichannel correlator according to claim 4, which includes means for rotating the pair of gratings with the angle of orientation between the gratings changing in a step-like manner.

11. A coherent optical multichannel correlator according to claim 1, wherein the means for modulating the beam of coherent light comprises a stationary grating mounted in the correlator, said grating having an orientation and grating constant dependent upon application of a magnetic field and means for applying a magnetic field to vary the grating constant and orientation of the grating.

12. A coherent optical multichannel correlator according to claim 11, wherein the grating consists of a magneto-optical material with stripe domains.