Method and apparatus for adaptive real-time optical correlation using phase-only spatial light modulators and interferometric detection

• US 5,276,636 A
• Filed: 09/14/1992
• Issued: 01/04/1994
• Est. Priority Date: 09/14/1992
• Status: Expired due to Fees

• Current Assignee: University of Louisville Research Foundation
• Original Assignee: Robert W. Cohn
• Inventors: Cohn, Robert W.
• Primary Examiner(s): Mai, Tan V.
• Application Number:
  US07/950,633
• Time in Patent Office: 477 Days
• Field of Search: 364/819, 364/820, 364/822, 364/604, 359/561, 359/29
• US Class Current: 708/816
• CPC Class Codes: G06E 3/005 using electro-optical or opto-electronic means

Abstract

A video-rate correlator constructed with a phase-only spatial light modulator and video camera. The phases of the Fourier spectra of a test and reference image are measured by real-time fringe scanning interferometry. The two phase images are then electronically subtracted. The optical Fourier transform of this difference produces the phase-only correlation response. This correlator is real-time adaptive, in that it uses live imagery, and neither the test or reference images need any preprocessing off-line. Especially small optical layouts, which also efficiently use light for correlation, can be configured through the use of specific embodiments, which use only a single phase-only spatial light modulator and Fourier transform lens.

Claims

1. An apparatus for performing optical correlation of a complex-valued two-dimensional test image and a complex-valued two-dimensional reference image, comprising:

(a.) means to determine the Fourier spectrum of a test and a reference image and produce a test image Fourier transform light distribution and a reference image Fourier transform light distribution;

(b.) means to interfere said test and reference image Fourier transform light distributions with three reference plane waves, said reference plane waves being phase-shifted from each other by known amounts, thereby producing three test image and three reference image interferogram patterns;

(c.) means to electronically convert with a real-time image sensor the recorded three test image interferogram patterns into a test image phase signal and convert the three reference image interferogram patterns into a reference image phase signal;

(d.) means to subtract the reference image phase signal from the test image phase signal to yield a difference signal and identically modulate a phase-only spatial light modulator with the difference signal producing a phase-only transmittance signal; and

,

(e.) means to Fourier transform the transmittance signal and produce a correlation plane image intensity signal.

2. The apparatus of claim 1, wherein the means to determine the Fourier spectrum of a reference image and produce a reference image Fourier transform light distribution and means to interfer said reference image Fourier transform light distribution with three reference plane waves, said three reference plane waves being phase-shifted from each other by known amounts, thereby producing three test image interferogram patterns comprises a mach-zehnder interferometer.

3. A method of performing optical correlation, comprising the steps of:

(a.) using lenses to Fourier transform images in real-time of a test and a reference image which are represented on spatial light modulators, producing a test image Fourier transform light distribution and a reference image Fourier transform light distribution;

(b.) interfering said test and reference image Fourier transform light distributions with three plane wave reference signals, said plane wave reference signals being phase-shifted from each other by known amounts, thereby producing three test image and three reference image interferogram patterns;

(c.) recording the interferogram patterns with a real-time image sensor;

(d.) electronically converting the recorded three test image interferogram patterns into a test image phase signal and converting the three reference image interferogram patterns into a reference image phase signal;

(e.) electrically subtracting the reference image phase signal from the test image phase signal yielding a difference signal and identically modulating a phase-only spatial light modulator with the difference signal producing a phase-only transmittance signal; and

,

(f.) using a lens to Fourier transform the transmittance signal producing a correlation plane image intensity signal.

4. The method of claim 3, further comprising the step of using a real-time image sensor to record the correlation plane image intensity signal and evaluating the correlation plane image intensity signal.

5. A method of performing real-time optical correlation, comprising the steps of:

(a.) using a lens to Fourier transform a reference image which is represented on a spatial light modulator, producing a reference image Fourier transform light distribution;

(b.) interfering said reference image Fourier transform light distribution with three plane wave reference signals, said plane wave reference signals being phase-shifted from each other by known amounts, thereby producing three reference image interferogram patterns;

(c.) recording the three reference image interferogram patterns with a real-time image sensor;

(d.) electronically converting the recorded three reference image interferogram patterns into a reference image phase signal;

(e.) modulating the phase of a phase-only spatial light modulator with a signal representing the negative of said reference image phase signal;

(f.) using a lens to Fourier transform a test image which is represented on an amplitude only spatial light modulator, producing a test image phase signal;

(g.) optically subtracting the reference image phase signal from the test image phase signal to produce a transmittance signal; and

,

(h.) using a lens to Fourier transform the transmittance signal producing a correlation plane image intensity signal.