Optical pattern recognition architecture implementing the mean-square error correlation algorithm

Claim 1

An optical pattern recognition architecture implementing the mean-square-error algorithm, MSE=Σ[I-R] 2 , for discriminating a reference pattern R in an input image I, comprising: light source means for outputting modulated light in accordance with a light source modulation signal applied to a light source modulation signal input thereof; optical deflector means for diffracting light incident at an aperture thereof in accordance with an optical deflector modulation signal applied to a signal input thereof for producing a spatial distribution of said incident light; means for focusing modulated light output by said light source means onto the aperture of said optical deflector means; means for generating a double-sideband suppressed-carrier amplitude modulated light source modulation signal I 1 (t) as the product of a time-varying reference image signal s 1 (t) applied thereto and a frequency offset carrier signal f o and for applying said light source modulation signal I 1 (t) to said light source modulation signal input of said light source means for causing said light source means to be temporally modulated in accordance therewith, said light source modulation I 1 (t) taking the form: I.sub.1 (t)=A.sub.1 [1+√2m.sub.1 s.sub.1 (t) cos (2πf.sub.o t)]; means for generating a double-sideband suppressed-carrier amplitude modulated optical deflector modulation signal I 2 (t) as the product of a time-varying input image signal s 2 (t) input thereto and a reference carrier f c and an offset frequency carrier f o , and for applying said optical deflector modulation signal I 2 (t) to said optical deflector modulation signal input of said optical deflector means for causing said modulated light output from said light source means to be diffracted into a time-delayed spatial modulation in accordance therewith, said optical deflector modulation I 2 (t) taking the form: I.sub.2 (t)=A.sub.2 [1+2m.sub.2.sup.2 s.sub.2.sup.2 (t)-2√2m.sub.2 s.sub.2 (t) cos (2πf.sub.o t)]; integrating light detector means having a detection plane for detecting and electronically integrating light incident on said detector plane and for outputting a mean-square-error correlation signal R(t) in correspondence therewith, said mean-square-error correlation signal R(τ) taking the form: ##EQU7## such that by adjusting the m 1 and m 2 for the input modulation, m 1 is equal to 2 m 2 , and a zero value of R(τ) represents a match correlation between said input image I and said reference pattern R; and means for imaging the spatially distributed light diffracted by said optical deflector means onto the detector plane of said integrating light detector means; where: s 1 (t) is the signal input to the light source modulation means; s 2 (t) is the signal input to the optical deflector modulation means; A 1 is the light intensity; A 2 is the diffraction efficiency; m 1 and m 2 are constants that determine the signal-to-bias ratio; f o is the frequency offset between the reference oscillator at f c and the DSB-SC modulation at f c +f o ; and a o and a 1 are constants chosen to bias the light source means and the optical deflector into their respective linear operating regions so that the light source means exhibits a linear intensity characteristic and the optical deflector means exhibits a linear amplitude characteristic.