Optical correlator system

An optical correlator system comprising

• light source means for providing a coherent beam of light having two oppositely circularly polarized component beams having two different frequencies;
• non-polarization sensitive beam splitting means for transmitting the two oppositely circularly polarized component beams and for reflecting a portion of emitted radiation;
• polarizing means for changing the oppositely circularly polarized component beams into two orthogonal linearly polarized component beams;
• polarization-sensitive beam splitting means for reflecting one of the linearly polarized beams and for transmitting the other of said linearly polarized beams in a determined direction;
• mirror means for directing the reflected one of said linearly polarized beams in the determined direction;
• optical polarization means for changing the reflected portion of emitted radiation to frequency component beams having colinear polarization directions;
• detector and processing means for providing an electrical reference signal from said frequency component beams which is the difference between the two frequencies;
• signal multiplier means for multiplying a signal function by a phase term under the control of said reference signal;
• reference multiplier means for multiplying a reference function by said phase term under the control of said reference signal;
• first recording means for recording a modulated waveform from said signal multiplier means;
• second recording means for recording a modulated waveform from said reference multiplier means;
• optical transfer means for projecting the waveform recorded on said first recording means onto the waveform recorded on said second recording means;
• optical means for projecting the Fourier transform of the amplitude of light output by said second recording means onto a plane;
• detecting means for detecting the pattern in the plane of the Fourier transform when v is substantially equal to zero, wherein v is the transform variable, said detecting means having an output providing said Fourier transform;
• filtering means controlled by said reference signal for filtering out the entire output of said detecting means except a temporal signal oscillating at 2.DELTA.f;
• and
• output means having an input inputting said temporal signal and an output outputting a signal which is the square of the correlation value.

An optical correlator system comprising

• light source means for providing a coherent beam of light having two oppositely circularly polarized component beams having two different frequencies f.sub.1 and f.sub.2 ;
• first beam splitting means for transmitting the two oppositely polarized component beams f.sub.1 and f.sub.2 and for reflecting a portion of emitted radiation;
• linear polarizing means for orthogonal linear polarization of said component beams f.sub.1 and f.sub.2 transmitted by said first beam splitting means;
• second beam splitting means for transmitting the linearly polarized beam f.sub.1 in a determined direction and reflecting the other linearly polarized beam f.sub.2 ;
• directing means for directing the reflected beam f.sub.2 in the determined direction;
• optical polarization means for changing the portion of emitted radiation reflected by said first beam splitting means to frequency component beams f.sub.1 and f.sub.2 having colinear polarization directions;
• processing means for providing from said frequency component beams an electrical reference signal .DELTA.f=f.sub.2 -f.sub.1 ;
• optical means for expanding and collimating said frequency component beams f.sub.1 and f.sub.2 ;
• signal processing means for modifying a signal function by a temporal frequency offset under the control of the electric reference signal .DELTA.f and recording a first modulating waveform;
• reference signal processing means for modifying a reference function by said temporal frequency offset under the control of said reference signal and recording a second modulating waveform;
• optical transfer means for recording the expanded and collimated beams under the control of the modified signal and reference functions;
• optical means for projecting the Fourier transform of the amplitude of light of the combined modulated beams onto a plane;
• detecting means for detecting the pattern in the plane of the Fourier transform when v is substantially equal to zero, wherein v is the transform variable, said detecting means having an output providing said Fourier transform;
• filtering means controlled by said reference signal for filtering out the entire output of said detecting means except a temporal signal oscillating at 2.DELTA.f;
• and
• output means having an input inputting said temporal signal and an output outputting a signal which is the square of the correlation value.

A method of optical correlation which avoids bias level terms in the optical correlation output, said method comprising the steps of

• deriving coherent polarized component beams having frequencies f.sub.1 and f.sub.2 from a light source;
• converting said component beams f.sub.1 and f.sub.2 to a reference electrical signal .DELTA.f=f.sub.2 -f.sub.1 ;
• correlating the sum f.sub.1 +f.sub.2 of said component beams under the control of a multiple of said reference electrical signal .DELTA.f;
• and
• projecting and detecting the Fourier transform of the amplitude of correlated light.

An optical correlator system comprising:

• a light source for providing a coherent beam of light having first and second component beams having frequencies f and f.sub.2 respectively;
• a conversion subsystem for converting said first and second component beams to a reference signal having a frequency .DELTA.f=f.sub.2 -f.sub.1 ;
• a correlator subsystem for correlating the sum of the first and second component beams under the control of said reference signal;
• a lens assembly for projecting the Fourier transform of the correlated light onto a detection plane;
• and
• an optical detector for detecting said Fourier transform of the correlated light on the detection plane.