US 8,078,663 B2 · Optical correlation apparatus and method

Abstract

This invention relates to a pattern recognition correlator and method for correlating input data with one or more reference data sets. The input data, which may be for instance digital amplitude modulated optical data, is used to modulate an optical signal to form a phase modulated optical signal. This temporal phase modulated optical signal is then converted into a parallel optical phase signal, preferably through use of an optical delay, and modulated by an optical phase modulator. When there is a correlation between the input data and the reference data the emerging wavefront is plane and can be strongly coupled to a detector. In the absence of correlation the emergent wavefront is not plane and so is not coupled as strongly to the detector. The detector output can therefore be used as an indication of correlation.

Claims34

Dependent claims

A correlation apparatus comprising an optical delay means for converting a temporal data input stream to at least one parallel optical data stream having a phase modulation replicating the input data and a reference phase modulator for applying a parallel phase modulation replicating at least one reference data set wherein the reference phase modulator and optical delay means are aligned so as to create a parallel optical signal which has been modulated in phase according to both input and reference data, wherein the optical delay means comprises a plurality of optical waveguide delay lines of different delay.

A method of correlating input data with reference data comprising the steps of;

taking a temporal phase modulated optical signal wherein the phase modulation represents the input data,
converting the temporal phase modulated optical signal into at least one parallel data optical signal having a phase modulation which represents the input data,
modulating said at least one parallel optical data signal with a phase modulation replicating a reference data,
interferometrically coupling the or each optical data signal modified by a reference modulation and directing onto a detector,
and using the detector output as an indication of correlation between the input data and the reference data, wherein the method further comprises:
an initial calibration step of performing a correlation with input data known to correlate with the reference data and measuring the output of the associated detector and using the output to set a threshold level, the steps of periodically repeating the calibration step, wherein the output of the detector during the calibration step is used to maintain the current threshold level, adjust the threshold level or indicate a need to re-set the phase states of the system, and wherein the step of modulating the parallel optical data with a phase modulation representing reference data is performed using an analogue spatial light modulator (SLM) and periodically the phase of at least part of the appropriate reference spatial phase pattern displayed on the SLM is adjusted to compensate for a phase drift in the radiation incident on the SLM at that point.

3 more elements

Dependencies are inferred from the claim text.

Optical correlation apparatus and method

Life of this patent

Optical correlation apparatus and method

Life of this patent

Abstract

Claims34