Active recognition system with optical signal processing

Abstract

An active recognition system comprises a transceiver, tracking electronics, an optical processor, and a data handler. The transceiver transmits chirped pulses and receives a series of reflected �replicas of the chirped pulse! replica pulses from �features of! an object �of interest!. The tracking electronics controls the transceiver to determine object range for gating the optical processor. The optical processor includes a 'signal' Bragg cell driven by the reflection signal so that �a! throughgoing light �beam! is angularly redistributed as a function of the local spatial frequency of the acoustic waveform within the modulation aperture of the signal Bragg cell. At a first focal plane, the light defines a one-dimensional light distribution that includes moving spots that correspond to respective reflection replicas. A chirp-compensating collimating lens �with a focal length of opposite sign from and equal to the effective focal length of the chirp signal! collimates the light diverging from the moving spots for subsequent focusing by a 'transform' lens at a final focal plane. A 'sweep' Bragg cell �, which is driven by a linear sweep,! sweeps the beam orthogonal to the direction of spot movement to provide a two-dimensional distribution at the final focal plane in which each reflection replica is represented as a diagonal trace. A charge-coupled-device at the focal plane captures the distribution for input to the data handler which �attempts to match! 'recognizes' the object by matching the acquired two-dimensional light distribution with the corresponding distributions for known objects. �A match provides a probable recognition.! The two-dimensional distribution provides for more sophisticated matching across different object orientations in real time. Since the two-dimensional distribution is acquired in real time, the present invention provides improved object recognition where recognition speed is critical.