Temporal Feature Extraction in Photorefractive Resonators

摘要

A holographic optical system listens to an incoming signal and extracts the mostcommon repetitive temporal features of that signal. An example might be to extract the features of Morse code, which consists of two tone lengths and two pause lengths. This optical system is self-organizing, in that very little a priori information is imbeded in the system to indicate what form the temporal signals take. The primary constraints imposed on the signal is (1) finite bandwidth; (2) limited feature duration and (3) rates of reoccurrence. The optical apparatus uses a photorefractively pumped multimode optical oscillator having a delay line in the feedback loop. The delay line serves to translate the temporal dimension into a spatial one, and it also builds into the system a notion of the direction of time. Temporal feature extraction takes place as a competitive interaction among sets of modes, which are termed chronomodes. Experiments illustrate the principles of such a system by extracting the two most probable temporal features from a signal imposed on a laser beam. (MM).