DEMODULATION REFERENCE SIGNAL SOURCE

摘要

An information retrieval system for extracting information from a pair of substantially coherent electromagnetic waves represented by phase therebetween each of which is incident on a photodetector, and having a demodulator which receives the photodetector output signal and which also recxives a reference signal. The reference signal is obtained through use of a phase shift detector which receives the photodetector signal to determine certain phase shifts occurring therein and provides this information to a reference signal supply to adjust the phase of its output signal which then serves as the reference signal for the demodulator.