Optical receiver for phase locking to a microwave subcarrier

Claim 1

A CIRCUIT FOR AN OPTICAL RECEIVER WHICH DETECTS A MICROWAVE SUBCARRIER AS A DISCRETE SPECTRAL COMPONENT AT A LOW DIFFERENCE FREQUENCY IN THE OUTPUT OF SAID OPTICAL RECEIVER, THE INPUTS TO SAID OPTICAL RECEIVER BEING A MICROWAVE SIGNAL AND AN OPTICAL CARRIER WITH SAID MICROWAVE SUBCARRIER, COMPRISING AN INPUT CHANNEL FOR RECEIVING SAID OPTICAL CARRIER, AN ELECTRO-OPTICAL MODULATOR DIRECTLY CONNECTED TO SAID INPUT CHANNEL AND THEREBY RECEIVING SAID OPTICAL CARRIER, SAID MICROWAVE SIGNAL BEING DIRECTLY LED TO SAID ELECTRO-OPTICAL MODULATOR TO PROVIDE MODULATION OF SAID OPTICAL CARRIER BY SAID MICROWAVE SIGNAL, A BEAM SPLITTER DIRECTLY RECEIVING THE OUTPUT OF SAID ELECTRO-OPTICAL MODULATOR TO PRODUCE FIRST AND SECOND OPTICAL BEAMS, WHEREIN MEANS FOR INTERFEROMETRIC FILTERING BY VARIATION OF OPTICAL PATH LENGTHS ARE PROVIDED FOR SAID FIRST AND SECOND OPTICAL BEAMS INDEPENDENTLY AND FOR SAID FIRST OPTICAL BEAM RELATIVE TO SAID SECOND OPTICAL BEAM, AND AN OPTICAL PRODUCT DETECTOR WITH FIRST AND SECOND INPUT CHANNELS INTO WHICH ARE LED, RESPECTIVELY, SAID FIRST AND SECOND OPTICAL BEAMS TO PRODUCE AN ELECTRICAL SIGNAL WHICH IS THE OUTPUT OF SAID OPTICAL RECEIVER, SAID OPTICAL PRODUCT DETECTOR BEING CAPABLE OF PRODUCING AN ELECTRICAL SIGNAL WHOSE FREQUENCY SPECTRUM CONTAINS THE LOW FREQUENCY COMPONENTS OF THE SPECTRUM OF THE PRODUCT OF SAID FIRST AND SECOND OPTICAL BEAMS, AND THEREBY CONTAINING A DISCRETE SPECTRAL COMPONENT AT SAID DIFFERENCE FREQUENCY WHICH IS THE DIFFERENCE OF THE FREQUENCIES OF SAID MICROWAVE SUBCARRIER AND SAID MICROWAVE SIGNAL.