HETERODYNE RECEIVING CIRCUIT FOR OPTICAL COMMUNICATION BY INJECTION SYNCHRONISM

摘要

PURPOSE:To reduce the size of a reception system by simplifying the frequency control system of a local oscillator by holding an intermediate frequency invariably constant by generating holding light for the interference of a signal by using a semiconductor laser for the local oscillator and by putting it in injection synchronizing operation. CONSTITUTION:A modulated signal from a transmitted-light source system 1 is transmitted to a receiving circuit 9 through an optical transmission line system 2. The received signal is split into two by a half-mirror 3; one component is supplied to a square-law detector 8 through a half-mirror 6, and the other is supplied to an injection synchronizing semiconductor laser 7 by being reflected by a mirror 4. The laser 7 is modulated directly at an intermediate frequency fIF and has side-band wave components, equivalent to the fIF, at both the sides of a carrier frequency. The carrier frequency component of signal light is applied to the laser 7 to synchronize with a side-band wave. The output light of the laser 7 is supplied to the detector 8 via mirrors 5 and 6 and the detector 8 sends a signal consisting of components having side-band waves of the signal around the fIF.