| 摘要 |
PURPOSE:To attain a heterodyne/homodyne optical communication with no strict stability needed for frequencies of a transmission reference light source and a local oscillation light source, by applying a feedback with a difference frequency signal between both said light sources to obtain a fixed difference frequency. CONSTITUTION:The light delivered from a reference oscillator 41 is branched into two parts by a branching coupler 43. The light of one side is modulated by a modulating signal SIG1 through a modulator 42 and transmitted to a station 6 of the remote side via an optical fiber 51. A photodetector 65 demodulates the received signal and obtains a signal proportional to the difference frequency between an optical frequency f1 given from the oscillator 41 of an end office 4 and an optical frequency f2 given from a reference oscillator 61 of an end office 6. This signal is applied to a feedback circuit 66. A photodetector 45 demodulates the modulated signal and at the same time detects a difference frequency (f1- f2) between oscillators 41 and 61 to supply it to a feedback circuit 46. The circuit 46 gives a fine adjustment to the optical frequency of the oscillator 41 in order to fix the difference (f1-f2). |
