OPTICAL DUPLEX TRANSMISSION SYSTEM

摘要

PURPOSE: To obtain an optical duplex transmission system which is provided with the optical circuit of simple constitution and is at a low cost. CONSTITUTION: An optical transmitter 1 transmits a digital optical signal Op superimposed and optical-intensity-modulated by main data signal b1 and the assistant data signal (a) of a lower clock rate the the signal b1 to an optical receiver 3 through an optical fiber cable 2. An optical detection element 31 in the optical receiver 3 converts the optical signal Op into an electric signal by DC combination and an preamplifier amplifies this electric signal to obtain the main data signals c1 and c2 of reproduction and reproducting inversion. A low-pass filter 33 passes a frequency component lower than that of the main data signal b1 among the signals c1 and c2. An AOC circuit 34 adds offset control voltage (d) to the input of the preamplifier 32 so that the offset part of this signal c1 and c2 becomes zero in response to this passed output. This offset control voltage (d) is amplified by an error amplifier 35 to obtain a reproduced assistant data signal (e).