SINGLE LINE TWO-WAY OPTICAL COMMUNICATION DEVICE

摘要

PURPOSE:To reduce the effect of crosstalk due to a reflected light by providing a coding circuit to a transmitter and providing an automatic threshold value control circuit having a time constant having a time being several times or over the code period and a decoding circuit to a receiver and using a polarized beam splitter for a directional coupler. CONSTITUTION:A transmitted optical signal is polarized and branched by a branching device 4 using the polarized beam splitter 5 and made incident to an optical fiber 3. The reflected light reflected at the near end (end (a)) of the optical fiber 3 is eliminated by the branching device 4 and not inputted to the receiver 2. On the other hand, the light reflected at the remote end (end (b)) of the optical fiber 3 and a signal light from an opposite station (station B) pass through the branch device 4 and are led to the receiver 2. After the light incident incident in the receiver 2 is converted into an electric signal by a PIN photo diode 10 and an amplifier 11, the signal is inputted to a comparator 12. Since a threshold voltage Vth of the comparator 12 is obtained from an automatic threshold value control circuit 13 having a time constant being 3-4 times of the period of code, the remote end reflected light 15 is neglected and only the signal light from the opposite station is reproduced.