A single transmission line bidirectional optical communication system.

摘要

A single transmission line bidirectional optical communication system comprises a directional coupler (10) including a polarising beam splitter (11) and an optical system for separating an optical output signal to be outputted to a single transmission line (100) and an optical input signal to be inputted from said single transmission line. An optical transmitting circuit (20) is provided for coding original data (DO) by using a clock signal (CKT) of predetermined frequency and for subsequently converting the coded data into an optical signal by means of a light emitting element (23). An optical receiving circuit (30) converts an optical input signal into an electric signal, amplifies the electric signal, recognises the electric signal through a comparator (33) including an automatic threshold controlling circuit for automatically setting a threshold level at a substantially average value of input signal intensities, and subsequently decodes the signal to reproduce and output the clock signal and data (D1). An optical output controlling circuit (40) controls whether or not an optical signal needs to be outputted from the optical transmitting circuit (20). A frequency discriminating circuit (50) discriminates the frequency of the reproduced clock signal (CKR) to output a status signal (STC) indicating said frequency. A clock controlling circuit (60) determines and outputs its own transmission clock frequency (CKT) according to the status signal (STC) coming from the frequency discriminating circuit (50) in the state in which no optical signal is outputted from the optical transmitting circuit (20) under the control of the optical output controlling circuit (40), and for outputting a status signal (STM) indicating the transmission clock frequency.