VERBESSERUNGEN AN UEBERTRAGUNGSSYSTEMEN.

摘要

A duplex communication system comprises a transmitter (OT) for deriving from a frequency modulated electrical carrier signal a corresponding optical signal for transmission over a bi-directional optical fibre communication path (BX) and a receiver (OR) for providing from a received frequency modulated optical signal a corresponding electrical signal. An optical directional coupler (DOC) is provided through which the optical signal from the transmitter (OT) is arranged to be fed to the bi-directional path (BX) and through which the received optical signal is arranged to be fed to the receiver (OR). Mixer means (MX1 and MX2) are arranged to be fed with the transmitted and received optical signals including the cross-talk components and the outputs from the mixer means are fed through filters (L1 and L2) to a demodulator (DEM) and a substractor (SU) in which a sample of the modulation carried by the transmitted signal is arranged to be subtracted from the demodulated received signal whereby unwanted feedback of the transmitted signal via the directional coupler (DOC) and electrically-induced cross-talk signals are substantially cancelled.