A MONITOR UNIT FOR MONITORING AN OPTICAL WAVEGUIDE

摘要

A monitor unit (1) for detecting physical interference of a communications fibre (4) in a transmission system (2) comprises a monitor circuit (9) coupled to the communications fibre (4). A portion of a signal being transmitted along the communications fibre (4) is coupled out of the fibre (4) and into the monitor unit (1). A filter (8) allows only one of two orthogonal polarisation field components to pass through it to the monitor circuit (9). By detecting fluctuations in the polarisation state of the filtered optical signal, the monitor circuit (9) allows the detection of external influences to be determined.