British Telecommunications Public Limited Company

British Telecommunications Corporation

William A Stallard

Andrew David Ellis

Richard C Booth

Alan R Beaumont

Barbara E Daymond-John

David G Cunningham

Derek Malyon

Robert Michael Percival

A fault signalling system for an optical fiber-based communications link having erbium doped fiber amplifier repeaters comprises a broadband optical source for generating a fault signal in the event of a fault occurring. Each repeater includes such a broadband source, which will output a characteristic fault signal onto the link for transmission to a receiving station, in the event of a fault being detected at that repeater. Advantageously, a control circuit which enables the source to emit its fault signal when appropriate is also used as part of an automatic gain control for the output of the amplifier repeater in normal operation.

Optical communication link fault signalling

Optical signal modulation device

An AGC for a laser amplifier uses a control tone modulated onto the optical signals. During use the modulation on the optical signals is superimposed on the drive current for the laser. The AGC derives a control signal by detecting the modulation in the drive current, multiplying it by the drive current. The drive current for the laser is adjusted to keep the control signal constant. In a preferred embodiment a low level sensor detects when the control tone falls below a threshold level and switches the circuit to a default configuration. The default configuration provides a distress signal to indicate a fault and to identify the affected amplifier. This preferred embodiment is particularly suitable for submarine telecommunications capable which include a plurality of inaccessible amplifiers.

Amplication of optical signals

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Colchester, United Kingdom

William A Stallard