Fibre monitoring in optical networks

Abstract

A method of monitoring an optical fibre comprises modulating an optical signal with a traffic signal; modulating the optical signal with an incoherent optical frequency domain reflectometry, IOFDR, test signal; transmitting the doubly modulated optical signal onto an optical fibre at a first end of the fibre; detecting scattered radiation output from the first end of the fibre; and analysing the detected scattered radiation using incoherent optical frequency domain reflectometry to determine a distance to a break in the optical fibre. Apparatus suitable for carrying out the method is also described, as well as an optical communications network employing the method.

1 . An amplifier for an optical communications network the amplifier configured to amplify an optical signal modulated with a traffic signal received from an output of a first optical fibre and to retransmit the amplified signal into a first end of a second optical fibre, the amplifier comprising:
 a modulator configured to further modulate the optical signal with an incoherent optical frequency domain reflectometry, IOFDR, test signal, and   a first detector configured to detect scattered radiation received from at least one of the first end of the second optical fibre or the output of the first optical fibre.   
     
     
         2 . An amplifier as claimed in  claim 1 , further comprising a second detector configured to detect a signal to be transmitted by the amplifier, which signal is modulated with both the traffic signal and the IOFDR test signal. 
     
     
         3 . An amplifier as claimed in  claim 1 , wherein the first detector is configured to detect radiation from the first end of the second optical fibre, and wherein the amplifier further comprises a third detector configured to detect scattered radiation received from the output of the first optical fibre. 
     
     
         4 . An amplifier as claimed in  claim 1 , wherein an output from the detector or detectors is provided to an incoherent optical frequency domain reflectometry, IOFDR, analyser configured to determine a distance to a break in the optical fibre by analysing the output of the detector(s) using incoherent optical frequency domain reflectometry. 
     
     
         5 . An amplifier for an optical communications network, the amplifier comprising:
 a pump laser configured to pump a gain medium of the amplifier,   a microprocessor configured to control operation of the amplifier, and   an input connector for receiving an optical signal to be amplified,   wherein the microprocessor is configured to modulate an output of the pump laser with an incoherent optical frequency domain reflectometry, IOFDR, test signal, and   wherein the amplifier further comprises a detector configured to detect scattered radiation received at the input connector, which radiation has been modulated with the IOFDR test signal.