OPTICAL SOURCE, COMMUNICATIONS NETWORK OPTICAL APPARATUS AND METHOD OF PROVIDING AN OPTICAL SIGNAL

摘要

An optical source (10) comprising: a first laser (12) arranged to generate a first optical signal (14) having a first state of polarisation and a first optical frequency; a second laser (16) arranged to generate a second optical signal (18, 48, 78) having a second state of polarisation, substantially orthogonal to the first state of polarisation, and having a second optical frequency, different to the first optical frequency by a preselected frequency difference, Δν; a polarisation beam coupler (20) arranged to combine the first optical signal and the second optical signal into a composite optical signal comprising both the first optical signal and the second optical signal having said substantially orthogonal states of polarisation; and an output (22) arranged to output the composite optical signal (24).