Variable gain optical amplifiers

Abstract

A variable gain optical amplifier comprises an EDFA for amplifying optical signals at different wavelengths and a pump driverfor optically pumping the EDFA to provide optical gain. An input detectoris provided for monitoring the power Pof input signals to the EDFA, and an output detectoris provided for monitoring the power Pof output signals from the EDFA. A gain control arrangement is provided for supplying a drive signal to the pump driverto control the optical gain including a feed forward arrangementfor supplying a feed forward signal dependent on the monitored input power P, and a feed back arrangementfor supplying a feed back signal dependent on the monitored output power P. In order to ensure rapid gain control the feed back arrangement comprises an adaptive proportional-integral (PI or PID) controllerfor controlling the optical gain at a required gain set point in accordance with proportional and integral control coefficients Kand Kcorresponding to a required gain profile, at least one of which is dynamically variable in dependence on the monitored output power P, the output signal from the controllerand the feed forward signal being added in an adderto produce the drive signal for the pump driver