Variable gain optical amplifiers

摘要

A variable gain optical amplifier comprises an EDFA for amplifying optical signals at different wavelengths and a pump driver 14 for optically pumping the EDFA to provide optical gain. An input detector 2 is provided for monitoring the power P_in of input signals to the EDFA, and an output detector 3 is provided for monitoring the power P_out of output signals from the EDFA. A gain control arrangement is provided for supplying a drive signal to the pump driver 14 to control the optical gain including a feed forward arrangement 20, 21, 22, 23 for supplying a feed forward signal dependent on the monitored input power P_in, and a feed back arrangement 5, 6, 7, 8, 9, 30 for supplying a feed back signal dependent on the monitored output power P_out. In order to ensure rapid gain control the feed back arrangement comprises an adaptive proportional-integral (PI or PID) controller 30 for controlling the optical gain at a required gain set point in accordance with proportional and integral control coefficients K_p and K_i corresponding to a required gain profile, at least one of which is dynamically variable in dependence on the monitored output power P_out, the output signal from the controller 30 and the feed forward signal being added in an adder 31 to produce the drive signal for the pump driver 14.