Patent ID: 7317570

Claim:
A variable gain optical amplifier comprising: amplifying means for amplifying optical signals at different wavelengths in a fiber-optic communications link, the amplifying means being in the form of a pump driver for optically pumping an optical fiber to provide optical gain; input power detection means for monitoring the power P in of input signals to the amplifying means; output power detection means for monitoring the power P out of output signals from the amplifying means; gain control means for supplying a drive signal to the pump driver to control the optical gain; feed forward means for supplying a feed forward signal to the gain control means dependent on the monitored input power P in ; and feed back means for supplying a feed back signal to the gain control means dependent on the monitored output power P out ; wherein the feed back means comprises an adaptive proportional-integral (PI or PID) controller 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 , and the gain control means is configured to combine the feed forward signal supplied by the feed forward means with the feed back signal supplied by the feed back means to produce the drive signal for the pump driver.