Abstract: 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 Pin of input signals to the EDFA, and an output detector 3 is provided for monitoring the power Pout 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 Pin, and a feed back arrangement 5, 6, 7, 8, 9, 30 for supplying a feed back signal dependent on the monitored output power Pout.

Abstract: A multichannel optical amplifier having an adjustable gain set point is controlled to permit substantially constant gain tilt control during a gain set-point change so that the channel powers are maintained during system modification. To this end the amplifier comprises an erbium doped fibre (EDF) loop and associated pump amplifier for amplifying an optical signal comprising channels of different wavelengths, a variable optical attenuator (VOA) for controlling the gain of the amplifier by applying a loss profile that varies with wavelength so that the different channels are amplified in accordance with a required gain tilt, preferably a zero gain tilt, and a PI controller for applying a gain tilt adaptation profile to compensate for an inherent gain tilt to produce the required gain tilt.