Bookham Technology Limited

Ian Peter McClean

Stephen David Fourte

Barrie Flintham

Olivier Moteau

Jonathon Stuart Drake

Gregory Dean May

Hazel Ann McInnes

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

Variable gain optical amplifiers

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. Furthermore the PI controller is arranged to change the gain tilt adaptation profile in response to a change in the gain set point to allow for the different gain characteristics of the amplifier at different gain set points.

Optical amplifiers

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Devon, United Kingdom

Ian Peter McClean