Patent ID: 7511883

Claim:
An optical amplifying method of an optical amplifier connected to an optical transmission line, the method comprising: detecting an optical input and optical output power of said amplifier; applying a logarithmic transformation to the detected optical input and output power to obtain a logarithmic transformed optical input and output power; obtaining a difference between a target gain and a measured gain of said optical amplifier obtained based on the logarithmic transformed optical input and output power to produce an error signal; applying said error signal to each of a proportional calculation and an integral calculation to create respective proportional and integral control signals, and adding proportional and integral control signals to create a drive current of at least one pump laser diode provided in said optical amplifier; controlling the gain of said optical amplifier with the drive current; and adjusting a control parameter of the proportional calculator in response to the logarithmic transformed optical output power, said control parameter being a proportional constant by which said error signal is multiplied to form said proportional control signal, said proportional constant being represented by a function of the of the of the logarithmic transformed optical output power as a result of the adjusting the control parameter in response to the logarithmic transformed optical output power whereby said proportional constant is increased according. to an increase of said logarithmic transformed optical output power.