Method and apparatus for minimising gain deviation in optical fibre amplifier

Commercially available optical fiber amplifiers have gain over a large optical bandwidth, and for many applications, especially long distance fiber communications, developing techniques to flatten the gain of EDFA's is important. High gain amplifiers give rise to gain ripple and are thus more difficult to flatten effectively and efficiently. The invention provides a method of amplifying a signal in an optical fiber in an optical fiber amplifier having a pre-determined operating temperature range, whereby the temperature of the fiber in the pre-determined operating temperature range is maintained, and the fiber has an optimal length so as to minimize gain ripple in the amplifier over the operating temperature range. The invention also provides an optical fiber amplifier having an optimal length of fiber, a heater (2) and a temperature monitor (3) both coupled thermally to the fiber. The temperature monitor is responsive to the temperature falling below the pre-determined operating temperature range of the amplifier to energize the heater, and is responsive to the temperature rising higher than the pre-determined operating temperature range of the amplifier to de-energize the heater.