Disposable absorbent undergarment

摘要

An optical fiber amplifier which is started up in a short time due to a low time constant while an output power rises and which outputs highly stable power due to a high controlled time constant and a high controlled gain after the rise of the output power. The optical fiber amplifier comprises an optical detector for monitoring a level of an output light which has branched and a comparison and decision circuit for controlling a gain variable amplifier and a variable time-constant circuit based on an output from the optical detector, so that a gain and a time constant of an exciting light source are controlled based on an output from the optical fiber amplifier. <IMAGE>