Special Issue on Fiber-Optics. Optical Fiber Amplifier.

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber amplifier operating, in a state where a noise figure is low by controlling excitation light power from an excitation light source. SOLUTION: This optical fiber amplifier 1 is equipped with an amplifier body circuit 2, that has a signal light input part 3, excitation light source 6, wavelength multiplexer 5, rare earth element doped optical fiber 7, and amplified signal light output part 9, an automatic gain control loop 13 so that the gain of the rare earth element doped fiber 7 is made constant, when oscillation light is circulated. Furthermore, the power is saturated, and an excitation light source control part 16 that monitors the power of the oscillation light circulating in the automatic gain control loop 13, and allows the power of the excitation light from the excitation light source 6 to be fed back, so that the oscillation light power is in the critical state between saturation and non-saturation states or to the non-saturation state.