An all-optical feedback loop is demonstrated which effectively suppresses slow, signal-induced gain
fluctuations in Er-doped fiber amplifiers (EDFA's). Gain control is achieved by operating the
amplifier in a ring laser configuration. Such a feedback loop which can be fabricated out of all-fiber
passive components could be easily implemented in any system using EDFA's.
"Passive all-optical gain control in erbium-doped fiber amplifiers", Proc. SPIE 1581, Fiber Laser Sources and Amplifiers III, (1 February 1992); doi: 10.1117/12.134975; https://doi.org/10.1117/12.134975