Optical gain control of erbium-doped fiber amplifiers with a saturable absorber

Optical gain control (OGC) can be used to lock the inversion of an erbium-doped fiber amplifier (EDFA), assuming that the gain medium is homogeneous. However, EDF´s exhibit certain degrees of spectral hole burning. As a result, when the OGC laser power and the spectral-hole depth at the laser wavelength change, the inversion of the EDFA changes accordingly with a fixed OGC cavity loss. In this work, a saturable absorber is placed in the OGC laser cavity to adjust the cavity loss dynamically and compensate the gain tilt caused by the OGC laser spectral hole burning. It is demonstrated that the steady state gain variation of a surviving channel in an optically gain controlled EDFA is improved from 1.3 dB (with a fixed loss) to 0.4 dB (with a saturable absorber in the cavity). The transient response of this gain control scheme is also discussed.