Stability of an Er-Yb-doped fiber distributed-feedback laser with external reflections

The maximum tolerable amplitude backreflection coefficient r(ext,c) into a fiber distributed-feedback laser before the onset of instability has been investigated. r(ext,c) was found to decrease with increasing external cavity lengths up to ~320 m and to be proportional to the relative linewidth of the relaxation oscillation resonance. The tolerable length of Rayleigh backscattering standard telecom fiber was found to be 135-200 m. An observed degradation in the laser stability and slope efficiency at low pump powers is believed to be due to UV-induced saturable absorbers.