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

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 cavi ty lengths up to similar to 320 m and to be proportional to the relative li newidth of the relaxation oscillation resonance. The tolerable length of Ra yleigh backscattering standard telecom fiber was found to be 135-200 m. An observed degradation in the laser stability and slope efficiency at low pum p powers is believed to be due to UV-induced saturable absorbers. (C) 1999 Optical Society of America.