SPECTRAL STABILITY AND SMOOTHNESS OF A PHASE-MODULATED FIBER LASER

A fiber laser is phase modulated in the presence of a weak external reflection, leading to a strong intensity modulation at the laser output. The modulation causes the optical spectrum to be substantially more stable and smooth. The usefulness of the improved spectrum is illustrated by two different experiments, one for the characterization of an optical filter by measurement of its influence on the laser spectrum and the other for the measurement of the spatial-mode group-delay difference in a two-mode fiber by use of white-light interferometry. In both experiments the noise level is substantially reduced when the phase-modulated source is used.