Dynamic gratings induced by mode instabilities in fiber lasers

摘要

We review the results of investigation of a special mode of self-pulsing, longitudinal-mode-instability regime, so-called self-induced laser line sweeping. This description reflects the fact that the self-pulsing (in the form of self-sustained relaxation oscillations) coexists with a spectacular laser line drift with time. It is accompanied by creation of dynamic refractive index gratings along the active fiber in the laser cavity. Such gratings have pitch of less than a micrometer, defined by half of the wavelength of the laser mode responsible for the grating build-up. Although longitudinal mode instabilities in fiber lasers are known for a long time, the associated refractive index gratings were studied just recently. An estimation of reflectivity of the dynamics gratings in self-swept fiber lasers is given using numerical model.