Abstract
Rare-earth-doped solid-state lasers utilize distributed-feedback ( DFB) resonators to generate ultra- narrow-linewidth emission down to a few kHz. The longitudinal modes of a single Fabry-Perot and a DFB resonator are influenced by the structure, the optical excitation configuration, and external feedback, as has been observed experimentally. Here we investigate the influence of bi-directional launching of light and external feedback on the longitudinal modes of single Fabry-Perot, double Fabry-Perot, and DFB resonators. These results can be exploited for the technological advancement of DFB lasers.