Theoretical optimization of cavity configurations for fiber lasers: enhancement of mode oscillation and slow-light effect

Abstract

This article theoretically investigates the optimization of various fiber Bragg cavities for sustaining laser oscillation and amplification in fiber lasers designed as distributed feedback reflectors and/or distributed Bragg reflectors. Coupled mode theory with the transfer matrix method have been used to obtain reflection and transmission spectra as well as group delay and dispersion for characterizing the proposed cavities. The optimum configuration gives symmetrical spectra with single-mode oscillation in the stop-band manifesting an enhanced slow-light process. Various cavity parameters such as cavity configuration, length, pitch, and structure of the grating are found to have a significant effect on the field confinement, oscillated modes, and dispersion of the spectrum. Cavities formed by phase-shifted FBGs showed better photon confinement, and better reinforcement of single-mode oscillations. By incorporating an extra etalon-like cavity (etalon), uniform spectra with wider stop-band can be manifested and single-mode oscillations with remarkable delay for the slow-light effect are maintained.