Investigation on Microcavity-Feedback Fiber-Loop Lasers by Rate Equation Models

Microcavity-feedback fiber-loop laser gives a promise for single-mode and tunable lasing. Here, a whispering gallery mode(WGM) microcavity-feedback fiber-loop laser is constructed and dynamic lasing mechanisms are investigated by rate equation models. For the single-mode lasing, the results show that the lasing efficiency can be maximized by tuning the coupling of waveguide and WGM microcavity, and two critical coupling rates exist for a fixed internal coupling coefficient of clockwise and counter-clockwise WGMs. By simply increasing the total length of fiber-loop laser, multi-mode lasing originated from one WGM feedback of a silica microsphere is explored, the lasing behaviors are well predicted by the rate equations and the WGM resonance linewidth can be effectively evaluated from the beat notes bandwidth of multiple lasings. We wish the results demonstrated here can be used for optimization on the lasing output of a fiber-loop laser with an external feedback mirror.