All-fiber narrow-linewidth ring laser with continuous and large tuning range based on microsphere resonator and fiber Bragg grating

We demonstrate an all-fiber single-longitudinal-mode (SLM) narrow-linewidth ring laser stabilized by a microsphere resonator and fiber Bragg gratings (FBGs) with a large continuous wavelength tuning range from 1540 nm to 1570 nm. In the experiment, stable lasing with a linewidth smaller than 5 kHz was obtained. The laser wavelength was linearly and continuously tuned in the range of 0.15 nm by increasing the pump power and discretely tuning with a step of 0.1 nm by stress-controlled FBGs. The tuning range of the proposed laser configuration was determined by the FBG, and the SLM state was ensured by the coupling between the few-mode tapered fiber and the microsphere, which was simpler in alignment than other ring lasers utilizing microresonators.