Compound comb filter based on Sagnac interferometer and phase shifted fiber Bragg grating using for tunable and switchable fiber ring laser

Abstract

A kind of stable, switchable and tunable erbium-doped fiber ring laser based on a Sagnac interferometer (SI) is presented and experimentally demonstrated. The SI is composed of a section of an elliptical-core spun fiber sandwiched between two polarization controllers (PCs) in a Sagnac loop. The proposed compound comb filter, which consists of an SI cascaded with a phase shifted fiber Bragg grating, is developed to suppress the mode competition in the laser oscillation. By adjusting the PCs, a stable and tunable single-wavelength lasing output can be achieved. The optical signal-to-noise ratio (OSNR) is better than 40 dB, and the 3 dB linewidth is less than 15 pm. Furthermore, stable dual-wavelength lasing outputs with different wavelength intervals of 0.132 nm, 0.336 nm and 0.418 nm can also be obtained by carefully adjusting the PCs. The power difference between the two lasing peaks is less than 2 dB, and the OSNR is about 50 dB.