Polarization-stable and single-frequency fiber lasers

We propose a novel structure of fiber laser to achieve single-frequency and polarization-stable oscillation without using a polarization-maintaining (PM) active fiber. The proposed structure has two stabilization mechanisms. First, the laser has a Fabry-Perot cavity composed of Faraday-rotator mirrors (FRM's) to stabilize the polarization-mode competition. We make comparison of polarization-mode stability in various types of cavity structure, and confirm that the Fabry-Perot cavity composed of a non-PM fiber and FRM's has ideal stability similar to the ring cavity composed of a PM fiber and a polarizer. Second, in order to stabilize the longitudinal mode, the laser has an intracavity etalon specially designed to maximize its finesse by removing undesired reflections from the etalon. In the experiment, we construct a fiber laser composed of a non-PM erbium-doped fiber (EDF), FRM's, and an intracavity Fabry-Perot etalon. The polarization-stable and single-frequency operation of the laser is demonstrated.