High birefringence fiber ring resonator with an inline reflector for single-frequency fiber lasers

A high birefringence fiber (HBF) ring resonator with an inline weak reflector is newly proposed to generate narrowband reflection peaks. When a linear polarizer is located at the input port, effective free spectral range (FSR) of the reflected linearly polarized light is dramatically enhanced in single physical ring setup due to the intrinsic vernier effect between the traveling orthogonally polarized lights along the fast and slow axes of the HBF. What’s more, the side reflectivity suppression ratio can reach 6 dB. To sum up, these special properties facilitate its application in single-frequency fiber lasers.