Broadly Tunable Fiber Laser Based on Merged Sagnac and Intermodal Interferences in Few-Mode High-Birefringence Fiber Loop Mirror

A broadly tunable fiber ring laser including a few-mode high-birefringence fiber (FM-HBF) loop mirror is proposed and demonstrated. The operation mechanism is based on simultaneous occurrence of Sagnac and intermodal interferences in the FM-HBF loop mirror and polarization dependence of the modal excitation in the FM-HBF. While adjusting only a polarization controller next to the FM-HBF in the loop arm, the lasing wavelength can be tuned at a discrete step defined by the intermodal interference. The tunable range exceeding 40 nm with sidemode suppression ratio over 40 dB and power uniformity better than 1 dB at a discrete step of about 2.2 nm has been successfully demonstrated for the proposed fiber ring laser.