In-fiber polarizer based on a 45° tilted fluoride fiber Bragg grating for mid-infrared fiber laser technology

We report the direct femtosecond laser inscription of a 45⁰ tilted fiber Bragg grating (TFBG) into the core of a ZBLAN fluoride fiber, creating an in-fiber polarizer for the mid-infrared region. Utilizing a 16 mm long intracavity TFBG, we demonstrate a 2.862 μm fiber laser with 21.6 dB output polarization extinction ratio (PER) and up to 0.37 W of output power with a slope efficiency of 31.3%. In addition, we experimentally demonstrate that the PER of the laser is a linear function of grating length. Our results show that TFBGs in fluoride fibers are a promising route to replace bulk optic polarizers in mid-IR laser cavities and this technology has the potential to realize low loss in-fiber polarizers for the development of ultrafast mid-IR all-fiber laser systems using nonlinear polarization rotation.