All-Fiber Mode-Locked Thulium Doped Fiber Laser using a Novel Femtosecond Laser Inscribed 45° Tilted Fiber Grating

Abstract

The recent development of mode-locked fiber lasers operating at ∼2μm is accelerating, driven by industrial and medical applications, particularly in the so-called "eye-safe" applications of laser surgery, biomedical imaging, medicine and sensing [1]. While being practical devices, given reproducible experimental conditions, fiber lasers continue to be an excellent research avenue to unveil a plethora of complex ultrafast dynamics. Developments on versatile all-fiber laser sources are attractive, due to their increased efficiency, robust and compact configurations. The development of artificial saturable absorbers, such as nonlinear polarization rotation (NPR) based on the optical Kerr effect, has enabled the realization of all-fiber formats. However, in hybrid laser designs, the use of bulk polarizers reduces the perceived advantage of the fiber-based format. In this communication, we employ a recently developed 45° tilted fiber grating (TFG) inscribed using femtosecond laser [2] as an in-line fiber polarizer in an all-fiber laser [3]. This grating inscription process offer advantages over traditional 45°-TFG UV-laser inscription, and is based on plane-by-plane, direct writing using a femtosecond laser, as it neither requires a phase mask nor a hydrogen loading process, as is usually the case.