Polarization-maintaining dissipative-soliton mode-locked thulium fiber laser with a nonlinear-amplifying-loop-mirror cavity operating at 1860 nm.

We demonstrate a polarization-maintaining (PM), all-fiberized, mode-locked thulium-doped fiber laser, providing a dissipative soliton with nJ-level pulse energy. The laser has a figure-of-eight cavity with a nonlinear amplifying loop mirror (NALM) as a saturable absorber. A bridge-fiber splicing method is applied to incorporate a commercial PM dispersion compensating fiber for cavity dispersion management. A fiberized Lyot filter is implemented in the cavity using PM single-mode fibers to facilitate dissipative-soliton mode-locked operation. Single-pulse, mode-locked operation is realized at a repetition rate of 15.5 MHz with an output power of 23.8 mW, corresponding to a pulse energy of 1.5 nJ. The output spectrum has a central wavelength of 1860 nm with a 3-dB bandwidth of 18.6 nm. The output pulses have a duration of 7 ps and can be compressed down to 539 fs using an external grating-pair compressor. The all-PM mode-locked thulium fiber laser is environmentally insensitive and shows good power stability, and offers great potential for use as a reliable laser source for biomedical imaging applications.