1.7-μm thulium fiber laser with all-fiber ring cavity

A 1.7-mu m thulium-doped all-fiber laser based on a ring-cavity configuration is demonstrated. The longwavelength lasing near the 1.9-mu m thulium emission peak was suppressed using a wavelength division multiplexer and single-mode-multimode-single-mode (SMS) fiber device, both of which served as a short-pass filter instead of the grating devices usually used in 1.7-mu m thulium fiber lasers. A stable hundred-milliwatt-level 1720-nm laser output with a narrow spectral linewidth on the order of gigahertz was obtained after the optimization of the output coupling, active fiber length, and SMS device. With a cascaded SMS filter, the output power was further scaled to 227 mW under a launched 1570-nm pump power of 2.8 W, while the slope efficiency was 10.3%. The wavelength coverage could be further extended by using different SMS devices and applying tension on them.