Stable, precisely controlled, and switchable thulium-doped fiber laser based on cascaded mode interference filters

This research experimentally demonstrates a switchable, single-wavelength, thulium-doped fiber laser based on the cascading of a multimode-single-mode-multimode (MSM) fiber filter and a two-mode fiber (TMF) filter. When the MSM fiber filter suffers from bending, the blue-shift of the output spectrum can be obtained. A switchable lasing wavelength output is realized by bending the MSM fiber filter to cover different channels of the TMF filter. The output wavelength can be switched from 1982.54 to 1938.81 nm with an optical signal-to-noise ratio of higher than 40 dB. The wavelength interval of the switchable output is an integral multiple of the wavelength interval of the TMF filter. The stability of the output wavelength was tested within 60 min, and the wavelength shift and output power fluctuation were found to be less than 0.01 nm and 0.31 dB, respectively, which demonstrates a stable output performance.