Switchable and tunable thulium-doped fiber laser based on mode interference filter

Abstract A cladding pumped thulium-doped fiber laser with tunable and switchable output was demonstrated. The single-mode-multimode-single-mode (SMS) fiber filters with different lengths of multimode fiber were fabricated and the tunability of the laser by axial strain with a sensitivity of ∼ 2.4 pm/μe was demonstrated experimentally. Single-wavelength output with an optical signal-to-noise ratio (OSNR) of up to 70 dB and a small tuning range of 2.76 nm was obtained. The fluctuations of the center wavelength and output power within 60 min were less than 0.04 nm and 0.27 dB, respectively, and the tuning sensitivity was ∼ 2.3 pm/μe. When the laser was operated in the dual-wavelength output mode, the OSNR reached 60 dB and the fluctuation of the output power was less than 1.53 dB within an observation time of 60 min. Furthermore, the output power was scaled up to 308 mW by changing the output coupling ratio and the different samples of SMS fiber filter were also applied in the fiber laser cavity to obtain different lasing channels. The proposed fiber laser is suitable for applications in sensing and communication systems.