Wavelength-Switchable Dual-Wavelength Fiber Laser at 2 μ m by Utilizing a Six-Mode Optical Fiber

In this study, a wavelength-switchable dual-wavelength thulium-doped fiber laser (TDFL) and holmium-doped fiber laser (HDFL) were presented. Dual-wavelength generation was achieved by utilizing the multimode interference (MMI) effect in a single-mode-six-mode-single-mode fiber structure, fabricated by splicing both ends of a six-mode fiber (6MF) to single-mode fibers (SMF). The output bandwidth of the TDFL and HDFL was 1954.65 nm to 1993.03 nm and 2068.63 nm to 2093.05 nm, respectively. A polarization controller (PC) was carefully adjusted to tune the output laser’s wavelength. Both setups demonstrated good stability, with SNR ranging from 48 to 55 dB for the TDFL and 41 to 50 dB for the HDFL. The power fluctuation was less than 1 dB. The maximum output power and slope efficiency of the TDFL were 24.3 mW and 5.90%, respectively, whereas those of the HDFL were 10.54 mW and 3.32%, respectively. A minimum linewidth of 0.07 nm was achieved across all wavelength configurations.