Selectively mode-locked high-order-mode 2-[formula omitted]m thulium fiber laser

Abstract

We report a high-power 2μm higher-order-mode thulium fiber laser passively mode-locked with a semiconductor saturable absorber mirror (SESAM). Based on both spatial-mode discrimination through tuning the SESAM’s feedback and spatial-mode-dependent spectral selection of a few-mode fiber Bragg grating (FBG), the fiber laser is stably mode-locked in the LP11 mode with average output power of 672 mW. The laser pulse has maximum pulse energy of 38.8 nJ with pulse duration of 3.93 ps, giving rise to peak power of 9.87 kW. In the LP11 mode-locked state, the laser wavelength has a single peak and is centered at 1939.5 nm with a spectral full width at half maximum (FWHM) of ∼2 nm. The laser beam quality M2 factor is measured to be 3.23 and 2.41 in the x and y directions, respectively. The LP11-mode-locked state is confirmed by both the spectral feature and beam profile of the output laser. This mode-locked higher-order-mode fiber laser thus provides a new and simple method to achieve mode-selective picosecond pulse generation from multimode fiber lasers.