Femtosecond laser inscription of Bragg gratings in Tm³⁺-doped fluorotellurite glass fibers for lasing at 2.3 µm

In this paper, fiber Bragg gratings (FBGs) are inscribed in Tm³⁺-doped fluorotellurite glass fiber (TDFTF) and applied to construction of a 2.3-µm all-fiber laser. The FBGs with a center wavelength of 2.3 µm are fabricated by using the femtosecond laser point-by-point method combined with the slit beam shaping technique. Both the reflectivity and insertion loss of FBGs are investigated for different pulse energies, grating orders, and grating lengths. The FBG with a reflectivity of 90.4% is inscribed at one end of a 1.5-m-long TDFTF. Employing a 1410-nm/1570-nm dual-wavelength upconversion pumping technique, lasing at 2.3 µm is achieved. The maximum unsaturated output power is 1.88 W, and the slope efficiency is 37%. High stability has been demonstrated for both the wavelength and output power of the laser over an hour. This research is crucial for advancing the development of high-power fiber lasers operating at 2.3 µm.