Thulium doped all-fiber laser based on a double-cladding Bragg grating via femtosecond laser plane-by-plane writing technology.

Abstract

The fiber Bragg grating (FBG) is fabricated by the femtosecond laser writing technique with a plane-by-plane (Pl-by-Pl) method in the double-cladding fiber (DCF). The refractive index modified (RIM) region formed by this method is 12 μm × 8 μm in size. Due to the Pl-by-Pl method, high-order Bragg resonances with reflectance greater than 99% can be achieved. The fabricated high-quality FBG features a narrow full width at 3 dB bandwidth of approximately 0.45 nm, a high reflectivity above 99%, and almost no side-mode peaks. To investigate the application of fabricated FBGs, we have built a thulium-doped all-fiber oscillator with purely forward-pumped structures. A thulium-doped fiber laser (TDFL) at a central wavelength of 1953.79 nm was constructed by using the prepared fiber grating. The signal-to-noise ratio (SNR) is above 56 dB. When the pump power is 19 W, the total output power of the continuous wave is 4 W, and the output efficiency is 25.6%. In addition, the numerical calculation has been carried out to further optimize the output power. This work provides a possible approach for designing and implementing a continuous Tm-doped fiber laser with enhanced output efficiency.