530 W all-fiber continuous-wave Tm-doped fiber laser

Abstract

In the past decades, thulium-doped fiber lasers (TDFLs) operating in an eye-safe range have attracted considerable attention, for they have extensive applications such as LIDAR, free space communication, medical diagnostics and pumping source for holmium-doped fiber laser or optical parameter oscillator. In this paper, we report a high power all-fiberized TDFL based on main-oscillator power-amplifier (MOPA) configuration. The preform is fabricated by the modified chemical vapor deposition method combined with solution doping technique and drawn into a core/clad size of 25/400 μm. The numerical aperture of the TDF is 0.1. The concentration of Tm<sub>2</sub>O<sub>3</sub> and Al<sub>2</sub>O<sub>3</sub> are 2.6 wt% and 1.01 wt%, respectively, measured by an electron probe micro-analyzer. The cladding absorption is 3 dB/m at 793 nm measured by cut-back method. The oscillator consists of 8 m 25/400 TDF mentioned above and a pair of fiber Bragg gratings. The oscillator yields maximum power of 91 W with pump power of 202 W and a 3 dB spectral bandwidth as narrow as 75 pm. In the amplifier stage, the bi-directional pumping scheme is employed. The narrow linewidth seed with output power of 57 W is scaled to 530 W through one-stage amplification, corresponding to a slope efficiency of 50%. The central wavelength of the Tm-doped MOPA is 1980.89 nm and the linewidth is broadened to 0.11 nm at 530 W. The measured <i>M</i> <sup>2</sup> factor at 100 W is less than 1.3. Neither obvious amplified spontaneous emission nor non-linear effect is observed, and the output power is only limited by pump power. To the best of our knowledge, this is the highest output power of TDF at present.