Output characteristics of a 2.05 μm narrow-linewidth small-signal thulium-doped fiber amplifier under different pumping schemes

This paper presents a study of the output characteristics of a 2.05 μm narrow-linewidth small-signal thulium-doped fiber amplifier under different pumping configurations. A 5 W seed source with a 2 kHz linewidth was modulated via an acousto-optic modulator and subsequently amplified in a fiber amplifier. Four pumping schemes were investigated: 1570 nm forward core pumping, 793 nm forward cladding pumping, simultaneous forward core-cladding pumping and forward core pumping combined with backward cladding pumping. Under conditions that suppress amplified spontaneous emission and stimulated Brillouin scattering, the corresponding output powers and slope efficiencies were 8.7 mW, 112 mW, 135 mW and 147 mW, and 0.4%, 5.5%, 5.6% and 6.1%, respectively. Among these, the scheme combining forward core pumping with backward cladding pumping demonstrated the best performance. The results demonstrate its potential as a high-power seed source for subsequent narrow-linewidth, high-energy fiber or solid-state amplification systems.