Effects of thulium (Tm) concentration and numerical aperture on the gain of thulium doped fiber amplifier (TDFA) for amplification in 2 µm region

Abstract The effect of numerical aperture and doping concentration of thulium on the gain of TDFA with a single pump is investigated in this paper. Thulium doped fiber length of 10 m is analyzed for commonly used optical pumps of 1050 nm, 1560 nm, 1700 nm, and 1740 nm wavelengths with a power of 100 mW. Also, the thulium concentrations of 15.6 × 1024 m−3, 20 × 1024 m−3, 30 × 1024 m−3, and 40 × 1024 m−3, and numerical apertures of 0.3 and 0.4 are tried for each pump wavelength. It has been found the conventional 1050 nm pump is the least efficient. And in all the cases, the 0.4 numerical aperture is resulting in better gain as compared to the numerical aperture of 0.3. The results in terms of gain are compared for all pumping cases. It is observed that the highest gain of 28.27 dB is obtained at 1830 nm wavelength using pump wavelength of 1740 nm when the doping concentration of 40 × 1024 m−3 and numerical aperture of 0.4 is selected.