Watt-level ultra-flattened mid-infrared supercontinuum with high power stability generation in an all-fiber structured Tm-doped fiber amplifier pumped ZBLAN single-mode fiber

Abstract

We demonstrate a 5-watt-level mid-infrared supercontinuum (MIR-SC) generation in a Tm-doped fiber laser (TDFL) pumped single-mode ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber. In the optimization of front end 2 µm laser system, the laser energy-transfer efficiency from 1.55 µm to 2 µm was improved to 25 % by using a 4 m-long single-mode Tm-doped fiber (SM-TDF), in combination with a tailored broad-band pass filter (bandwidth>1.8 µm), the pulse spectrum was well shaped, the spectral contrast was substantially improved and the follow-up laser amplification efficiency was significantly optimized. In the realization of all-fiber structured MIR-SC power boosting process, we successfully achieved the high robustness and ultra-low loss fusion splicing point between silica and ZBLAN fiber in the high power measurement condition. By comprehensively taking the above-mentioned measures, we eventually obtained a MIR-SC covering 1.9 µm to 4 µm, with average power as high as 5.4 W, power stability with a root mean square (RMS) value of 0.03 % in 2 h, spectral fluctuation less than 0.1 dB in the wavelength range from 2.1 µm to 3.5 µm and without any residual pump peaks appeared in the spectrum. To the best of our knowledge, this is the first investigation on the all-fiber structured MIR-SC generation with so high the long-term power stability and spectrum flatness simultaneously in average power of above 5-Watt level.