Watt-level ultra-flat wideband supercontinuum generation in GeO2 fiber by femtosecond

The high-power ultra-flat supercontinuum (SC) sources play an important role in various fields. In this letter, we experimentally demonstrated an all-fiber, high-power, ultra-flat SC source in GeO2 highly nonlinear fiber (HNLF) pumped by a femtosecond fiber laser system. The system is mode-locked by a semiconductor saturable absorber mirror with an all-polarization-maintaining (PM) structure. Based on the technology of chirped pulse amplification, a maximum power of 3.12 W was realized with a repetition rate of 80 MHz at 1.56 mu m, and the pulse duration was compressed to 124 fs in a segment of PM single-mode fiber. Furthermore, by optimizing the length of the HNLF, a wideband SC spectrum of nearly 700 nm was obtained at10 dB with a maximum power of 1.82 W, and the flatness of the spectrum was better than 5 dB in the range of 1600-2200 nm. We observed that the pulse evolved into a noise-like pulse with a narrowest pulse duration of 62 fs. Thanks to the all-PM structure of the fiber laser, the long-term stability of SC power was manifested with a relative fluctuation as low as 0.53 % over 6 h.