Towards high-power all-fiber 2–5 μm supercontinuum generation in step-index chalcogenide fiber

Fiber-based mid-infrared supercontinuum (SC) sources benefit from their flexible structure and good beam quality that are suitable for spectroscopy and metrology. Chalcogenide fibers are good candidates for MIR SC generation because they exhibit high nonlinear refractive indices and wide transmission range. Due to the lack of robust MIR pump lasers, most of the current chalcogenide fibers based SCs have to adopt free-space complex and expensive optical parametric amplifiers as the pump light, with the sacrifice of the robustness and compactness. In this paper, an all-fiber based spectrally-flat 2-5 pm SC laser with high-power is reported in cascaded fluoride and chalcogenide step-index fibers. An all-fiber fluoride fiber based SC laser which spans from 2-4.2 pm is used as the pump light, which is then pumped into a step-index As
₂
S
₃
fiber with core diameter of 7 pm to generate the final SC laser with spectrum beyond 5 pm. The pump coupling to the As
₂
S
₃
fiber is realized with two methods separately. With the setup of aspheric lens coupling, the obtained SC laser has a 10 dB spectral bandwidth of 3000 nm spanning from 2050 to 5050 nm, corresponding to an average power of 57.6 mW. While with the all-fiber mechanical splicing, the 10 dB spectral bandwidth of the SC laser shrinks slightly, spanning from 2140 to 4980 nm range, and the average output power is further scaled up to 97.1 mW. To the best of our knowledge, it is the first time that a real high-power all-fiber chalcogenide-based MIR SC laser is present with flat spectrum beyond 5 pm. It offers a practical solution for high-power robust and reliable 2-5 pm broadband fiber laser.