The polarization-aided tunable high-power femtosecond Raman solitons generation from 1.96 to 3.1 μm in fibers cascaded system

•For the first time, verified the effects of incident pulse polarization on Raman solitons generation in fluoride fibers.•Achieved the mid-infrared Raman solitons with central wavelength continuously tunable from 1.96 to 3.1 µm.•Obtained the highest soliton power at 3.1 μm of above 350 mW, and pulse duration near 100 fs.•Built a widely tunable and almost all-fiber mid-infrared femtosecond-soliton laser source with high compactness. We present the demonstration of a polarization-aided high-power ultra-broadband tunable mid-infrared (MIR) Raman soliton-based femtosecond laser in fibers cascaded nonlinear system. We found and verified that the incident pulse polarization has effects on the characteristics of the Raman solitons generation in different types of fluoride fibers. For the first time to the best of our knowledge, we achieved the MIR Raman solitons with central wavelength continuously tunable from 1.96 to 3.1 µm by optimizing the input pulse parameters. The solitons with a maximum average power of above 350 mW, accounting for nearly 83% of the total output power, and the pulse width of these tunable Raman solitons remains below 200 fs. Thanks to the nearly all-fiber configuration, which results in the pump laser with root mean square (RMS) value of power fluctuation around 0.24% in 2 h, and the 3.1-µm soliton with far-field beam M2 value around 1.1. Additionally, the corresponding numerical simulations on these solitons radiation were also conducted, the results are in good agreement with the experimental one.