Generation of tunable Raman soliton and dispersive wave beyond 4 μm in centimeter-length fluorotellurite fibers.

3-5-μm mid-infrared (MIR) ultrafast laser sources have garnered significant attention due to their critical applications in spectroscopy, environmental monitoring, and imaging. However, 4-5-μm compact fiber laser sources remain a significant technological challenge due to the lack of MIR fibers with good chemical stability, thermal stability, high nonlinearity, and low loss. Here, we develop fluorotellurite fibers based on 60TeO2-20BaF2-10AlF3-10Y2O3 (TBAY) glasses with a wide transmission window, demonstrating tunable Raman soliton and dispersive wave (DW) generation beyond 4 µm in centimeter-length fluorotellurite fibers pumped by a 3.54 μm femtosecond laser source. Fluorotellurite fibers with a loss of 0.39 dB/m were fabricated using a rod-in-tube method. The high numerical aperture (NA ~ 1.1@3.5 μm) of TBAY fibers allows the zero-dispersion wavelength (ZDW) to be tuned over a wide range by varying the core diameter of the fibers. The dispersion-engineered TBAY fibers with a core diameter of 6.5 μm enabled 4584 nm Raman soliton generation, while fibers with a core diameter of 3 μm enabled 4177 nm DW generation. We conducted detailed experiments to investigate the influence of pump power and fiber length on SSFS and dispersive wave dynamics. Theoretical analysis and numerical simulations based on the generalized nonlinear Schrödinger equation corroborate the experimental results. Our results show that TBAY fibers are promising nonlinear media for constructing compact ultrafast laser sources in the 4-5 μm wavelength range.