Numerical Demonstration of the Soliton Self-Frequency Shift Process Beyond 8 μm in a Tellurite-Chalcogenide Fiber Cascaded Structure

We investigate theoretically the mid-infrared (MIR) Raman soliton self-frequency shift (SSFS) process in the TeO
₂
-BaF
₂
-Y
₂
O
₃
(TBY) fiber and AsSe
₂
-As
₂
S
₅
fiber. The numerical analysis of the SSFS process in the TBY fiber is performed, revealing the impacts of the pumping wavelength and fiber core diameter on the SSFS effect. A new quantity measuring the frequency shift ability of a Raman shifter fiber is derived to interpret the complex relation between the frequency shift amount and the fiber parameter observed in simulations. Further, we propose some general ways to optimize the wavelength extension, conversion efficiency, pulse duration, and spectrum cleanliness for all Raman soliton lasers. For the first time, we propose the idea of coupling the tellurite fiber with chalcogenide fiber to further enhance the SSFS effect in MIR. With experimentally achievable high-power seed pulses at 1.9
μ
m and 2.8
μ
m, we demonstrated wavelength conversion from 1.9 to 7.5
μ
m and 2.8 to 8.1
μ
m through the SSFS process by cascading the TBY fiber with a AsSe
₂
-As
₂
S
₅
fiber in suitable coupling parameters. Our work could offer meaningful guidance to optimize the Raman soliton lasers and enlighten a feasible way to extend the SSFS process to a longer wavelength range.