All-fiber mid-infrared supercontinuum generation with high coherence in chalcogenide fiber pumped by 2.8 µm Raman femtosecond solitons

Abstract

We present an all-fiber mid-infrared supercontinuum (MIR-SC) generation in As₂S₃ chalcogenide glass fiber, powered by a 2.8 µm femtosecond laser generated through the soliton self-frequency shift (SSFS) effect in fluoride fiber. To ensure high-quality femtosecond laser pulse production, we thoroughly investigated the SSFS effect in three types of fibers using 2.0 µm femtosecond laser as pump source. Ultimately, we obtained 2.8 µm soliton pulses with an average power of 241 mW, a conversion efficiency of 42.5 % and a peak power reaching 36.5 kW in an 8 m-long ZrF₄-BaF₂-LaF₃-AlF₃-NaF (ZBLAN) fiber. By injecting the 2.8 µm pulses into a segment of As₂S₃ fiber, where this wavelength situated rightly in the normal dispersion region of this fiber, a SC spanning from 1.83 to 4.0 µm was generated with excellent spectral flatness. Furthermore, we simulated the spectral evolution of the pulses in the As₂S₃ fiber, the simulation results showing strong agreement with experimental observations. The spectral coherence factor ${|g}_{12}^{\left(1\right)}|$ was estimated close to 1 across the entire spectral range, indicating a good coherence of this SC.