Mid-infrared Supercontinuum Generation In As₂S₃ Fibers Pumped By Fiber Laser

Mid-infrared supercontinuum source which encompasses the molecular vibrational absorptions of numerous gases,liquids and solids make it having important application prospects in the fields of molecular spectroscopy,combustion monitoring,biomedical imaging,biology and chemistry sensing,early cancer diagnostics.All fiber-based supercontinuum sources benefitting from their good beam quality,improved special coherence and compact structure have become the hot topic of supercontinuum generation.In the pursuing of longer wavelength generation,chalcogenide glass fiber show its great potential in the production of mid infrared supercontinuum due to its high light transmittance and high nonlinear refractive index in mid infrared wave band.And it is the only nonlinear fiber which could expand supercontinum spectrum to longer than 10?m.This paper mainly focus on the supercontinuum generation in the As₂S₃ fiber with fiber based structure.And the study is shown below.1.A brief historical review of mid-infrared SC generation is present which including the research background and the applications of mid-IR SC sources.And the progress of infrared SC generation in soft glass fibers recently is gave.By comparing characteristic parameters of different kind of chalcogenide fiber like loss spectrum,group velocity dispersions,nonlinear coefficient,damage threshold and transformation temperature,finally As₂S₃ fibers are considered to be the nonlinear fiber for mid-IR SC generation.2.We investigate mid-infrared SC generation in a step-index As₂S₃ glass fiber directly pumped by a picosecond pump laser at 2?m.The core diameter of the step-index As₂S₃ fiber is 9?m?170?m cladding?while the NA of it is 0.3.Given the relative large core diameter and high NA,the As₂S₃ fiber is few-moded at 2?m.By adjusting the butt-coupling position to avoid excitations of higher order modes and cladding mode meanwhile increasing coupled power of fundamental mode,an efficient cascaded SRS related SC with at least five Stokes peaks and 366 mW output power was achieved.3.Methods to obtain mid-infrared supercontinuum in As₂S₃ fiber by cascade a nanosecond shortwave-infrared supercontinuum pump source are proposed.Supercontinuum sources spanning from 2 to 4?m are demonstrated in As₂S₃ fibers with different core diameters of 7?m and 9?m.Most of the power is converted into the mid-infrared region through successive spectral red-shifts.The maximum output power of the mid-infrared supercontinua is¹40 mW.Experimental investigation of fusion splicing between silica and chalcogenide fiber are carried out.By optimizing splice parameters,a low-losst fusion splicing of silica to chalcogenide fiber is realized.The splicing loss is about 0.2 dB.A 1.8 to 4.2?m high-mode mid-infrared supercontinuum is presented in an all-fiber chalcogenide-based system with output power of 133 mW.The stability of the supercontinuum source is improved.In addition,the beam profile of the output SC demonstrated its high-mode operation within the wide spectral range between 1.8 to 3.5?m.Furthermore,the cause of the damage on splicing point is analyzed and some improvement is proposed.