| Supercontinuum is broadband and coherent light generated by propagating intensive optical pulses through a highly nonlinear medium.This phenomenon is caused by the interaction of nonlinear effects such as self-phase modulation,cross-phase modulation,stimulated Raman scattering and four-wave mixing in pulsed laser in nonlinear media,which leads to the widening of the supercontinuum.The mid-infrared spectral region is of great technical and scientific interest because most molecules display fundamental vibrational absorptions in this region.The supercontinuum across the mid-infrared molecular ‘fingerprint region'(2?16?m),which is a key importance for applications such as early civil,aerospace,military,medical and other fields.It has been widely used in the fields of fluorescence imaging,total reflection fluorescence microscopy(TIRF),fluorescence lifetime imaging(FLIM),optical coherence tomography(OCT),molecular recognition and infrared directional confrontation.However,chalcogenide glasses are promising for broadband SC generation due to their high third order nonlinearity,low nonlinear absorption and wide transmission window from 1 to 20?m depending on the compositions of the glasses.These properties make chalcogenide glasses ideal for the generation of broadband MIR SC.Due to materials dispersion,zero dispersion point(ZDW)of traditional structural ChG glass fiber is generally at more than 5?m in the far infrared region.The reason why the commercially available pumping sources with a wavelength of 1.5 or 2.0?m are unable to achieve a flat and wide spectrum lies in that the cascade SRS and SPM nonlinear effect in optical fiber in is limited.The tapered fiber technology is an important fiber post processing method.By means of tapering,sulfur-based fiber can control fiber dispersion and nonlinear flexibly,which is expected to achieve the development of all fiber mid infrared supercontinuum source.At present,most of international reports tend to adopt as containing chalcogenide glass(such as As2S3 or As2Se3)as matrix material of optical fiber.However,there exist potential risks in the process of preparing materials for glass fiber,drawing and subsequent tapering.Meanwhile,chalcogenide glass third order nonlinear coefficient of chalcogenide glass which contains as also needs to be improved.Ge-Sb-Se glass is a kind of environment-friendly and new chalcogenide glass system,which has good mechanical properties and infrared optical properties,higher thermal stability,excellent viscosity and temperature characteristics.But so far,there have been no reports about studies on the preparation of Ge-Sb-Se glass fiber taper or the output characteristics of infrared supercontinuum.Based on literature studies on the mid-infrared supercontinuum of the pyramid-type sulfur fiber,the present paper carries out the preparation of Ge-Sb-Se tapered optical fiber,and explores deeply about the sulfur-based fiber drawing process.Employing Rsoft optical software,the group velocity dispersion of Ge-Sb-Se sulfur-based tapered optical fiber is simulated,and then calculated and analyzed.At the same time,Mode Solutions optical software is used to analyze chalcogenide transition region of the tapered fiber in intensity and cone energy transmission efficiency.Finally,the femtosecond laser pumping Ge-Sb-Se sulfur-based tapered fiber is used to achieve the output of mid-infrared supercontinuum. |
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