用于高相干中红外SC谱产生的全正色散硫系光纤研究

The mid-infrared (MIR) region (2-16 μm) is of great importance because most molecules display of fundamental vibration absorption spectra located in this region, leaving distinctive spectral fringerprints, which can also be adopt to track the scent of greenhouse gases, CO2 , CH4 and others in monitoring global warming. As a broadband light source, the coherence property of supercontinuum(SC) is important for its applications such as frequency metrology, coherent spectroscopy. The SC spectra generated in normal dispersion regime can keep the coherence property of the pump laser because self-phase modulation (SPM) and optical wave breaking (OWB) are self-seeded processes. Usually, pumping fibers with all-normal dispersion (ANDi) by femtosecond lasers is commonly used for coherent SC generation..Chalcogenide (ChG) fibers are good candidates for MIR SC generation. But they are confused by the multiphonon absorption band of Se-Se above 12 μm. And the fabrication of ANDi ChG fiber is the most challenge work to date. .In this project, a low-loss ANDi step-index Te-based ChG fiber without containing Se will be designed and fabricated. The zero dispersion wavelength (ZDW) of the fiber will be shifted from 10.5 μm to 16 μm (beyond its transmission range) based on its large material dispersion (>10.5 μm). Multiple-clad will be introduced and optimized to enlarge waveguide dispersion. Coherent SC generation will be investigated by pumping the fiber with femtosecond pulses out from optical parametric amplifier (OPA). Through aiming at breaking the development bottleneck of long-wavelength infrared, resolving the lack of high nonlinear fiber for MIR SC generation, clarifying the physical mechanism and regulation mechanism of dispersion and nonlinear effects in Te-based ChG fiber, and resolving the entanglement of nonlinearity in coherent SC generation, this project will provide a high-performance nonlinear fiber for MIR SC source, and lay a solid scientific foundation for the application of MIR laser, as well as boost the development in long-wavelength infrared.

中红外（2-16μm）光谱学需要高相干的中红外超连续谱（SC）光源。全正常色散光纤对于高相干SC谱光源具有关键作用。针对现有中红外光纤材料缺乏和全正色散微结构光纤的制备难题，本项目提出基于大材料色散零点的Te基硫系玻璃，利用色散位移获得全正色散阶跃型Te基硫系光纤(无Se)的制备方案，围绕低损耗全正色散Te基硫系光纤的结构设计和正色散区频谱展宽作用机理的两个关键科学问题，通过对高色散Te基硫系玻璃的组分优化和多包层结构设计实现16μm处色散零点，采用飞秒激光+OPA泵浦获得高相干中红外SC输出，皆在突破现有长波红外技术的发展瓶颈，解决“中远红外SC光源”发展过程中缺乏高性能非线性光纤可用的材料难题，阐明Te基光纤中色散管理与高非线性效应作用的物理规律和调控机制，解决激光SC谱产生的非线性机理纠缠、光学选频不定和状态难控的科学难题，为中红外激光技术向长波红外区域延伸奠定坚实的科学基础。

中红外（2-16微米）光谱学需要高相干的中红外超连续谱（SC）光源。全正常色散光纤对于高相干SC谱光源具有关键作用。针对现有中红外光纤材料缺乏及全正色散微结构光纤的制备难题，本项目提出了基于大材料色散零点的Te基硫系玻璃研究，利用多包层光纤结构的色散位移设计以实现全正色散Te及硫系光纤的研究方案，围绕低损耗全正色散Te基硫系光纤的结构设计和正色散区频谱展宽作用机理的两个关键科学问题，基于大材料色散Te基硫系玻璃的大材料色散零点特性，设计并优化了W型多包层光纤结构实现了光纤色散零点红移至16微米以远，同时优化了玻璃组分、改进了熔制工艺制备了高纯高均匀性Te基硫系玻璃，改进挤压工艺制备了芯包界面完美无缺陷的光纤预制棒，辅以聚合物涂覆保护制备了低传输损耗的实用型全正色散Te基硫系光纤，光纤的工作波段为3.5-12微米，最低损耗0.69dB/m，从数值模拟和实验两方面研究了该光纤在飞秒脉冲泵浦下的频谱展宽特性，采用OPA激光泵浦获得了谱宽覆盖2-14微米波段的超平坦、高相干中红外SC谱。通过该项目的执行，我们掌握了W型多包层结构光纤的色散补偿特性设计，初步探明了Te基硫系光纤中的色散管理规律与非线性效应作用机制；为中红外激光技术向长波红外区域的延伸奠定了良好的先行基础。