中红外低损耗全硫系玻璃Bragg光纤隔离挤压制备及带隙特性研究

The development of mid-infrared (MIR) (2-16 μm) was strongly depended on the exploration of low-loss MIR flexible fiber, which is of the main concern as that most molecules fingerprint region were located with fundamental vibration absorption, which can also be adopt to track the scent of greenhouse gases in monitoring global warming. In cases of shortages of MIR low-loss fiber material and fabrication technology of IR photon bandgap fiber (conventionally air-core and polymer-cladding), a new Bragg fiber is proposed here for the aim of high power IR laser transmission, whose claddings are composed of multi-layered and refractive-index-contrasted chalcogenide glass-films, which arouse a wide photon bandgap and much transparence to the IR laser of specialized wavelength; then, a novel isolated extrusion technique will be adopt to the fabrication of hollow core Bragg fiber with all-chalcogenide glasses as cladding. With those well-designed parameters of contrastive refractive index of cladding glasses, period number and thickness, air core diameter, the fiber bandgap and transmission mode will be adjusted, for the aim of specialized IR laser transmitting with low loss and low-order mode. Basically, those are important for exploring the photonics bandgap principle and fluid molding mechanisms of this fiber, uncovering the relationship among bandgap width/depth and fiber parameters, such as cladding glass compositions, index contrast, period number and structure defect. And then, with the help of glass compositions optimizing based on high index Te-based chalcogenide glass and low index chalcohalide glass, structure designing of periodic cladding, core diameter customizing and heat &fluent processes analyzing, a precise extrusion technique will be adopted to the fabrication of fiber preform with isolated multi-layers, succeeded by a controllable fiber drawing. It is expected to solve the problem that there is no flexible fiber available to transmit MIR high power laser, i.e. achieving the goal of transmitting a specialized IR laser with low-loss and high optical quality, making a breakthrough in the bottleneck of MIR laser transmission, declaring the regulatory of photon crystal in MIR waveguide, solving the problems of blending waveguide modes, low threshold of power limit and bad flexibility of the current waveguide medium to the MIR high power laser, paving the way for expanding the application of MIR laser more conveniently.

分子指纹和温室气体检测技术发展的核心任务之一是开发中红外(2-16µm)低损耗柔性传导光纤。针对目前中红外低损耗光纤材料缺乏、聚合物Bragg光纤红外透过局限、玻璃流体成型和缺陷对带隙影响机理不明等问题，本项目提出采用大折射率差硫系玻璃组合做为包层制备红外宽带隙空心Bragg光纤。阐明短玻璃的高温流体成型机理，探明玻璃种类、折射率差、光子周期和缺陷等参数对Bragg光纤带隙宽度、深度（对应光纤损耗）的调控机理。通过高折射率Te硫系玻璃和低折射率硫卤玻璃的组分优化、光纤结构设计和玻璃热流体成型控制的机理分析，开发出针对Bragg光纤的分层隔离挤压和可控拉丝工艺，实现中红外关键波段激光的低损耗光纤传输，突破中红外激光集成技术的发展瓶颈，解决当前中红外高功率激光器传输中波导模式混乱、损耗高、阈值功率低和柔韧性差等科学难题，为中红外激光技术更广泛应用奠定坚实的科学和材料基础。

针对中远红外硫系玻璃基质材料的键力弱、激光损伤阈值低、光纤成型困难等问题，本项目瞄准中远红外高性能光纤的迫切需求，在宽带隙、低损耗硫系玻璃光纤开发领域，围绕高纯硫系玻璃准备、低损耗阶跃硫系光纤制备、新型微结构光纤开发、光子带隙型硫系Bragg光纤等基础研究领域，积极探索适合于微结构光纤制备的红外硫系玻璃组分优化，涉及各种低损耗的S、Se、Te硫系玻璃组分，同时开展适合于高能激光传输应用的新型硫系玻璃组分优化及玻璃光学光谱性质研究，对常用的As-S，As-Se，Ge-As-S，Ge-As-Se，Ge-As-Se-Te等易于成纤的红外硫系玻璃组分进行了优化，优化光纤制备工艺，并利用新型挤压法制备出了完美结构的芯-包层结构的硫系玻璃光纤，进而开发出低损耗的硫系光纤，其损耗最低可至0.2dB/m@4µm，然后根据挤压过程的流体不变原理又开发出低损耗的硫系悬吊芯、多包层及Bragg光纤。利用光纤的微结构设计实现了光学性能的灵活调控。研究成果发表在Optics Letters, Journal of Lightwave Technology、物理学报等国内外知名学术期刊上，合计35篇（其中SCI二区以上9篇），封面论文1篇，ESI高被引论文1篇，并申请10项中国/美国专利。项目主持人于2020年获批浙江省万人计划“青年人才”计划资助，受邀在国内外学术会议上做邀请报告9次。项目执行期间共培养博士研究生4名，硕士研究生21名，其中赵浙明获2019年浙江省优秀博士学位论文提名论文，焦凯和钟明辉分别获2021年和2022年浙江省优秀硕士论文。