中文摘要：

提出了一种包层周期呈线性啁啾分布的新型空心布拉格光纤（HC—BF）包层结构设计，旨在满足基于中红外吸收光谱的多组分痕量气体检测应用需求。数值研究了这种准周期包层结构H＆BF中近掠入射条件下TE和TM模的带隙结构和模式损耗特性，并与常规周期包层结构HC—BF进行了对比。结果表明，对于包层周期线性啁啾分布结构的HC—BF，通过增大包层周期线性增加量和包层层数均可以有效拓展光子带隙（PBG）宽度，并且其展宽效果随两者增加而明显增强，同时PBG中心波长产生红移。在展宽的PBG波长范围内，该新型包层结构HC—BF依然能够保持0．01dB／m量级的低传输损耗，表明其具有优良的中红外宽带低损耗传输特性。

英文摘要：

A novel design of hollow-core Bragg fibers （HC-BFs） with linearly-chirping distributed dielectric cladding is proposed, for demand of the multi-component trace-gas detection based on the mid-infrared （mid-IR） absorption spectrum. The photonic band-gap （PBG） structures and transmission-loss characteristics for the TE and TM modes under nearly glancing incidence condition in such a quasi-periodic HC-BF are numerically investigated and compared with a conventional one with periodic cladding. The results show that the quasi-periodic cladding can effectively enlarge the PBG width by increasing the linear increment of cladding period and dielectric-layer number. The enlargement effect enhances with the increment of both structure parameters. Meanwhile, the central wavelength of the PBG shifts to the longer wavelength. In the enlarged wavelength range of PBG, the HC-BF with linearly-chirping distributed dielectric cladding still has the low loss, in the order of 0.01 dB/m, showing the excellent performance of mid-IR low-loss broadband transmission.