Broadband mid-infrared hollow core photonic bandgap fiber for multicomponent trace-gas sensing

As a class of hollow core photonic bandgap fiber (HC-PBGF), hollow core Bragg fibers (HC-BFs) with broadband transmission for multi-component trace-gas sensing have attracted much interest in recent years. In this paper, we numerically investigate the PBG characteristics of HC-BFs with the conventional periodic cladding (CPC) and with our previously proposed linearly-chirped cladding (LCC). The results show that the LCC structure is more suitable for broadening the omnidirectional PBG (OPBG) range by regulating the linear increment of cladding period or the layer number, which provide us with more degrees of freedom for designing a broadband HC-BF. Based on that, an optimized Te/PS (tellurium/polystyrene)-based HC-BF with the LCC for the wavelength range of OPBG covering the whole range of 3 to 5um is designed. Moreover, by using the ray-optics method, the transmission loss of HE11 mode is also calculated, verifying the feasibility of the Te/PS-based LCC with mid-infrared broadband low-loss transmission ranging from 3 to 5 mu m.