Hollow Core Bragg Fibers With a Heterostructured Cladding Based on Ternary One-Dimensional Photonic Crystal for Mid-infrared Broadband and Low-Loss Transmission

We propose a hollow core Bragg fiber (HC-BF) with a heterostructured cladding based on the ternary 1-D photonic crystal (T-1DPC) in this paper. The distinguishing ternary unit cell of T-1DPC is formed from a polyetherimide (PEI) layer sandwiched by two As₂Se₃ layers of the same thickness. We demonstrate its capability for mid-infrared broadband and low-loss transmission by numerically simulating and analyzing the omnidirectional photonic bandgap (OPBG) and the modal loss characteristics. The results show that the T-1DPC-based heterostructured cladding can effectively broaden the OPBG, which is only due to the blue-shift of the lower bandgap edge wavelength. Compared with that for the binary-1DPC-based HC-BF, the transmission loss for the T-1DPC-based HC-BF can be reduced by three orders of magnitude over most of the OPBG range. The large loss contrast is essentially attributed to the enhancement of the multilayer reflection from the T-1DPC-based cladding. Most notably, for a T-1DPC-based cladding with three groups, the transmission band with loss lower than 0.01 dB/m for the HE₁₁ mode can cover almost the whole 3 to 5 μm range, with the exception of several loss peaks near the short-wavelength edge. Even with the cladding material absorption included, the transmission loss for the HE₁₁ mode in the T-1DPC-based HC-BF can be still lower than 0.1 dB/m over the whole OPBG range.