Coexistence of Photonic Bandgap Guidance and Total Internal Reflection in Photonic Crystal Fiber Based on a High-Index Array With Internal Air Holes

We show that both photonic bandgap guidance and modified total internal reflection can simultaneously occur in a chalcogenide-tellurite photonic crystal fiber (PCF) whose cladding is composed of a high-index array with internal regions being air. The coexistence of these two guidance mechanisms is corroborated by numerical simulations based on a plane wave expansion method and an analytical model. Despite being scalar and for high-index contrast material systems, the analytical model can accurately predict the band structures of the PCF. A PCF with seven ring units removed as the fiber core is designed to guide in the 580-950-nm wavelength range by the photonic bandgap effect and in the 2.0-4.6-μm wavelength range by total internal reflection. Such a PCF can be an interesting platform for nonlinear phenomena occurring across the two guidance regions.