Interpreting light guidance in antiresonant and photonic bandgap waveguides and fibers by light scattering: analytical model and ultra-low guidance

Here, we introduce a quasi-analytic model that allows studying mode formation in low refractive index core waveguides through solely focusing on the cladding properties. The model isolates the reflection properties of the cladding from the modes via correlating the complex amplitude reflection coefficient of the cladding to the complex effective index of the fundamental core mode. The relevance and validity of the model are demonstrated by considering a single-ring anti-resonant fiber, revealing unexpected situations of exceptionally low loss. Our model explains mode formation by light scattering, which conceptually provides deep insights into the relevant physics. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing