Rigorous sufficient conditions for index-guided mode in microstructured dielectric waveguides

TL;DR

This paper establishes rigorous sufficient conditions for the existence of index-guided modes in complex dielectric waveguides, including photonic-crystal fibers and anisotropic structures, using a variational proof method.

Contribution

It introduces a general, rigorous criterion for mode guidance in diverse dielectric waveguides, extending beyond traditional conditions.

Findings

Guarantees cutoff-free index-guided modes under certain conditions

Provides guidance criteria for structures with averaged refractive index increase

Uses a variational method inspired by quantum mechanics localization proofs

Abstract

We derive a sufficient condition for the existence of index-guided modes in a very general class of dielectric waveguides, including photonic-crystal fibers (arbitrary periodic claddings, such as ``holey fibers''), anisotropic materials, and waveguides with periodicity along the propagation direction. This condition provides a rigorous guarantee of cutoff-free index-guided modes in any such structure where the core is formed by increasing the index of refraction (e.g. removing a hole). It also provides a weaker guarantee of guidance in cases where the refractive index is increased ``on average'' (precisely defined). The proof is based on a simple variational method, inspired by analogous proofs of localization for two-dimensional attractive potentials in quantum mechanics.