Fibers based on propagating bound states in the continuum

TL;DR

This paper demonstrates that circular arrays of dielectric cylinders can support nearly bound states in the continuum with extremely high Q-factors, enabling potential applications in novel optical fiber designs and orbital angular momentum transmission.

Contribution

The study introduces a new class of propagating nearly BICs in dielectric cylinder arrays with high Q-factors and explores their properties and potential applications in optical fibers.

Findings

Nearly BICs with Q-factors of order exp(λN) in dielectric arrays.

Identification of different types of nearly BICs and their decay properties.

Potential use of these modes for transmitting electromagnetic signals with orbital angular momentum.

Abstract

We show that a circular periodic array of $N$ dielectric cylinders supports nearly bound states in the continuum (BICs) propagating along the cylinders. These propagating nearly BICs with extremely large $Q$ factors of order $exp(\lambda N)$ are surrounded by resonant modes weakly leaking into the radiation continuum. We present leaky zones in the vicinity of different types of BICs: symmetry protected nearly BICs with the resonant width proportional to the squared propagation constant $\Gamma \sim k_z^2$, non-symmetry protected nearly BICs with finite propagation constant $k_c$ with $\Gamma\sim (k_z-k_c)^2$ and non-symmetry protected nearly BICs with $\Gamma\sim k_z^4$. The latter propagating nearly BICs can serve for transmission of electromagnetic signal paving a way to novel type of optical fibers. We also demonstrate weakly leaking resonant modes which carry orbital angular momentum.