Near-bound states in the radiation continuum in circular array of dielectric rods

TL;DR

This paper investigates near-bound states in the radiation continuum in circular arrays of dielectric rods, revealing how true BICs in linear arrays translate into high-Q near-BICs in circular configurations with exponential divergence of quality factors.

Contribution

It analytically and numerically demonstrates the existence of near-BICs in circular arrays, showing their divergence behavior and the ability to tune non-symmetry protected near-BICs.

Findings

Near-BICs have exponentially large quality factors with increasing array size.

Symmetry protected near-BICs diverge as e^{λN} where λ depends on material properties.

Non-symmetry protected near-BICs can be tuned by adjusting rod radii.

Abstract

We consider E polarized bound states in the radiation continuum (BICs) in circular periodical arrays of $N$ infinitely long dielectric rods. We find that each true BIC which occurs in an infinite linear array has its counterpart in the circular array as a near-BIC with extremely large quality factor. We argue analytically as well as numerically that the quality factor of the symmetry protected near-BICs diverges as $e^{\lambda N}$ where $\lambda$ is a material parameter dependent on the radius and the refraction index of the rods. By tuning of the radius of rods we also find numerically non-symmetry protected near-BICs. These near-BICs are localized with exponential accuracy outside the circular array but fill the whole inner space of the array carrying orbital angular momentum.