Radial and axial photonic galleries of dielectric rings

Abstract

A new picture of the photonic eigenmodes of dielectric rings with a rectangular cross section is presented, which is fundamentally different from those of whispering gallery modes of the disc. The low-frequency photonic spectrum is formed by two types of galleries: one type begins with radial Fabry-Pérot-like resonances, and the other with axial Fabry-Pérot-like resonances, in both cases the galleries continue with a set of equidistant longitudinal modes. The new results are: (1) a linear dependence of the wavelength of radial and axial Fabry-Pérot-like resonances on the width or height of the ring, respectively, has been demonstrated; (2) it is established that all longitudinal resonances follow the spectral shifts of the corresponding Fabry-Pérot-like resonances when the width or height of the ring changes, i.e. each gallery is a separate photonic package. As a result, galleries can intersect in parametric space, leading to impressive resonance effects, including bound states in the continuum. The analysis is based on numerical calculations and experiments in near- and far-fields. Our results open the door to new fundamental phenomena and enhanced functionality of dielectric ring resonators.