High-Q supercavity modes in subwavelength dielectric resonators (1706.02099v1)

Abstract: Recent progress in nanoscale optical physics is associated with the development of a new branch of nanophotonics exploring strong Mie resonances in dielectric nanoparticles with high refractive index. The high-index resonant dielectric nanostructures form building blocks for novel photonic metadevices with low losses and advanced functionalities. However, unlike extensively studied cavities in photonic crystals, such dielectric resonators demonstrate low quality factors (Q-factors). Here, we uncover a novel mechanism for achieving giant Q-factors of subwavelength nanoscale resonators by realizing the regime of bound states in the continuum. We reveal strong mode coupling and Fano resonances in high-index dielectric finite-length nanorods resulting in high-Q factors at the nanoscale. Thus, high-index dielectric resonators represent the simplest example of nanophotonic supercavities, expanding substantially the range of applications of all-dielectric resonant nanophotonics and meta-optics.

• The paper demonstrates that bound states in the continuum enable high-Q supercavity modes in subwavelength dielectric resonators, achieving Q-factors up to 65,000.
• The paper employs resonant-state expansion and mode-coupling analysis to show that precise geometric tuning of high-index materials like silicon minimizes radiation losses.
• The paper's findings offer significant implications for low-loss photonic device development, impacting sensing, lasing, and on-chip integration.

High-Q Supercavity Modes in Subwavelength Dielectric Resonators

In recent years, nanophotonics has expanded its utility and application by exploiting strong Mie resonances in dielectric materials. The paper "High-Q supercavity modes in subwavelength dielectric resonators" authored by Rybin et al. explores the specific mechanisms that enable enhanced light confinement in subwavelength dielectric resonators, achieving exceptionally high quality factors (Q-factors) through the realization of bound states in the continuum (BIC). This paper highlights a potential for significant practical applications across various domains of photonics and optics.

The core contribution of this work is the identification of a novel approach for enhancing the Q-factors of dielectric resonators, which are typically limited by radiation damping. The authors demonstrate that by leveraging the phenomenon of BIC, subwavelength resonators can exhibit remarkably high Q-factors. Specifically, they show that for dielectric nanorods, high-Q factors can be achieved through strong coupling of modes that results in Fano resonances, leading to supercavity regimes where light is trapped efficiently yet remains spectrally broad.

The paper presents an analysis of resonance dynamics in dielectric resonators, focusing on scenarios where high refractive index materials such as silicon are employed. It reveals that by engineering the aspect ratio of the resonator, it is possible to induce a regime of avoided crossing between Mie-type and Fabry-Perot-type modes. This phenomenon is illustrated with precise calculations of scattering spectra and eigenfrequencies of cylindrical dielectric resonators, utilizing methods like the resonant-state expansion. These calculations elucidate the conditions under which mode coupling can minimize radiation losses, thereby enhancing the Q-factor significantly, with reported values reaching up to 65,000 for certain geometries.

One of the notable features of this paper is the quantitative detail it provides about the conditions necessary for BIC in practical dielectric structures. The authors observe that achieving very high Q-factors necessitates the adjustment of geometric parameters and dielectric permittivity to optimize the interference effects that suppress radiation. Such results are particularly relevant for applications requiring low-loss optical confinement, such as enhancing nonlinear optical effects, sensing, lasing, and on-chip photonic integration.

The implications of these findings are manifold. For practical devices, the ability to engineer small-scale resonators with high-Q modes opens avenues for compact, efficient photonic devices with enhanced performance metrics. Theoretically, the achievement of bound states in continuum within nanostructures could further inform the development of metamaterials and photonic devices exhibiting novel properties and behaviors.

Future research in this area may explore the diversification of dielectric materials that can be exploited for BIC states, the impact of structural imperfections on Q-factor performance, and integration strategies for encompassing this concept into functional photonic circuits. The potential of extending these techniques to quantum photonics and exploring the quantum-optical analogs of such high-Q resonators is another promising direction.

In conclusion, Rybin et al.'s investigation into high-Q supercavity modes using BIC in dielectric resonators marks a substantial advancement in nanophotonic research, providing both a robust theoretical framework and practical insights into the manipulation of light at the nanoscale. Their methodologies and findings contribute significantly to the development of highly efficient photonic devices and expand the theoretical understanding of light-matter interactions in densely packed structures.