Nonradiating Photonics with Resonant Dielectric Nanostructures (1903.04756v1)

Abstract: Nonradiating sources of energy have traditionally been studied in quantum mechanics and astrophysics, while receiving a very little attention in the photonics community. This situation has changed recently due to a number of pioneering theoretical studies and remarkable experimental demonstrations of the exotic states of light in dielectric resonant photonic structures and metasurfaces, with the possibility to localize efficiently the electromagnetic fields of high intensities within small volumes of matter. These recent advances underpin novel concepts in nanophotonics, and provide a promising pathway to overcome the problem of losses usually associated with metals and plasmonic materials for the efficient control of the light-matter interaction at the nanoscale. This review paper provides the general background and several snapshots of the recent results in this young yet prominent research field, focusing on two types of nonradiating states of light that both have been recently at the center of many studies in all-dielectric resonant meta-optics and metasurfaces: optical {\em anapoles} and photonic {\em bound states in the continuum}. We discuss a brief history of these states in optics, their underlying physics and manifestations, and also emphasize their differences and similarities. We also review some applications of such novel photonic states in both linear and nonlinear optics for the nanoscale field enhancement, a design of novel dielectric structures with high-$Q$ resonances, nonlinear wave mixing and enhanced harmonic generation, as well as advanced concepts for lasing and optical neural networks.

• The paper introduces nonradiating states by demonstrating optical anapoles and bound states in the continuum that overcome losses in conventional plasmonic systems.
• The paper employs a combination of theoretical analysis and experimental validation to reveal effective field localization and enhanced light-matter interactions in dielectric nanostructures.
• The paper highlights the potential of these phenomena for developing innovative low-loss devices, including sensors, harmonic generators, and high-Q lasers.

Nonradiating Photonics with Resonant Dielectric Nanostructures

The paper "Nonradiating Photonics with Resonant Dielectric Nanostructures" explores recent advances in an emerging field of nanophotonics that focuses on nonradiating states of light within dielectric resonant structures. The authors delve into the theoretical and experimental investigations of two primary nonradiating states: the optical anapoles and photonic bound states in the continuum (BICs). This work outlines the significance of these exotic states in overcoming limitations experienced in conventional plasmonic systems, such as high losses, by providing effective control over light-matter interactions at the nanoscale.

Overview of Nonradiating States

Nonradiating states in photonics refer to electromagnetic configurations that do not radiate energy into the far field, primarily by destructive interference of multipolar components. Historically studied mainly in quantum mechanics and astrophysics, they recently gained attention from a photonic perspective due to their potential to localize electromagnetic fields effectively. This paper centers on anapoles and BICs as significant nonradiating state examples within all-dielectric structures.

Optical Anapoles

The concept of optical anapoles exemplifies a nontrivial nonradiating state where the far-field radiation is canceled, achieved through the destructive interference of electric dipole and toroidal dipole modes. The historical context traces back to early theories in electrodynamics that suggested such states could exist under specific conditions. The paper highlights experimental demonstrations of anapole states in dielectric nanoparticles, which show minimal scattering even at resonant frequencies, thereby providing pathways to low-loss applications in photonics. These anapoles have been crucial in achieving field enhancements within nanoscale volumes, fostering advancements in applications such as enhanced harmonic generation.

Bound States in the Continuum

Photonic BICs represent another critical nonradiating state that resides within the continuous radiation spectrum, yet remains spatially localized and non-dissipative. Originating from quantum mechanics, these states have intrigued researchers across wave physics due to their potential to facilitate high-Q resonances. These states can emerge in structured photonic environments, such as metasurfaces and photonic crystal slabs, leading to applications in lasing and sensors. The paper reviews mechanisms like symmetry protection and parameter tuning to achieve BICs, emphasizing their role in achieving large electromagnetic field localizations and enhanced light-matter interactions.

Practical and Theoretical Implications

The exploration of nonradiating states in dielectric nanostructures provides substantial theoretical and practical opportunities. The high-Q resonances resulting from anapoles and BICs offer promising advancements in nonlinear photonics, including significant improvements in harmonic generation efficiencies. Moreover, these states unlock novel design strategies for photonic devices, allowing for the development of low-loss, resonantly enhanced metasurfaces and metamaterials that could surpass traditional plasmonic devices in performance and scope.

An application area explored is the use of all-dielectric metasurfaces supporting anapole and BIC resonances for sensing and spectroscopy, leveraging their capacity to concentrate electromagnetic energy in small volumes. These properties are pivotal for enhancing detection capabilities in biosensing applications. Furthermore, BICs have motivated the development of innovative laser technologies, exploiting their unique ability to support high-quality modes for coherent light emission.

Future Speculations

The paper of nonradiating states in photonics opens new horizons in the development of optical devices with enhanced functionalities. Future research may focus on the integration of these concepts into complex systems, such as neuromorphic photonic circuits and subwavelength optical networks. Moreover, expansion into hyperbolic and topological photonics could leverage the unique properties of nonradiating states to explore new paradigms in light manipulation beyond the diffraction limit.

In summary, the paper provides a comprehensive review of the fascinating and technically significant field of nonradiating photonics, advocating for continued exploration of these phenomena to realize cutting-edge technologies in optics and photonics.