Multipolar second-harmonic generation from high-$Q$ quasi-BIC states in nanoresonators

Abstract

Multimode interference and multipolar interplay govern functionalities of optical nanoresonators and nonlinear nanoantennas. Recently, excitation of the high-quality supercavity modes (quasi-BIC states) in individual subwavelength dielectric particles has been predicted to boost the nonlinear frequency conversion at the nanoscale. Here, we put forward the multipolar model which captures the physics behind linear and nonlinear response driven by such high-$Q$ modes in nanoresonators. We show that formation of the quasi-BIC state in the AlGaAs nanodisk can be understood through multipolar transformations of coupled leaky modes. In particular, the hybridized axially symmetric TE-polarized modes can be viewed as superpositions of multipoles, with a basis of parent multipoles constituted mainly by magnetic dipoles and octupole. The quasi-BIC point in the parameter space appears where dipolar losses are totally suppressed. The efficient optical coupling to this state is implemented via azimuthally polarized beam illumination matching its multipolar origin. We establish a one-to-one correspondence between the standard non Hermitian coupled-mode theory and multipolar models that enables transparent interpretation of scattering characteristics. Using our approach, we derive the multipolar composition of the generated second-harmonic radiation from the AlGaAs nanodisk and validate it with full-wave numerical simulations. Back-action of the second-harmonic radiation onto the fundamental frequency is taken into account in the coupled nonlinear model with pump depletion. A hybrid metal-dielectric nanoantenna is proposed to augment the conversion efficiency up to tens of per cent and actualize the nonlinear parametric downconversion. Our findings delineate the in-depth conceptual framework and novel promising strategies in the design of functional elements for nonlinear nanophotonics applications.

References in corpus (15)

• Individual nanoantennas empowered by bound states in the continuum for nonlinear photonics
• High-Q supercavity modes in subwavelength dielectric resonators
• Giant nonlinear response at the nanoscale driven by bound states in the continuum
• Bound states in the continuum and Fano resonances in the strong mode coupling regime
• Multipolar origin of bound states in the continuum
• Multipolar nonlinear nanophotonics
• Optical anapoles in nanophotonics and meta-optics
• Nonlinear optics at all-dielectric nanoantennas and metasurfaces
• Third-harmonic generation in photonic topological metasurfaces
• Spontaneous photon-pair generation at the nanoscale
• Multipolar third-harmonic generation driven by optically-induced magnetic resonances
• Second-harmonic generation in Mie-resonant dielectric nanoparticles made of noncentrosymmetric materials
• Beam engineering for selective and enhanced coupling to multipolar resonances
• Multipolar second-harmonic generation by Mie-resonant dielectric nanoparticles
• Nonlinear generation of quantum-entangled photons from high-Q states in dielectric nanoparticles

Cited by in corpus (11)

• Interference traps waves in open system: Bound states in the continuum
• Enhanced Light-Matter Interaction in Two-Dimensional Transition Metal Dichalcogenides
• Polarization-controlled dynamically switchable high-harmonic generation from all-dielectric metasurfaces governed by dual bound states in the continuum
• Pushing the Limit of High-Q Mode of a Single Subwavelength Dielectric Nanocavity
• Lasing action in single subwavelength particles supporting supercavity modes
• Enhanced sum-frequency generation from etchless lithium niobate empowered by dual quasi-bound states in the continuum
• Enhancing Goos-Hänchen shift based on magnetic dipole quasi-bound states in the continuum in all-dielectric metasurfaces
• Tuning nonlinear second-harmonic generation in AlGaAs nanoantennas via chalcogenide phase change material
• Enhanced second harmonic generation in high-$Q$ all-dielectric metasurfaces with backward frequency conversion
• Thermo-optical reshaping of SHG emission from dimerall-dielectric nanoresonators
• Excitation of a bound state in the continuum via spontaneous symmetry breaking