Abstract
Abstract We put forward the multipolar model which captures the physics behind linear and nonlinear response driven by high-quality (high-Q) supercavity modes in subwavelength particles. We show that the formation of such trapped states associated with bound states in the continuum (quasi-BIC) can be understood through multipolar transformations of coupled leaky modes. The quasi-BIC state appears with increasing the order of the dominating multipole, where dipolar losses are completely suppressed. The efficient optical coupling to this state in the AlGaAs nanodisk is implemented via azimuthally polarized beam illumination matching its multipolar origin. We establish a one-to-one correspondence between the standard phenomenological non-Hermitian coupled-mode theory and multipolar models. The derived multipolar composition of the generated second-harmonic radiation from the AlGaAs nanodisk is then validated 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 due to increasing quality factors of the involved resonant states. Our findings delineate novel promising strategies in the design of functional elements for nonlinear nanophotonics applications.
Highlights
Controlling light at the nanoscale has been a vibrant field of research for many years motivated by its various applications for optical nanoantennas, integrated photonic circuitry, optical computing, and high-speed ultrathin photonic devices [1,2,3,4,5]
We put forward the multipolar model which captures the physics behind linear and nonlinear response driven by high-quality supercavity modes in subwavelength particles
With the use of the finite element method (FEM) in COMSOL Multiphysics, we perform the eigenmode analysis numerically and plot dispersion as a function of the normalized geometric parameters defined as the disk aspect ratio r/h and the size parameter r/λ0, where λ0 is the mode wavelength
Summary
Controlling light at the nanoscale has been a vibrant field of research for many years motivated by its various applications for optical nanoantennas, integrated photonic circuitry, optical computing, and high-speed ultrathin photonic devices [1,2,3,4,5]. A recently suggested approach to trap light in individual subwavelength dielectric nanoresonators is based on high-quality supercavity modes associated with the physics of quasi-bound states in the continuum (quasi-BIC) [32,33,34]. These states are in some sense similar to BICs in infinite periodic dielectric structures: their high finesse is due to the destructive interference of several far-field radiation channels. We perform full-wave numerical simulations of SHG taking into account nonlinear effects of back-action and propose the BIC-inspired design of a hybrid metal-dielectric nanoantenna where the effect of pump depletion is further increased suggesting a promising application for the frequency downconversion
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
