Ultrasensitive and Broadband Optical Toroidal Modes in all-Dielectric Nanostructures
Journal
Laser and Photonics Reviews
Journal Volume
16
Journal Issue
3
Date Issued
2022
Author(s)
Abstract
Dynamic toroidal dipole (TD) with its peculiar characteristic of broken space-inversion and time-reversal symmetries plays an important role in the fundamental physics of light–matter interaction. Here, TD metamaterials comprised of amorphous silicon nanopillar arrays embedded in spin-on-glass layer are experimentally demonstrated. Upon normal incidence of plane wave, the transverse toroidal moment and the associated anapole-like state are excited in optical regime. The strong TD response stems from a complete head-to-tail configuration of the magnetic dipole moments within each individual nanopillar. Both the experimental and simulation results show that such TD mode sustains a large structural tolerance and can be spectrally tuned by elongating the cylindrical axis perpendicular to the light polarization, corresponding to a cross-sectional variation from circular to elliptical shapes. The excited TD mode is found to exhibit ultrahigh refractive index sensitivity compared to other multipoles, resulting in a sensitivity of 459 nm (470 nm) per external refractive index change in the experiment (calculation). This approach provides a simple and straightforward path in realizing toroidal metamaterials and establishes a new flat-optics platform for realizing active metadevices, sensors, and nonlinear nanophotonics. © 2022 Wiley-VCH GmbH
Subjects
anopole mode; dielectric metasurfaces; Mie resonances; refractive-index sensing; toroidal dipole
SDGs
Other Subjects
Amorphous silicon; Excited states; Light; Refractive index; Spin glass; Dipole mode; Fundamental physics; Light-matter interactions; Nanopillars array; Optical-; Silicon nanopillars; Spin-on-glass; Time reversal symmetries; Toroidal modes; Ultrasensitive; Metamaterials
Type
journal article