Manipulating Optical Scattering of Quasi-BIC in Dielectric Metasurface with Off-Center Hole

Abstract

Bound states in the continuum (BICs) correspond to a particular leaky mode with an infinitely large quality-factor (Q-factor) located within the continuum spectrum. To date, most of the research work reported focuses on the BIC-enhanced light matter interaction due to its extreme near-field confinement. Little attention has been paid to the scattering properties of the BIC mode. In this work, we numerically study the far-field radiation manipulation of BICs by exploring multipole interference. By simply breaking the symmetry of the silicon metasurface, an ideal BIC is converted to a quasi-BIC with a finite Q-factor, which is manifested by the Fano resonance in the transmission spectrum. We found that both the intensity and directionality of the far-field radiation pattern can not only be tuned by the asymmetric parameters but can also experience huge changes around the resonance. Even for the same structure, two quasi-BICs show a different radiation pattern evolution when the asymmetric structure parameter d increases. It can be found that far-field radiation from one BIC evolves from electric-quadrupole-dominant radiation to toroidal-dipole-dominant radiation, whereas the other one shows electric-dipole-like radiation due to the interference of the magnetic dipole and electric quadrupole with the increasing asymmetric parameters. The result may find applications in high-directionality nonlinear optical devices and semiconductor lasers by using a quasi-BIC-based metasurface.

Catalytic Metasurfaces Empowered by Bound States in the Continuum

“…However, extending these ideas into the field of photocatalysis, where they could enable ways of triggering chemical transformations with light, has so far not been investigated. Established BIC-based metasurface demonstrations have utilized high refractive index materials like Si, 47,48 where pushing the operating range toward the blue part of the visible spectrum is still challenging due to significant dielectric losses associated with the interband transitions. 49 The blue side of the optical regime is particularly interesting for catalysis because the band gap and band alignment of many relevant semiconductors lie in the 2−3 eV region and because the energy of (hot) electron−hole pairs in metals is in most cases high enough for promoting hydrogen generation or oxygen evolution, among other important chemical transformations.…”

Quasi-Trapped Guided Mode in a Metasurface Waveguide for Independent Control of Multiple Nonlocal Modes

“…In a meticulously designed metasurface, a nonradiative trapped mode can be observed, as illustrated in the lower dotted line in Figure b. − However, any disruption in the 2-fold rotational symmetry around the z -axis leads to a transformation of this trapped mode into a QTM, which subsequently emits radiation in the + z -direction. Although LGM emanates from the guided mode inherent in the waveguide layer, QTM originates from the Bloch mode of the metasurface layer, which also can be excited without the waveguide slab (Figure S2 of Supporting Information).…”

“…When this symmetry is disrupted owing to structural deformations or alterations in the angle of incidence, the pure BIC transmutes into a quasi-BIC, capable of exhibiting a finite quality factor. Recently, multipole-based trapped modes have garnered attention as a variant of symmetry-protected BIC. − The disrupted symmetry of the trapped modes causes energy leakage into a free space by the resulting radiative multipoles. As a result, the trapped modes transform into the quasi-trapped mode (QTM), which can also be seen as a type of symmetry broken induced quasi-BIC.…”

Design and Tuning of Substrate-Fabricated Dielectric Metasurfaces Supporting Quasi-Trapped Modes in the Infrared Range

“…The considered geometry of building blocks in the form of disks with a hole was already widely used to create metasurfaces supporting the QTM, ,,,− and the obtained results were generalized for various configurations . The feature of this work is the development and experimental verification of a general strategy for the design of building blocks for a metasurface placed on a given substrate and supporting the QTM resonance at a given wavelength.…”