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Metasurfaces composed of silicon-nanogap unit have a variety of optical resonances, including bound states in the continuum (BIC). We show comprehensive numerical results on metasurfaces of Si-nanogap units, analyze the optical resonances, and clarify optically prominent resonances as well as symmetry-forbidding resonances that are the BIC, based on the numerical analyses of optical spectra and resonant electromagnetic-field distributions. Introducing asymmetry in the unit cell, the BIC become optically allowed, being identified as magnetic dipole, electric quadrupole, and magnetic quadrupole resonances. Moreover, the optical resonances are examined in terms of refractive-index sensing performance. A pair of the resonances associated with electric-field localization at nanogap was found to be sensitive to the refractive index contacting with the metasurfaces. Consequently, the gap-mode resonances are shown to be suitable for a wide range of the refractive-index sensing over 1.0--2.0.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: all-dielectric metasurface, silicon nanogap, BIC, optical sensing, refractive index

Date published: 2024-11-10

Publisher: Multidisciplinary Digital Publishing Institute (MDPI)

Journal:

• Photonics (ISSN: 23046732) vol. 11 issue. 11 1053

Funding:

• 日本学術振興会 JP24K01389

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.3390/photonics11111053

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Updated at: 2024-11-13 08:31:31 +0900

Published on MDR: 2024-11-13 08:31:31 +0900