Experimental demonstration of a silicon-slot quasi-bound state in the continuum in near-infrared all-dielectric metasurfaces

Algorri, J.F., Dell'Olio, F., Ding, Y., Labbé, F., Dmitriev, V., López-Higuera, J.M., Sánchez-Pena, J.M., Andreani, L.C., Galli, M., Zografopoulos, D.C. (2023) Optics and Laser Technology, 161, art. no. 109199.

We theoretically and experimentally investigate a metasurface supporting a silicon-slot quasi-bound state in the continuum (qBIC) mode resonating in the near-infrared spectrum. The metasurface is composed of circular slots etched in a silicon layer on a sapphire substrate. The symmetry of the metasurface unit cell is reduced in order to provide access to the symmetry-protected mode, whose properties are investigated by finite-element full-wave and eigenfrequency analysis. The measured transmittance spectra verify the excitation of the investigated qBIC mode with experimental quality factors exceeding 700. The near-field distribution of the resonant qBIC mode shows strong field confinement in the slots, leading to high sensitivity values for refractometry.