WITHDRAWN: Fano-modulated chiral metasurface for near-infrared sensing via bound states in the continuum

Abstract

Here, we report polarization-sensitive chiral metasurface with broken in-plane inverse symmetry to exploit symmetry-protected quasi-bound states in the continuum (quasi-BIC) for highly sensitive and sharply resonant surface interactions enabling refractive index sensing in near infrared region. Chirality is induced by rotating silicon nanofins placed on top of dielectric spacer with a gold backplate, creating a chiral arrangement that results in a strong chiroptical response. Our chiral metasurface offers controllable spectral linewidth and chiral selectivity in dual-wavelength bands where each band can be excited simultaneously or independently by controlling meta-atom geometry offering multispectral index sensing. We report a novel phenomenon of controlling interplay of chirality between two closely positioned wavelength bands to tailor symmetry breaking for a specific resonant mode (chiral) while preserving symmetry for other mode (achiral). Additionally, we report the phase-sensitive evolution of Fano resonance from pure reflectance dip when controlled by dielectric spacer height, and further demonstrated phase-insensitive control of Fano resonance amplitude. We divided Fano resonance into distinct spectral peak and dip to improve light manipulation within the metasurface. Our proposed sensor demonstrates sensitivity and a quality factor of about 435 nm/RIU and 3888, respectively. Furthermore, we compared different phenomenon (chiral selectivity, quasi-BIC, Fano) and sensing parameter values for different metasurface configurations (including single nanofin and absence of a spacer) and observed that the configuration without a spacer achieved the highest sensitivity of approximately 640 nm/RIU.