Dual Fano-like resonances in a CMOS-compatible all-dielectric metasurface for refractive index sensing

A numerical investigation has been conducted on a near-infrared all-dielectric metasurface refractive index sensor. The sensor is constructed using amorphous silicon (a-Si) nanoresonators placed on a silicon dioxide (SiO₂) substrate. Two distinct Fano-like resonances with narrow linewidths and strong refractive-index sensitivity were observed. With a high figure of merit (FOM) of 356.00 and quality factor (Q-factor) of 1120.21, a peak sensitivity of 511.45 nm/RIU was attained at the first resonance, ensuring precise and high-resolution detection. An FOM of 63.11, a Q-factor of 337.38, and a sensitivity value of 437.41 nm/RIU are obtained from the second resonance. Electric dipole (ED) excitation is the dominant mechanism for both resonances, according to a multipole decomposition study. Magnetic dipole (MD), toroidal dipole (TD), electric quadrupole (EQ), and magnetic quadrupole (MQ) make up additional contributions. The metasurface demonstrates dual Fano-type resonances and strong polarization-dependent angular stability, remaining robust up to a 70° polarization angle and an incident angle of 35°. The proposed sensor has a lot of potential for integration into chip-scale photonic systems for high-performance environmental and biochemical detection since it is constructed with CMOS-compatible materials and fabrication techniques.