All-dielectric bilayer complementary metasurfaces supporting quasi-bound states in the continuum induced by intrinsically broken out-of-plane symmetry

An all-dielectric metasurface based on Fano resonance with tunable dual-peak insensitive polarization for high-performance refractive index sensing

A symmetric all-dielectric metasurface based on silicon and GaAs is proposed and numerically studied. In the mid-infrared region, two Fano resonant peaks with a reflectance exceeding 90% are observed. By altering the geometric parameters of the metasurface, the wavelength location and quality factor (Q-factor) of the resonant peaks can be tuned. The highest Q-factors can be 9609.67 and 3476.33, respectively. The proposed metasurface structure for optical refractive index sensing shows high performance and is insensitive to the plane wave's polarization state. In the refractive index range of 1.00 to 1.10, the highest sensitivity and figure of merit (FoM) are 1901.34 nm RIU-1 and 2492.04 RIU-1, respectively. The highest sensitivity is 2248.57 nm RIU-1 and FoM is 977.64 RIU-1 in the refractive index range of 1.30 to 1.40. These research results will help improve and innovate related sensing technologies and devices.

Active Control and Sensing Application of Ultra-Narrowband Circular Dichroism in Multilayer Chiral Nanorod Arrays

Narrowband circular dichroism (CD) has attracted wide attention for its high sensitivity in detecting chiral molecules and catalysis. However, designing a chiral metasurface with excellent sensing performance that can be dynamically tuned still poses challenges. This paper introduces lithium niobate, an electrically tunable material, and a distributed Bragg reflector into chiral nanorod structures to form multilayer chiral nanorod arrays (MCNAs). Simulation results show that MCNAs can generate four strong ultra-narrowband (UNB) CD signals in the visible light spectrum. The UNB CD signal intensity was up to 0.86, and the minimum full width at half-maximum (FWHM) was up to 0.21 nm. The surface electric field and current distribution of MCNAs indicate that the four UNB CD signals mainly originate from the x and y direction Tamm resonances in the chiral nanorod layer. The refractive index of lithium niobate can be tuned by changing the electric field, allowing the active tuning of UNB CD signals. In addition, the sensing performance of MCNAs in the SARS-CoV-2 solution was analyzed, and the figure of merit (FOM) can reach an astonishing 2092. These findings not only assist with the design of UNB chiral devices but also offer new possibilities for the environmental monitoring and ultrasensitive detection of chiral molecules.