Excitation of high-Q out-of-plane lattice resonance at normal incidence and applications in sensor

Out-of-plane surface lattice resonances (OSLRs) arising from coherent interaction of sub-radiant dipoles in an array, show great potential in realizing extremely high quality factors (Q factors) and strong electric-field enhancements. However, current high-performance OSLRs predominantly operate under homogeneous refractive index (RI) conditions or require specific asymmetric environments, analogous to in-plane surface lattice resonances (SLRs), which impose some constraints on their practical applicability, especially in sensing scenarios. To overcome this limitation, we demonstrate a vertically-oriented V-shaped antenna (VVA) array capable of exciting high-Q OSLRs independent of the ambient RI environments. By leveraging two geometric parameters relating to structural symmetry, the proposed design enables precise control over electromagnetic coupling between symmetric and asymmetric plasmon modes, which facilitates high-performance OSLPs excitation under normal incidence. Through systematic optimization, we achieve OSLRs with a spectral linewidth of about 3 nm (Q≈230 at λ=700 nm) in air-substrate environments. Sensor's performances are validated through refractive index detections in different concentrations of glucose/water solutions, attaining a record figure of merit (FOM) of about 170. This value has exceeded the upper limits of commercial sensors (∼ 108 in FOM) based on propagating surface plasmon resonances (PSPR). Meanwhile, the detection of low-concentration urea/water solution with detection limit down to 20 μmol/ml demonstrates its potential as a biochemical sensor.