High-Q multimodal guided-surface lattice resonances in index-discontinuous environments

Surface lattice resonances (SLRs) in metasurfaces have become a transformative platform for subwavelength optical devices. However, current high quality-factor (high-Q) SLR implementations are fundamentally limited by their dependence on homogeneous dielectric environments. To overcome this limitation, we introduce guided-surface lattice resonances (gSLRs) by integrating nanoparticle arrays within slab waveguides. This configuration facilitates efficient coupling between scattered light and Bloch modes, enabling high-Q multimodal resonances even in index-discontinuous environments, realizing a quality-factor (Q-factor) of 1489. The coupling strength and resonance intensity of these multimodal gSLRs can be continuously modulated by adjusting the vertical displacement of the nanoparticle arrays within the slab layers. To augment the sensitivity to local dielectric variations, we investigate gSLRs in metasurfaces integrated with metallic substrates, demonstrating suitability for biosensors. A mathematical sensing model, incorporating biochemical reaction kinetics and optical responses, is established and validated through bovine serum albumin (BSA) sensing, achieving a limit-of-detection as low as 0.65 pM.