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The surface lattice resonance (SLR) is a prominent mechanism to produce ultranarrow spectrum line shape, which can enhance the localized electric field and restrain radiation losses. However, the present research mainly focuses on the single-mode SLR and does not involve the multiplexing and higher-order SLRs. To promote the practicability of SLR, we propose bimodal reflection-type SLRs excited by the natural light based on three kinds of asymmetric optical metasurfaces systemically, which are applied to refractive index sensing with high figures of merit (FoMs) experimentally. The rectangular lattice metasurface breaks the C4 symmetry and produces concurrently (±1, 0) and (0, ±1) order SLRs, with FoMs of 33.50 and 28.85, respectively. In addition, the metasurface composed of two different patches belongs to a spatial multiplexing design and can also realize nearly identical SLR responses. Furthermore, the asymmetric dimer metasurface excites two SLRs with distinct orders meanwhile, where the high-order SLR originates from the trapping of the corresponding Rayleigh anomaly waves. The above-mentioned metasurface designs have flexibility and regularity, whose resonance wavelengths, sensitivities, and bimodal combinations can be attained at will by tuning period lengths, arranging different patches, or forming a dimer meta-atom. The research takes a significant step for bimodal SLR development and application, especially in the sensing field.
Li et al. (2024) studied this question.