Interplay of localized, lattice, and guided resonances in asymmetric plasmonic dimer arrays

Plasmonic nanoarrays are imperative in demonstrating multiple optical resonances owing to hybridization of localized resonances with lattice-mediated diffraction modes, beneficial for various nanophotonics applications. Herein, we demonstrate the critical role of dielectric asymmetry and excitation geometry in governing the optical resonances in a periodic asymmetric silver nanodimer (ASD) nanoarray. This simulation work demonstrates the transition of spectral modes from the localized state of localized surface plasmon resonance (LSPR) to delocalized guided resonance (GR) and surface lattice resonance (SLR) by systematic variation of dielectric contrast between the superstate and substrate and probing the system under polarization and angle resolved excitation, without altering the structural geometry. Polarization dependent studies showcase the dominance of gap driven plasmonic coupling along axial polarization, whereas transverse polarization favours diffraction mediated dispersive features. Angle resolved measurements reveal the progressive emergence of quasi-bound states in the continuum (qBIC) characteristics at certain incidence and azimuthal excitation. Collectively, tuning the dielectric environment and excitation configuration provides an independent and effective tool for controlling modal resonances including specific behavior, spectral position, linewidth and radiative coupling. This framework presents a unified strategy for achieving spectrally selective resonances in nanophotonics systems.