Dual-Mode Asymmetric Transmission based on Asymmetric and Orthogonal Gratings: Polarization-Dependent and -Independent Modes

A dual-mode asymmetric transmission (AT) nanodevice based on the asymmetric and orthogonal grating-film-grating (AO-GFG) structure is proposed and systematically investigated theoretically. The device supports two distinct localized surface plasmon resonance (LSPR) modes for forward transmission, corresponding to the polarization-dependent (M1) and the polarization-independent (M2) resonances, respectively. This results in the fact that when x-polarized light is incident, only M2 exists; when y-polarized light is incident, both M1 and M2 exist. Besides, both modes yield the maximum isolation ratio of more than 10 dB. The electric field distributions further indicate that M2 exhibits strong confinement and efficient tunneling through the metallic film, while M1 shows weaker but more polarization-sensitive hybridization. The coexistence and tunability of these two modes constitute the physical basis of dual-mode AT, highlighting the AO-GFG structure as a promising platform for high-isolation and polarization-tunable plasmonic devices in the visible and near-infrared regions.