Subwavelength Plasmonic Antennas Based on Asymmetric Split-Ring Resonators for High Near-Field Enhancements.

Abstract

Plasmonic antennas generating strong near-field enhancement primarily rely on electric dipole resonance, a mechanism that also limits their further optimization. Here we propose an asymmetric split-ring resonator (ASRR) that induces differential charge distribution across the split gap. Through asymmetric structural modulation, charges are highly localized at the designated terminal, enabling efficient near-field enhancement. This configuration was initially developed via a hybrid framework integrating evolutionary optimization with residual neural networks and subsequently simplified into an ASRR prototype using Occam's Razor principle. The ASRR dimer demonstrates >6-fold electric-field intensity enhancement compared to conventional nanorod dimers at subwavelength scale, while exhibiting a superior Purcell factor and fluorescence enhancement. This breakthrough creates new opportunities in surface-enhanced spectroscopy and light-matter interactions.