Subwavelength plasmonic antennas based on asymmetric split-ring-resonators for high near-field enhancements

As for plasmonic antenna structures that generate localized near-field enhancement, the most effective current implementations are based on electric dipole resonance modes, but this approach also imposes limitations on their further optimization. Here we introduce an ASRR structure whose ASR mode enables differential charge distribution across both sides of the split. Through asymmetric regulation, charges at one end can become highly localized, thereby achieving efficient near-field enhancement. The formation of this structure was initially driven by a hybrid computational framework integrating evolutionary optimization with residual neural networks, and subsequently simplified into an ASRR prototype using the Occam's Razor principle. The ASRR dimer structure can achieve an electric field intensity enhancement over 6.5 times larger than a traditional nanorod dimer, while maintaining a compact size (<1/3 the working wavelength). The ASRR configuration also demonstrates superior Purcell factor and fluorescence enhancement. These results can find applications in surface-enhanced spectroscopy, nonlinear optics, and quantum light-matter interactions.