Plasmonic Resonances in Metallic Nanoparticles and Optical Nanowire Antennas: Fundamentals, Modeling, and Applications

Abstract

Metallic nanostructures have emerged as fundamental building blocks in modern nanophotonics due to their ability to confine and manipulate light at dimensions far below the diffraction limit. This review presents a comprehensive examination of resonance phenomena in metallic nanoparticles and optical nanowire antennas, emphasizing their physical principles, modeling strategies, and functionality as nanoscale resonators. The optical response of these systems originates from collective oscillations of conduction electrons, producing localized surface plasmon resonances (LSPR) in nanoparticles and surface plasmon polaritons (SPPs) in extended nanowire geometries. These resonances enable strong electromagnetic field enhancement, spectral tunability, and enhanced light–matter interaction across visible and near-infrared wavelengths. The paper systematically analyzes size-, shape-, and material-dependent resonance behavior in metallic nanoparticles, including quantum size effects and plasmon hybridization in coupled systems. Optical nanowire antennas are discussed as nanoscale analogues of radio-frequency antennas, supporting dipolar, higher-order, and Fabry–Pérot resonant modes with controllable radiation characteristics. Analytical approaches such as Mie theory and quasi-static approximation are reviewed alongside advanced computational techniques including FDTD, FEM, DDA, and BEM for accurate modeling of complex geometries. Furthermore, the work highlights practical applications of these plasmonic resonators in surface-enhanced Raman scattering (SERS), biosensing, photothermal therapy, photovoltaics, nano-lasers, and integrated photonic circuits. Current limitations such as Ohmic losses, fabrication constraints, thermal instability, and quantum-scale effects are critically examined. Emerging directions including low-loss alternative materials, active tunability, hybrid plasmonic–dielectric platforms, and AI-assisted design are discussed as promising pathways toward next-generation nanoscale resonator technologies. This review provides a unified framework for understanding and engineering metallic nanostructures as efficient and tunable optical resonators.