Study On Multipole Resonance Characteristics Of Silica-Based Composite Structure Nanoantennas

Optical nanoantennas have become one of the research hotspots in the field of micro and nano optics,with a wide range of promising applications in areas such as photothermal biosensing,spontaneous radiation,nanolaser,nonlinear switching and solar cells.Previous research has focused mainly on electric and magnetic multipoles.As research progresses,it is found that the once neglected cyclic multipole is an important component in multipole unfolding.The properties of the cyclic dipole in many fields of application make it an integral part of nanophotonics.The existence of phase length/phase extinction interactions between the cyclic dipole and the electric dipole has led to the formation of Super-dipole and Anapole resonance modes,resulting in a large number of practical and valuable nanophotonics-related applications.In this paper,we investigate the near-field enhancement characteristics of silicon-based nanoantennas under optical excitation from the basic principle of plasmonic resonance,using simulation to investigate the near-field of compositeΦ-shaped nanoantennas and multilayer disc nanoantennas,and illustrate the correlation between the multipole resonance of optical nanoantennas and the Super-dipole and Anapole resonant modes.The correlation between the Super-dipole and Anapole resonance modes of optical nanoantennas is illustrated,providing theoretical guidance for the design and application of silicon-based nanoantennas with new structures.A metal-high refractive index dielectric compositeΦ-shaped nanoantenna structure was designed to explore the formation mechanism of electrical"hot spots".Simulation results show that the nano-antenna supports various resonant modes such as electric dipole,cyclic dipole and magnetic quadrupole to achieve near-field enhancement.The effect of the size of the superimposed butterfly-shaped nano-antenna and the number of pinch angles on the near-field enhancement characteristics is explored,and the physical nature of the antenna is explained using the Super-dipole mode resonance theory.The combination of a dielectric antenna with a metallic antenna is able to substantially increase the electric field strength,achieving a maximum electric field（|E|/|E₀|）value in excess of 100,which is near 20-times increase in the maximum electric field enhancement compared to the initial strip-slit nanoantenna.This structure opens up new possibilities for single-particle enhanced spectroscopy or single-photon emission enhancement.A gold-silica-silicon triple-layer optical nanoantenna is proposed,using theoretical analysis and simulations to achieve near-field electric field enhancement values in excess of500 by varying the material and number of layers of the disc antenna.analysis of the scattering variations of electric and circular dipoles,and numerical simulations of a dielectric disc with Anapole modes,greatly enhance the application in areas such as surface-enhanced Raman scattering and quantum emitters.applications in the fields of surface-enhanced Raman scattering and quantum emitters.The numerical calculation of the Purcell coefficient（PF）under the excitation of an electric dipole source,up to 2500,yields a maximum sensitivity value of 927 nm/RIU and a quality factor of 7.6 RIU^-1,which improves the sensing performance compared to conventional refractive index sensors.The study also explores the structural model of the multi-slit butterfly nano-antenna and analyses the electromagnetic field distribution and absorption spectrum of the nano-antenna.The results show that the multi-gap butterfly nano-antenna structure designed in this paper can achieve an average absorption rate of over 90%.This provides a theoretical basis and new ideas for the design of silicon-based composite structures for nano-antennas.