Optical Properties Of Plasmonic Nanoantennas Based On Quantum-photonic Analogues

The interactions between noble metal nanostructures and light are mainly manifested as surface plasmon resonance(SPR).In this regard,such nanostructures are often refereed to plasmonic nanoantennas(PNs).PNs are the basic compostions of optical metamaterial and meta surface.Understanding the optical properties of PNs is the prerequisite of designing various functional metamaterials and metasurfaces.Meanwhile,photonic system and electronic system have analogies in many aspects.Thus,based on PNs,it is feasible to mimic some quantum effects originally found in condensed-matter system.On the other hand,such quantum-photonic analogical study provides more flexiable ideas and general approaches to tune the propetries of PNs.Nevertheless,there are many differences between PNs and traditional(microwave or RF)antennas.To fully explore the unique characteristics of PNs(such as strong near-field enhancement,tunable resonance frequencies,etc.),it has been demonstrated that the quantum-photonic analogical study is an efficient way.To this end,such studies have been explosive but remain rather insufficient.This thesis aims to explore the optical properties of PNs(model patterns,scattering properties and optical-mechanical effect,etc.)inspired by certain quantum-photonic analogical effects.Along the line of multimode interactions in PNs,this thesis carries out following studies:The interactions between different order of SPR antenna modes(AMs)in PNs are discussed.Particularly,the optical-mehanical effects induced by Fano resonance are exmanined.By using Maxwell stress tensor integration,the optical forces of PNs surpporting Fano resonance are rigorously calculated.It is found that Fano resonance leads to sign reversal of the optical binding force between the antenna arms.The corresponding near field feartures are analyized in detail.It is indicated that the optical binding force reversal is caused by the phase variation at Fano resonance.Furthermore,the optical binding force in a PN sustaining multiple Fano resonances shows repeated sign reversals.The results suggest that the optical forec reversal is a ubiquitous phenomenon in plasmonic nanostructures supporting Fano resonance.This unique effect is of significance in self-assembling of PNs and in optical micro-manipulation.The properties of magnetic cavity modes(CMs)in the dielectric gap of PNs are explored.The underlying mechanism and macroscopic optical features of the CMs of metal-dielectric-metal(MDM)patch PNs are discussed.It is shown that the CMs contain magnetic multipole and toroidal dipole components.Then,the properties of CMs of laterally open and close PNs are comparably studied.The results show that the boundary condtition considerably affacts the resonance frequencies and the optical characteristics of CMs.More specially,metallic lateral coating can eliminate the magnetic multipoles and retain all the cavity modes with vortex-like magnetic field distributions.Finally,the resonance frequencies of PNs with different geometries are theoretically presented.The predictions agree well with the full wave numerical calculations.For resonance frequencies below 600 THz,the discrepancy is less than 5% for a MDM patch antenna we designed.Based on that,coherent coupling between AM and CM in PNs are studied.With appropriate geometry and permittivity of the loaded dielectric material of PN,the AM interacts with the CMs.It is shown that the magnetic dipoalr CM with azimuthal number 1 is orthogonal with the AM,yielding superscattering phenominon;While the magnetic toroidal dipolar CM with azimuthal number 0 strongly competes with the AM,yielding Fano or electromagnetically induced transparency(EIT)profile in the optical spectrum.According to the optical features of the different modes,a model of coupled oscillators is established to understand the coexistence of enhanced and suppressed scattering.The resonance frequencies of both AM and CMs versus the geometry and load material of the PN are studied theoretically and numerically.These results provide efficient guideline to tune AM or CMs independently.Lastly,an analogue related to the degree of spin is preliminarily studied.With respect to the spin-orbit coupling effects related to transeverse spin of SPP,the possibilities of unidirectional excitation of SPP,and spin-dependent scattering direction by PN are explored.The radiation properties of circular polarized electric dipole(CPED)and K dipoles satisfying Kerker condition are analyzed in detail.It turns out that both CPED and K dipole can excite SPPs undirectionally.The theoretical results are confirmed by numrical simulations.Moreover,it is proposed that the spin-orbital coupling of SPPs can be used to tune the scattering direction of PN.Exemplary numerical results show that the transverse scattering direction of sphre-wire coupled PN can be controlled by the helicity of an incident wave.In summary,quantum-photonic analogies greatly enrich the photonic phenomena and design principles for PNs.This thesis provides several scenarios for designing and manipulating optical properties of PNs using this concept.Meanwhile,some photonic phenomena discussed in the relevant PNs are also helpful for understanding the corresponding quantum effects.The presented results may find applications in optical micro-manipulation,high sensitivity plasmonic sensing,scattering cloaking,structured beam generation,photoluminescence control,spin-dependent directional light emission,etc.