Spin Readout And Super-resolution Localization Of Emission Source Based On Coupling With Surface-plasmon-polariton Waveguide

In this thesis,for the coupling from the emission source to the surface plasmon polariton(SPP)waveguide mode supported on the metallic nanowires,general theories of chiral coupling are further developed,and the spin readout and super-resolution localization of emission source were realized.This will be beneficial to the chip-based optical information processing and molecular super-resolution localization.The finished research works are explained in the following.First,for the coupling of an emitter to the SPP waveguide mode,general theories of chiral coupling are further developed,and the spin readout of the emitter is realized.The chiral coupling of an emitter to waveguide mode stems from that the propagation direction of the excited waveguide mode is locked to the transverse spin(T-spin)of a circularly polarized emitter.This chiral coupling can be largely enhanced in terms of unidirectivity,controllability,efficiency and spontaneous emission rate by introducing resonant modes as coupling interfaces.In this thesis,based on reciprocity theorem,we firstly present an intuitive and rigorous approach for analyzing the direct/ indirect chiral coupling(i.e.waveguide without/with additional coupling structures that may support resonant modes),and thereout,derive the conditions for the occurrence of chiral coupling as well as some general relations between the chiral-coupling directionality and the T-spin of the field or emitter.these theories are generally applicable to any direct/indirect chiral-coupling systems and to any lossless/lossy.Based on the above theories,we propose an indirect chiral-coupling system on the platform of SPP,with a nanocavity supporting Fabry-Perot(FP)resonance of dual SPP modes serving as a novel coupling interface.The FP resonance provides flexible design freedoms which can modulate the chirality of the T-spin(and the resultant chiral-coupling directionality)to flip or disappear,and removes the restriction that the chiral emitter must be located in the evanescent field of waveguide mode.A unidirectivity up to 99.9% along with a high coupling efficiency and enhancement of spontaneous emission rate is achieved.Two first-principles-based SPP models for the reciprocal and original problems are built up to verify the decisive role of the FP resonance in achieving the chiral coupling.By comparing with the direct chiral-coupling system(without FP nanocavity),and calculating the indirect chiral-coupling system with substrate added,the performance advantages and robustness of the proposed indirect chiral-coupling system are confirmed.For the proposed direct/indirect chiral-coupling system above,a point emitter is mimicked by the nanotip in scanning near-field optical microscope(SNOM)in experiment.We numerically simulated the chiral coupling between the nanotip emission and the designed structure,and experimentally observed the chiral-coupling-induced unidirectional excitation of the SPP waveguide mode in direct/indirect chiral-coupling system.Second,based on the coupling of molecular fluorescence to the guided SPPs on the silver NWs,a scheme for a remote two-dimensional nanometric localization of fluorescent molecules was proposed,in which the molecular fluorescence is collected by a waveguide and transmitted to the remote ends of the waveguide for analysis,thus realizing a separation of the fluorescence-collection position(at the remote ends of the waveguide)and the fluorescent-molecules position(on the waveguide).By detecting the scattering fluorescence of SPPs at the ends of the NW and analyzing the fluorescence lifetime,radial localization of molecules was realized,with a localization accuracy better than 5 nm.Theoretical calculation results indicate that the guided SPPs on the silver NW are dominantly coupled from radially polarized molecules,and the total spontaneous emission rate(determining the fluorescence lifetime)of molecules strongly depends on the radial location of the molecules.The calculated fluorescence lifetime of the radially polarized molecules depending on their radial location is consistent with the experimental results.Based on that the propagation loss of SPPs depends exponentially on the propagation distance,the relation between the SPP intensities detected at the two ends of the NW were theoretically derived out.By experimentally measuring the intensity ratio of the scattering fluorescence of the SPPs at the two ends of the NW,the axial localization of molecules were realized with a localization accuracy better than 0.28 times of the fluorescence wavelength.