Directional Excitation And Focusing Of Surface Plasmon Polaritons Based On Nanoantennas Arrays

Surface plasmon polaritons(SPP) are tightly confined electromagnetic waves that propagating along a metal-dielectric interface arising from the coupling of light with collective oscillations of electrons. Due to their significant field enhancement and subwavelength field confinement, SPP have a broad range of applications from bio- and chemical sensing, photovoltaic devices, lithography, integrated optical devices, to nonlinear optics. Controllable excitation of SPP within micro- and nano-scale is very important for various SPP applications. Moreover, focusing SPP with plasmonic lens can generation plasmonic vortex and realizing subwavelength localization, which have important applications in optical tweezers, lithography and enhanced Raman spectroscopy. This thesis mainly investigates nanoantenna arrays based SPP tunable directional excitation, plasmonic vortex field excitation and SPP centrally symmetric focusing. A novel and miniature polarization detection method is also proposed.A V-shaped nanoantennas array etched in gold thin film is designed. Theoretical researches and numerical simulations show that this array can be used to tunable directional excite SPP. The designed V-shaped nanoantenna supports two plasmon resonant modes with opposite symmetries. The SPP excited by these two modes are symmetric and anti-symmetric. When the incident light is arbitrarily polarized, the excited SPP in ?x directions are the interference results of the two SPP with opposite symmetries. So the power of SPP excited in ?x directions can be manipulated by controlling the polarization state of incident light. Unidirectional excitations of SPP in ?x directions are realized with circularly and elliptically polarized incident light. Further optimization of structure parameters, tunable directional and unidirectional excitations of SPP with linearly polarized incident light are realized.Based on nanoslits that etched in gold thin film and arrayed by Archimedes curves, a plasmonic lens is constructed. The plasmonic vortex generation properties of this plasmonic lens with linearly polarized incident light are theoretically and numerically studied. Results show that with specific directions polarized linearly polarized incident light, the SPP excited in different azimuth angle of the plasmonic lens have same amplitude but different phase. The excited SPP propagate to the center of the plasmonic lens and interference with each other resulting in a centrally symmetric intensity distribution and azimuth angle varying phase distributions, i.e. plasmonic vortex field. The order of the plasmonic vortex field is n?1, where n is the ratio between the maximum and minimum radiuses difference of inner Archimedes curve of the plasmonic lens and the SPP wavelength. +1 or-1 depends on the polarization direction of incident light and the nanoslits orientation of the plasmonic lens. Moreover, by cutting the Archimedes curves of the plasmonic lens into segments, highly ordered plasmonic vortex fields are generated with small plasmonic lens size. The order is m?n ?1, where m is the number of segments.A rectangular holes arrayed plasmonic lens is proposed and the SPP focusing properties of this plasmonic lens with different polarized incident light are investigated. Research results show that this plasmonic lens can centrally symmetric focus SPP with arbitrarily polarized incident light. The field distributions inside the plasmonic lens are always zero ordered Bessel function distributed. The size of the focal spot taken from the numerical simulation result is about 0.35 times of incident wavelength. When the incident light is linearly polarized, the field distribution inside the plasmonic lens is insensitive to the polarization direction. When the incident light is elliptically polarized, the field distribution inside the plasmonic lens is insensitive to the inclination angle of elliptically polarization state, but changes with the ellipticity angle of elliptically polarization state. Particularly, the focal spot intensity is maximized for right-handed circular polarization incidence, and is twice that for linearly polarized incident light, while that is minimal and almost null for left-hand circularly polarization incidence.The SPP focusing properties of two nanoslits arrayed plasmonic lenses are studied. A novel and miniature polarization detection method based on these two plasmonic lenses is also proposed. Theoretical and numerical results show that these two plasmonic lenses can always focus excited SPP to their centers with arbitrarily polarized incident light, resulting in zero ordered Bessel function distributed field distributions. Moreover, the amplitudes of field distributions inside these plasmonic lenses are sensitive to the polarization states of incident light. Utilizing the intensity polarization sensitivities, only by measuring four intensities at the center of these two plasmonic lenses, the full Stokes parameters of incident light are can be detected, which means that the polarization state of incident light is detected. The sizes of these two plasmonic lenses are both only about 6μm.