| In recent decades,with the development of micro processing technology,artificial metal micro nano structure has attracted more and more attention.Among them,based on the surface plasmon metal micro and nano structure,due to its excellent properties,have attracted a lot of research interest and in which contains the second harmonic and third harmonic nonlinear effect,fluorescence and other linear effect made many important discoveries and achievements.When the surface plasmon resonance is excited,which can greatly enhanced the local electric field strength,which can greatly enhanced the efficiency of nonlinear optical processes that sensitive to field a variety of and also surface plasmon resonance will tuning the electromagnetic field phase which can used for various optical regulation.Due to the surface plasmon resonance often sensitive on the structure of the geometry and the dielectric environment,so it aspect has a wide application in biomedical,optical sensing,weak light detection,light control,photoelectric control etc.This paper focuses on the metal micro-nano-structure based on the surface plasmon.Research the second harmonic generation,third harmonic generation and control,radiation control of fluorescence,and graphene based optical modulator.The specific contents include:(1)We theoretical simulate and experimental measurement the far-field radiation behavior of the medium metal core-shell structure for three harmonic generations.For the metal shell,leads to the formation of a spherical cavity,at the appropriate wavelength can produce high quality factor,low dispersion cavity mode;and outer surface of the spherical shell also supports broadband sphere mode,it interference with the cavity modes to form the Fano type resonance.Highly collimated diffraction orders of THG signals which satisfy the quasi-phase matching condition are achieved.Moreover,when specific plasmonic cavity mode is excited by the pump laser,much stronger THG signal may be achieved in diffraction orders located in the k-E plane.Thus the farfield THG behavior can be strongly tuned by pump polarization.However,unlike most other polarization controlled nonlinear processes,the localization property of the spherical cavity modes make the excitation efficiency independent from the pump polarization,although the overall nanoparticles array is anisotropy.Numerical calculations shows that the intensity difference between each diffaction order is due to the combination of the coherent interference of the whole array and the anisotropic nonlinear radiation of every single nanoparticle.(2)We investigate experimentally the fluorescence reshaping effect of spectral and spatial in dye doped dielectric-metal core-shell resonators(DMCSRs).By wrapping a nearly perfect metal shell layer around a dye-doped dielectric sphere,the coupling of the dye molecules to a set of sharp electric and magnetic based Mie cavity plasmon resonances supported by DMCSRs is enabled.As a result,a strong modification of the fluorescence emission spectrum is experimentally observed.We are able to demonstrate that the strong reshaping effects are the results of the coupling of dye molecules to those narrow-band cavity plasmon resonances.In addition to the spectral reshaping,we further demonstrate that the fluorescence emission can be spatially redirected in completely different radiation patterns and different polarizations that correspond to the different multipolar cavity plasmon resonances.These unique emission properties make the dye-doped DMCSRs attractive candidates for applications in fluorescence sensing and low-threshold lasing.(3)THG from planar chiral metamaterials consisting of a square array of gammadion-shaped metal-insulator-metal nano structures is investigated theoretically.Left-handed circularly polarized(LCP)and right-handed circularly polarized(RCP)fundamental beams are demonstrated to be able to generate circularly polarized third harmonic generation with opposite handedness,but their third harmonic generation efficiencies differ by over one order of magnitude,thus resulting in strong circular dichroism in third harmonic generation.Through regulation of geometric configuration can also tuning the output phase of third harmonic generation.And tuning the chiral outputting,focusing of the nonlinear signal was achieved.Moreover,such a third harmonic generation-circular dichroism can be exploited to design a nonlinear Fresnel zone plate,where adjacent zones are two enantiomers composed of gammadion-shaped metal-insulator-metal nanostructure and its mirror structure,to directly focus the transmitted third harmonic generation signals.In addition,by adjusting the unit of the adjacent area,we demonstrate that the nonlinear FZP can change the polarization state of THG at focus.We do hope that the concepts demonstrated in this work can find potential applications such as frequency converters,all-optical switches,optical parametric amplifiers,and three dimensional nonlinear optical metamaterials.In addition,the third harmonic generation of triangle metal nanoparticles for circularly polarized fundamental situation was researched by numerical simulation,due to the effect of the selection rule,in a circularly polarized wave in positive triangle structure and produce the third harmonic is far lower than the structure slightly asymmetric can produce the third harmonic;linearly polarized fundamental situation is not different.(4)We theoretically investigated the second harmonic surface currents in complementary split-ring resonators(CSRRs)based on the hydrodynamic model and find that the second harmonic surface currents in CSRRs mainly comes from the protrusion of CSRRs,so they can hardly influence one another when CSRRs are arranged into arrays.The generated second harmonic currents are mostly parallel to the polarization of the incident fundamental wave beam,so the inversion of CSRRs can induce ? phase shifts on the second harmonic radiation of CSRRs.We simulate the nonlinear metamaterial-based photonic crystals(NLMPCs)built from CSRRs,exhibiting the engineered nonlinear diffraction.Furthermore,we have performed experiments and the results match well with the theoretical predictions.That is to say,we have confirmed that CSRRs can be a proper alternative to split-ring resonators.This enables the further use of the concept of quasi-phase matching of NLPCs to realize the control of nonlinear interactions in metamaterials and the high transmission of CSRR provides more potential for nonlinear optical devices.We can realize nonlinear binary-phase Fresnel zone plate(FZP)as shown in according the results above,as well as other potential application such as frequency converters,all-optical switches,scanners,optical amplifiers and three-dimensional nonlinear optical metamaterials,(5)We propose a high-speed plasmonic optical modulator(POM)with high modulation depth that comprising of a Ag nanowire acting as a single mode plasmonic waveguide,of which wrapped by a graphene monolayer as the electrically controllable absorbing material.In addition,a thin dielectric spacing layer is introduced to provide electrical insulation between the Ag nanowire and the graphene monolayer.We investigate the wavelength response of it.And as a proof-of-principle investigation,we select the working wavelength at 785 nm and 1550 nm.By optimizing the geometric parameters of the device such as the radius of Ag nanowire and the thickness of the dielectric layer,a high-performance sub-wavelength graphene-based POM is achieved with modulation depth of 0.46 dB/?m at 785 nm and 0.12 dB/?m at 1550 nm for single-mode operation.Furthermore,the radial component of the electric field can be greatly enhanced along the outer surface by using the dielectric with higher permittivity as the insulating layer.As the results,it enhances the optical absorption by the graphene layer.Consequently,the modulation depth of POM could theoretically be much improved up to?4.45 dB/?m(785 nm)using a thinner high-index spacing layer.Such plasmonic-mode-based design has a greater advantage to develop ultra-compact optical modulator towards deep sub-wavelength scale.This design by principle can be scaled over a broad frequency range as long as the device configuration is being optimized for the target wavelength.Our proposed POMs have the advantages of deep sub-wavelength footprints,high modulation depth and high-speed characteristics,the switching speed for the 3 dB bandwidth up to 200 GHz for 785 nm and 600 GHz for 1550 nm,which has promising potential to realize on-chip optical ultra-compact interconnects. |
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