Researches On Manipulation Of Optical Properties In Asymmetric Metal Microstructure

The applications of photonic device in micro/nano scale have been always a big challenge due to the limitations of the optical diffraction.However,the appearance of surface plasmons(SPs),which are excited on metal-dielectric surface,solves all of above problems.Owing to the characteristic of localized field enhance and subwavelength confinement,the SPs can route the electromagnetic(EM)wave at subwavelength scale.Additionally,according to the difference in propagated length,we can divided the SPs into surface plasmons polaritons(SPPs)mode and localized surface plamons(LSPs)mode.Utilizing the excellent optical property of the SPPs or LSPs,many novel optical effect and devices have been realized.In this thesis,we design and propose several possible methods for achieving the optical property manipulations on metallic microstructures.The main content include:1.Chiral plasmonic structure have been shown to possess more superior optical property than the conventional metamaterial amd metasurface structures.Here,we proposed a stacked 3D microstructure composed of a metallic nanorod and a split-ring-resonator(SRR),in which the bright-bright mode of electromagnetically induced transparency phenomenon can be excited with a broadband transparent window.When the above nanorod is laterally shifted to form a chiral structure,the selectively excited EIT effect by right circular polarization(RCP)and left circular polarization(LCP)can be achieved.These new findings could be employed to distinguish RCP and LCP light and also have potential application in optical polarization switching.2.We designed a graphene-based unidirectional surface plasmon polaritons(SPPs)launcher,which is composed of asymmetric plasmonic nanoantenna coupled with a graphene sheet separated by a SiO2 spacer from a gold substrate.The non-indentical cavities in the whole structure facilitate the simultaneous excitation of two localized surface plasmons resonances.Through tunning the resonance phase of the localized surface plasmons in these plasmonic cavities,the unidirectional propagation effect can be acquired.Further electric field distributions show that the tunability of the cavity is proportional to the field intensity in the graphene region.Our results indicate that the proposed active device is promising for future electrically controlla-ble,unidirectionally propagating broadband plasmonic light sources.3.Combining with the characteristic of SPPs localized field enhance and the capacitor doping effect of graphene,we try to study the graphene-based SPPs modulators and photodetectors in experiment and theory.Numerical calculations reveal that only longitudinal field of SPPs can be absorbed by graphene.Thus,the waveguide arrays are proposed to apply in designing graphene-based SPPs modulators.Compared to previously study,the novel structure can improve one order of magnitude of modulation depth.It is definitely a good performance in furture optics device designing.