Surface Plasmon Polaritons Excitation In Visible Regime At The Interface Between Indium Tin Oxide And Lithium Niobate

The rate transferring and storage requirements are increasing in the age of big data.Nevertheless,traditional photonics and electronics components have been unable to cover the developing demands,and new photonics devices become a choice owing to high bandwidth and easy integration.However,the diffraction limit is restricting further miniaturization of photonic devices.In recent years,surface plasmon polaritons(SPPs)have become hot spots to deal with the limitation.As an electromagnetic propagating mode at the interface between conductor and dielectric,SPP can localize energy in subwavelength scale,enhancing the electric field.Meanwhile,the excitation and propagation are not restricted by diffraction limit.Thus,there are wide application prospects in communication,data transmission,biosensor,solar cell,and so on.The traditional excitation of SPP is based on metal materials,which introduces the inherent loss and low performance of SPP devices,limiting widespread applications.Therefore,low-loss semiconductor materials have become a research hotspot.At present,it provides new opportunities for SPPs that generating two-dimensional electron/hole gases(2DEG or 2DHG)at semiconductor interface by polarity catastrophe.This thesis is based on lithium niobate(LN)and indium tin oxide(ITO)to study the interface 2DEG and explores the possibility of supporting visible SPPs.The coupling between incident lights and SPPs brings a series of novel phenomena and we expanded them to the uncovered polar lithium tantalate.Our studies support theoretical and experimental basis for designing new photonic devices and photonic circuits.Firstly,strong spontaneous polarization based on lithium niobate surface achieves the metallization of ITO/LN interface,inducing electrostatic modification.Using diffusion equation and Thomas-Fermi screening model,the carrier density distribution and inner electric field distribution in ITO films adjacent to Li Nb O3 were calculated.The results show that the thickness of modified layer is in nanometers,where the carrier density is comparable to gold and silver,indicating the metallized interface.The Drude model and density functional theory are applied to calculate the permittivity,which show that the modified layer in visible light and near infrared region implements the negative real part of permittivity with high-density carrier.Thus,the ITO/LN interface can support SPPs excitation in this region.Then,we considered that the spontaneous polarization difference at two LN surfaces would introduce different interfaces.The polarization charges also show different electrical properties.Further experiments confirmed the optical properties'difference between the two ITO/LN interfaces,including the measurements of optical responses.It was found that positive or negative polarization charges could also affect the interfaces optical properties.Furthermore,based on metallic layer and gratings,different sets of SPPs were realized at the two interfaces.The SPP propagation characteristics are also analyzed at different interfaces,not only enhancing the coupling between incident lights energy,but also providing the opposite directions of energy transfer.The exponential gain coefficient could achieve 1.73×10⁵ cm^-1 by measuring the very first reflection of the ITO coated Z-cut Fe-doped LN,which is three orders of magnitude higher than the previously reported experimental value,comfirming the subwavelength energy coupling via SPPs.The phenomena of asymmetric scattering and Young's double slit like interference induced by SPP excitation were analyzed,confirming two sets of independently SPPs at two ITO/LN interfaces.Meanwhile,SPPs can inherit the coherence of incident light.According to the opposite accumulated charges at the+Z and-Z interfaces between ITO and LN induced by photovoltaic and pyroelectric effects,the?phase difference between the two interface gratings is revealed,which successfully explains the opposite trend of the very first reflection at the two interfaces.Furthermore,the possibility of SPP excitation with weakly coherent lights was preliminarily analyzed by changing the polarization state and optical path.Finally,the electrostatic modification induced by spontaneous polarization of polar materials was studied with uncovered copper doped lithium tantalate crystals and the SPP excitation on the surface was realized.Thus,the method of SPP excitation in ITO/LN system was extended to the general polar ferroelectric materials.Density functional theory was used to analyze the electrostatic modification caused by charge accumulation at the surfaces of lithium tantalate.Meanwhile,the surface metallization was confirmed experimentally and the SPP excitation was realized with phase grating.The coupling process between SPP and beams is analyzed and the transmission rings and scattering patterns along the surface are explained.The research in this thesis expands the materials supporting two-dimensional electrons gas,and provides theoretical basis and experimental guidance for low loss and tunable SPP devices.There is a broad application prospect in many fields,such as two-dimensional materials,opto-logic gates,photoelectric control,electro-optical device integration,etc.