Simulation Research On The Optical Enhancement Characteristic Of Dielectric Nanostructures

With the rapid development of science and technology,semiconductor devices have the trend towards high-speed and miniaturization.Compressing light to a nanometer size has become a prospect for the development of optical integrated circuits.Nanophotonics aims to break the diffraction limit and realize the control technology of light in the deep sub-wavelength range.The nanostructures designed with new optical phenomena in nanophotonics can realize the enhancement of optical properties.At the same time,the use of dielectric materials overcomes the limitations from the material loss of metal.There are mainly two popular photonic structure designs in current researches:one is a cavity structure based on Surface Plasmon Polaritons(SPPs)design,which realizes enhanced electromagnetic fields in nanoparticles or nanomembrane.The other is the use of Photonic Crystals(Photonic Crystals,PCs)designed microcavity structure to achieve ultra-high quality factor.SPPs describe the electromagnetic waves confined between the interface of two media,which have opposite dielectric constants.For a specially designed waveguide structure,when light with specific wavelength incident to the structure,the coupling of the surface state and the slit will release the energy in the form of the light field,which greatly enhances the transmission.At the same time,the coupling effect of SPPs local groove mode and incident light interference diffracted wave will also form highly directional emitted light.The photonic crystal is a periodic structure,and the photonic bandgap can be changed by tuning the structure parameters,thereby manipulating the transmission properties of light.The designed photonic crystal microcavity structure can achieve a bound state with no leakage in the radiation continuum(Bound States in the Continum,BIC),resulting in a system with ultra-high quality factor.This thesis mainly studies the optical characteristics of the extraordinary optical transmission and the beaming effect by tuning the pattern on the input and output corrugation of the InSb slit waveguide.By means of altering the temperature,doping concentration of InSb and the geometrical parameters of the input corrugation,the greatly enhanced transmission are obtained.The properties of the beaming intensity and focal length are thoroughly analyzed by changing the number and depth of the output groove at a fixed wavelength.The investigations of the unique SPPs properties of the InSb slit grating structure pave the way towards a wide range of novel applications in future plasmonic devices at THz range.The beaming effect can be applied to the devices that can transmitor receive light along a specific direction for a given wavelength,such as the spectral multiplexing and the fiber coupling..In addition,in practical applications,the tunability of the resonant wavelength improves the flexibility of these devices.This thesis also proposes a novel design that takes advantages of both the direct bandgap dielectric material GeSn and the BIC phenomenon,and it possesses higher-Q factors than traditional optical microcavities.First,the correlation properties of multi-type BICs have been theoretically analyzed in two different structures.By calculating the band diagram and reflection spectrum,the physical processes of the formation of BICs are explained in detail.Next,the distinguished high-Q factor has been proved,and the modulation effects of structural parameters on the Q value of the vertical symmetry broken structure have been demonstrated in detail.In the end,we study the effects of the material parameters.By comparing the Q factors of different materials,a GeSn alloy has been proved to have the maximum Q value and optimized optical emission performance.The obtained results declare that with higher Sn content,the designed GeSn-based BIC optical cavity can not only emit light at a specific wavelength with higher intensity,but also possess a high-Q factor.This discussion provides useful guidelines for practical applications of photonic structures in lasers.