The Mode Characteristics Of Surface Plasmon Microcavities

In recent years,the whispering gallery mode microcavity has become a research hotspot because of its extremely high quality-factor.The surface plasmon polariton(SPP)attracts more and more researchers' attentions because of its strong field-binding ability to confine light waves to sub-wavelength sizes.Surface plasmon microcavity combines these two advantages,possesses the advantages of high quality factor and minimal mode volume,and has become a new type of photonic device with excellent application prospects.This paper mainly analyzes the mode characteristics of two kinds of metal-clad dielectric microcavities,the main contents are as follows:We use analytical and numerical methods to investigate surface plasmon microcavities.The analytical method starts from Maxwell's equations,combines the boundary conditions to obtain the characteristic equation of the microcavity.This characteristic equation describes almost all the characteristics of the microcavity.Based on the weak form of the finite element method,the numerical method simplifies the two-dimensional model into a one-dimensional model so as to accurately and efficiently solve the cylindrical surface plasmon microcavities.The solution time is reduced from original several minutes or tens of minutes to a few seconds after model simplification.For the metal-coated microsphere cavity,the dispersion curves and the modal field distributions were obtained by solving its characteristic equation.It was found for the first time that the symmetrical SPP mode exhibited different dispersion characteristic from other modes.Due to this abnormal dispersion characteristic,the symmetrical SPPs mode can strongly couple with the asymmetrical SPP mode and TM modes(transverse magnetic modes)to generate the supermodes.The supermodes possess both high Q factor(>1000)of photonic modes and high surface amplitude enhancement of SPP modes,which brings supermodes a broad application prospect.For example,supermodes have the advantages of high Q factor and high sensitivity in the sensing field and their sensing FoM can be over 1100.We proposed a novel double-layer metal-clad microcapillary cavity and studied its modal coupling characteristic.Due to the abnormal dispersion characteristic of the symmetrical SPP mode,we observed not only anticrossing phenomenon of strong coupling,but also double anticrossing of SPP/TM/SPP three-mode coupling in a single microcavity for the first time.This third order supermodes also have high Q factor(>1000)and high surface amplitude enhancement,and they have good application prospects in sensing and nonlinear optics.Moreover,if we change the refractive indices of media inside and outside the microcapillary at the same time,full-band tunable double anticrossing is attainable.In addition,the modal field distributions and evolutions of the supermodes can be explained by the effective potential theory.In this paper,the modal characteristics of the plasmonic microcavities are studied in detail.The supermodes have advantages of high Q factor and high sensitivity,which brings them broad application prospects in the fields of sensing and nonlinear optics.Our work provides guidance for the manipulation evolutions of arbitrary modes in any plasmon microcavities.Through our method,the coupling between modes can be arbitrarily customized.