Research On Resonant Coupling Of The Localized Surface Plasmon Mode And Cavity Mode In Surface Plasmon Polaritons

Surface plasmon polaritons(SPPs)are electromagnetic waves due to the electron oscillations on metal surfaces.Surface plasmon polaritons limit the electromagnetic field to a cross-section much smaller than the wavelength of light,breaking through the diffraction limit of light.Based on this characteristic,surface plasmon polaritons have wide applications,such as nanosensors,sub-wavelength integrated optical circuits,and enhanced nonlinear effects.In recent years,the resonance of surface plasmon polaritons in metallic structures has aroused everyone’s interest.The resonance of the localized surface plasmon resonance mode and cavity modes in surface plasmon polaritons originate from different physical mechanism,and the interaction between the two resonance modes is generated.In this paper,the interaction of localized surface plasmon polariton mode and cavity mode are mainly studied.The three two-dimensional metallic cavity structures that triangular cavity,trapezoidal cavity and W-shaped cavity are designed.The interaction of localized surface plasmon polariton mode and cavity mode in three cavities are investigated through the finite difference time domain(FDTD)method.It was found that surface plasmon polariton resonance(SPPR)bright and dark modes are excited on the sides of triangular cavity and trapezoidal cavity.A wedge-shaped metallic structure is added to the trapezoidal cavity and its shape changes to W-shaped cavity,localized surface plasmon polariton(LSPR)mode is excited on the tip of wedge-shaped metallic structure.With the increase of the height of the wedge,the LSPR with narrow bandwidth interferes destructively with SPPR dark and bright modes with wide bandwidth on the sides of cavity,forming localized surface plasmon induced transparency(LSPIT)and Fano resonance(LSPFR),respectively.Comparative to general cavity modes with at least one dimension larger than half of wavelength in two dimensional structures,the LSPR can be confined to an ultra-small scale with both two dimensions less than half of wavelength.The LSPIT and LSPFR can be applied to enhance the spatial resolution of sensor and design sensors to sense particle’s size,position and refractive index in several-nm scale.