Characteristics Of Plasmonic Filters Based On Cascaded Cavities

Surface plasmon polaritons (SPPs) are electromagnetic waves propagating along the interface between metal and dielectric. Under the interaction between the free electrons in metals and the photons, the waves attenuate exponentially in the direction perpendicular to the interface. The unique properties of surface plasmon polaritons have been considered as carriers of energy and information to overcome the diffraction limit in conventional optics. In recent years, due to the development of nanometer process technology, various nanostructures fabrication are relatively easy, surface plasmon polaritons have become the focus of scholars’attention. Researchers have paid great attention to metal-insulator-metal (MIM) structure in recent years for its potential applications in manipulating and controlling light at nanoscale. Various devices based on the MIM waveguides have been studied numerically and experimentally, such as the optical couplers, beam splitters, Mach-Zehnder(M-Z) interferometer, Y-shaped waveguide, etc. Scholars have been attracted to plasmonic filter based on MIM structure due to its simple fabrication and excellent performance.The simulations of various MIM-based plasmonic filters are investigated by using FDTD methods with PML boundary conditions. Based on the improvement of the existent structures, the cascaded slot cavities filter and nanoring-slot-cascaded filter are proposed. The cascaded slot cavities filter can effectively decrease the FWHM. The nanoring-slot-cascaded filter can separate the resonance modes in the nanoring to realize single channel filtering with narrow FWHM. The main content includes:1. Utilizing the FDTD methods to carry out the simulations of filters based on various MIM structures, such as tooth-grooves, ring resonator, nanodisk and slot cavity. Deeply understanding the principle of different structures and influences of key geometrical parameters through the simulation results.2. By making improvement of the previous structures, the filter based on cascaded slot cavities is proposed. Through adjusting the geometrical parameters of the filter (position of the output waveguide, length of the slot cavity, coupled distance, etc.) to study the influences to the output spectra.3. The nanoring resonator has many resonance modes and filter based on nanoring can realize FWHM with only several nanometers in condition of perfect conductor. In order to obtain filter with single channel, a slot cavity is cascaded with it. The matching rule between the effective radius of the nanoring and the length of the slot cavity is discussed. The coupling distance and the relation between central wavelengths and radius of nanoring (length of slot cavity) are also deeply studied.