Quasi-TPPs/Fano resonance systems based on an MDM waveguide structure and its sensing application

In this paper, quasi-Tamm plasmon polaritons (TPPs)/Fano resonance systems based on metal-dielectric-metal (MDM) waveguides are proposed. TPPs are surface electromagnetic modes formed at the interface between a metal and a one-dimensional dielectric photonic crystal (PhC). A metal plasmonic Bragg reflector (PBR) in a MDM waveguide is equivalent to a dielectric PhC, which is realized by periodic MDM waveguide width modulation and leads to the photonic bandgap. By introducing a thin Ag baffle and a PBR in MDM waveguide core, the quasi-TPPs are excited at the interface between the Ag baffle and the PBR, when the phase-matching condition is met. The proposed structure can be fabricated with focused ion beam or electron beam direct-writing lithography, avoiding complex fabrication procedures of manufacturing dielectric PhC by filling the MDM waveguide core with different dielectric materials. Furthermore, an MDM waveguide side-coupled resonator system is constructed to generate Fano resonance by placing a PBR on the side of the MDM waveguide and an Ag baffle in the waveguide core. The Fano resonance originates from the interference between a broad continuum state provided by the Ag baffle and a discrete state provided by quasi-TPPs. The sensing performance of the Fano resonance system is investigated. In this design, the open PBR structure replaces the traditional closed resonant cavity, which makes it more convenient to contact with analytes. The numerical simulations demonstrate that a high sensitivity of 1500 nm/RIU and figure of merit value of 4.08×105 are achieved.