sandwiched between two dielectric slab waveguides. The resonator is situated in a
nanometer-scaled metal–insulator–metal plasmonic waveguide. Due to the dimensional
confinement from the dielectric waveguide to the nanoscaled plasmonic waveguide, electric
fields are enhanced greatly, which will further reduce the threshold value. Moreover, a semi-
analytic method, based on the impedance theory and the transfer matrix method, is …