Plasmonic racetrack resonator with high extinction ratio under critical coupling condition

In this paper, an ultracompact plasmonic racetrack resonator based on single mode metal-insulator-metal plasmonic gap waveguide with high coupling efficiency is investigated both analytically and numerically. The coupling properties of a plasmonic waveguide to a racetrack resonator at 1.55 μ m wavelength are studied with various coupling lengths. An extinction ratio of −34.5 dB and a free-spectral range of 303 nm at the critical coupling point can be achieved. Such a plasmonic resonator design provides a promising realization for highly effective modulators and wide band filters.