Submicron-Radius Plasmonic Racetrack Resonators in Metal-Dielectric-Si Hybrid Plasmonic Waveguides

Plasmonics enables miniaturization of the dimensions of photonic devices beyond the diffraction limit, such as submicrometer-radius resonators. However, the experimentally demonstrated circular-ring resonators based on the complementary metal–oxide–semiconductor-compatible metal–dielectric-Si hybrid plasmonic waveguide (HPW) exhibit a small extinction ratio (ER) of ${\sim}{\rm 4}~{\rm dB}$ when the radius is reduced to 1 $\mu{\rm m}$ because of the relatively weak coupling efficiency between the ring and bus HPWs. The ER is significantly improved by increasing the coupling length; a plasmonic racetrack resonator with 0.7- $\mu{\rm m}$ radius is measured to have ER of ${\sim}{\rm 13}~{\rm dB}$ and that with 1.5- $\mu{\rm m}$ radius has ER of ${\sim}{\rm 30}~{\rm dB}$ around 1550-nm telecom wavelengths. Numerical simulation predicts that the radius can be reduced to 0.5 $\mu{\rm m}$ with ER of ${>}{\rm 20}~{\rm dB}$ , making this ultracompact plasmonic racetrack resonator a promising building block for future dense Si electronic-photonic integrated circuits.