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.