Toward Athermal Plasmonic Ring Resonators Based on Cu- ${\rm TiO}_{2}$ -Si Hybrid Plasmonic Waveguide

Owing to the negative thermo-optic coefficient (TOC) of ${\rm TiO}_{2}$ , the real part of effective modal index of Cu- ${\rm TiO}_{2}$ -Si hybrid plasmonic waveguide (HPW) will be temperature-independent at a certain thickness ratio between the ${\rm TiO}_{2}$ interlayer and the Si core. Cu- ${\rm TiO}_{2}$ -Si HPWs and waveguide-ring resonators (WRRs) are fabricated on SOI wafers using standard CMOS technology and are characterized around 1550-nm telecom wavelengths. The HPWs exhibit a propagation loss of ${\sim}{\rm 0.2}~{\rm dB}/\mu{\rm m}$ and negligible bending loss when the bending radius is larger than ${\sim}{1}~\mu{\rm m}$ . WRRs with radii of 1.5–2.5 $\mu{\rm m}$ exhibit an extinction ratio of ${\sim}{\rm 15}\hbox {--}30~{\rm dB}$ and a Q-value of ${\sim}{\rm 140}$ . A WRR with a 220-nm Si core and 58-nm ${\rm TiO}_{2}$ is measured to have a thermo-optic effect of ${\sim}{\rm 52}~{\rm \pm}/{\rm K}$ , which is about half of the ${\rm SiO}_{2}$ counterpart. The TOC of the as-deposited amorphous ${\rm TiO}_{2}$ is then extracted to be ${\sim}-1.0\hbox {--}1.5\times- 10^{-4}~{\rm K}^{-1}$ . Athermal plasmonic WRRs are expected by either increasing the thickness of ${\rm TiO}_{2}$ (with ${-}1.0\times 10^{-4}~{\rm K}^{-1}~{\rm TOC}$ ) to ${\sim}{120}~{\rm nm}$ or improving the TOC of ${\rm TiO}_{2}$ (with 58-nm thickness) to the reported value of ${-}1.8\times 10^{-4}~{\rm K}^{-1}$ .