We demonstrate silicon/SiO

$_{2}$

/polysilicon lateral MOS-Capacitor (MOSCAP) RRM operating above 50GHz with modulation amplitude enhanced by a large plasma absorption within the MOS junction. A MOSCAP ring resonator modulator (RRM) model has been built using Lumerical software, in which the plasma effect is defined by adopting a reported superlinear rather than linear plasma absorption equation, which aligns well with our experimental results. The performance of the MOSCAP RRMs has been analyzed with different thicknesses of insulator oxide (

$ t_{\text{ox}}$

). The modulation performance is enhanced with thinner

$ t_{\text{ox}}$

down to 3 nm, giving a lower insertion loss and larger optical modulation amplitude (OMA) when benchmarked with a conventional depletion type RRM with a low

\begin{equation*} V_{\pi }L \end{equation*}

of 2.6-4.0 V

$\cdot$

mm under a bias voltage

$V_{\text{b}}$

0-3V. High-speed operation of the MOSCAP RRM with radius 15

$\mu$

m demonstrated an average power insertion loss (IL

$ _{\text{ave}}$

) of 3.5 dB and one level insertion loss (IL

$ _{\text{one}}$

) of 2 dB for achieving a 3 dB dynamic ER at a data rate of 30 Gb/s and bit-error-rate (BER)

\begin{equation*} < 1 \times 10^{-12} \end{equation*}

. The same performance is possible at 50 Gb/s when feed-forward-equalization is enabled on the detection side. We also show the possibility of operating at 224 Gb/s using 4-level pulse amplitude modulation (PAM-4) for a MOSCAP RRM incorporating two active segments. The MOSCAP RRM provides an attractive solution to surpass the performance of the conventional depletion-type RRM, for which future performance scaling is limited with increased doping density towards

$1 \times 10^{19} cm^{-3}$