Abstract

We propose a novel ring-assisted Mach–Zehnder modulator (RAMZM) design by utilizing highly over-coupled ring modulators with lightly-doped low loss pn junctions, to achieve better trade-offs between insertion loss, extinction ratio, optical modulation amplitude and modulation bandwidth. The design and optimization on both device and circuit levels are presented in this article. A prototype is fabricated in a standard silicon photonic technology. Second-order microrings with 15 $\mu$ m diameter are used in the design. Frequency- and time-domain measurement results show a $\mathbf{\text{26}\;dB}$ static extinction ratio and $\mathbf{\text{10}\;dB}$ extinction ratio at $\mathbf{\text{12}\;Gbps}$ . Ring-induced insertion loss is $\mathbf{\text{4.6}\;dB}$ , and $\mathbf{\text{3}\;dB}$ small-signal modulation bandwidth is measured to be 30 GHz.