Performance comparison of coupled-resonator optical waveguide Mach-Zehnder modulators with III-V SIS structures.

As bandwidth demand continues to grow in chip-to-chip interconnects, silicon photonic optical modulators responsible for I/O require faster, more efficient, and more compact. Mach-Zehnder modulators utilizing the slow light effect achieve both higher modulation efficiency and miniaturization compared to conventional designs by reducing light propagation speed and effectively shortening the phase-shifter length. Among slow-light Mach-Zehnder modulators, those utilizing a series of phase-shifted grating resonators provide simplified fabrication processes and stable bandwidth. In this study, we propose an optical modulator that applies a semiconductor-insulator-semiconductor capacitor based carrier-accumulation scheme to these modulators instead of the conventional PN junction-based carrier-depletion approach, achieving high efficiency with greater effective index change and lower driving voltage. By incorporating III-V materials, we secured larger effective index changes and lower absorption loss. Comparative analysis with Si regarding effective refractive index variation and loss demonstrates ultimately higher bandwidth and lower transmitter penalty compared to both crystalline Si and poly-Si implementations. The proposed optical modulator significantly reduces length to tens of micrometers while maintaining high bandwidth, delivering modulation performance comparable to micro-ring modulators. Consequently, this approach is expected to be activated alongside advances in semiconductor manufacturing technology and play a crucial role in next-generation high-bandwidth communications.