Theoretical Analysis of Energy Efficiency and Bandwidth Limit of Silicon Photonic Modulators

Parallel optical interconnects at the extreme scale hold the key to resolve the grand challenge of moving enormous amount of data between on-chip cores and within multi-chip modules. Silicon photonic modulators, as one of the most pivotal devices conducting electronic to photonic signal conversion, must excel in energy efficiency and bandwidth density in order to meet the stringent requirement of extreme scale photonic interconnects. In this manuscript, the energy efficiency and bandwidth limit of ultra-compact resonator-based silicon photonic modulators are analyzed from three fundamental perspectives: free carrier dispersion strength of the active materials, Purcell factors of the resonators, and electrical configuration of the capacitors. Our simulation results reveal convincing advantages of photonic crystal nanocavity over micro-ring and micro-disk resonators in terms of energy efficiency and device footprint. While for the electro-optic modulation region, metal-oxide-semiconductor (MOS) capacitors truly outperform reversed PN junctions due to the large capacitance density. However, all resonator-based silicon photonic modulators suffer the intrinsic trade-off between energy efficiency and resistance-capacitance-delay limited bandwidth. The general model developed herein lays the theoretical foundation and identify possible routes to achieve atto-joule per bit energy efficiency and how to approach the bandwidth limit of silicon photonic modulators.