Noise and Information Capacity in Silicon Nanophotonics

Modern computing and data storage systems increasingly rely on parallel architectures. The necessity for high-bandwidth data links has made optical communication a critical constituent of modern information systems and silicon the leading platform for creating the necessary optical components. While silicon is arguably the most extensively studied material in history, one of its most important attributes, i.e., an analysis of its capacity to carry optical information, has not been reported. The calculation of the information capacity of silicon is complicated by nonlinear losses, which are phenomena that emerge in optical nanowires as a result of the concentration of optical power in a small geometry. While nonlinear loss in silicon is well known, noise and fluctuations that arise from it have never been considered. Here, we report fluctuations that arise from two-photon absorption, plasma effect, cross-phase modulation, and four-wave mixing and investigate their role in limiting the information capacity of silicon. We show that these fluctuations become significant and limit the capacity well before nonlinear processes affect optical transmission. We present closed-form analytical expressions that quantify the capacity and provide an intuitive understanding of the underlying physics.