ABSTRACT
While silicon is arguably the most extensively studied material in
history, one of its most important attributes, 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, phenomena that emerge in optical nanowires as
a result of the concentration of optical power in a small geometry.
These losses are absent in silica glass optical fiber and other
common communication channels. While nonlinear loss in silicon
is well known, noise and fluctuations that arise from it have never
been considered. Here we report sources of fluctuations that arise
from two-photon absorption, free-carrier plasma effect, and four-
wavemixing, and use these results to investigate the theoretical limit
of the information capacity of silicon. Our results show that noise
and fluctuations due to nonlinear absorption become significant
and limit the information capacity well before nonlinear loss itself
becomes dominant. An interesting finding is the relation between
the capacity and minority carrier lifetime unveiling an intriguing
connection between semiconductor physics and information theory.
This applies to the case where four-wave mixing can be curbed.
In case where it cannot, we show that the noise it creates limits
the capacity in coherent communication. Our analysis also includes
generation-recombination noise. We present closed-form analytical
expressions that quantify the capacity and provide an intuitive
understanding of the underlying physics. Our results provide the
capacity limit and its origin, and suggest solutions for extending
it via coding and coherent signalling. The amount of information
that can be transmitted by light through silicon is the key
element in future information systems. Results presented here are
applicable not only to silicon but also to other semiconductor optical
channels.
