  The selection of an optimal photodetector area is closely linked to the
attainment of higher data rates in optical wireless communication receivers. If
the photodetector area is too large, the channel capacity degrades due to lower
modulation bandwidth of the detector. A smaller photodetector maximizes the
bandwidth, but minimizes the captured signal power and the subsequent
signal-to-noise ratio. Therein lies an opportunity in this trade-off to
maximize the channel rate by choosing the optimal photodetector area. In this
study, we have optimized the photodetector area in order to maximize the
channel capacity of a free-space optical link for a diverse set of
communication scenarios. We believe that the study in this paper in general --
and the closed-form solutions derived in this study in particular -- will be
helpful to maximize achievable data rates of a wide gamut of optical wireless
communication systems: from long range deep space optical links to short range
indoor visible light communication systems.
