  The design of a compact high-speed and wide field of view (FOV) receiver is
challenging due to the presence of two well-known trade-offs. The first one is
the area-bandwidth trade-off of photodetectors (PDs) and the second one is the
gain-FOV trade-off due to the use of optics. The combined effects of these two
trade-offs imply that the achievable data rate of an imaging optical receiver
is limited by its FOV, i.e., a rate-FOV trade-off. To control the
area-bandwidth trade-off, an array of small PDs can be used instead of a single
PD. Moreover, in practice, a large-area lens is required to ensure sufficient
power collection, which in turn limits the receiver FOV (i.e., gain-FOV
trade-off). We propose an imaging receiver design in the form of an array of
arrays. To achieve a reasonable receiver FOV, we use individual focusing lens
for each PD array rather than a single collection lens for the whole receiver.
The proposed array of arrays structure provides an effective method to control
both gain-FOV trade-off (via an array of lenses) and area-bandwidth trade-off
(via arrays of PDs). We first derive a tractable analytical model for the SNR
of an array of PDs where the maximum ratio combining has been employed. Then,
we extend the model for the proposed array of arrays structure and the accuracy
of the analytical model is verified based on several Optic Studio-based
simulations. Next, we formulate an optimization problem to maximize the
achievable data rate of the imaging receiver subject to a minimum required FOV.
The optimization problem is solved for two commonly used modulation techniques,
namely, OOK and direct current biased optical orthogonal frequency division
multiplexing with variable rate quadrature amplitude modulation. It is
demonstrated that a data rate of ~ 24 Gbps with a FOV of 15 is achievable using
OOK with a total receiver size of 2 cm by 2 cm.
