In this paper the information transfer rate of a single-photon avalanche diode (SPAD) array is investigated. The SPAD array is modelled as a discrete-time Gaussian channel with signal-dependent mean and variance. The SPAD dead time is a parameter which affects the extent of this signal dependency. The SPAD array channel capacity and the properties of the capacityachieving input distributions are studied. Using a numerical algorithm, the capacity and the optimal input distributions subject to peak and average power constraints are obtained for
various array sizes, dead times and background count levels. Index Terms—Single-photon avalanche diode (SPAD), SPAD array, photon counting, dead time, capacity.