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A small array of single photon avalanche detectors (SPADs) has been designed and fabricated in a standard 0.18 μm CMOS process to test a new photon detecting system for optical communications. First numerical results are presented which show that using arrays of SPADs reduces the optical power density required at the receiver. Experimental results then show that the new system preserves the photon counting ability of the SPADs. Finally a simple method is presented which can be used to estimate the size of array needed to achieve a particular target bit error rate at a specific optical power density. Together these results indicate that by replacing the avalanche photodiode in a receiver with the new system it will be possible to count the received photons.

We present the first three-dimensional, functional images of the human brain to be obtained using a fibre-less, high-density diffuse optical tomography system. Our technology consists of independent, miniaturized, silicone-encapsulated DOT modules that can be placed directly on the scalp. Four of these modules were arranged to provide up to 128, dual-wavelength measurement channels over a scalp area of approximately 60 × 65 mm2. Using a series of motor-cortex stimulation experiments, we demonstrate that this system can obtain high-quality, continuous-wave measurements at source-detector separations ranging from 14 to 55 mm in adults, in the presence of hair. We identify robust haemodynamic response functions in 5 out of 5 subjects, and present diffuse optical tomography images that depict functional haemodynamic responses that are well-localized in all three dimensions at both the individual and group levels. This prototype modular system paves the way for a new generation of wearable, wireless, high-density optical neuroimaging technologies.

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Visible light communications (VLC) is an alternative method of indoor wireless communications that requires sensitive receivers. Ideally, single photon avalanche detectors (S PADs) could be used to create more sensitive receivers. However, the dead-time, finite output pulse width and photon detection efficiency of existing S PAD arrays limits their sensitivity and bandwidth. In this paper an accurate equation for the impact of dead-time on the sensitivity of a S PAD array is presented. In addition the impact of the width of the output pulses on the on-off keying (OOK) data rate is investigated. Finally, a comparison between receivers containing an APD and a large array of S PADs shows that although the receiver containing the S PAD is more sensitive in the dark the APD-based receiver is more sensitive in normal operating condition. However, the models that predict the performance of both receivers suggest that newer S PAD arrays will enable significant improvements in receiver sensitivity.