Demonstration of Lasercom and Spatial Tracking with a Silicon Geiger-Mode APD Array

We present a demonstration of a high-rate photon counting receiver with the potential to act as a spatial tracker based on a silicon Geiger-mode avalanche photodiode array GM-APD. This array enables sensitive high-rate optical communication in the visible and near infrared regions of the spectrum. The array contains 1024 elements arranged in a 32x32 pixel square. This large number of elements supports high data rates through the mitigation of blocking losses and associated data rate limitations created by the reset time of an individual Geiger-mode detector. Measurement of bit error rates demonstrate that receiver sensitivities of 5.55 dB detected photons-per-bit for 78.8 Mbs on-off-keying and 2.54 dB detected photons-per-bit for 19.4 Mbs 16-ary pulse-position modulation are accessible with strong forward error correction. Additionally, the array can record the spatial coordinates of each detection event. By computing the centroid of the distribution of spatial detections it is possible to determine the angle-of-arrival of the detected photons. These levels of performance imply that Si GM-APD arrays are excellent candidates for a variety of free space lasercom applications ranging from atmospheric communication in the 1 micron or 780 nm spectral windows to underwater communication in the 480 nm to 520nm spectral window.