Large aperture “photon bucket” optical receiver performance in high background environments

The potential development of large aperture ground-based “photon bucket” optical receivers for deep space communications is receiving considerable attention. However, high quality optical apertures in the 10-30 meter range are costly and difficult to build with accurate surfaces to ensure narrow fields-of-view (FOV). One approach currently under consideration is to polish the aluminum reflector panels of large 34-meter microwave antennas to high reflectance, and accept the relatively large FOV generated by state-of-the-art polished aluminum panels with surface accuracies on the order of a few microns, corresponding to several-hundred micro-radians FOV. Sunlight scattered by the atmosphere becomes significant at micron wavelengths when pointing to within a few degrees of the sun, even with narrow bandwidth optical filters. Assuming pulse-position modulation (PPM) and Poisson-distributed photon-counting detection, a “polished panel” photon-bucket receiver with large FOV will collect hundreds of background photons per PPM slot, along with comparable signal photons due to its large aperture. Here we demonstrate that communications performance in high-background high-signal environments depends more strongly on signal photons than on background photons, implying that large increases in background energy can be compensated by a relatively small increase in signal energy, which in turn can be accomplished by a modest increase in receiver aperture.