Emerging technologies, free-space optical communications

Abstract

Technology of free-space laser communications at the component, subsystem, and system levels has advanced enough to successfully validate the lasercom technology at the maximum Mars range with data rates approaching 500 Mb/s – nearly two orders of magnitude beyond the state-of-the-art radio-frequency communications systems. There is opportunity for significant additional link margin improvement. When realized, the additional link margin may be used to reduce mass, power consumption, size, and complexity of the flight transceiver. The enhanced data rate capability will, for example, enable streaming high-quality video from other planets to the Earth. The “light science” enabled by lasercom (akin to radio science) remains a largely unexplored field. Key remaining engineering challenges include circumventing attenuation due to dense clouds/fog, communicating while the receiver field of view is within a 1� of the Sun, and addressing the inadequacy of ground station infrastructure. While future Earth-based optical receivers may be located on airborne or Earth-orbiting platforms to circumvent atmospheric issues, technology and operational demonstrations for the first decade or so of deep-space laser communications will likely rely on lower risk and less-expensive ground-based receivers. Ground station diversity can adequately mitigate cloud cover. Large-diameter membrane filters located at the entrance aperture of ground-based telescopes, or telescopes designed to circumvent Sun interference, will aid with communications at small Sun angles. The advent of affordable, large-diameter, non-diffraction-limited ground telescopes should make infrastructure development realizable.