A survey of technology-driven capacity limits for free-space laser communications

There are a number of options for modulation formats in optical fiber and free-space lasercom systems. There are a seemingly even greater number of options for receiver architectures. Although essentially all of these possibilities and combinations have been analyzed in journal publications, conferences, and textbooks, it seems to the author that much of this information has not been compiled in such a way that the community can easily appreciate relationships between performance and related costs of these many options. In this brief overview, then, we will compare the power and bandwidth efficiencies of coded and uncoded systems using some of the most commonly used formats and receivers. We will also examine some of the more recent results in quantum-optimum receivers in the same context.