Would Scaling to Extreme Ultraviolet or Soft X-Ray Communications Resolve the Capacity Crunch?

Abstract

Optical networks are facing fundamental capacity scalability problems owing to Shannon limits in silica fiber, frequently summarized as the “optical networks capacity crunch.” We explore the possibility of scaling communication capacities through the use of significantly higher carrier frequencies, such as the extreme ultraviolet or the soft x-ray spectral region, in analogy to the 3–7 orders of magnitude increase in carrier frequencies when optical fiber replaced microwave transmission technologies in the late 1970s. We find that only very limited capacity gains on the order of 10 may be achieved relative to the 1550-nm telecommunications band without fundamentally increasing a system's received energy per bit, its relative bandwidth, or its degree of spatial parallelism. Conversely, we predict the required reduction of waveguide losses that would be needed to make higher carrier frequencies a viable proposition from an energy efficiency point of view. Our analyses include the use of as of yet unexplored quantum communication techniques, whose required energy per bit we find to be lower-bounded by $\boldsymbol{kT}/\log _2\boldsymbol{e}$ at any carrier frequency, which may have implications beyond the communications applications discussed in this paper.