Quantum communications over optical fiber networks

Quantum communications is an emerging field with many promising applications. Its usefulness and range of applicability in optical fiber will depend strongly on the extent to which quantum channels can be reliably transported over transparent reconfigurable optical networks, rather than being limited to dedicated point-to-point links. This presents a number of challenges, particularly when single-photon quantum and much higher power classical optical signals are combined onto a single physical infrastructure to take advantage of telecom networks built to carry conventional traffic. In this paper, we report on experimental demonstrations of successful quantum key distribution (QKD) in this complex environment, and on measurements of physical-layer impairments, including Raman scattering from classical optical channels, which can limit QKD performance. We then extend the analysis using analytical models incorporating impairments, to investigate QKD performance while multiplexed with conventional data channels at other wavelengths. Finally, we discuss the implications of these results for evaluating the most promising domains of use for QKD in real-world optical networks.