Two of my papers were published in Advanced Optical Technologies, recently, as part of a topical issue on applied quantum technologies.
The first paper deals with encoding the polarization of light signals for quantum key distribution (QKD). In principle, light is very good at maintaining its polarization, but in practice things like thermal effects in optical fibers and physical orientations causes polarizations to get rotated in sometimes unpredictable ways. There are various techniques to control and correct for these effects. This paper proposes an approach based on sampling the QKD signals themselves, and analyzes the performance in terms of how much light needs to be sampled. It turns out you can do very well to preserve the polarization with a relatively few signals.
The second paper looks at whether ‘adaptive optics’ techniques can be used to help transmit QKD signals from ground to an orbiting satellite. Adaptive optics uses fast sensors and deformable elements (e.g., mirrors, phase plates) to correct turbulence-induced variations, enhancing pointing precision and, thus, the total signal collected at the receiver. It turns out to be tricky to use this effectively when they satellite is in low-Earth orbit due its fast motion over the ground station—by the time the reference signal has been measured and a correction applied, the satellite has moved so far that the signal beam won't pass through the same bit of atmosphere. (This ‘anisoplanatism’ effect can be bypassed somewhat with a leading ‘laser guide star’, although that's a more complex system.) We also looked at the geostationary orbit case—with no apparent motion, the benefit of adaptive optics is clearer.
Both of these papers are rooted in work that began way back at the beginning of 2011! So I'm very glad the material is finally seeing the light of day, a mere nine and a half years later.
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