Quantum key distribution (QKD), both satellite based and in optical-fiber communications, constitutes a core technology for securing the information networks of the future. But in fiber networks, dispersion—the prism-like smearing-out of frequencies and arrival times as broadband light propagates through the fiber—can play havoc with the delicate timing correlations between entangled photon pairs that such quantum encryption requires.
Now, researchers at the National University of Singapore (NUS) have tested out a neat trick for avoiding dispersion effects in fiber-based QKD, without adding dispersion-compensating equipment or making other changes to the installed fiber cable network.
The secret lies in engineering the wavelength and spectral characteristics of the entangled photons themselves, so that they lie near the so-called zero-dispersion wavelength of single-mode fiber, around 1310 nm.
Tweaking the photon source in this way, the team showed, can preserve the timing correlations between the entangled pairs across fiber spans ranging from 10 to 80 km—even in realistic, multi-segment fiber runs with varying dispersion characteristics. The technique, the researchers believe, could make implementing quantum encryption an easier proposition in metropolitan fiber networks with substantial installed infrastructure.
Post time: May-13-2019