Coexistence of Quantum and 1.6 Tbit/s Classical Data Over Fibre-Wireless-Fibre Terminals

Abstract

In this paper a fibre free-space fibre link that allows a quantum key distribution (QKD) signal and high-speed data to be transmitted in a single optical beam is presented. This setup has the potential to provide ultra-high data rate secure wireless connectivity within indoor spaces. Both quantum and classical channels were transmitted using wavelengths in the C band, over a range of 2.5 m in free space and in the presence of a 200 lx background illumination. Raman noise caused by the light propagating in the optical fibres which provide connections to the free-space segment, together with geometric loss of the free-space link are the major impairments. Results yield secret key rates of 2.343 kbit/s when the QKD signal is sent without high-speed data (and associated Raman noise), and rates of 1.305 -1.996 kbit/s when high-speed data is also transmitted (depending on spectral separation of QKD and classical information). Further, it is shown that the secret key rate can be optimised by increasing loss to attenuate the Raman noise by misalignment of the link. Improvement of the secret key rate from 1.305 kbit/s to 1.887 kbit/s was shown using this method.

Building a quantum wireless network

“…An experiment was undertaken at the University of Bristol, linking their fibre-based QKD and classical systems with a free-space segment. Full details are reported in [8]. Overall, transmission of 1.6Tbit/s classical data combined with a QKD channel operating with a secret key rate of several kbit/s was demonstrated.…”

“…In [1,2] an analysis of an indoor system is undertaken and in [3][4][5] short range handheld QKD systems demonstrations are reported. There has also been work on transmitting light from optical fibres through free-space in indoor environments (see for instance [6][7][8]) and these can be adapted to transport QKD signals. Such systems typically collimate light from a singlemode fibre and steer the resulting collimated beam through free-space to a collimator which then couples light into a destination fibre.…”

A beam steering platform enabling handheld low-cost quantum key distribution

“…QKD has been intensively studied for long range links and in fibre networks [1,2]. Recent publication tend to focus on the integration of QKD into lower network layers bringing QKD closer to the user [3][4][5][6]. Minimised QKD systems have been reported and first handheld systems have been demonstrated [7][8][9].…”