Abstract
To move beyond dedicated links and networks, quantum communications signals must be integrated into networks carrying classical optical channels at power levels many orders of magnitude higher than the quantum signals themselves. We demonstrate the transmission of a 1550 nm quantum channel with up to two simultaneous 200 GHz spaced classical telecom channels, using reconfigurable optical add drop multiplexer (ROADM) technology for multiplexing and routing quantum and classical signals. The quantum channel is used to perform quantum key distribution (QKD) in the presence of noise generated as a by-product of the co-propagation of classical channels. We demonstrate that the dominant noise mechanism can arise from either four-wave mixing or spontaneous Raman scattering, depending on the optical path characteristics as well as the classical channel parameters. We quantify these impairments and discuss mitigation strategies.
Highlights
Over the past decade, there have been significant advances in optical networking technology that have increased the configurabi Iity and transparency of fi bre networks [I]
The addition of a reconfigurable optical add drop multiplexer (ROADM) network element opens up the possibility for transparent path reconfiguration between quantum key distribution (QKD) endpoints, which can enable scalable quantum networking over metro-size regions [21] without requiring secured, optical-electrical-optical (OEO)-based key regeneration, which have been proposed by other groups [19]
We show that the dominant impairment can arise from Raman scattering as was previously shown [13] and from four-wave mixing (FWM)
Summary
Four wave mixing arises from the interaction between two or more pump fields and the l'l nonlinearity of the optical fibre. FWM product powers at the aforementioned levels can have a significant impact on QKD system performance because they can add substantial noise relative to the dark fibre case where the detector dark count rates on the order of I E-5/ns limit the system performance. The fibre attenuation value at a particular wavelength is fixed The consequence of these two effects is that the propagation distance is the only parameter which changes the amount of scattered light at a specific wavelength for a given launch power. To understand the extent of the impact of Raman noise on quantum channels, we measure the Raman spectra generated by a 1560 nm cw pump propagating over several different fibre lengths of standard single-mode fiber (Corning SMF-28e®). In the experiments that follow , we have chosen fiber lengths that allow the strength of the Raman scattering at a given wavelength to be varied in order to isolate the effects of different impairments
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