We demonstrate quantum key distribution (QKD) with classical signals in a seven-core fiber using dense wavelength division multiplexing. Quantum signals are transmitted in an outer core separately and intercore crosstalk (IC-XT) is the main impairment of them. In order to alleviate IC-XT, we propose a quantum-classical interleave scheme. Then the properties of IC-XT are analyzed based on the measurement results which indicate counter-propagation is a better co-existence method than co-propagation. Finally, we perform QKD experiments in the presence of two classical channels with a channel spacing of 100 GHz between quantum channel and the nearest classical channels. The experiment results prove counter-propagation almost immune to IC-XT, which is consistent with our analysis. Also, the feasibility of the transmission over the range of metropolitan area networks is validated with our scheme.Index Terms-quantum key distribution, multicore fiber, wavelength-space division multiplexing. arXiv:1811.04198v1 [quant-ph]
Quantum access networks allow a large number of users to access quantum networks, which can be regarded as an important part of the practical application for quantum communication. However, current quantum access networks have not considered as the peer-to-peer multimedia service between optical network units (ONUs) that have become the dominant service in the access networks. Thus, we propose a quantum access network that can support direct quantum and classical ONU-ONU communication by using an N:N splitter. In addition, we improve the efficiency of quantum key distribution (QKD) from both the physical and the data link layer. For the former, we analyze spontaneous Raman scattering (SRS) that is the main impairment source to QKD due to the co-propagation of the classical and quantum signal. Then, we propose a collision-avoiding scheme to reduce the influence of the SRS. For the latter, a dynamic time slot assignment protocol is proposed to reduce discarding secure keys greatly. The two methods are verified by simulations, and the results show that each method can effectively optimize QKD performance. INDEX TERMS Quantum key distribution, quantum access network, direct ONU-ONU communication, spontaneous Raman scattering.
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