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British and Irish Conference on Optics and Photonics (BICOP)

Co-existence of 9.6 Tb/s Classical Channels and a Quantum Key Distribution (QKD) Channel over a 7-core Multicore Optical Fibre

E. Hugues-Salas, Rui Wang, George Theodore Kanellos, Reza Nejabati, Dimitra E. Simeonidou

Published Dec 1, 2018• 11 citations
Publisher

Abstract

This paper presents a record-high co-existence DP-16QAM coherent transmission of 9.6Tb/s for classical channels with one discrete-variable quantum key distribution channel over a 7-core Multicore fibre. We demonstrate that effective secret key generation is possible even with the combined crosstalk effect of the six adjacent cores over the quantum channel. Additional measurements show the impact on the secret key rate and QBER by adding coherent optical channels in different cores.

DOI
10.1109/bicop.2018.8658328

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This paper presents a record-high co-existence DP-16QAM coherent transmission of 9.6Tb/s for classical channels with one discrete-variable quantum key distribution channel over a 7-core Multicore fibre. We demonstrate that effective secret key generation is possible even with the combined crosstalk effect of the six adjacent cores over the quantum channel. Additional measurements show the impact on the secret key rate and QBER by adding coherent optical channels in different cores.
The feasibility of transmitting discrete-variable quantum key distribution channels with carrier-grade classical optical channels over multicore fibers is experimentally explored in terms of achievable quantum bit error rates, secret key rates as well as classical signal bit error rates. A coexistence transmission record of 11.2 Tb/s is achieved for the classical channels simultaneously with a DV-QKD channel over a 1 km-long 7-core multicore fiber. Coexistence over the same multicore fiber core is identified as a dominant factor for the performance of the quantum channel requiring optical bandpass filtering of 17 nm for the quantum channel to avoid the effect of Raman noise. Also, counter-propagation of classical channels and quantum channels probe more tolerance to noise proliferation than co-propagation. In addition, the performance of the quantum channel is maintained when more than three cores are used for the classical channels. Furthermore, by adding a second DV-QKD channel in the multicore fiber, the simultaneous transmission of classical channels as well as the generation of quantum-secured keys of two QKD channels is achieved with an operational range of 10 dB of launched power into the MCF.
Quantum key distribution (QKD) guarantees unconditional security and has thus been intensely studied both from a theoretical and an experimental point of view [1]. However, limitations due to transmission loss and noise are still detrimental for these systems performance in terms of reachable distance and key rates, having so far confined QKD implementations to the use of dedicated channels and hence reduced a successful integration with the classical network, with few exceptions [2–6]. In this work we demonstrate a step forward in the co-existence of QKD with classical bright signals, exploiting a 7.9-km long 37-core heterogeneous multicore fiber (MCF) [7], and a space division multiplexing (SDM) technique to achieve a total of 87 Mbit/s secret key generation rate (SKR) in the finite key scenario with a simultaneous co-propagating classical signal of 10 Gbit/s.
Quantum key distribution (QKD) can provide secret keys with security rooted in quantum mechanics, but operation alongside high-capacity classical traffic remains limited by the excess-noise budget of weak quantum states in conventional solid-core fiber. Here, we combine ultralow-loss anti-resonant hollow-core fiber with residual-carrier-assisted discrete-modulation continuous-variable QKD (DM-CV-QKD) to address both propagation-induced coexistence noise and low-SNR phase recovery. Over a 24.3-km hollow-core link with 3.3-dB end-to-end loss, a dual-polarization 15-Gbaud DM-CV-QKD channel achieves an average asymptotic secret-key rate (SKR) of 153.22 Mb/s and a finite-size SKR of 149.99 Mb/s, while 39 coherent wavelength-division-multiplexed channels deliver an aggregate data rate of 7.6 Tb/s and a net data rate of 7.2 Tb/s. The system can even sustain a positive SKR under a high classical launch power of up to 15 dBm, without an optical bandpass filter (BPF). Finite-size analysis against collective attacks further yields a projected positive secret-key rate at a 100-km-equivalent condition. These results show that an anti-resonant hollow-core fiber, combined with carrier-assisted phase recovery, can greatly extend the operating regime of shared-fiber quantum-secured coherent links, pointing to a promising approach for integrating high-rate CV-QKD with high-capacity optical networks.
Multicore-fibres (MCF) have emerged as an attractive solution for capacity scaling in optical communication. Securing such links with Quantum Key Distribution (QKD) is critical with the advent of Quantum computers. For practical deployment, QKD is required to operate alongside high-speed classical communication over field-deployed fiber infrastructure. In this work, the performance of QKD is experimentally evaluated in coexistence with high-speed classical data transmission over field-deployed underground and aerial multicore fiber links. The QKD system is implemented with Coherent One-Way Slim protocol, with dedicated Quantum and classical channels for Quantum communication and QKD post-processing. The deployed 4-core MCF infrastructure at IIT Madras provides an effective transmission length of 48 km through loopback operation. QKD performance over the MCF is evaluated in terms of quantum bit error rate (QBER) under varying attenuation, controlled noise injection, and inter-core crosstalk over both singlecore fiber and MCF links. The experimental results show that inter-core crosstalk has a stronger impact in MCF, leading to increased excess noise at the quantum receiver. For a 32-GBaud PM 16-QAM classical modulation format, stable QKD operation is maintained when the spectral separation is approximately six to eight times the occupied bandwidth.