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arXiv:2106.14560 · European Conference on Optical Communication

1.6 Tbps Classical Channel Coexistence With DV-QKD Over Hollow Core Nested Antiresonant Nodeless Fibre (HC-NANF)

Obada Alia, R. S. Tessinari, Thomas D. Bradley, Hesham Sakr, Kerrianne Harrington, J. R. Hayes, Y. Chen, Periklis Petropoulos, David John Richardson, Francesco Poletti, George Theodore Kanellos, Reza Nejabati, Dimitra E. Simeonidou

Published Sep 13, 2021• 11 citations
arXivHTMLPDF

Abstract

We demonstrate for the first time the coexistence of a quantum-channel and 8×200 Gpbs 16-QAM optical channels with launching powers as high as -9dBm/channel in a 2 km HC-NANF. Comparative analysis with single-mode fibre reveals that the quantum-channel could not be sustained at such power-levels.
DOI
10.1109/ecoc52684.2021.9605918

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quant-pharXiv:2512.04605•Dec 5, 2025
The feasibility of coexisting a quantum channel with carrier-grade classical optical channels over Hollow Core Nested Antiresonant Nodeless Fibre (HC-NANF) is experimentally explored for the first time in terms of achievable quantum bit error rate (QBER), secret key rate (SKR) as well as classical signal bit error rates (BER). A coexistence transmission of 1.6 Tbps is achieved for the classical channels simultaneously with a quantum channel over a 2 km-long HC-NANF with a total coexistence power of 0 dBm. To find the best and worst wavelength position for the classical channels, we simulated different classical channels bands with different spacing between the quantum and classical channels considering the crosstalk generated from both Raman scattering and four-wave-mixing (FWM) on the quantum channel. Following our simulation, we numerically estimate the best (Raman spectrum dip) and worst locations (Raman spectrum peak) of the classical channel with respect to its impact on the performance on the quantum channel in terms of SKR and QBER. We further implemented a testbed to experimentally test both single-mode fibre (SMF) and HC-NANF in the best and worst-case scenarios. In the best-case scenario, the spacing between quantum and classical is 200 GHz (1.6 nm) with 50 GHz (0.4 nm) spacing between each classical channel. The SKR was preserved without any noticeable changes when coexisting the quantum channel with eight classical channels at 0 dBm total coexistence power in HC-NANF compared to a significant drop of 73% when using SMF at$-$24 dBm total coexistence power which is 250 times lower than the power used in HC-NANF. In the worst-case scenario using the same powers, and with 1 THz (8 nm) spacing between quantum and classical channels, the SKR dropped 10% using the HC-NANF, whereas in the SMF the SKR plummeted to zero.
Quantum Key Distribution (QKD) technology has been considered as the ultimate physical layer security due to its dependencies on the physical laws of physics to generate quantum keys. However, for QKD to become functional for practical scenarios, it must be integrated with the classical optical networking infrastructure. Coping with optical nonlinearity from the classical represents a major challenge for QKD systems. In this paper, we take the advantage of the ultra-low nonlinearity of Hollow Core Nested Antiresonant Nodeless Fibre (HC-NANF) to demonstrate the coexistence of discrete-variable quantum key distribution channel with carrier-grade classical optical channels over a 2 km HC-NANF.
We experimentally demonstrate the coexistence of three entanglement-based quantum channels with carrier-grade classical optical channels over 11.5 km hollow core nested antiresonant nodeless fibre, in a four user quantum network. A transmission of 800 Gbps is achieved with four classical channels simultaneously with three quantum channels all operating in the C-band with a separation of 1.2 nm, with aggregated coexistence power of -3 dBm. We established quantum key distribution in the four-node full-mesh quantum network with Bell state fidelity of up to 90.0 ± 0.8%. The secret key rate for all the links in the network are passively preserved over 55 hours of experimental time.
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.
The performance of quantum key distribution (QKD) is heavily dependent on the physical properties of the channel over which it is executed. Propagation losses and perturbations in the encoded photons' degrees of freedom, such as polarisation or phase, limit both the QKD range and key rate. The maintenance of phase coherence over optical fibres has lately received considerable attention as it enables QKD over long distances, e.g., through phase-based protocols like Twin-Field (TF) QKD. While optical single mode fibres (SMFs) are the current standard type of fibre, recent hollow core fibres (HCFs) could become a superior alternative in the future. Whereas the co-existence of quantum and classical signals in HCF has already been demonstrated, the phase noise resilience required for phase-based QKD protocols is yet to be established. This work explores the behaviour of HCF with respect to phase noise for the purpose of TF-QKD-like protocols. To achieve this, two experiments are performed. The first, is a set of concurrent measurements on 2 km of HCF and SMF in a double asymmetric Mach-Zehnder interferometer configuration. The second, uses a TF-QKD interferometer consisting of HCF and SMF channels. These initial results indicate that HCF is suitable for use in TF-QKD and other phase-based QKD protocols.