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Journal of Optical Communications and Networking

Demonstration of a three-node wavelength division multiplexed hybrid quantum-classical network through multicore fiber

Joshua Dugre, Samuel Fritsch, R. Krishna Mohan

Published Nov 18, 2024• 4 citations
Publisher

Abstract

This paper presents the practical development of a hybrid quantum-classical network through multiple links of four- and seven-core industrial jacketed multicore fiber. The network utilizes dense wavelength division multiplexing to propagate the C-band quantum and classical information in the same core, making full use of the unidirectional nature of quantum key distribution. Total network transmission of 1.16 Tbps is achieved with a total network secret key rate of approximately 7.4 kbps through a combination of 1 and 2 km links of multicore fiber. The deployment configurations presented are independent of the classical modulation format, and the maximal transmission rate for an operational hybrid network is found to be dependent only on classical optical power occupying the quantum channel wavelength. A model was developed to estimate the impact classical optical channels will have on coexisting quantum channels, which may allow engineers to quickly validate hybrid network designs.

DOI
10.1364/jocn.537196

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This paper presents the practical development of a hybrid quantum-classical network through multiple links of four- and seven-core industrial jacketed multicore fiber. The network utilizes dense wavelength division multiplexing to propagate the C-band quantum and classical information in the same core, making full use of the unidirectional nature of quantum key distribution. Total network transmission of 1.16 Tbps is achieved with a total network secret key rate of approximately 7.4 kbps through a combination of 1 and 2 km links of multicore fiber. The deployment configurations presented are independent of the classical modulation format, and the maximal transmission rate for an operational hybrid network is found to be dependent only on classical optical power occupying the quantum channel wavelength. A model was developed to estimate the impact classical optical channels will have on coexisting quantum channels, which may allow engineers to quickly validate hybrid network designs.
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.
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.
The feasibility of a quantum-classical hybrid network using multicore fiber is explored and key performance metrics of the quantum channel with respect to co-propagating classical light are examined. Multiple commercial time bin quantum key distribution systems from ID Quantique are characterized using direct injection techniques to determine optimal operational parameters for the classical optical channels in order to minimize the quantum bit error rate and maximize secret key generation. A phenomenological model that determines the expected quantum bit error rate for a wide range of injected input wavelengths and powers is utilized to evaluate the quantum key distribution system performance. Analysis shows that the performance limitations exhibited by the tested commercial quantum key distribution systems in a hybrid network based on multicore fiber could be overcome by a strategic choice of the classical channel parameters.
This paper presents a quantum key distribution (QKD) system that combines classical and quantum signals in a single optical channel for quantum key distribution application. We carefully optimize the communication link by placing the bright classical channel wavelength longer than the weak quantum one, number and specification of wavelength division multiplexers, and maximizing on-off extinction in the intensity modulator to minimize crosstalk of bright classical photons onto the quantum channel. Our experiments demonstrate a secret key rate (SKR) of 4.39 kbps for an emulated channel length of 65.5 km with less than 3% quantum bit error rate (QBER). The experimental study discussed here is relevant for utilization of existing optical fiber networks for QKD, making the system more robust for practical usage.
The feasibility of a quantum-classical hybrid network using multicore fiber is explored and key performance metrics of the quantum channel with respect to co-propagating classical light are examined. Multiple commercial time bin quantum key distribution systems from ID Quantique are characterized using direct injection techniques to determine optimal operational parameters for the classical optical channels in order to minimize the quantum bit error rate and maximize secret key generation. A phenomenological model that determines the expected quantum bit error rate for a wide range of injected input wavelengths and powers is utilized to evaluate the quantum key distribution system performance. Analysis shows that the performance limitations exhibited by the tested commercial quantum key distribution systems in a hybrid network based on multicore fiber could be overcome by a strategic choice of the classical channel parameters.
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.