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Characterization of Commercial QKD Systems for Multicore Fiber-Based Hybrid Networks

Samuel Fritsch, Joshua Dugre, R. Krishna Mohan

Published Oct 2, 2023• 0 citations
Publisher

Abstract

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.

DOI
10.36227/techrxiv.24216771.v1

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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.
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.
A hybrid quantum network using multicore fibers, that supports both classical and quantum communications is implemented. Commercially available Quantum Key Distribution (QKD) systems were tested for loss tolerance, vulnerability to direct injection attacks, and the ability to generate secret keys in the presence of co-propagating classical communications was investigated. The loss of visibility, increase in the quantum bit error rate, and failure to generate secret keys is observed when an externally injected optical power typically exceeds -26 dBm. The dependence of the QKD operational vulnerability on copropagating signal wavelengths and implications for hybrid communications are discussed.
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.
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.
By exploiting the core aspects of quantum mechanics, quantum key distribution (QKD) offers a solution to the critical challenge of secure communication, facilitating the exchange of a provably secure secret key between remote parties. Despite its potential, QKD faces challenges such as low secret key rates, short propagation distances, and low noise tolerance; however, high-dimensional QKD is a promising strategy to mitigate these constraints. High-dimensional QKD extends the Hilbert space dimension beyond two by utilizing multiple degrees of freedom of the electromagnetic field. While several studies address high-dimensional QKD in multicore fibers, which provide degrees of freedom associated with a particular core choice, these works do not consider cases with significant crosstalk between cores. In this work, we present the estimated secret key rate and quantum bit error rate as functions of the parameters of a four-dimensional hybrid time-path QKD system, considering the crosstalk between cores.
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.