[Paper Review] Wavelength Assignment in Hybrid Quantum-Classical Networks

Sima Bahrani, Mohsen Razavi+1 more|arXiv (Cornell University)|Jan 28, 2017

Quantum Information and Cryptography21 references3 citations

TL;DR

This paper proposes near-optimal wavelength assignment strategies in hybrid quantum-classical DWDM networks to minimize crosstalk and maximize secret key rates in quantum key distribution (QKD) channels. By using linear approximations of key rate functions and optimizing wavelength allocation across multiple quantum and classical channels, the method achieves significant performance gains—especially in noise-dominated regimes—outperforming conventional two-band separation approaches by enabling interspersed quantum and classical wavelength bands.

ABSTRACT

Optimal wavelength assignment in dense-wavelength-division-multiplexing (DWDM) systems that integrate both quantum and classical channels is studied. In such systems, weak quantum key distribution (QKD) signals travel alongside intense classical signals on the same fiber, where the former can be masked by the background noise induced by the latter. Here, we investigate how optimal wavelength assignment can mitigate this problem. We consider different DWDM structures and various sources of crosstalk and propose several near-optimal wavelength assignment methods that maximize the total secret key rate of the QKD channels. Our numerical results show that the optimum wavelength assignment pattern is commonly consisted of several interspersed quantum and classical bands. Using our proposed techniques, the total secret key rate of quantum channels can substantially be improved, as compared to conventional assignment methods, in the noise dominated regimes. Alternatively, we can maximize the number of QKD users supported under certain key rate constraints.

Motivation & Objective

• To address the challenge of crosstalk in hybrid quantum-classical DWDM networks where weak QKD signals coexist with intense classical data channels.
• To improve the total secret key rate of QKD channels by optimizing wavelength assignment, especially in noise-dominated regimes.
• To develop near-optimal, computationally efficient wavelength assignment methods that outperform conventional two-band separation strategies.
• To enable scalable support for multiple QKD users under key rate constraints by optimizing resource allocation.

Proposed method

• Proposes linear approximations of the secret key rate function in terms of error rates and background noise, valid for small error probabilities.
• Derives a linear key rate model as a function of multi-path and crosstalk noise powers, enabling efficient optimization.
• Uses a linear programming approach to minimize total crosstalk noise, which correlates with maximizing total key rate.
• Applies the method to both full-duplex and dual-fiber DWDM network architectures to evaluate performance across different topologies.
• Validates the approach via numerical simulations across various channel counts and link lengths.
• Considers two main crosstalk sources: Raman scattering and adjacent channel crosstalk, modeling their impact on QKD performance.

Experimental results

Research questions

• RQ1 Can optimal wavelength assignment in hybrid DWDM networks significantly improve the total secret key rate of QKD channels compared to conventional two-band separation?
• RQ2 Does interspersed allocation of quantum and classical channels outperform separate bands in minimizing crosstalk and enhancing QKD performance?
• RQ3 How accurate is the linear approximation of the secret key rate in predicting optimal wavelength assignments under realistic noise conditions?
• RQ4 What is the trade-off between maximizing total key rate and supporting the maximum number of QKD users under key rate constraints?
• RQ5 How does the performance of the proposed method vary with different numbers of classical and quantum channels in noise-dominated regimes?

Key findings

• The optimal wavelength assignment pattern is not a simple two-band separation but consists of multiple interspersed quantum and classical bands, which significantly outperforms conventional methods.
• The proposed near-optimal method achieves total key rates nearly identical to the theoretical optimum, especially in noise-dominated scenarios.
• For a fixed number of classical channels, there exists an optimal number of quantum channels that maximizes the total secret key rate.
• The method improves total key rate substantially in noise-limited regimes, demonstrating the effectiveness of crosstalk-aware wavelength assignment.
• When maximizing the number of QKD users under a minimum key rate constraint, the total key rate may decrease, indicating a trade-off between user count and aggregate performance.
• The linear approximation of the key rate function is accurate within a mean square error of less than 1.89×10⁻⁴ for error rates below 0.0953, validating its use in optimization.