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Asia Communications and Photonics Conference

A Core and Wavelength Allocation Scheme for Synergistic Transmission of Classical and Quantum Signals

Xueqin Ren, Yongmei Sun, Weiwen Kong, Yaoxian Gao

Published Nov 5, 2022• 2 citations
Publisher

Abstract

Wavelength division multiplexing (WDM) and space division multiplexing (SDM) can be used to implement coexistence of the classical and quantum signals. But some noises are introduced due to the SDM/WDM techniques, such as Raman, Four-wave mixing and inter-core crosstalk noises, which will restrict the performance of the quantum key distribution system (QKD). In this paper, we consider that the classical optical communication system is also affected by such noises. So, in order to improve the performance of the coexistence system based on WDM and SDM, we propose a dual optimized core and wavelength allocation (DOCWA) scheme to realize the synergistic transmission of classical and quantum signals over multi-core fiber. Experiments verify that the proposed scheme can suppress noise photons on classical and quantum channels up to 152.71% and 167.28% compared to the quantum equal frequency spacing scheme, respectively.

DOI
10.1109/acp55869.2022.10088744

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Wavelength division multiplexing (WDM) and space division multiplexing (SDM) can be used to implement coexistence of the classical and quantum signals. But some noises are introduced due to the SDM/WDM techniques, such as Raman, Four-wave mixing and inter-core crosstalk noises, which will restrict the performance of the quantum key distribution system (QKD). In this paper, we consider that the classical optical communication system is also affected by such noises. So, in order to improve the performance of the coexistence system based on WDM and SDM, we propose a dual optimized core and wavelength allocation (DOCWA) scheme to realize the synergistic transmission of classical and quantum signals over multi-core fiber. Experiments verify that the proposed scheme can suppress noise photons on classical and quantum channels up to 152.71% and 167.28% compared to the quantum equal frequency spacing scheme, respectively.
In this paper, we propose core and wavelength allocation schemes for the simultaneous transmission of classical signals and quantum key distribution (QKD) over multi-core fiber (MCF), aiming to maximize the secure key rate, and evaluate the proposed schemes in sending-or-not-sending-QKD (SNS-QKD) and Bennett-Brassard-1984-QKD (BB84-QKD). First, we formulate the noise power on quantum channels, and propose a theoretical model of backward cascaded noise of four wave mixing and inter-core crosstalk considering modulation frequency of the classical signals. Also, the impact of noises on secure key rate is calculated in SNS-QKD and BB84-QKD. Then, we propose a core allocation algorithm in order to reduce the noise interference to quantum cores, and the quantum equal frequency spacing (qEFS) and the quantum unequal frequency spacing (qUFS) wavelength allocation schemes are proposed in the same-core (SC) and the different-core (DC) distribution. Finally, we perform numerical simulation and experimental evaluation for the proposed schemes. Compared with the conventional channel allocation (CCA) scheme in SNS-QKD, the proposed schemes can extend the secure transmission distance up to 78.8%. In BB84-QKD, the secure transmission distance can be extended up to 127.1% under SC-qUFS scheme. Experimental results show that the proposed schemes can suppress noise photons up to 57.54% compared to CCA scheme.
The quantum-classical coexistence can be implemented based on wavelength division multiplexing (WDM), but due to Raman noise, the wavelength spacing between quantum and classical signals and launch power from classical channels are restricted. Space division multiplexing (SDM) can now be availably achieved by multicore fiber (MCF) to reduce Raman noise, thereby loosening the restriction for coexistence in the same band and obtaining a high communication capacity. In this paper, we realize the quantum-classical coexistence over a 7-core MCF. Based on the SDM, the highest launch power of 25 dBm is achieved which has been extended nearly 19 times in previous work. Moreover, both the quantum and classical channels are allocated in the C-band and the minimum wavelength spacing between them is only 1.6 nm. The coexistence system eliminates the need for adding a narrowband filter.
In this paper, we investigate the impact of classical optical communications in quantum key distribution (QKD) over hollow-core fiber (HCF), multi-core fiber (MCF) and single-core fiber (SCF) and propose wavelength allocation schemes to enhance QKD performance. Firstly, we theoretically analyze noise interference in QKD over HCF, MCF and SCF, such as spontaneous Raman scattering (SpRS) and four-wave mixing (FWM). To mitigate these noise types and optimize QKD performance, we propose a joint noise suppression wavelength allocation (JSWA) scheme. FWM noise suppression wavelength allocation and Raman noise suppression wavelength allocation are also proposed for comparison. The JSWA scheme indicates a significant enhancement in extending the simultaneous transmission distance of classical signals and QKD, reaching approximately 100 km in HCF and 165 km in MCF under a classical power per channel of 10 dBm. Therefore, MCF offers a longer secure transmission distance compared with HCF when classical signals and QKD coexist in the C-band. However, when classical signals are in the C-band and QKD operates in the O-band, the performance of QKD in HCF surpasses that in MCF. This research establishes technical foundations for the design and deployment of QKD optical networks.
Quantum-key-distribution (QKD) enabled optical networks can provide secure keys for different kinds of applications to ensure the high security of communication processes. As the number of wavelength channels in a single-core fiber is limited, space division multiplexing (SDM) has been considered to be a valuable technique to provide more wavelength resources, which solves the problem of insufficient channel capacity. Due to the rapid expansion of data volume, the SDM-based QKD network has been regarded as an important paradigm. At the same time, resource allocation in multi-core optical networks is a problem worthy of studying. In this work, four routing, core, and wavelength allocation (RCWA) algorithms are proposed in the multi-core optical network for quantum service requests and classical service requests, which are referred to as RCWA without perception (RCWA-WP), RCWA with crosstalk perception (RCWA-XTP), RCWA with spectrum perception (RCWA-SP), and RCWA with core perception (RCWA-CP). Simulations are carried out to evaluate the network performance in terms of blocking probability, key utilization, and average crosstalk intensity. The comparative results indicate that the RCWA-SP algorithm can improve network performance and reduce the blocking probability, while the RCWA-XTP algorithm can reduce inter-core crosstalk during transmission.
The quantum-classical coexistence can be obtained using wavelength division multiplexing (WDM), however, the crosstalk between quantum and classical signals due to Raman noise must be handled with extra attention. Multi-core fiber (MCF) provides a good solution for the coexistence based on space division multiplexing (SDM). In this work, we propose and experimentally demonstrate hybrid transmission of ultrastable optical frequency reference and quantum key distribution (QKD) over homogeneous MCF. The scheme achieves optical frequency stabilization at the remote site by beating the loopback frequency signal with a local reference to extract link phase noise, which is then compensated via voltage-controlled oscillator (VCO) feedback. Prior to the experiment, we first analyze the critical challenges in MCFs including inter-core crosstalk and inter-core spontaneous Raman scattering. To minimize the crosstalk between the signals, the quantum signal and the optical frequency propagate through separate fiber cores. Successful hybrid transmission of optical frequency references and QKD is achieved across 20 km seven-core fiber. The frequency instability of1.2×10−171.2 \times 10^{-17}1.2×10−17at 1 s and4.2×10−194.2 \times 10^{-19}4.2×10−19at 10000 s, and secure key rate of 317.28 kbps can be realized in this integrated transmission system. The scheme benefits from two merits, ultrastable optical frequency offers high-precision clocks to QKD, and QKD provides one-time-pad keys to encrypt the time data. These results demonstrate the feasibility and tolerance of our QKD system with high-precision frequency reference and the viability of multi-core fibers for next-generation quantum networks.
In quantum-classical coexistence systems, classical noise and system loss can significantly affect the performance of quantum key distribution (QKD), while the fixed-parameter QKD (FPQ) cannot adapt to varying conditions. In this paper, we propose a local search algorithm (LSA) for QKD to optimize the parameters in wavelength division multiplexing (WDM) and space division multiplexing (SDM) systems. Simulation results show that LSA can achieve 99.9% performance of the exhaustive search algorithm, while significantly reducing computational complexity. Moreover, LSA improves QKD performance by 31.9% over standard single mode fiber and 24.5% over multicore fiber in quantum-classical coexistence systems.