Abstract In the contemporary era of information technology, cybersecurity has emerged as a pivotal subject. Quantum key distribution (QKD) networks have been implemented in various regions worldwide, demonstrating their superior secure communication capabilities in practice. The integration of QKD with traditional fiber optic networks will facilitate the deployment of upcoming quantum technologies. The recently proposed mode-pairing quantum key distribution (MP-QKD) protocol can drastically improve the transmission distance of QKD, thereby obviating the necessity for complex optical field setups. This paper focuses on the co-transmission of MP-QKD with classical signals in three types of optical fibers (single-mode fiber, few-mode fiber, and multi-core fiber). The Raman noise power in the co-transmission system is calculated, and the performance of MP-QKD is analyzed. The analytical results demonstrate the superiority of MP-QKD compared to other MDI-types in co-fiber transmission scenarios.
Abstract In the contemporary era of information technology, cybersecurity has emerged as a pivotal subject. Quantum key distribution (QKD) networks have been implemented in various regions worldwide, demonstrating their superior secure communication capabilities in practice. The integration of QKD with traditional fiber optic networks will facilitate the deployment of upcoming quantum technologies. The recently proposed mode-pairing quantum key distribution (MP-QKD) protocol can drastically improve the transmission distance of QKD, thereby obviating the necessity for complex optical field setups. This paper focuses on the co-transmission of MP-QKD with classical signals in three types of optical fibers (single-mode fiber, few-mode fiber, and multi-core fiber). The Raman noise power in the co-transmission system is calculated, and the performance of MP-QKD is analyzed. The analytical results demonstrate the superiority of MP-QKD compared to other MDI-types in co-fiber transmission scenarios.
Quantum key distribution (QKD) is one of the most practical applications in quantum information processing, which can generate information-theoretical secure keys between remote parties. With the help of the wavelength-division multiplexing technique, QKD has been integrated with the classical optical communication networks. The wavelength-division multiplexing can be further improved by the mode-wavelength dual multiplexing technique with few-mode fiber (FMF), which has additional modal isolation and large effective core area of mode, and particularly is practical in fabrication and splicing technology compared with the multi-core fiber. Here, we present for the first time a QKD implementation coexisting with classical optical communication over weakly-coupled FMF using all-fiber mode-selective couplers. The co-propagation of QKD with one 100 Gbps classical data channel at -2.60 dBm launched power is achieved over 86 km FMF with 1.3 kbps real-time secure key generation. Compared with single-mode fiber using wavelength-division multiplexing, given the same fiber-input power, the Raman noise in FMF using the mode-wavelength dual multiplexing is reduced by 86% in average. Our work implements an important approach to the integration between QKD and classical optical communication and previews the compatibility of quantum communications with the next-generation mode division multiplexing networks.
We theoretically study the issues for long-distance transmission of quantum key distribution (QKD) coexisting with classical signals. The recently proposed phase-matching QKD protocol can drastically improve the transmission distance of QKD. However, in the coexistence system, the noise generated by classical signals, especially spontaneous Raman scattering noise, is a big challenge. Moreover, the classical optical amplifier, which is necessary for the realistic long-distance classical communication, makes the noise more serious. In view of this, we establish the unified Raman noise model for three discrete-variable QKD protocols (BB84, measurement-device-independent and phase-matching QKD protocols) in the presence of classical optical amplifiers, which can be applied to both single-core single-mode fiber and multicore fiber. Then, we derive the key rate of the three QKD protocols coexisting with classical signals using the proposed unified Raman noise model. Finally, simulation results show that multicore fiber is promising for simultaneous long-distance transmission of QKD and the dense wavelength division multiplexing system.
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) provides information-theoretic security for communication. The mode-pairing (MP) protocol emerges as a promising solution for long-distance QKD by eliminating the need for a global phase reference while maintaining the repeaterlike rate-loss scaling. Recent implementations have demonstrated its potential, but they either rely on costly ultrastable lasers or struggle with phase fluctuations from commercial lasers, particularly over long distances. As a result, surpassing the repeaterless bound with a practical system remains a challenge. In this work, we demonstrate a practical high-performance MP-QKD system using commercial lasers. To address phase fluctuations, we propose a frequency-tracking scheme based on fast Fourier transformation, enabling us to extend the pairing length to 2 × 10 5 pulses ( 160 μ s ). We propose a model to carefully analyze the phase noise and optimize the system parameters. Our system achieves an optimal secret key rate of 47.8 bit / s over 403 km of standard fiber (76.5 dB loss), exceeding the repeaterless bound by a factor of 2.92. Furthermore, we compare MP-QKD and twin-field QKD under various practical conditions and clarify the distinct application scenarios of the two protocols. These results confirm the feasibility of MP-QKD using cost-effective commercial technologies, paving the way for scalable quantum communication networks.
Quantum key distribution (QKD) is a secure communication method for sharing symmetric cryptographic keys based on the principles of quantum physics. Its integration into the fiber-optic network infrastructure is important for ensuring privacy in optical communications. Multi-core fibers (MCFs), the likely building blocks of future high-capacity optical networks, offer new opportunities for such integration. Here, we experimentally demonstrate, for the first time, the coexistence of discrete-variable QKD and high-throughput classical communication in the C-band over a field-deployed MCF with industry standard cladding diameter of 125 μm. Specifically, we demonstrate successful secure-key establishment in one core of a 25.2-km uncoupled-core MCF, while simultaneously loading the remaining three cores with full C-band counter-propagating classical traffic at an aggregate net rate of 110.8 Tb/s. By proposing and experimentally validating an improved analytical model for inter-core spontaneous Raman scattering noise, we find that this configuration is optimal for our deployed MCF link as it is immune to four-wave mixing, that becomes relevant when the quantum and classical signals are propagating in the same direction. Our findings make an important step forward in demonstrating the integration of QKD and classical transmission in uncoupled-core multi-core fibers for next-generation optical communication networks.
With the rapid development of high-security applications such as finance, cloud computing, and key government services, network security issues have become increasingly prominent. Against this backdrop, quantum key distribution (QKD) technology has emerged as an important solution to address the security challenges of optical networks. Based on the principles of quantum mechanics, this technology can achieve unbreakable key distribution during communication, providing intrinsic security for the exchange of confidential information. It is currently one of the most promising long-term security protection technologies for optical networks.Due to the high cost of independently deploying quantum communication networks, integrating quantum channels with classical optical networks for transmission has become the most feasible solution at present. Meanwhile, the continuous development of technologies such as high-order modulation and wavelength division multiplexing has brought the transmission capacity of conventional single-mode fibers close to their theoretical Shannon limit, and mode division multiplexing(MDM) can effectively solve the problem of transmission capacity.However, quantum signals are highly susceptible to crosstalk caused by classical signals during the simultaneous transmission with classical signals. This paper conducts a simulation experiment on a quantum-classical fusion system based on MDM. The results show that the quantum signals are not significantly interfered with by the classical signals during simultaneous transmission, and this system is suitable as a simultaneous transmission scheme for large-scale networking of quantum secure communication.