Quantum cryptography uses the basic principles of quantum physics to ensure the security of information transmission. In theory, it has unconditional security and can provide new technical guarantees for information security in various fields of society. In order to save the cost of deploying the QKD network, the QKD network can be combined with the existing classical communication network, so that the quantum signal and the classical signal can be transmitted through the same fiber. However, there are still many key technical problems in the fusion network of quantum communication and classical communication. This paper proposes a technique of classical-quantum signals simultaneous transmission sharing a same fiber based on mode division multiplexing. This scheme improves the problem that a large mode gain difference between different modes caused by EDFA and leads to a decrease in the transmission capacity of the system in the existing long distance mode division multiplexing transmission system.
Quantum cryptography uses the basic principles of quantum physics to ensure the security of information transmission. In theory, it has unconditional security and can provide new technical guarantees for information security in various fields of society. In order to save the cost of deploying the QKD network, the QKD network can be combined with the existing classical communication network, so that the quantum signal and the classical signal can be transmitted through the same fiber. However, there are still many key technical problems in the fusion network of quantum communication and classical communication. This paper proposes a technique of classical-quantum signals simultaneous transmission sharing a same fiber based on mode division multiplexing. This scheme improves the problem that a large mode gain difference between different modes caused by EDFA and leads to a decrease in the transmission capacity of the system in the existing long distance mode division multiplexing transmission system.
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.
Mode-division multiplexing using multimode optical fibers has been intensively studied in recent years, in order to alleviate the transmission capacity crunch. Moreover, the need for secure information transmission based on quantum encryption protocols leads to investigating the possibility of multiplexing both quantum and classical signals in the same fiber. In this work, we experimentally study the modal multiplexing of both quantum and classical signals at telecom wavelengths, by using a few-mode fiber of 8 km and modal multiplexers/demultiplexers. We observe the existence of random-mode coupling at the quantum level, leading to cross-talk among both degenerate and non-degenerate channels. Our results demonstrate the feasibility of using few-mode fibers for simultaneously transmitting classical and quantum information, leading to an efficient implementation of physical information encryption protocols in spatial-division multiplexed systems.
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.
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.
In order to realize classical-quantum signals simultaneous transmission sharing a same fiber in quantum communication, it is proposed that signals are transmitted over multiple separate channels. The channels are divided by different wavelengths, pseudo-codes, and spatial modes. Based on the development status of quantum communication over optical fiber, this paper expounds the demand of quantum communication for multiplexing technology, and introduces the basic principle and research status of three existing multiplexing technologies. In this paper, the key technologies involved in the multiplexing system based on few mode fiber are discussed in depth, and the problems in signal transmission are analyzed.
We demonstrate the realization of quantum key distribution (QKD) when combined with classical optical communication, and synchronous signals within a single optical fiber. In the experiment, the classical communication sources use Fabry-Pérot (FP) lasers, which are implemented extensively in optical access networks. To perform QKD, multistage band-stop filtering techniques are developed, and a wavelength-division multiplexing scheme is designed for the multi-longitudinal-mode FP lasers. We have managed to maintain sufficient isolation among the quantum channel, the synchronous channel and the classical channels to guarantee good QKD performance. Finally, the quantum bit error rate remains below a level of 2% across the entire practical application range. The proposed multiplexing scheme can ensure low classical light loss, and enables QKD over fiber lengths of up to 45 km simultaneously when the fibers are populated with bidirectional FP laser communications. Our demonstration paves the way for application of QKD to current optical access networks, where FP lasers are widely used by the end users.