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arXiv:2412.17578

Modal division multiplexing of quantum and classical signals in few-mode fibers

Danilo Zia, Mario Zitelli, Gonzalo Carvacho, Nicolò Spagnolo, Fabio Sciarrino, Stefan W. Wabnitz

Published Dec 23, 2024• 0 citations
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Abstract

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.

DOI
10.48550/arxiv.2412.17578

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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.
Space-division multiplexing using multimode optical fibers has been applied to quantum-level signals with time-bin and phase encoding, achieving megaqubits per second over 8 km of few-mode fiber. Time windowing is efficiently employed to eliminate modal crosstalk between quantum channels. The dead time of the single-photon detectors in each quantum channel, typically regarded as a bottleneck in quantum transmission, is synchronized with the time-window intervals, thereby optimizing the detection rates.
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 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.
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