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IEEE Photonics Conference

Quantum and Classical Signals Mode Division Multiplexing in a 8 km Few-Mode Fiber

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

Published Nov 10, 2024• 1 citation
Publisher

Abstract

We experimentally demonstrate the mode-division multiplexing of quantum and classical signals at telecom wavelengths, using a 8 km long few-mode graded-index fiber and multiplane-light-conversion based modal multiplexers and demultiplexers. We observe the signature of random-mode coupling at quantum level, producing limited cross-talk among degenerate and non-degenerate channels.

DOI
10.1109/ipc60965.2024.10799905

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We experimentally demonstrate the mode-division multiplexing of quantum and classical signals at telecom wavelengths, using a 8 km long few-mode graded-index fiber and multiplane-light-conversion based modal multiplexers and demultiplexers. We observe the signature of random-mode coupling at quantum level, producing limited cross-talk among degenerate and non-degenerate channels.
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We classically measure the entire propagation matrix of a few-mode fiber and use a spatial light modulator to undo modal mixing and recover single-photons launched onto each of the eigenmodes of the fiber at one end, but arriving as mixed modal superpositions at the other. We exploit the orthogonality of these modal channels to improve the isolation between a quantum and classical channel launched onto different spatial and polarization modes at different wavelengths. The spatial diversity of the channels provides an additional 35dB of isolation in addition to that provided by polarization and wavelength.
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.