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IEEE Photonics Technology Letters

Joint Optical Phase Retrieval and Computing for Secure Networks Using Mode Division Multiplexing

Dennis Pohle, Pin-Hsun Lin, Filipe Marques Ferreira, Eduard Axel Jorswieck, Jürgen W. Czarske

Published Mar 26, 2026• 1 citation
Publisher

Abstract

Knowledge of the channel matrix in multimode fiber based space division multiplexing requires precise retrieval of crosstalk in amplitude, phase and polarization. We use an additional multimode fiber as an optical reservoir to recover SDM signals of 10 spatial modes with a pearson correlation of 0.963 and achieved simulationally phase retrieval of 23 modes using a standard 50 μm-core MMF. The reference-less approach of phase retrieval within the network can potentially be extended to end-to-end long-haul systems and enables physical-layer and quantum-secure networking by optical precoding.

DOI
10.1109/lpt.2026.3678176

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Knowledge of the channel matrix in multimode fiber based space division multiplexing requires precise retrieval of crosstalk in amplitude, phase and polarization. We use an additional multimode fiber as an optical reservoir to recover SDM signals of 10 spatial modes with a pearson correlation of 0.963 and achieved simulationally phase retrieval of 23 modes using a standard 50 μm-core MMF. The reference-less approach of phase retrieval within the network can potentially be extended to end-to-end long-haul systems and enables physical-layer and quantum-secure networking by optical precoding.
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Recent developments in the field of space-division multiplexing (SDM) for fiber-optic communication systems suggest that the spatial diversity offered by SDMcan be used not only to increase system capacity, but also to achieve provable security against physical layer attacks. In this work, we outline some of the mathematical framework necessary to assess the security benefits of the SDM. We substantiate our conjecture that allocating the maximal allowable power to each mode is optimal in terms of physical layer security. Further more, we expand the scope of our security analyses to include distortion as a quantitative metric for secrecy and study how the rate of reliable communication between the legitimate transmitter-receiver pair can be chosen to maximize reconstruction (decoding) errors of the eavesdropper.
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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.
The light propagation through a multimode fiber is used to increase information security during data transmission without the need for cryptographic approaches. The use of an inverse precoding method in a multimode fiber-optic communication network is based on mode-dependent losses on the physical layer. This leads to an asymmetry between legitimate (Bob) and illegitimate (Eve) recipients of messages, resulting in significant SNR advantage for Bob. In combination with dynamic mode channel changes, there are defined hurdles for Eve to reconstruct a sent message even in a worst-case scenario in which she knows the channel completely. This is the first time that physical layer security has been investigated in a fiber optical network based on measured transmission matrices. The results show that messages can be sent securely using traditional communication techniques. The technology introduced is a step towards the development of cyber physical systems with increased security.