Physics-informed neural networks provide mode decomposition based on intensity-only images in high-dimensional quantum communication using multimode fibers.
Abstract The ability to engineer the spatial wavefunction of photons has enabled a variety of quantum protocols for communication, sensing, and information processing. These protocols exploit the high dimensionality of structured light enabling the encoding of multiple bits of information in a single photon, the measurement of small physical parameters, and the achievement of unprecedented levels of security in schemes for cryptography. Unfortunately, the potential of structured light has been restrained to free-space platforms in which the spatial profile of photons is preserved. Here, we make an important step forward to using structured light for fiber optical communication. We introduce a classical encryption protocol in which the propagation of high-dimensional spatial modes in multimode fibers is used as a natural mechanism for encryption. This provides a secure communication channel for data transmission. The information encoded in spatial modes is retrieved using artificial neural networks, which are trained from the intensity distributions of experimentally detected spatial modes. Our on-fiber communication platform allows us to use single spatial modes for information encoding as well as the high-dimensional superposition modes for bit-by-bit and byte-by-byte encoding respectively. This protocol enables one to recover messages and images with almost perfect accuracy. Our classical smart protocol for high-dimensional encryption in optical fibers provides a platform that can be adapted to address increased per-photon information capacity at the quantum level, while maintaining the fidelity of information transfer. This is key for quantum technologies relying on structured fields of light, particularly those that are challenged by free-space propagation.
The ability to engineer the spatial wavefunction of photons has enabled a variety of quantum protocols for communication, sensing, and information processing. These protocols exploit the high dimensionality of structured light enabling the encodinng of multiple bits of information in a single photon, the measurement of small physical parameters, and the achievement of unprecedented levels of security in schemes for cryptography. Unfortunately, the potential of structured light has been restrained to free-space platforms in which the spatial profile of photons is preserved. Here, we make an important step forward to using structured light for fiber optical communication. We introduce a smart high-dimensional encryption protocol in which the propagation of spatial modes in multimode fibers is used as a natural mechanism for encryption. This provides a secure communication channel for data transmission. The information encoded in spatial modes is retrieved using artificial neural networks, which are trained from the intensity distributions of experimentally detected spatial modes. Our on-fiber communication platform allows us to use spatial modes of light for high-dimensional bit-by-bit and byte-by-byte encoding. This protocol enables one to recover messages and images with almost perfect accuracy. Our smart protocol for high-dimensional optical encryption in optical fibers has key implications for quantum technologies relying on structured fields of light, particularly those that are challenged by free-space propagation.
As the demand for data capacity continues to grow, optical fiber communication systems are progressively approaching their theoretical limits, thereby motivating the exploration of high-dimensional (HD) degrees of freedom such as orbital angular momentum (OAM). However, strong intermodal coupling in multimode fibers (MMFs) poses substantial challenges for the transmission and recovery of HD optical information. Here, we propose and experimentally demonstrate an HD OAM-array-based multichannel multitask optical communication framework via a single MMF. By encoding different information tasks into HD OAM superposition states across multiple wave-vector (k) channels, the proposed scheme enables the simultaneous transmission of heterogeneous optical information within a unified fiber platform. At the receiver, a residual neural network constrained by a multi-channel quantum-state fidelity loss function directly reconstructs the transmitted signals from single-frame speckle intensity measurements, without requiring phase retrieval or channel inversion. Experiments demonstrate the synchronous communication of multichannel classical image signals and HD mutually unbiased basis states through the same MMF, while maintaining high reconstruction fidelity and low interchannel crosstalk under strong modal mixing conditions. This approach provides a scalable route toward high-capacity hybrid classical–quantum optical communication in fiber systems.