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.
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.
Optical vortex beams carrying orbital angular momentum (OAM) offer unique advantages in high-dimensional optical information processing. However, in the context of free-space links, the full reconstruction of high-dimensional OAM spectra remains challenging due to scattering-induced distortions. Here, we employ a residual convolutional neural network with a custom quantum-state-fidelity loss function (QLF-ResNet) that reconstructs and demultiplexes high-dimensional OAM light fields from a single distorted speckle pattern. Specifically, we achieve an average fidelity of 97.2% for nine-dimensional OAM states and maintain fidelity above 91.9% with only 6.25% of original data, illustrating resilience to information loss, thus enabling robust data encoding and multiplexing. For this, we employ high-dimensional OAM encoding to achieve efficient, high-fidelity transmission of RGB images under strong scattering conditions. These results underscore the promise of our current approach for precise OAM state reconstruction in intricate real-world environments, paving the way for advancements in next-generation optical communications.
High-dimensional quantum key distribution (HD-QKD) enhances information efficiency and noise tolerance by encoding data in large Hilbert spaces. The orbital angular momentum (OAM) of light provides a scalable basis for such encoding and supports high-dimensional photonic communication. Practical OAM-based implementations remain constrained by challenges in state generation, transmission, and detection. This survey offers a consolidated overview of OAM-encoded HD-QKD, outlining fundamental principles, representative experiments, and system-level limitations. Recent progress in hybrid encodings, mode sorting, adaptive optics, and TF, CV, MDI, and DI frameworks is summarized with emphasis on practical feasibility.
Orbital angular momentum (OAM) of photons provides a promising approach to enhance the capacity, robustness, and functionality of quantum communication systems in optical fibers. With many twist states available, OAM enables high-dimensional encoding, significantly increasing data rates and noise tolerance. This review explores sources, channels, and system architectures for OAM-based quantum communication in fibers. It compares free-space and integrated emitters, discussing in-fiber pair generation and mode conversion pathways that produce fiber-ready single photons and entangled states. For the channels, it details design principles and trade-offs for step-index and ring-core fibers that minimize intermodal coupling and reviews milestones in kilometer-scale single-photon transmission and high-dimensional entanglement transport. On the system side, the review examines coupling, multiplexing, and detection techniques—including mode (de)multiplexers, lanterns, and programmable sorters—and discusses transmission-matrix-based control methods to mitigate dispersion and bending effects. The review concludes with practical guidance and open challenges, such as improving mode selectivity and stability under real-world conditions; developing compact, efficient detectors for many modes; and integrating co-designed error correction schemes. These directions aim to bridge laboratory demonstrations with the deployment of scalable, high-dimensional fiber networks that harness OAM to significantly boost capacity, resilience, and functionality.
Accurate reconstruction of the complex spectrum of orbital angular momentum (OAM) superposition states is crucial for their application in high-capacity optical communications and quantum information, yet existing methods are often constrained by system complexity, extensive data requirements, or incomplete information retrieval. Here, we propose and experimentally demonstrate an iterative algorithm that enables high-fidelity recovery of the complex OAM spectrum of high-dimensional superpositions from only a few sparsely sampled patterns. The method integrates the Laguerre-Gaussian (LG) modal basis as an a priori constraint, which enables the direct retrieval of spectral coefficients by circumventing intermediate field reconstruction. To validate its performance, we reconstructed a test field composed of a random superposition of 21 LG modes, achieving fidelities of 99.3% in simulation and 97.2% in experiment using only four sparse sampling patterns. This work provides an efficient and robust tool for characterizing high-dimensional structured light, with significant potential in optical communication and quantum science.
Higher dimensional communications are of interest for multiple reasons including increasing classical transmission capacity and more recently the quantum state transfer through these fibers using the many modes within the fibers. For quantum communications, this enables an increase in the number of bits per photon, increasing quantum fidelity, increasing error threshold and enabling hyperentanglement transfer among other possibilities. High dimensional quantum state transfer can be transported through multimode fiber using the many modes available. However, this transfer medium is limited by mode coupling among the various spatial and polarization modes. Here we consider how this mode coupling impacts the transfer process. We consider the fiber's modal properties including orbital angular momentum, modal group numbers, and principal modes. We also investigate and propose input and output optical components as well as fiber properties that mitigate the deleterious effects of mode coupling. We propose methods to circumvent this mode coupling using optical fibers, optical components and devices that are commercially available today or those that are undergoing intense global research such as Flat Optics.
Quantum communication consists of the reliable transmission of quantum states among several parties and looks toward the long-term goal of a Quantum Internet. Quantum Internet could open up a whole universe of new applications, spanning from fundamental physics and secure communications to remote quantum computing. Multiple degrees of freedom can be used for the distribution of the quantum states, such as polarization, frequency, time and space. In particular, Orbital Angular Momentum (OAM) of light is one of the most promising thanks to its unbounded nature, albeit challenging to manipulate. OAM has been largely investigated both for classical and quantum communications, allowing for enhanced data rate in classical links and determining a high-dimensional basis for quantum communication. Here, we report our recent results related to quantum states encoded in the orbital angular momentum of light, proving the capability of preparing, manipulating, transmitting and measuring high-dimensional quantum states through a multimode fibre.