Harnessing light that carries orbital angular momentum (OAM) could dramatically boost the capacity of optical communication and high-dimensional signal processing. A particularly desirable but difficult goal is nonreciprocal transmission—allowing such twisted light beams to travel efficiently in one direction while blocking them in the reverse direction. This challenge is especially acute in hot atomic systems, where random thermal motion blurs the delicate intensity patterns of OAM superstates. Here, we show that incoherent optical pumping can effectively suppress these thermal effects, thereby enabling robust nonreciprocal transmission of OAM superstates. We achieve a forward transmission of 85%, a backward isolation of 22.7 dB, and a measurement accuracy exceeding 99.9% for distinguishing OAM superstates separated by only 0.01 in topological charge. We further verify the overall performance of the nonreciprocal system by transmitting a grayscale image, obtaining a bit error rate below 0.07%. Our results establish a flexible and scalable platform for nonreciprocal high-dimensional OAM photonics, offering promising routes toward advanced optical communications and quantum information processing.
Harnessing light that carries orbital angular momentum (OAM) could dramatically boost the capacity of optical communication and high-dimensional signal processing. A particularly desirable but difficult goal is nonreciprocal transmission—allowing such twisted light beams to travel efficiently in one direction while blocking them in the reverse direction. This challenge is especially acute in hot atomic systems, where random thermal motion blurs the delicate intensity patterns of OAM superstates. Here, we show that incoherent optical pumping can effectively suppress these thermal effects, thereby enabling robust nonreciprocal transmission of OAM superstates. We achieve a forward transmission of 85%, a backward isolation of 22.7 dB, and a measurement accuracy exceeding 99.9% for distinguishing OAM superstates separated by only 0.01 in topological charge. We further verify the overall performance of the nonreciprocal system by transmitting a grayscale image, obtaining a bit error rate below 0.07%. Our results establish a flexible and scalable platform for nonreciprocal high-dimensional OAM photonics, offering promising routes toward advanced optical communications and quantum information processing.
Nonreciprocal transmission of structured light has possible applications in high-capacity optical communication and high-dimensional signal processing. Here, we demonstrate the magnet-free and cavity-free optical nonreciprocity of an orbital-angular-momentum (OAM) beam using optical-pumping technology with the assistance of the Doppler effect in hot atoms. By using optical pumping to induce a direction-dependent population transfer of the ground-state atoms, we realize optical nonreciprocity for the signal laser that is carrying OAM. Interestingly, an isolation ratio close to 30 dB and maximum transmission over 0.86 can be achieved simultaneously without the use of an optical cavity. Due to the unique amplitude and helical phase profile of the structured light, our proposal may open an avenue for exploring the singularity characteristics of optical nonreciprocity using structured light.
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.
Magnet-free optical nonreciprocity has significant applications in quantum communication, quantum networks, and optical information processing. In this research, considering a degenerate two-level thermal atomic system with the Doppler effect of thermal atoms, the nonreciprocal amplification (NRA) of dual-path degenerate four-wave mixing (FWM) signals is achieved under the action of a co-propagating pumping field. On this basis, spatially multiplexed multiple FWM processes are formed by introducing another counter-propagating pumping field, thereby achieving the reciprocal amplification (RA) of the dual-channel FWM signals. Furthermore, by using multiple sets of spiral phase plates to load spiral phases on the signal light and the pumping light respectively, higher-order Laguerre-Gaussian vortex beams carrying different optical orbital angular momentum (OAM) are generated and participate in the FWM process, achieving the transfer of the OAM of the pumping light to the amplified FWM fields. Simultaneously, using the Mach-Zehnder interferometer, the conservation characteristics of the OAM of each FWM signal in the NRA-RA conversion are further analyzed. Furthermore, experimental results demonstrate that in the multiple FWM process induced by a pair of counter-propagating pump fields, the OAM of the amplified FWM signal in each channel varies with that of the pump field. However, the overall process maintains the OAM conservation. This study provides a feasible solution for expanding the channel capacity using OAM based on NRA-RA system, showing that the OAM has potential application prospects in achieving high-capacity optical communication and multi-channel signal processing.
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.
Abstract As an emerging channel resource for modern optics, big data, internet traffic and quantum technologies, twisted photons carrying orbital angular momentum (OAM) have been extended their applicable boundary in different media, such as optical fiber and atmosphere. Due to the extreme condition of loss and pressure, underwater transmission of twisted photons has not been well investigated yet. Especially, single-photon tests were all limited at a level of a few meters, and it is in practice unclear what will happen for longer transmission distances. Here we experimentally demonstrate the transmission of single-photon twisted light over an underwater channel up to 55 m, which reach a distance allowing potential real applications. For different order OAM states and their superposition, a good preservation of modal structure and topological charge are observed. Our results for the first time reveal the real transmission performance of twisted photons in a long-distance regime, representing a step further towards OAM-based underwater quantum communication.
Recently,the free space optical communication system based on orbital angular momentum( OAM) states multiplexing has become one of the hot topics in optical communications and quantum optics,because OAM states are new dimensional information carriers. An efficient orbital-angular-momentum-multiplexed free-space optical communication scheme is proposed,where the efficient orbital angular momentum states separation method is adopted. With this OAM separation method,different orbital angular momentum states can be obtained simultaneously from the superposition OAM state beam,which greatly saves time and the expensive devices for demodulating the information from the information-carrying OAM states. Numerical simulation results show that the proposed scheme can reduce time and the number of the devices at the receiver for the information retrieving. The bit error rate of the system can be less than 10- 4when the signal-to-noise ratio of the system is greater than 23 dB. Therefore,this OAMmultiplexed free-space optical communications scheme is proved to be feasible.