Vortex beams carrying orbital angular momentum (OAM) modes hold the promise of facilitating high-dimensional symbol mappings for information encryption. However, challenges persist in achieving both high-security and high-capacity encryption with OAM modes, mainly due to limitations in encoding degrees of freedom and compatible decoding methods. Herein, we present an encryption scheme that integrates truncated OAM modes with phase encoding. Truncated OAM modes are hybrid modes that emerges from mode dispersion caused by the absence of amplitude modulation during generation. By combining the generation function with phase encoding, we can modulate the mode dispersion, creating a discrete set of truncated modes. This introduces a phase degree of freedom for encoding information onto the mode spectrum, achieving high-security encryption. The exponential expansion of the phase factors enables the construction of higher-order symbol maps, thereby increasing encryption capacity. As a proof-of-concept, we implemented an optical information encrypting link using 4 OAM modes and 32-order phase encoding, resulting in over 3×104 modulation orders. The neural network successfully decoded the encryption information with 100% accuracy. This scheme offers the potential to incorporate additional OAM modes in the generating function and further partition the phase encoding, enabling even higher-dimensional symbol mapping. These advancements open up new possibilities for advancing high-security and high-capacity information encryption based on OAM modes.
Vortex beams carrying orbital angular momentum (OAM) modes hold the promise of facilitating high-dimensional symbol mappings for information encryption. However, challenges persist in achieving both high-security and high-capacity encryption with OAM modes, mainly due to limitations in encoding degrees of freedom and compatible decoding methods. Herein, we present an encryption scheme that integrates truncated OAM modes with phase encoding. Truncated OAM modes are hybrid modes that emerges from mode dispersion caused by the absence of amplitude modulation during generation. By combining the generation function with phase encoding, we can modulate the mode dispersion, creating a discrete set of truncated modes. This introduces a phase degree of freedom for encoding information onto the mode spectrum, achieving high-security encryption. The exponential expansion of the phase factors enables the construction of higher-order symbol maps, thereby increasing encryption capacity. As a proof-of-concept, we implemented an optical information encrypting link using 4 OAM modes and 32-order phase encoding, resulting in over 3×104 modulation orders. The neural network successfully decoded the encryption information with 100% accuracy. This scheme offers the potential to incorporate additional OAM modes in the generating function and further partition the phase encoding, enabling even higher-dimensional symbol mapping. These advancements open up new possibilities for advancing high-security and high-capacity information encryption based on OAM modes.
Information security is a critical challenge in free-space optical (FSO) communications. Several methods have been applied to prevent eavesdropping during information transmission. We propose four operations: addition, subtraction, multiplication, and division of the orbital angular momentum (OAM) mode to achieve security in the encoding and decoding of information transmission for optical communications. The transmitted information is decoded by the addition, subtraction, multiplication, and division of the OAM modes according to the values of the topological charges at different diffraction orders of the vortex beam generated by the vortex Dammann grating. The results show that correct information can be obtained when the four operations of the OAM modes are applied. This method can be used to prevent eavesdropping during information transmission in FSO communication systems.
In recent years, optical information processing has become increasingly important due to its ability to handle large amounts of data efficiently. Amplitude, phase, spatial frequency, wavelength, and polarization are the physical dimensions used for information encoding into the light beam. Information encoding using orbital angular momentum (OAM) carried by a vortex beam is gaining interest in this regard. Such beams provide high-dimensional orthogonal states for encoding and have shown more stability in turbulent media than Gaussian beams, especially in the case of free space propagation. This study demonstrates an image encryption method utilizing an array of OAM light modes. The approach uses a non-interferometric intensity recording-based encoding scheme, which offers ease of implementation. Quick response codes have been utilized for encoding to avoid information loss from non-uniform distribution of light and aberrations. The encryption scheme is highly secure because the encrypted light beam contains only partial information about the object, preventing complete information retrieval without proper key information.
The increasing demand for higher-capacity, high-performance optical networks and computing has fueled the exploration of new photonic degrees of freedom for information encoding. Our work addresses this need by investigating the feasibility of utilizing transverse orbital angular momentum (t-OAM) of light, a more recently identified degree of freedom than its longitudinal counterpart, as a viable candidate for these potential applications. We present results demonstrating the feasibility of leveraging t-OAM as a new family of modes for implementing classical entanglement, which provided the basis for generating a novel t-OAM and circular polarization mode-entangled beam. Additionally, we developed and demonstrated a proof-of-concept optical information-processing pipeline based on spatiotemporal optical vortices (STOVs) carrying t-OAM. Using this system, we demonstrated arithmetic capabilities, including the addition and subtraction of spatiotemporal topological charge values, which can be either integer or fractional. These new capabilities open pathways toward harnessing t-OAM of light as a new degree of freedom to enhance optical computation and communication.
Optical vortex beams (OVBs) carrying orbital angular momentum (OAM) offer access to an unbounded set of orthogonal states, enabling a dramatic increase in the information capacity for optical communication systems. However, practical OAM detection in telecommunication platforms remains challenging due to background noise, detector limitations at infrared communication wavelengths, and the destructive nature of conventional sampling methods. Here, we introduce an all-optical, nearly nondestructive OAM detection method based on sum-frequency generation (SFG) that overcomes these limitations by transferring the information on the OAM into a distinct frequency domain. In our scheme, two OVBs─one carrying OAM-encoded information and the other serving as a reference─are coupled within a beta-barium borate (BBO) crystal to generate an SFG signal. Our theoretical and experimental studies demonstrate that SFG efficiency is governed by the spatial overlap of the interacting vortex profiles, providing mode-selective and OAM-resolved detection. Crucially, as only a small fraction of the input photons undergo conversion into the nonlinear signal, the original beams remain functionally intact. Since detection is performed exclusively on the upconverted signal in a spectrally distinct visible wavelength region, the signal-to-noise ratio can be improved. Moreover, the SFG signal is generated only when specific OAM states and temporal overlap conditions are simultaneously satisfied, enabling ultrafast and conditionally gated access to the OAM information. This nonlinear selectivity offers enhanced physical-layer security and high-throughput capabilities. Together, our approach provides a robust and versatile platform for advanced OAM-based optical communications and high-capacity photonics applications.
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.
Vortex beams (VBs) shift keying is a digital communication technique that encodes data by rapidly switching or shifting the orbital angular momentum (OAM) state of a light beam, improving the performance of free-space optical communication. However, current VB-based shift keying secure systems still face several issues, such as limited capacity, the need for model retraining during key renewal and in some cases, vulnerability to ciphertext-only or known-plaintext attacks. In this article, we address these critical challenges by integrating VB array, phase encoding, spatial coherence modulation and deep learning techniques. By utilizing 9 spatial channels each with 16-ary phase differences in the proof-of-principle experiments, the information content carried by a single symbol reach 36 bits. Moreover, a double-encryption transmission scheme is proposed, leveraging the coherence structure and spatial reading trajectory of the VB array. This method has been experimentally verified to provide ultra-high security at the physical layer, effectively resisting both ciphertext-only and known-plaintext attacks. The corresponding bit error rates and pixel error rates can highly reach at least 3.7 × 10−1 and 8.6 × 10−1, respectively. Our work offers the potential for next generation VB-array-based high security FSO communication. Vortex-beam-based shift keying secure systems enhance secure digital communications, while it faces challenges such as limited capacity and vulnerability to attacks. This paper presents a double encryption scheme leveraging coherent structures and spatial reading trajectories whichenables key updates without retraining, and maintains high security.