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APL Photonics

Optical encryption via four operations of orbital angular momentum

Yangsheng Yuan, Zihan Cong, Yaru Gao, Jianghao Li, Yuefeng Zhao, Bernhard J. Hoenders, Yangjian Cai, Hui Zhang

Published Jul 1, 2025• 4 citations
Publisher

Abstract

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.

DOI
10.1063/5.0250395

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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.
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.
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.
Orbital angular momentum (OAM), a new dimension of photons, has potentials in lots of domains as high-dimensional data coding/decoding. Here we experimentally demonstrate a free-space data transmission system based on 8 bits multi-state OAM shift keying, where multiplexed optical vortices containing 8 various OAM states are employed to constitute 8 bits binary symbols. In the transmitter, the data coding of OAM shift keying is realized by switching a series of special-designed holograms. And in the receiver, the decoding is done by a single Dammann vortex grating along with image processing. We experimentally transmit data, including a gray-scale image, in free-space for 10 meters, showing zero bit-error-rate. The demonstrated results indicate a wide prospect for the future high-dimensional large data rate optical security communications.
The light's orbital angular momentum (OAM) is a consequence of the spiral flow of the electromagnetic energy. In this paper, an analysis of light beams with OAM used for free space optics (FSO) is conducted. The basic description and conception of light's OAM are reviewed. Both encoding information into OAM states of single light beam and encoding information into spatial structure of the mixed optical vortex with OAM are discussed, and feasibility to improve the FSO's performance of security and obstruction of line of sight is examined.
In this paper we propose an information encoding method based on a segmented vortex beam. The segmented vortex beam with a single uniform-intensity ring and a combination of multiple topological charges is designed for information encoding. The radius of the beam can be designed to be arbitrary, with multiple orbital angular momentum states superimposed along the ring. We encoded the information into the segmented vortex beam in the transmitting unit for information transmission. Due to the segmented phase structure of the beam, information can be encoded in each segment, and the information capacity is significantly increased. Additionally, enormous combinations of encoded information in the beam can greatly enhance the security of the encoded information. This proposed method has great potential in free-space optical communication.
A novel encoding method based on the orbital angular momentum (OAM) mode and radial mode of composite vortex beams is proposed. The superposition of two vortex beams generates 32 different types of composite vortex beams: one of them is a Laguerre–Gaussian (LG) beam with a fixed OAM mode and radial mode, and the other is a LG beam containing four radial modes (p = 0, 1, 2, 3) and eight OAM modes with the same interval (l = ±3, ±5, ±7, ±9). A specially designed composite fork-shaped grating (CFG) is utilized to generate the intensity array pattern, and the received composite vortex beam is diffracted into a Gaussian beam with the relevant coordinates. Based on the coordinates and the number of bright rings in the intensity pattern, the OAM modes and radial modes of the two vortex beams composing the superposition state are determined, and finally the received composite vortex beam is decoded into the initially propagated information sequence. The correctness and effectiveness of the proposed encoding are confirmed through the comparative analysis of the correlation of the optical fields at both the transmitter and receiver in the two scenarios of interval and non-interval encoding. The proposed encoding method can significantly improve the efficiency of information transmission and its resistance to interference, holding great potential for future applications in free-space optical communication.