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Chinese Optics Letters

Demonstration of high-dimensional free-space data coding/decoding through multi-ring optical vortices

Shiyao Fu, Yanwang Zhai, Heng Zhou, Jianqiang Zhang, Ci Yin, Chunqing Gao

Published Jan 1, 2019• 22 citations
Publisher

Abstract

Multi-ring optical vortices are a kind of structured beams that carry orbital angular momentum (OAM) and have concentrical doughnut intensity distributions. In this Letter, we present both theoretically and experimentally a scheme that employs the dimensions of both the OAM states and radial index of multi-ring optical vortices simultaneously to accomplish high-dimensional free-space data coding/decoding transmissions. Such a scheme can further improve the coding efficiency when limited OAM states are available. In the proof-of-concept experiment, 64-ary coding/decoding employing 16 OAM states and four radial indices are present. Also, the coding/decoding performance when facing various atmosphere turbulences is evaluated. Furthermore, a 64 × 64 gray image (totally, 32,768 bits) is also transmitted through multi-ring optical vortices coding in free-space successfully, showing good transmission performance.

DOI
10.3788/col201917.080602

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Multi-ring optical vortices are a kind of structured beams that carry orbital angular momentum (OAM) and have concentrical doughnut intensity distributions. In this Letter, we present both theoretically and experimentally a scheme that employs the dimensions of both the OAM states and radial index of multi-ring optical vortices simultaneously to accomplish high-dimensional free-space data coding/decoding transmissions. Such a scheme can further improve the coding efficiency when limited OAM states are available. In the proof-of-concept experiment, 64-ary coding/decoding employing 16 OAM states and four radial indices are present. Also, the coding/decoding performance when facing various atmosphere turbulences is evaluated. Furthermore, a 64 × 64 gray image (totally, 32,768 bits) is also transmitted through multi-ring optical vortices coding in free-space successfully, showing good transmission performance.
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.
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.
Structured light carrying optical vortices have gained significant attention in information security as they offer high-dimensional orthogonal states for encoding. These states are usually associated with the orbital angular momentum of light. In this letter, we demonstrate a novel method for binary image encryption using structured phase encoding. The structured phase is obtained by multiple lattices of spatially distributed phase singularity points with varying azimuthal indices. It has been shown that data encoding using orthogonal sets of optical vortex modes enable noise-free decryption and provide robustness against atmospheric turbulence in short propagation distance.
The orbital angular momentum (OAM) of a photon describes the helical wavefront of a beam, and has recently attracted much attention due to their potential applications in diverse domains. OAM offers a new dimension, which can be encoded as various data symbols for a data-transmission system. Meanwhile, such encoding can be done simultaneously with other encodings as amplitude shift keying, for instance, the mixed OAM-amplitude shift keying (OAM-ASK), to increase further the encoding efficiency. Here we propose an OAM-ASK based data-transmission system, where the data encoding is realized by a single hologram. Additionally, the encoded data can be decoded perfectly through a single hologram too. As a proof-of-concept, we transmit a gray-scale image in free-space through octal OAM with binary amplitude (totally 4 bit per symbol), and 32-ary OAM with quaternary amplitude (totally 7 bit per symbol) over 10 meters. The favorable experimental results show 0 bit-error-rate. This work opens a new insight in mixed OAM-ASK and will inspire various applications.
Multicasting is necessary when distributing signals between multiple users. In this Letter, we demonstrate an orbital angular momentum (OAM) encoding-based free-space one-to-many multicasting link, where digital signals are encoded into a series of time-varying OAM states and transmitted from one transmitter to multiple receivers with various locations. Moreover, encoding N various signals simultaneously in one transmitter and sending them at the same time to N various receivers separately, is also demonstrated. As a proof-of-concept, four different gray images are coded by one transmitter simultaneously and multicast to four various receivers separately. The favorable decoding results returned by the four receivers show good multicasting performance.
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.