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Nature Communications

Ultrahigh-speed optical encryption enabled by spatiotemporal noise chaffing

Jianyang Shi, Chaoxu Chen, Haoyu Zhang, Penghao Luo, Wei Yuan, Fang Dong, Ziwei Li, Chao Shen, Haiwen Cai, Junwen Zhang, Xinyuan Fang, Nan Chi, Miṅ Gu

Published Nov 19, 2025• 9 citations
Publisher

Abstract

Optical encryption provides strong physical-layer security but is limited by the slow response of spatial light modulators. We propose and experimentally demonstrate a spatiotemporal noise chaffing system inspired by the “chaffing and winnowing” principle for ultrahigh-speed temporal encryption. By exploiting the symmetric spatial properties and orthogonality of conjugated orbital angular momentum (OAM) states, high-speed temporal signals (“wheat”) and spatial noise (“chaff”) are simultaneously encoded. This mechanism suppresses information leakage by degrading the temporal signal-to-noise ratio while enabling authorized recovery. Furthermore, a variable-weight multimodal OAM (VW-multimodal OAM) scheme combined with a multimodal generation neural network (MGNN) exponentially expands the key space beyond 10¹⁰. Experimentally, a record secure transmission rate of 1.25 Tbps per mode is achieved in an eight-channel wavelength-division-multiplexed coherent link. The product of rate and key space surpasses existing methods by five orders of magnitude, establishing a new photonic-security paradigm for future ultrafast and secure communication networks. Optical encryption provides strong data protection but has been limited by the modulating bandwidth of spatial devices. Here, the authors demonstrate a spatiotemporal noise chaffing system using conjugated orbital angular momentum modes to achieve terabit-per-second secure transmission and expand the encryption key space beyond 10¹⁰.

DOI
10.1038/s41467-025-65111-5

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Optical encryption provides strong physical-layer security but is limited by the slow response of spatial light modulators. We propose and experimentally demonstrate a spatiotemporal noise chaffing system inspired by the “chaffing and winnowing” principle for ultrahigh-speed temporal encryption. By exploiting the symmetric spatial properties and orthogonality of conjugated orbital angular momentum (OAM) states, high-speed temporal signals (“wheat”) and spatial noise (“chaff”) are simultaneously encoded. This mechanism suppresses information leakage by degrading the temporal signal-to-noise ratio while enabling authorized recovery. Furthermore, a variable-weight multimodal OAM (VW-multimodal OAM) scheme combined with a multimodal generation neural network (MGNN) exponentially expands the key space beyond 10¹⁰. Experimentally, a record secure transmission rate of 1.25 Tbps per mode is achieved in an eight-channel wavelength-division-multiplexed coherent link. The product of rate and key space surpasses existing methods by five orders of magnitude, establishing a new photonic-security paradigm for future ultrafast and secure communication networks. Optical encryption provides strong data protection but has been limited by the modulating bandwidth of spatial devices. Here, the authors demonstrate a spatiotemporal noise chaffing system using conjugated orbital angular momentum modes to achieve terabit-per-second secure transmission and expand the encryption key space beyond 10¹⁰.
Providing physical layer security at the lowest network layer in fiber-optic communication systems is a technical challenge worldwide. Here, we propose and experimentally demonstrate a pure hardware optical encryption scheme based on temporal spreading and self-feedback phase encryption for high-speed and long-distance physical-layer secure optical communication. A record high bit-rate-distance product of 6400 Gb/s km is successfully achieved by the secure transmission of a 32 Gb/s on-off-keying modulated confidential signal over a 200 km optical fiber link. The demonstrated scheme is fully compatible with conventional optical transmission systems and can be operated in a pluggable manner, which may pave a new path to ultra-high-speed physical-layer secure optical communication in the future.
The growth of the Internet traffic does not appear to be levelling off any time soon and it is projected to continue to grow exponentially in the years to come. Although there are many proposals on how to deal with the incoming bandwidth capacity crunch, the security of optical networks seems to be almost completely neglected. By taping out the portion of DWDM signal, the huge amount of data can be compromised. Therefore, the security of future optical networks is becoming one of the major issues to be addressed sooner rather than later. To address the security issues of future optical networks the quantum key distribution (QKD) and chaotic cryptography have been proposed. To avoid the high cost of QKD, the properly designed fiber Bragg gratings (FBGs) as optical encryption devices have been advocated recently. In this invited paper, we follow a different strategy. It is well known that we can associate with a photon both spin angular momentum (SAM), related to polarization; and orbital angular momentum (OAM), related to azimuthal dependence of the complex electric field. Because the OAM eigenstates are orthogonal, this additional degree of freedom can be utilized for the physical-layer security in optical networks. Given that the spatial modes in spatial domain multiplexing (SDM) fibers such as few-mode fibers (FMFs), few-core fibers (FCFs), and few-mode-few-core fibers (FMFCFs) can be decomposed in terms of OAM eigenkets, the OAM can be used to enable the physical-layer security in both fiber-optics- and free-space optics-based optical networks.
We propose and experimentally demonstrate a novel physical layer encryption scheme for high-speed optical communication. A 10 Gb/s on-off keying signal is secretly transmitted over 100 km standard single-mode fiber. The intensity-modulated message is secured by the encryption mechanism, which is composed of an external noise source and an internal time-delayed feedback loop. The external noise serves as an entropy source with sufficient randomness. The feedback loop structure in the transmitter introduces a time-domain encryption key space, and a corresponding open-loop configuration at the receiver side is used for synchronization and decryption. Experiment results show the effectiveness of the proposed scheme. For a legitimate terminal, bit error rate below 10−8 can be obtained. Decryption degradations with the mismatch of different hardware parameters are researched. The time delay in the feedback loop provides a sensitive encryption key. For other hardware parameters, the system is robust enough for synchronization. Meanwhile, the time-delay signature of the loop is able to be well concealed by the external noise. Moreover, the proposed scheme can support density wavelength division multiplexing transmission with a relatively simple structure. This work also provides a new concept to establish optical secure communication by combining a time-delayed feedback chaotic system and random noise.
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.
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.