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Optics Express

Real-time stealth optical transmission via dither-remodulation in a bias controller of a Mach-Zehnder modulator

Yuanxiang Wang, Weidong Shao, Jinyang Wu, Hongyu Li, Linsheng Zhong, Xiaoxiao Dai, Qi Yang, Lei Deng, Deming Liu, Mengfan Cheng

Published May 10, 2023• 10 citations
Publisher

Abstract

The physical layer transmission security is a promising technology against security threats. As an effective supplement to the encryption strategy, steganography has received widespread attention. We report a real-time 2 kbps stealth transmission in the 10 Gbps dual polarization QPSK public optical communication. The stealth data is embedded in dither signals via precise and stable bias control technique for a Mach-Zehnder modulator. In the receiver, the stealth data can be recovered from the normal transmission signals by low SNR signal processing and digital down conversion. The stealth transmission has been verified to pose almost no impact on the public channel over a 117 km distance. The proposed scheme is compatible with existing optical transmission systems, so that no new hardware needs to be employed. It can be accomplished and is exceeded economically by adding simple algorithms, which utilizes only a small amount of FPGA resources. The proposed method can cooperate with encryption strategies or cryptographic protocols at different network layers to reduce the communication overhead and improve the overall security of the system.

DOI
10.1364/oe.488321

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The physical layer transmission security is a promising technology against security threats. As an effective supplement to the encryption strategy, steganography has received widespread attention. We report a real-time 2 kbps stealth transmission in the 10 Gbps dual polarization QPSK public optical communication. The stealth data is embedded in dither signals via precise and stable bias control technique for a Mach-Zehnder modulator. In the receiver, the stealth data can be recovered from the normal transmission signals by low SNR signal processing and digital down conversion. The stealth transmission has been verified to pose almost no impact on the public channel over a 117 km distance. The proposed scheme is compatible with existing optical transmission systems, so that no new hardware needs to be employed. It can be accomplished and is exceeded economically by adding simple algorithms, which utilizes only a small amount of FPGA resources. The proposed method can cooperate with encryption strategies or cryptographic protocols at different network layers to reduce the communication overhead and improve the overall security of the system.
We report a real-time 150 kbps stealth transmission within public optical communication of 10 Gbps dual polarization QPSK. The stealth data is modulated onto the frequency tuning signals of a fast-tuning laser source in the transmitter, which causes slight frequency dithering for the transmitted optical signal. In the receiver, the stealth receiver recovers the stealth data from the estimated frequency offset by the QPSK DSP algorithm. The experiments show the stealth transmission has few impacts on the public channel over a 300 km distance. The proposed method is fully compatible with existing optical transmission systems, and the only hardware change is to upgrade the transmitter laser to support frequency tuning through an external analog port for receiving stealth signal. The proposed stealth scheme can combine with cryptographic protocols to improve the integrated security of the system, and can be used as signaling transport for low level network control to reduce the communication overhead.
To counter heterodyne measurements, correlation attacks, and known plaintext attacks, seed key refresh is critical to the security of a quantum noise stream cipher system. Integrated key distribution is an important means to reduce the deployment cost, as key exchange and public transmission are performed over the same channel. In this paper, we propose a novel method for integrated key distribution by optical steganography based on dither-remodulation in a bias controller of the Mach-Zehnder modulator. No extra wavelength or bandwidth is used for the stealth channel, which is transmitted together within the public channel. The concealing depth of the stealth signal reaches −36.2 dB, and its steganographic effect provides additional security, which further improves the overall security of the optical physical layer. The bidirectional stealth transmission can support light-weight temporary key exchange mechanism, combined with asymmetric encryption algorithm, to achieve high security and forward/backward security of seed keys. We experimentally demonstrate a real-time integrated key distribution via optical steganography in a QNSC system. The experimental results show that a real-time bidirectional stealth link is established at a rate of 1 kbps in a fiber transmission distance of 97 km for a public QNSC transmission at a rate of 32 Gbps, providing a seed key refresh frequency of over 1 Hz.
We propose and demonstrate a data fragment multipath transmission scheme to achieve a secure optical communication based on polarization regulation. A dual-polarization Mach–Zehnder modulator (DPMZM) is driven by digital signals which are scattered by field-programmable gate array (FPGA) and transmitted in multiple paths. By utilizing two orthogonal polarization states, we have achieved a signal transmission under different optical parameters, and the transmission rate of the two paths can reach over 10 Gbps through a 20 km fiber with 2.5 Gbps hopping rate. In addition, we establish a theoretical model to analyze the security of the system and simulate brute force cracking; the probability of cracking the minimum information unit is 1.53 × 10−53. This proves that it is difficult to obtain a user data even using the fastest computers. Our scheme has provided, to our knowledge, a new approach for physical layer security.
Secure optical communications involve securing data transmitted over optical networks, primarily using technologies like optical encryption to protect data in transit. We have developed an optical steganography communication technique based on a quantum dot coherent comb laser, laser channels have strong correlated phase relationship. Each stealth channel uses two comb lines, which operates through two paired Mach-Zehnder interferometers. One line carries data, while the other serves as a reference. At the transmitter, phase modulation adds data to one comb line. An optical delay introduces a mismatch between the two lines to make the data undetectable to others. At the receiver, a programmable tunable delay matches the assigned delays from the different stealth channels. If the tunable delay matches the delay difference between the two-comb lines, the signal is recovered. The system uses physical-layer encryption instead of digital encryption to ensure robust security, scalability, and real-time data protection without computational processing.
Mach-Zehnder modulators (MZMs) are the most commonly used external modulators for optical communication links. The bias point of MZMs may drift due to environmental changes in practical applications, leading to system performance degradation. The latest decoy-state twin-field quantum key distribution (TF-QKD) system requires multiple modulators to generate multi-level light intensities and maintain an ultra-high extinction ratio between the signal-state light and vacuum-state light. This is essential to ensure the QKD security and extend the transmission distance. To meet this tight requirement, this paper presents an efficient bias control technique of multistage MZMs based on the dither signal method. Considering the complex signal processing algorithms involved in the dither signal method, this work designs a high-throughput hardware architecture based on field programmable gate array (FPGA) platform to realize real-time feedback control. It is comprised of three modules: the dither generation module, the fast Fourier transform (FFT) module, and the bias control module. Both static and dynamic extinction ratio tests were conducted to verify the performance of the system. Especially, this paper proposes an innovative and dynamic measurement method based on the highly sensitive single-photon detector to support the direct extinction ratio test of high-speed signals. The experimental results show that the system can stably maintain an ultra-high extinction ratio of 66.92 dB, demonstrating itself suitable for the majority of optical communication systems with very tight extinction ratio requirements. The feedback control time is about only 0.5 seconds per stage, which is fast enough to compensate for the usual environmental drift. In the temperature stability experiments, when the temperature varies between 26-64°C, the proposed system achieves a 74% reduction of the extinction ratio fluctuation compared to the result without using the feedback system.