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Optics Express

High-speed coherent optical encryption/decryption system based on cross-phase encoding

Rui Li, Xiaoxue Gong, Qihan Zhang, Wenshuai Qin, Weigang Hou, Lei Guo

Published Jul 3, 2025• 6 citations
Publisher

Abstract

The optical network supporting emerging bandwidth-intensive services has become the cornerstone of the 5G era. However, the development of optical fiber eavesdropping and quantum computing has brought huge security challenges to traditional cryptography. As an effective approach to improving optical layer transmission security, all-optical logic gate encryption has important research significance. This paper proposes a high-speed coherent optical encryption and decryption system based on phase encoding with all-optical logic gates. The system ingeniously designs the phase encoding and decoding scheme between two quadrature phase-shift keying (QPSK) signals, which doubles the encryption and decryption efficiency. In addition, the integration of physical-layer key distribution (PLKD) and physical-layer encryption (PLE) contributes to a reduction in overall system complexity. By adopting real-time signal processing in an all-optical domain, the single-wavelength rate of system security communication can reach 100 Gbps. The system is also applicable to other phase-modulated signals and provides a feasible scheme to enhance transmission security in wavelength division multiplexing (WDM) optical networks featuring high speed, low latency, and high flexibility.

DOI
10.1364/oe.567505

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The optical network supporting emerging bandwidth-intensive services has become the cornerstone of the 5G era. However, the development of optical fiber eavesdropping and quantum computing has brought huge security challenges to traditional cryptography. As an effective approach to improving optical layer transmission security, all-optical logic gate encryption has important research significance. This paper proposes a high-speed coherent optical encryption and decryption system based on phase encoding with all-optical logic gates. The system ingeniously designs the phase encoding and decoding scheme between two quadrature phase-shift keying (QPSK) signals, which doubles the encryption and decryption efficiency. In addition, the integration of physical-layer key distribution (PLKD) and physical-layer encryption (PLE) contributes to a reduction in overall system complexity. By adopting real-time signal processing in an all-optical domain, the single-wavelength rate of system security communication can reach 100 Gbps. The system is also applicable to other phase-modulated signals and provides a feasible scheme to enhance transmission security in wavelength division multiplexing (WDM) optical networks featuring high speed, low latency, and high flexibility.
Protecting the security of optical network is a major worldwide challenge. The conventional schemes for securing communications are based on cryptography at the MAC layer and its higher layers, which are facing a great threat with the development of quantum computers. Optical encryption is a promising way for building security on the physical layer of optical communications. In this work, we propose a novel optical encryption scheme for wavelength division multiplexing (WDM) fiber-optic communication systems, by utilizing the private chaotic phase scrambling. Secure transmission of 50 Gbps signal over 50-km standard single-mode fiber is experimentally and numerically demonstrated. The results show that the WDM signal is efficiently encrypted into a noise-like signal, due to the spectral broadening effect of chaotic phase scrambling. Since the processes of encryption and decryption are totally implemented in the optical domain, the proposed scheme can encrypt the entire network traffic with low latency and high speed. Moreover, the proposed encryption scheme is compatible with the existing WDM optical networks, and only one pair of encryption and decryption devices is sufficient to encrypt all WDM channels, thus the scheme can be easily implemented at low hardware cost.
A scheme for optical parallel encryption/decryption of quadrature phase shift keying (QPSK) signals is proposed, in which three QPSK signals at 10 Gb/s are encrypted and decrypted simultaneously in the optical domain through nondegenerate four-wave mixing in a highly nonlinear fiber. The results of theoretical analysis and simulations show that the scheme can perform high-speed wiretapping against the encryption of parallel signals and receiver sensitivities of encrypted signal and the decrypted signal are −25.9 and −23.8 dBm, respectively, at the forward error correction threshold. The results are useful for designing high-speed encryption/decryption of advanced modulated signals and thus enhancing the physical layer security of optical networks.
High-order modulation format optical signals are widely deployed in modern optical networks but remain insufficiently protected at the physical layer, leading to significant security vulnerabilities. This work proposes an all-optical secure transmission scheme for 16QAM signals based on phase coding and dispersive stretching. The scheme employs symmetric cascaded in-phase and quadrature Mach–Zehnder modulators (IQMZMs) to realize phase encoding and decoding, providing a simple structure with good suitability for photonic integration. The universality of constant-envelope key signals within the proposed architecture is investigated, providing references for key-format and device selection in practical applications and important guidance for future research on all-optical digital encryption. To the best of our knowledge, this is the first demonstration of all-optical digital encryption and decryption of 16QAM signals using high-order modulated key signals. Compared with existing schemes of the same category, the key space increases by a factor of2n2^{n}2n, wherennndenotes the number of symbols. Furthermore, the key signal undergoes dynamic temporal broadening through dispersive processing, enabling steganographic transmission. Simulation results at a bit rate of 100 Gb/s demonstrate significant security enhancement with high stability and reliability. Overall, the proposed scheme provides an effective approach to enhancing physical-layer security in high-order modulation optical transmission systems.
Aiming at the current eavesdropping security issues in the physical layer of optical networks, a new hybrid optical encryption scheme based on Highly Nonlinear Fiber (HNLF) and Super Structured Fiber Bragg Grating (SSFBG) is proposed in this paper. In the scheme, degenerate Four Wave Mixing (FWM) is used to encrypt and decrypt user information, and optical coding technology is used to encode and decode the key information. Therefore, the encoding and secret transmission of the key signal can be realized simultaneously. The security of the system is measured by comparing the waveform of the encrypted signal transmitted in the channel with the waveform of the original transmitted signal, and the effectiveness of the system is measured by the bit error rate at the system receiver side. The simulation results show that the frequency and phase of the user data information are disturbed, and the optical power of the encoded key signal is as low as -34.4 dBm. Therefore, the eavesdropping channel cannot obtain effective data information nor detect the key signal, which demonstrates the safe transmission of Quadrature Phase Shift Keying (QPSK) signal.
Data security plays an increasingly important role in modern telecommunications. The advent of quantum computational processors presents a significant threat to today's widely employed public key encryption algorithms, necessitating the adoption of new approaches to data encryption. Whilst quantum key distribution guarantees unconditional security for cryptographic key exchange in optical communication networks, the data rate is slow (Mbit/s), especially when compared to conventional optical communication. Here we present a highly secure encryption approach in which the encryption key, generated by quantum key distribution at a rate of up to 2.9 Mbit/s, was used to seed physical layer encryption performed using time domain spectral phase encoding (TDSPE). This allowed us to demonstrate encrypted 40 Gbit/s quadrature phase shift keyed data communications over 52.3 km of installed optical fiber, which cannot be eavesdropped using brute force computational attacks. Any attempt to eavesdrop the encrypted signal in the physical layer is highly time-sensitive – the phase states must be measured and decrypted prior to optical signal attenuation, which means that the attack procedure typically needs to be completed within a few milliseconds. This work represents the first example of quantum-enhanced physical layer encryption at realistic optical data rates that is fully secure from brute force computational attacks and the first demonstration of TDSPE using continuous-wave laser source and quadrature phase shift key modulation.
In conventional optical communication systems, the transmission signals are regular digital signals. Due to the openness of optical fiber networks, it is rather easy for eavesdroppers to obtain the transmission signals from the public fiber-link and then intercept the message directly. To address this crucial security challenge, in this work we propose a high-speed secure optical communication system in virtue of physical random temporal encryption based on private physical random phase modulation and phase-to-intensity conversion. The proposed physical random temporal encryption is performed by a module composed of a phase modulator (PM) and a chirped fiber Bragg grating (CFBG), and the corresponding decryption is achieved with a similar module composed of an inverse-phase driven PM and an oppositedispersion CFBG. By distributing a constant-amplitude random-phase signal to the local semiconductor lasers deployed in the encryption module and decryption module, a pair of synchronized physical random PM driving signals that are not exchanged on public link can be independently generated, which guarantees the receiver end can correctly decrypt the original transmission message. Our numerical results demonstrate that with the proposed encryption scheme, the regular transmission signal is encrypted as a noise-like signal that can greatly enhance the security of message, and moreover, based on the private synchronized physical random phase modulation, the privacy of encryption and decryption are guaranteed, which prevents the eavesdroppers from intercepting transmission message. This work provides a promising strategy for the implement of high-speed high-security physical-layer optical communication.