Secure Optical Network Transmission of 16QAM Signals Enabled by Phase Coding and Dispersive Stretching

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Abstract
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 of $2^{n}$, where $n$ denotes 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.
Funding Information
  • National Key Research and Development Program of China (2023YFB2905900)
  • National Natural Science Foundation of China (U24B20134)
  • National Natural Science Foundation of China (62222103)
  • Chongqing Municipal Education Commission (KJZD-K202400608)
  • State Key Laboratory of Information Photonics and Optical Communications
  • Beijing University of Posts and Telecommunications (IPOC2025ZR02)

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