Fiber-optic physical layer key generation and distribution based on the phase of the error vector in end-to-end systems

This paper proposes an end-to-end physical layer secure key generation and distribution (E2E-PLSKGD) scheme based on error vector phase (EVP) for fiber transmission systems. It addresses compatibility issues in existing PLSKGD caused by additional random sources or devices, as well as limitations in application scenarios and insufficient key generation rate (KGR) from amplitude or phase modulation of intensity-modulated signals. We introduce a position-enhanced transformer (PE-transformer) architecture with adaptive position coding (APC) for accurate E2E modeling in coherent optical systems. Leveraging the inherent high randomness of signal phase in fiber systems, legitimate parties use the PE-transformer to build E2E models via bidirectional transmission, compute error vectors, and extract EVP noise as key quantization sequences. Using data from new negotiation cycles and transfer learning (TL), local E2E source models are rapidly updated to target models, enhancing key security. Simulations show superior E2E modeling, with R-Square values >0.95, excellent waveform fitting, and consistent data distributions across distances. Pearson correlation coefficients (CC) of EVP sequences between legitimate parties exceed 0.8 across 50-80 km distances and -2 dBm to 4 dBm launch powers, indicating strong correlation. Experimental validation on a 120 km fiber system shows an EVP sequence correlation of 0.72, with real-time post-processing achieved via FPGA. At a 5G baud rate, error-free KGR reaches 0.8 Gbps. The proposed architecture enables precise E2E modeling, offering a new approach for dynamic, high-quality key generation and a potential method for AI-empowered fiber transmission security.