Hybrid chaotic encryption algorithm with polar coding for probabilistic shaping orthogonal frequency division multiplexing passive optical network

A hybrid chaotic encryption algorithm is proposed to enhance the reliability and security of the probabilistic shaping orthogonal frequency division multiplexing passive optical network. The original chaotic sequences for hybrid encryption are generated by the classical four-dimensional hyperchaotic Chen system, and symbol-level encryption is achieved by performing I and Q phase rotation and two levels of symbol confusion on the quadrature amplitude modulation (QAM) symbols. In addition, the probabilistic shaping (PS) technique and polar coding are combined to improve the transmission performance, which achieves the double improvement of security and effectiveness. The hybrid chaotic encrypted signals are verified on a net bit rate of 24.09 Gb/s 16QAM orthogonal frequency division multiplexing passive optical network simulation system, which is transmitted through a 25-km standard single-mode fiber. The results show that the proposed algorithm can enhance the security performance with an enormous key space of 10127. At the bit error rate (BER) of 3.8×10−3, the proposed algorithm achieves an optical signal noise ratio (OSNR) gain of 3 dB over the unencrypted signal and an OSNR gain of 2.3 dB over the conventional constellation shift encryption scheme. The proposed encryption algorithm combines polar coding and PS, which significantly improves the BER performance while maintaining the mutual information (MI) gain of 1 bit/symbol and improves the MI performance by 0.1 bit/symbol compared with the single PS technique.