Chaotic Dynamical Enhanced Optical Physical Layer Encryption in OFDM-PON System Based on Echo State Network

In this paper, we propose an optical physical layer encrypted scheme in an orthogonal frequency division multiplexed passive optical network (OFDM-PON) based on a nonlinear dynamical enhanced chaotic system generated by Echo State Network (ESN). The proposed-system gets more complex chaotic behavior using three-dimensional Henon mapping iterative chaotic mapping with infinite collapses (ICMIC) cascade mapping (3-D HICM). ESN generates the sequences that are used to produce the masking vectors to encrypt the bit, constellation and subcarriers, which can resist the degradation of chaotic dynamics. Compared with other networks, ESN can reduce the computational cost by omitting the process of obtaining weights by gradient descent method and randomly generating input and internal weights. Its normalized root mean square error (NRMSE) is less than 0.14. The correlation coefficient (CC) of chaotic sequences by 3-D HICM cascade mapping and ESN is more than 0.99. By comparison, the sensitive value of all sequences increases after generating by ESN. Especially, the sensitive value of the x sequence increases by 8 orders of magnitude, which shows the best improvement effect. The generated 16-quadrature amplitude modulation (16QAM) OFDM signal transmits 126.88 Gb/s data rate across a 2 km fiber span of 7-core fiber. The bit error rate (BER) is analyzed during the experiments, and the results show that the proposed system can improve efficiency and security in OFDM-PON systems.