Chaotic Walsh–Hadamard Transform for Physical Layer Security in OFDM-PON

This letter proposes and experimentally demonstrates an approach to jointly enhance the physical layer security and improve an optical orthogonal frequency division multiplexing (O-OFDM) transmission in passive optical network. It is proven that the Walsh-Hadamard Transform (WHT) matrix can effectively reduce the peak-to-average power ratio (PAPR) of OFDM signals after independent row/column permutations. A hyper digital chaos is adopted to generate the chaotic permutated WHT matrix for OFDM data encryption, which provides a total key space of ~ 10¹⁷⁸ to enhance the physical layer confidentiality. An 8.9-Gb/s encrypted 16-QAM O-OFDM signal transmission is successfully demonstrated over 20-km standard single-mode fiber, where the receiver sensitivity is improved by ~ 1 dB (BER@10⁻³ ) due to the PAPR reduction through the chaotic WHT precoding. Moreover, the scheme does not require any additional sideband information and provides low computational complexity.