Physical-layer data encryption using chaotic constellation rotation in OFDM-PON

Physical-layer data encryption schemes are required to enhance the data security during transmission in passive optical networks (PONs). Encryption schemes using digital chaos provide a huge key space which results in high-level security for the user data. Here, a novel physical-layer encryption scheme using chaotic radial constellation rotation is proposed and experimentally demonstrated for orthogonal frequency division multiplexing PON (OFDM-PON). A one-dimensional (1D) chaos is employed to generate the digital chaotic sequences for data encryption. The proposed encryption scheme offers less computational complexity due to the use of 1D chaos. The initial values are pre-shared between the optical line terminal (OLT) and optical network unit (ONU), which provide a key space of 10
¹⁵
. At the OLT, the original data is firstly encrypted by a chaotic XOR operation, and then further encrypted using the chaotic phase offsets. This multi-fold encryption generates an overall key space of 10
³⁰
. The proposed encryption scheme is verified by experiments, where a 9.4-Gb/s encrypted 16 quadrature amplitude modulation (16-QAM) optical OFDM signal transmission is successfully carried over 20 km standard single-mode fiber (SSMF). The bit error rate (BER) of the received encrypted signal was calculated for a legitimate ONU as well as an illegal ONU. The encrypted OFDM signal is also compared with the original OFDM signal for performance analysis. The transmission performance is improved for the proposed encryption scheme due to the reason that the introduction of chaotic radial rotation reduces the effect of phase noise in the encrypted OFDM signals.