Highly Reliable Multilayer Encryption Scheme With Constellation Shaping Based on Joint Index Modulation

This paper proposes a highly reliable multilayer encryption scheme with constellation shaping based on joint index modulation. Multilayer encryption is used to ensure the security of the scheme. We utilize the 3D-Zhang chaotic system to realize the multidimensional perturbation of bits, subcarriers, and symbols of the original signal. The key information is masked with the signal using joint index modulation (JIM). The cooperative transmission of the initial value of the chaotic system is realized through the position information of the silent subcarriers and the constellation modes of the corresponding subcarriers. The scheme interleaves the initial values of the two chaotic systems to encode them as index bits, realizing the first layer of masked keys. Additional constellation shaping is achieved by optimizing the index mapping rules and changing the distribution of constellation points in the center and in the dual mode. The rotational encryption of the constellation is realized using a one-dimensional sinusoidal chaotic system after the completion of JIM, and the second layer of spherical shell masking of the key information is completed. The experimental implementation demonstrates the successful transmission of a 14 Gb/s 3D-JIM -8QAM signal over a 2 km weakly coupled seven-core fiber. Results confirm that the multi-layer encryption approach ensures secure signal transmission even under partial key leakage, without introducing degradation to the system's transmission performance. Compared to a random constellation distribution, the optimized index mapping scheme provides a coding gain of 0.75 dB at an FEC (Forward Error Correction) threshold of 3.8×10⁻³. The proposed scheme achieves error-free key transmission, with a bit error rate (BER) consistently maintained at 0. Notably, even minor key misalignments result in a BER of 0.5, facilitating timely key updates. The scheme boasts a vast key space of 10¹⁵⁰, effectively resisting brute-force attacks. Due to its high reliability and robust security features, the proposed scheme demonstrates strong potential for applications in future optical access networks.