Variable rate high-security OCDM transmission scheme based on multi-order joint modulation.

This paper proposes a variable rate high-security OCDM transmission scheme based on multi-order joint modulation, aiming to address the limitations of traditional encryption techniques in terms of flexibility. Initially, a chaotic selection sequence is used to dynamically allocate information bits to three modulation formats: 16-quadrature amplitude modulation (16QAM), 8-phase shift keying (8PSK), and quadrature phase shift keying (QPSK). Additionally, a pseudo-mapping masking factor is employed to construct a joint encryption mechanism with a pseudo-16QAM mapping. The system also introduces a variable-rate transmission mechanism, which adjusts the bit allocation ratio dynamically to adapt to different communication requirements. The proposed scheme is experimentally validated in a 2 km weakly coupled seven-core fiber system. When the modulation ratio of 16QAM, 8PSK, and QPSK is (12:3:2), the maximum information transmission rate reaches 126 Gb/s, while at a ratio of (3:3:11), the minimum rate is still stable at 87.5 Gb/s. Hence, a variable rate modulation with a range from 87.5 Gb/s to 126 Gb/s can be theoretically realized. Furthermore, the system cannot decode the data when the correct key is not available at the illegal receiver, which ensures effective data security. In addition, the scheme provides a key space of up to 10, significantly enhancing the resistance to attacks, flexibility and transmission efficiency of the system. This work presents an innovative solution for high-security optical communication systems in the future.