Experimental demonstration of a dual-dynamic encryption strategy for IM-DD systems with key update and symbol scrambling

The vulnerability of intensity modulation direct detection (IM-DD) systems to physical-layer eavesdropping poses a significant threat to data center interconnects (DCI). In this Letter, we propose a dual-dynamic strategy for physical-layer encryption to enhance the security of IM-DD systems. The scheme synergistically combines dynamic key update and dynamic rule-based pulse-amplitude modulation (DR-PAM) symbol scrambling to achieve efficient security protection. The master key is dynamically updated according to a pre-negotiated rule, enabling the generation of a distinct session key for each data frame via a hash function. This approach ensures real-time operation without frequent key negotiation. To our knowledge, the DR-PAM is the first universal symbol scrambling scheme supporting arbitrary PAM orders. Experimental results demonstrate that at 56 Gbit/s and 112 Gbit/s data rates, legitimate receivers achieve performance identical to unencrypted links, while illegal receivers are completely unable to decrypt the data. The proposed encryption scheme has better compatibility with existing transmission systems and introduces no performance penalty, thus delivering a secure, real-time, and practical solution for cost-sensitive, high-speed DCI.