Dual-domain real-time optical transmission system based on adaptive cascaded chaos enhancement

To address the demand for real-time secure transmission in optical communication systems, we propose a real-time optical transmission scheme based on adaptive cascaded-chaos-enhanced dual-domain encoding. A two-dimensional (2D) chaotic system is constructed by cascading Sine and Tent maps, and an adaptive dynamic enhancement mechanism is introduced to compensate for chaotic degradation caused by hardware fixed-point implementation. The generated chaotic sequences are employed to perturb PAM4 symbols in the symbol domain and to introduce random clock offsets in the time domain via (first-in-first-out) FIFO-based dynamic delay, thereby realizing dynamic symbol-time dual-domain encryption (DSTDE). The proposed scheme is implemented on a field-programmable gate array (FPGA) and experimentally validated over a 25 km single-mode fiber (SMF). Experimental results show that the legitimate receiver achieves a bit error rate (BER) as low as 3.8 × 10^-3 with an effective key space of 10²⁴, whereas unauthorized receivers-or those accessing only a single encryption domain-exhibit a BER consistently above 0.4, confirming the security and robustness of the system. To the best of our knowledge, this work represents the first integration of adaptive chaotic enhancement into real-time optical communication, providing an efficient and hardware-feasible physical-layer encryption framework for secure optical fiber transmission.