Microwave Chaotic Signal Generation With Suppressed Time-Delay Signature Based on a Coupled Optoelectronic Oscillator

Broadband microwave chaos is readily generated in optoelectronic oscillators (OEOs), but its time-delay signature (TDS) is obvious and harmful to the security of chaos. In this article, microwave chaotic signal generation with suppressed TDS is investigated based on a coupled optoelectronic oscillator (COEO) composed of a fiber ring laser (FRL) and an OEO. A theoretical model of the chaotic COEO is presented and numerical simulation results demonstrate that increasing optical bandwidth in the system improves TDS suppression. Owing to the enriched dynamics introduced by the nonlinear coupling between FRL loop and OEO loop, the system naturally has the ability to suppress TDS. In the experiment, periodic, quasi-periodic, and chaotic states in the route to chaos are observed. The enhancement of both bandwidth and chaotic randomness through the implementation of high OEO loop gain is demonstrated. Systematic comparative experiments demonstrate that broadband optical filtering effectively facilitates TDS suppression and improves spectral flatness. The proposed chaotic COEO can not only generate broadband microwave chaos with suppressed TDS, but also provide a simple and flexible research platform for nonlinear coupled time-delay dynamical systems.