Generation of Microwave Frequency Comb, Chaotic, and Single-Frequency Microwave Signal in a Short-Cavity-Based Optoelectronic Oscillator

In this letter, a short-cavity-based optoelectronic oscillator (SC-OEO) is proposed and experimentally analyzed for different kinds of microwave signal generation. With the same frequency bandwidth and OEO gain conditions, the gain obtained for each mode in the SC-OEO is much larger than that in a long-cavity-based OEO, making it easier to achieve phase-locking state, then generating a stable microwave frequency comb (MFC), and realizing a self-mode-locking state. In the experiment, a self-fundamental mode-locking SC-OEO is realized, where an MFC with a free spectrum range (FSR
₁
) of 36.38 MHz is generated in the range of 20 GHz. The corresponding temporal signal is a periodic square-wave signal with a period T
₁
of 27.47 ns, which is equal to the time delay of the OEO loop. Harmonic-locking SC-OEO with an FSR
₂
= 0.5FSR
₁
= 18.19 MHz is also achieved, generating a periodic square wave pulse with a period T
₂
= 2T
₁
= 54.94 ns. By increasing the system gain, the proposed SC-OEO can evolve from the self-mode-locking state into chaotic state to generate a chaotic microwave signal with an effective bandwidth of 11.76 GHz. The proposed SC-OEO also can work at single-frequency oscillation state with no filter, which generates a microwave signal of 13.4 GHz. The experimental analysis of the SC-OEO provides an effective way to further study the rich nonlinear dynamics characteristics and complex microwave signal generation of the OEO system.