Self-Mode-Locking Phenomenon and Microwave Signal Generation in Optoelectronic Oscillators

Mode-locking optoelectronic oscillators (OEOs) have emerged as one of the recent research frontiers in the OEO field. In an OEO cavity, the mode-locking of longitudinal modes can be realized through passive mode-locking, active mode-locking, and self-mode-locking. These methods can generate a series of microwave combs with similar intensities or produce microwave pulses. Both passive and active mode-locking demand the incorporation of additional control devices, such as saturable absorbers and microwave sources, into the basic OEO system. This not only complicates the OEO system but also poses challenges for its future applications. We hereby propose a microwave signal generation system based on a long-fiber-cavity self-mode-locking OEO. This system leverages high gain and high nonlinearity to induce mode-locking among the longitudinal modes of the loop, thus generating modulated signals, microwave pulse and microwave frequency comb. By precisely adjusting the loop gain, the mode-locking frequency can be varied, which further varies the modulation frequency of the output signal, the pulse repetition rate and the comb intervals of the microwave frequency comb. This significantly enhances the usability of the system. Moreover, benefiting from the energy storage capacity of the long fiber, the intracavity signal exhibits excellent phase noise performance. Therefore, this system holds great potential for wide-ranging applications in fields such as communication and radar.