Direct-modulated active mode-locking optoelectronic oscillator for microwave frequency comb signals

Abstract The optoelectronic oscillator (OEO) has been widely investigated to generate ultrapure microwave signals. For many applications, microwave signals with large bandwidth and multiple frequency bands, such as broadband microwave frequency comb (MFC) signals, are also needed. Conventional MFC signals are generated by active mode-locking OEO (AML-OEO) using devices such as Mach–Zehnder modulators (MZM) and delay fibers, which make the system structure more complicated and take a long time to build up stable oscillation at an oscillation mode. In this paper, A direct-modulated AML-OEO (DM-AML-OEO) is demonstrated with the advantages of compact design, cost-effectiveness, and straightforward integration. Mode-locked pulses are generated by direct-modulated Laser Diode (LD) which have low-phase noise. Furthermore, different comb spacings of MFC signals can be readily attained by adjusting the frequency of the active modulation signal (AMS) while supermodels are confined. In the experiments, the DM-AML-OEO produced MFC signals that exhibited a central frequency of 718 MHz and a frequency spacing of 100 kHz.