Generation of microwave frequency combs based on dual-frequency injected optoelectronic oscillator

We report a dual-frequency actively mode-locked optoelectronic oscillator (AML-OEO) which can generate MFCs with more comb lines and wider spectrum bandwidth. For a traditional single-frequency AML-OEO, normally, there is a tradeoff between wider spectrum bandwidth and more comb lines. In addition, our spectrum bandwidth can also be flexibly tuned by adjusting the frequency of injection signals. The proposed scheme is theoretically analyzed and experimentally demonstrated. For the same line spacing of 661.01 kHz, experiment results show that the comb lines increase from 7 (single-frequency injection) to 73 (dual-frequency injection) within power variations of ± 10 dB. Moreover, the spectrum bandwidth increases by ∼9 times.