Continuously and Precisely Tunable Microwave Frequency Comb Generation Based on Actively Mode-Locked OEO

A novel actively mode-locked (AML) optoelectronic oscillator (OEO) for microwave frequency comb (MFC) generation is proposed and experimentally demonstrated. The novelty of the scheme is that the generated MFCs can be continuously and precisely tuned by adjusting a microwave photonic filter (MPF) with periodic passband response, which contains a dual-drive Mach-Zehnder modulator (DDMZM) and an electrical delay component. In the OEO cavity, the MFC signal is steadily generated by injecting a signal and phase-locking between adjacent oscillation modes. We set the frequency of the injected signal equal to the free spectrum range (FSR) of the MPF to ensure that the frequencies of the MFC match the passband frequency. By adjusting the length of the electrical delay line, the frequencies of the generated MFCs can be precisely tuned. Experimentally, the MFCs with the frequency interval of 48.05 MHz and 66.08 MHz are generated by our proposed AML-OEO. The frequency of the MFCs signal can be precisely tuned in 100 kHz steps. In addition, the phase noise of the main mode of the MFC signal is as low as −135 dBc/Hz@10 kHz and the supermode noise suppression ratio is around 35 dB.