Microwave frequency combs generation in harmonically mode-locked optoelectronic oscillator based on injection locking

A harmonically mode-locked optoelectronic oscillator (HML-OEO) based on injection locking is proposed to generate microwave frequency combs (MFCs) with a high supermode noise suppression ratio (SNSR) and high frequency stability. N th -order harmonic mode locking is achieved via frequency mixing of the oscillation signal and an intermediate-frequency (IF) signal with a frequency interval equal to N times the free spectral range (FSR) in the loop. The supermode noise of the HML-OEO is suppressed by the injection of a single-tone microwave signal, which is aligned with the frequency of one longitudinal mode, in order to enhance the gain competitiveness of one group of longitudinal modes. Furthermore, the correlation of the adjacent pulses can be improved by the injection-locked effect. In the numerical simulation, a microwave frequency comb with a center frequency of 10 GHz and a SNSR of 81.1 dB is generated under the condition of 3 rd -order harmonic mode locking, by injecting the microwave signal with a power of −40 dBm. Furthermore, the correlation of adjacent pulses generated in the proposed HML-OEO is superior to that before injection locking.