Generation of dual-band microwave comb signals based on active mode-locked optoelectronic oscillators

We report a dual-wave microwave comb signal generation system based on an active mode-locked optoelectronic oscillator (AML-OEO), with the output signal being a dual-center frequency microwave comb signal. We utilize an equivalent dual-band filter based on parallel filters, where both parallel filters are narrow-band filters. When the optoelectronic oscillator loop is running freely, the output signal is a single-frequency signal with a frequency equal to the bandwidth of one of the narrow-band filters in the equivalent dual-frequency filter. When an excitation signal with a frequency equal to the difference between the two filters is injected through the mixer, the oscillation mode of the loop changes and the output signal becomes a dual-frequency signal with a frequency equal to the center frequency of each of the two narrow-band filters. The mode intervals of the optoelectronic oscillator are calculated from the spectrogram, and after injecting an active mode-locked signal with the same frequency and mode interval size, it can be observed that multimode oscillations occur at two frequencies. Replacing different optical fibers to change the loop length and thus the mode interval, a dual-frequency microwave comb signal with a larger number of combs can be generated when an active mode-locked signal at the fundamental frequency is injected. The center frequency can be tuned by replacing the filter with a narrower center frequency and has a narrower bandwidth and lower price compared to commercial dual band filters.