Microwave frequency combs (MFCs) have important applications in communication and sensing owing to their characteristics of large number of comb lines, wide frequency range, and high precision of comb spacing. In many applications, MFCs are required to emit signals with tunable center frequency and variable comb spacing to accommodate different operating frequency bands and accuracies. Here, we demonstrate a tunable MFC by injecting a low-frequency electrical signal into a tunable optoelectronic oscillator (OEO). Tuning of MFC's center frequency and comb spacing are realized, allowing a frequency tuning range from 1 to 22 GHz and 50 comb lines within a 5 MHz bandwidth obtained in the MFC generator. In addition, the introduction of the silicon nitride micro-disk resonator (SiN-MDR) in the system paves the way for the integration of MFC generator.
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