We review recent trends in the generation of a frequency comb in a microresonator, which is also known as a microcomb. The review includes both its history and applications. We explain on the basics in relation to how phase-locked and soliton states are achieved. Then, issues such as the coupling with optomechanics are discussed, which reveal the rich physics involved in this system. Finally, we describe how to extend the comb generation bandwidth by using stimulated Raman scattering and third harmonic generation.
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