Abstract

Soliton microcmb [1] devices based on integrated waveguides are miniaturized optical frequency combs, which are ideal for portable applications for timing, spectroscopy and metrology. Chip-based soliton microcomb devices have already been employed for coherent telecommunications, dual-comb spectroscopy, ultrafast ranging, astrophysical spectrometer calibration, and for creating integrated frequency synthesizers and atomic clocks. A particularly promising application is to build soliton-microcomb-based photonic integrated microwave oscillators, whose center frequency can be freely designed and actively tuned by users. Yet, so far, soliton microcombs at microwave repetition rate have not been reported on integrated material platform, such as silicon nitride (Si₃N₄) [2], mainly due to high optical loss in waveguides caused by the fabrication process.

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