Continuous scanning of a dissipative Kerr-microresonator soliton comb for broadband, high-resolution spectroscopy.

Dissipative Kerr-microresonator soliton combs (hereafter called soliton combs) are promising to realize chip-scale integration of full soliton comb systems providing high precision, broad spectral coverage, and a coherent link to the micro/mm/THz domain with diverse applications coming on line all the time. However, the large soliton comb spacing hampers some applications. For example, for spectroscopic applications, there are simply not enough comb lines available to sufficiently cover almost any relevant absorption features. Here, we overcome this limitation by scanning the comb mode spacing by employing Pound-Drever-Hall locking and a microheater on the microresonator, showing continuous scanning of the soliton comb modes across nearly the full free-spectral range of the microresonator without losing soliton operation, while spectral features with a bandwidth as small as 5 MHz are resolved.