Harnessing resonant noise emission to measure cavity-pump detuning for microcomb stabilization

We demonstrate an in situ detection technique to track the effective cavity-pump detuning without any active perturbation of the pump laser that is generating soliton microcombs in the cavity. The technique utilizes a narrow band notch filter to isolate the pump from the cavity output, a commonly used technique to avoid the saturation of the photodetector in the detection circuitry of the microcomb repetition frequency, and measures the effective detuning by detecting the peak of the resonant profile, corresponding to the hot cavity resonance, present at the isolated pump. The technique is applicable to determine the effective detuning regardless of the existence of soliton states in the cavity.