Frequency-scanned microresonator soliton comb with the tracking of the frequency of all comb modes

TL;DR

This paper presents a method for rapid frequency scanning of microresonator soliton combs with enhanced feedback and a novel interferometric technique to measure the frequency shifts of all comb modes simultaneously.

Contribution

It introduces a combined feedback and feedforward control scheme for ultrafast scanning of soliton combs and a new measurement method for all mode frequency shifts.

Findings

Achieved 70 GHz scan in 500 μs with enhanced feedback.

Demonstrated measurement of all comb mode frequency shifts using a dual-wavelength interferometer.

Enabled estimation of frequency shifts across all comb modes.

Abstract

Rapid and large scanning of a dissipative Kerr-microresonator soliton comb with the characterization of all comb modes along with the separation of the comb modes is imperative for the emerging applications of the frequency-scanned soliton combs. However, the scan speed is limited by the gain of feedback systems and the measurement of the frequency shift of all comb modes has not been demonstrated. To overcome the limitation of the feedback, we incorporate the feedback with the feedforward. With the additional gain of > 40 dB by a feedforward signal, a dissipative Kerr-microresonator soliton comb is scanned by 70 GHz in 500 $\mu$s, 50 GHz in 125 $\mu$s, and 25 GHz in 50 $\mu$s (= 500 THz/s). Furthermore, we propose and demonstrate a method to measure the frequency shift of all comb modes, in which an imbalanced Mach-Zehnder interferometer with two outputs with different wavelengths is used. Because of the two degrees of freedom of optical frequency combs, the measurement at the two different wavelengths enables the estimation of the frequency shift of all comb modes.