Effects of a quiet point on a Kerr microresonator frequency comb

TL;DR

This paper experimentally demonstrates that operating a Kerr microresonator frequency comb at a quiet point significantly reduces frequency instability and enhances phase lock performance, improving microcomb stability for practical applications.

Contribution

It provides the first experimental validation that a quiet point reduces frequency instability and enhances phase lock performance in a high-repetition-rate Kerr microresonator comb.

Findings

Fractional frequency instability of 1.5×10⁻⁹ at 1 second at the quiet point

44 times lower instability compared to free-running microcomb

Relative fractional frequency instability of 6.8×10⁻¹³ in phase locking

Abstract

A quiet point, an operating point of pump-resonance detuning that minimizes frequency fluctuation due to nonlinear effects inside a resonator, has been employed for phase noise reduction of a soliton Kerr microresonator frequency comb (microcomb). Naturally, it is expected that the use of the point will also improve performances of a microcomb in terms of frequency stability and faithfulness in a phase locked loop. In this study, we experimentally investigate the effect in a microcomb with a repetition frequency of 300~GHz. We obtain a lowest fractional frequency instability at a quiet point of $1.5\times 10^{-9}$ at 1 second, which is 44 times lower than free-running instability. Phase-locking of a microcomb to a stabilized fiber comb is demonstrated to evaluate performance in a feedback loop, where in-loop-limited relative fractional frequency instability between the microcomb and the fiber comb of $6.8 \times 10^{-13}$ is obtained as an indicator of the stability limitation.