Frequency comb generation in a pulse-pumped normal dispersion Kerr mini-resonator

TL;DR

This paper demonstrates that pulsed pumping enables frequency comb generation in normal dispersion Kerr mini-resonators without dispersion perturbations, and shows how to tune the comb's center frequency and spacing, revealing new soliton states.

Contribution

It introduces pulsed pumping as a method to generate combs in normal dispersion resonators without localized perturbations, and demonstrates tunability of comb parameters and new soliton states.

Findings

Spectrally flat combs with 3 THz bandwidth generated.

Center frequency tunable by over 2 THz.

Line spacing adjustable between 0.54 and 10.8 GHz.

Abstract

Kerr microresonators driven in the normal dispersion regime typically require the presence of localized dispersion perturbations, such as those induced by avoided mode crossings, to initiate the formation of optical frequency combs. In this work, we experimentally demonstrate that this requirement can be lifted by driving the resonator with a pulsed pump source. We also show that controlling the desynchronization between the pump repetition rate and the cavity free-spectral range (FSR) provides a simple mechanism to tune the center frequency of the output comb. Using a fiber mini-resonator with a radius of only 6 cm we experimentally present spectrally flat combs with a bandwidth of 3 THz whose center frequency can be tuned by more than 2 THz. By driving the cavity at harmonics of its 0.54 GHz FSR, we are able to generate combs with line spacings selectable between 0.54 and 10.8 GHz. The ability to tune both the center frequency and frequency spacing of the output comb highlights the flexibility of this platform. Additionally, we demonstrate that under conditions of large pump-cavity desynchronization, the same cavity also supports a new form of Raman-assisted anomalous dispersion cavity soliton.