Stimulated generation of deterministic platicon frequency microcombs

TL;DR

This paper demonstrates the generation of bright square platicon pulses in chip-scale normal dispersion microresonators, achieving ultra-short pulse states through stimulated pumping and thermal stabilization, advancing frequency comb technology.

Contribution

It reports the first observation of square pulse formation in normal dispersion microresonators and explores tuning and stabilization methods for platicon frequency combs.

Findings

Bright 17 ps platicon pulses observed

Thermal stabilization extends mode-locking to 2 ps pulses

Frequency combs with 19 GHz flat spectrum achieved

Abstract

Dissipative Kerr soliton generation in chip-scale nonlinear resonators has recently observed remarkable advances, spanning from massively-parallel communications, self-referenced oscillators, to dual-comb spectroscopy. Often working in the anomalous dispersion regime, unique driving protocols and dispersion in these nonlinear resonators have been examined to achieve the soliton and soliton-like temporal pulse shapes and coherent frequency comb generation. The normal dispersion regime provides a complementary approach to bridge the nonlinear dynamical studies, including the possibility of square pulse formation with flat-top plateaus, or platicons. Here we report observations of square pulse formation in chip-scale frequency combs, through stimulated pumping at one free-spectral-range and in silicon nitride rings with +55 fs2/mm normal group velocity dispersion. Tuning of the platicon frequency comb via a varied sideband modulation frequency is examined in both spectral and temporal measurements. Determined by second-harmonic auto-correlation and cross-correlation, we observe bright square platicon pulse of 17 ps pulsewidth on a 19 GHz flat frequency comb. With auxiliary-laser-assisted thermal stabilization, we surpass the thermal bistable dragging and extend the mode-locking access to narrower 2 ps platicon pulse states, supported by nonlinear dynamical modeling and boundary limit discussions.