Dissipative Kerr soliton generation in chip-scale nonlinear resonators has recently observed remarkable advances, spanning from massively parallel communications, to self-referenced oscillators, and 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 flattop 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 autocorrelation and cross correlation, we observe bright square platicon pulse of 17 ps pulse width 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.

Fang Lu Mesoscopic Optics and Quantum Electronics Laboratory, University of California Los Angeles, Los Angeles, California 90095, USA;Department of Electrical, Computer, and Energy Engineering, University of Colorado Boulder, Boulder, Colorado 80309, USA;Institute of Microelectronics, Singapore, Singapore;Université de Bourgogne Franche-Comté, ICB, UMR CNRS 6303, Dijon, France;e-mail: haoliu1991@ucla.edu;e-mail: cheewei.wong@ucla.edu

[1]Hao Liu;Shu-Wei Huang;Wenting Wang;Jinghui Yang;Mingbin Yu;Dim-Lee Kwong;Pierre Colman;Chee Wei Wong-.Stimulated generation of deterministic platicon frequency microcombs)[J].光子学研究（英文）,2022(08):1877

platicon,flattop,platicons,fs2

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