Tailoring microcombs with inverse-designed, meta-dispersion microresonators

TL;DR

This paper presents an inverse-design method to tailor the dispersion profiles of microresonators, enabling precise control over microcomb spectra for various applications, demonstrated through fabrication and experimental validation.

Contribution

It introduces a genetic algorithm-based inverse-design approach for creating custom dispersion profiles in microresonators, expanding the design possibilities for microcombs.

Findings

Successfully designed dispersion profiles matching target spectra

Fabricated microresonators with programmable mode splitting

Achieved spectral shaping of microcombs through meta-dispersion control

Abstract

Nonlinear-wave mixing in optical microresonators offers new perspectives to generate compact optical-frequency microcombs, which enable an ever-growing number of applications. Microcombs exhibit a spectral profile that is primarily determined by their microresonator's dispersion; an example is the $ \operatorname{sech}^2 $ spectrum of dissipative Kerr solitons under anomalous group-velocity dispersion. Here, we introduce an inverse-design approach to spectrally shape microcombs, by optimizing an arbitrary meta-dispersion in a resonator. By incorporating the system's governing equation into a genetic algorithm, we are able to efficiently identify a dispersion profile that produces a microcomb closely matching a user-defined target spectrum, such as spectrally-flat combs or near-Gaussian pulses. We show a concrete implementation of these intricate optimized dispersion profiles, using selective bidirectional-mode hybridization in photonic-crystal resonators. Moreover, we fabricate and explore several microcomb generators with such flexible `meta' dispersion control. Their dispersion is not only controlled by the waveguide composing the resonator, but also by a corrugation inside the resonator, which geometrically controls the spectral distribution of the bidirectional coupling in the resonator. This approach provides programmable mode-by-mode frequency splitting and thus greatly increases the design space for controlling the nonlinear dynamics of optical states such as Kerr solitons.