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Tailoring broadband Kerr soliton microcombs via post-fabrication tuning of the geometric dispersion

TitleTailoring broadband Kerr soliton microcombs via post-fabrication tuning of the geometric dispersion
Publication TypeJournal Article
Year of Publication2021
AuthorsG. Moille, D. Westly, N. George Orji, and K. Srinivasan
JournalAppl. Phys. Lett.
Volume119
Date PublishedSEP 20
Type of ArticleArticle
ISSN0003-6951
Abstract

Geometric dispersion in integrated microresonators plays a major role in nonlinear optics applications, especially at short wavelengths, to compensate the natural material normal dispersion. Tailoring of geometric confinement allows for anomalous dispersion, which, in particular, enables the formation of microcombs that can be tuned into the dissipative Kerr soliton (DKS) regime. Due to processes like soliton-induced dispersive wave generation, broadband DKS combs are particularly sensitive to higher-order dispersion, which, in turn, is sensitive to the ring dimensions at the nanometer-level. For microrings exhibiting a rectangular cross section, the ring width and thickness are the two main control parameters to achieve the targeted dispersion. The former can be easily varied through parameter variation within the lithography mask, yet the latter is defined by the film thickness during growth of the starting material stack and can show a significant variation (few percent of the total thickness) over a single wafer. In this Letter, we demonstrate that controlled dry-etching allows for fine tuning of the device layer (silicon nitride) thickness at the wafer level, allowing multi-project wafers targeting different wavelength bands and post-fabrication trimming in air-clad ring devices. We demonstrate that such dry etching does not significantly affect either the silicon nitride surface roughness or the optical quality of the devices, thereby enabling fine tuning of the dispersion and the spectral shape of the resulting DKS states. (C) 2021 Author(s).

DOI10.1063/5.0061238