Probing material absorption and optical nonlinearity of integrated photonic materials
Optical microresonators with high quality (Q) factors are essential to a wide range of integrated photonic devices. Steady efforts have been directed towards increasing microresonator Q factors across a variety of platforms. With success in reducing microfabrication process-related optical loss as a limitation of Q, the ultimate attainable Q, as determined solely by the constituent microresonator material absorption, has come into focus. Here, we report measurements of the material-limited Q factors in several photonic material platforms. High-Q microresonators are fabricated from thin films of SiO₂, Si₃N₄, Al_(0.2)Ga_(0.8)As, and Ta₂O₅. By using cavity-enhanced photothermal spectroscopy, the material-limited Q is determined. The method simultaneously measures the Kerr nonlinearity in each material and reveals how material nonlinearity and ultimate Q vary in a complementary fashion across photonic materials. Besides guiding microresonator design and material development in four material platforms, the results help establish performance limits in future photonic integrated systems.
Additional Information© The Author(s) 2022. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Received 30 November 2021. Accepted 26 May 2022. Published 09 June 2022. The authors thank H. Blauvelt and Z. Yuan for helpful comments, Z. Liu for discussions on data processing, as well as D. Carlson for preparing the Ta₂O₅ SEM image. Q.-X.J. acknowledges the Caltech Student Faculty Program for financial support. This work was supported by DARPA under the DODOS (HR0011-15-C-0055) and the APHi (FA9453-19-C-0029) programs. These authors contributed equally: Maodong Gao, Qi-Fan Yang, Qing-Xin Ji. Data availability. The data that support the plots within this paper and other findings of this study are available on figshare (https://doi.org/10.6084/m9.figshare.c.5967105). All other data used in this study are available from the corresponding author upon reasonable request. Code availability. The analysis codes will be made available upon reasonable request. he authors declare no competing interests. Peer review information. Nature Communications thanks Vladimir Aksyuk and the other anonymous reviewer(s) for their contribution to the peer review of this work.
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