Kavli Affiliate: Kerry J. Vahala
| First 5 Authors: Maodong Gao, Qi-Fan Yang, Qing-Xin Ji, Heming Wang, Lue Wu
| Summary:
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
SiO$_2$, Si$_3$N$_4$, Al$_{0.2}$Ga$_{0.8}$As and Ta$_2$O$_5$. 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.
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