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Using thermo-optical nonlinearity to robustly separate absorption and radiation losses in nanophotonic resonators



Mingkang Wang, Diego J. Perez, Vladimir Aksyuk


Low-loss nanophotonic resonators have been widely used in fundamental science and applications thanks to their ability to concentrate optical energy. Key for resonator engineering, the total intrinsic loss is easily determined by spectroscopy, however, quantitatively separating absorption and radiative losses is challenging. While the concentrated heat generated by absorption within the small mode volume results in generally unwanted thermo-optical effects, they can provide a way for quantifying absorption. Here propose and experimentally demonstrate a technique for separating the loss mechanisms with high confidence using only linear spectroscopic measurements. We use the optically measured resonator thermal time constant to experimentally connect the easily-calculable heat capacity to the thermal impedance, needed to calculate the absorbed power from the temperature change. We report the absorption, radiation, and coupling losses for ten Si microdisk whispering-gallery modes of three different radial orders. Similar absorptive loss rates are found for all modes, despite order-of-magnitude differences in the total dissipation rate due to widely differing radiation losses. Measuring radiation losses of many modes enables distinguishing the two major components of radiation loss originating from scattering and leakage. The all-optical characterization technique is applicable to any nanophotonic resonators subject to thermo-optical effects.
Optics Express


thermo-optical effect, photonic cavity, nanophotonic resonator, photonic sensing


Wang, M. , Perez, D. and Aksyuk, V. (2021), Using thermo-optical nonlinearity to robustly separate absorption and radiation losses in nanophotonic resonators, Optics Express, [online],, (Accessed May 20, 2024)


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Created March 1, 2021, Updated October 14, 2021