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Top views of a silica microtoroid before (a) and after (b) PDMS coating. An obvious increase in the minor diameter can be observed (about , from about 3.2 to ) with the unchanged major diameter of . (c) AFM image of a portion of peripheral ring surface of the coated microtoroid. Inset: The section profile along the -direction, showing a roughness of .
Resonant wavelength shift vs temperature change based on room temperature at several PDMS coating thicknesses. From the top to bottom, the thickness gradually increases. The solid lines are linear fittings. Inset: The transmission spectra of a fundamental WGM for several temperatures when the coating thickness is about .
The energy fraction in PDMS vs different PDMS thicknesses (black solid curve). The sensitivity obtained from Eq. (1) (red dashed curve) and the numerical simulation (blue dotted curve). Here, the thermal-optic and expansion coefficients for PDMS (silica) are and ( and ), respectively. The refraction indexes of PDMS and silica are 1.41 and 1.45.
Detection limit of the PDMS-coated microresonator thermal sensor vs input power.
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