Photonic thermometer by silicon nitride microring resonator with milli-kelvin self-heating effect

Whispering gallery mode (WGM) photonic thermometer had achieved ultra-high sensitivity and resolution. However, while pursuing extremely high quality factor and thereafter high precision, power-induced self-heating within microcavity can bring a significant systematic error. We propose a photonic sensor with less than milli-kelvin self-heating effect utilizing silicon nitride (Si₃N₄) microring resonator with a loaded quality factor of 4.75 × 10⁵. By investigating thermal broadening transmission spectra under various probing powers, effective absorption coefficient and thermal relaxation constant of the device were obtained where thermo-refractive and Kerr effect were accounted. Self-heating temperature rise was predicted to be mitigated to 245 μK under a proposed measurement condition, and this ultra-low self-heating effect was experimentally proved. The proposed approach can be used to establish metrological standards for photonic thermometry and various sensing applications.