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

•A silicon nitride microring resonator is proposed as a photonic thermometer.•Kerr and thermo-refractive effects are accounted for evaluating self-heating (SH).•A calibration and an optimization strategy to reach milli-kelvin SH are proposed.•The SH temperature rise is reduced to 245μK with a maximum negative error of 8%.•The proposed thermometer has a sensitivity of 19.37 ± 0.07 pm/K and a range of 94.3 K. 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.