Chip-scale self-referenced thermometer based on cascaded ring resonators.

This article focuses on the development and characterization of a self-referenced temperature sensor based on a silicon cascaded microring resonator (CMRR) incorporating a titanium oxide (TiO₂)-coated reference ring and a sensing ring. By leveraging the negative thermo-optic coefficient (TOC) of TiO₂ to offset the positive TOC of silicon, the reference ring achieves a low temperature sensitivity of 4.53 pm/K, while the sensing ring maintains a high sensitivity of 75.06 pm/K, resulting in a differential sensitivity of 70.53 pm/K for the CMRR. This differential sensing method effectively suppresses external noise sources such as laser fluctuations and self-heating, enabling a high stability with temperature fluctuations as low as 15.88 mK when tested in a triple point of water system. The primary noise source identified is self-heating induced by laser power, and the device demonstrates improved stability and sensitivity compared to previous microring resonator temperature sensors without requiring complex experimental setups.