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

Abstract

In this paper, we proposed a self-referenced temperature sensor with ultra-high stability based on a silicon cascaded microring resonator (CMRR) comprising a reference ring coated with titanium oxide (TiO2) and a sensing ring. By exploiting the negative thermo-optic coefficient (TOC) of the TiO2 to counterbalance the positive TOC of Si, the temperature sensitivity of the reference ring was greatly reduced to 4.53 pm/K, while the sensing ring is 75.06 pm/K. As a result, the sensitivity of the CMRR is 70.53 pm/K utilizing the differential sensing method. It is of particular significance that this sensing scheme mitigates the impact of external noises such as laser fluctuations and self-heating noises, enabling the development of a highly stable on-chip temperature sensing device. By immersing the sensor in the triple point of water system with ultra-high stability, the device performs a temperature fluctuation of 15.88 mK, which is an improvement of more than an order of magnitude over microring resonator temperature sensors. Further analysis indicates that the noise derived from the self-heating effects of the device is about 13.76 mK, which represents the primary noise source in CMRR stability. This work manifests that the CMRR can serve as a paradigm for precise temperature monitoring.