Practical ring-resonator thermometer with an uncertainty of 10 mK

Silicon ring resonators are currently being assessed by several national metrology organizations as thermometers for use in calibration laboratories and in high-accuracy commercial applications. In this paper, we report the improvements to our first prototype of Si ring-resonator thermometer including narrower ring resonances, different light polarization in the ring and smaller-footprint probe housing. We evaluated the second prototype in the stirred liquid bath between 23 °C and 80 °C over the span of 11 months and we present, for the first time, the full uncertainty budget for the packaged ring-resonator thermometer. The combined 10-mK standard uncertainty for our ring-resonator thermometer is not only identical to the repeatability reported previously for an unpackaged ring resonator but it also includes an 11-month long-term stability component. This result heralds a commercial ring-resonator thermometer.