Tiny optical temperature sensors split light into two beams, which travel through different materials and are then brought back together. The resulting interference pattern gives information about the light and the surrounding temperature. One of the standout features of the device is that it does not require mirrors, and instead guides light through loops to bring it back to the interference point. It can measure a wide range of temperatures, and was also around 20 times more sensitive to small temperature changes than existing fiber-optic sensors.