Photonic contact thermometry based on 3 µm thick silicon cascaded ring resonators

We demonstrate a photonic temperature sensor based on three silicon cascaded ring resonators (CRRs) integrated on a 3 µm thick silicon-on-insulator (SOI) platform for contact thermometry. A CRR-based sensor achieves an expanded free spectral range (FSR) of 23 nm, enabling a broader operational temperature range compared with the FSR of 1 nm for the single ring resonator. The thick SOI platform offers several advantages, including low propagation loss (less than 0.1 dB cm-1), negligible polarization dependence (approaching zero birefringence) and high-power handling capability (greater than 10 mW) without any resonance shape deformation from two-photon absorption (TPA). Optical coupling was achieved through edge-coupled fibre packaging to the photonic chip. The sensor exhibits a temperature sensitivity of 85 pm K-1 with an uncertainty of 16.1 mK, measured over a temperature range from -20 to 90°C. This article is part of the Theo Murphy meeting issue 'The redefined kelvin: progress and prospects'.