A Silicon Microring Resonator for Refractive Index Carbon Dioxide Gas Sensing

Silicon microring resonators (MRRs) are promising for on-chip optical gas sensing due to their strong light-matter interaction, compact footprint, and mass-scalable fabrication potential. However, for refractive index sensors, it is essential to consider the cross-sensitivity to temperature induced by the thermal-optic effect in MRRs. To address this challenge, we demonstrate a silicon MRR coated with gas-sensitive polyhexamethylene biguanide hydrochloride as the upper cladding for carbon dioxide sensing. The engineered MRR exhibits distinct temperature and gas sensitivities for TE₀ and TE₁ modes. With the linear independent responses, a gas sensitivity of -0.90 pm/ppm within a range of 700 ppm is demonstrated in conjunction with the temperature compensation. The response and recovery times of gas sensing are measured as ∼3.5 and 1.5 min. Our study paves the way for on-chip optical gas sensing with temperature compensation.