Stable optofluidic Fabry-Pérot resonator for liquid and gas sensing

In this paper, a stable optofluidic Fabry-Pérot (FP) resonator consisting of silicon cylindrical Bragg mirrors combined with a central capillary-tube is investigated. The cylindrical Bragg mirrors provides an in-plane confinement of light while the central capillary tube full of fluid improves the out-of-plane light confinement. Through the Finite-Difference Time-Domain (FDTD) technique with perfectly matched layers (PMLs) absorbing boundary conditions, a sensitivity of 592 nm per refractive index unit (RIU) with a detection limit (DL) of less than 10−3 RIU is obtained for liquid refractometry. For gas refractometry, a sensitivity of 1053 nm per refractive index unit (RIU) with a detection limit (DL) of 5 × 10−4 RIU is achieved. Such sensitivity is, to our knowledge, the highest ever reported for an RI gas refractometer based on stable optofluidic FP resonator. The proposed device has promising performances which suggest its potential use in future sensing applications.