In this paper, an approach to measure both the refractive index (RI) and the pressure simultaneously using two Whispering-Gallery Modes (WGMs) in a microdisk resonator is theoretically proposed. Due to the difference in the energy distribution of the first and second order WGMs, the sensitivity of two modes toward the variation of RI and pressure applied to the device show differences. An RI sensitivity of 29.07 nm/RIU and pressure sensitivity of 0.576 pm/kPa for WGM (1,36), and an RI sensitivity of 38.68 nm/RIU and a pressure sensitivity of 0.589 pm/kPa for WGM (2,28) are obtained through the 3D finite-difference time-domain (3D-FDTD) simulation. Dual parametric sensing can be achieved by solving the second-order inverse sensitivity matrix. Therefore, strain–optical coupling behavior is effectively eliminated. The dual sensing scheme we proposed provides a novel approach to overcome the difficulty of multi-sensing applications based on the flexible photonic device.
Spatial refractive index sensor using whispering gallery modes in an optically trapped microsphere
