Dual-mode microring resonator for humidity sensing with temperature compensation

On-chip refractive index (RI) sensors, which use resonant shifts of micro-cavities to detect environment change, have the advantages of high sensitivity, real-time detection, and compact footprints. However, the crosssensitivity of the temperature variation severely interferes with sensing results. In this paper, we present a dual-mode microring resonator (MRR) with a cladding layer of polyhexamethylene biguanide hydrochloride (PHMB) for relative humidity (RH) sensing to overcome the limitation. Specifically, the influences of the RHinduced RI change of the PHMB cladding and temperature variations on the effective RIs of TE0 and TE1 modes can be decoupled based on the transmission spectral measurements. Using this method, we have demonstrated the temperature-compensated RH sensing which achieved a maximum sensitivity of -54.7 pm/% RH and a limit of detection of 0.8 %RH under the room temperature condition. Besides, a computational model based on the sensing response of the device was proposed and verified, which demonstrated that the structure can accurately measure changes in RH and temperature simultaneously. Our methodology has the potential to become a new reference for developing on-chip RI sensors with temperature compensation.