Simultaneously Monitoring Humidity and Temperature Based on Waveguide Bragg Grating Sensor Chip

Herein, we proposed and demonstrated a novel relative humidity (RH) sensing chip with temperature compensation, which is based on waveguide Bragg grating (WBG) assisted with polyvinyl alcohol (PVA) and polydimethylsiloxane (PDMS) composite film. Half of the cladding of the WBG region was corroded with hydrofluoric acid, which results in a split of the Bragg peak into two peaks. The PVA-PDMS composite film coated on the surface of the corroded region shows a high sensitivity to RH due to the hydrophilic hydroxyl groups of PVA film. PDMS not only enhances the stability of the composite film but also reduces the refractive index (RI) of the PVA film, which restricts the energy loss of the light passing through. In our experiment, average RH sensitivities of −12.2 pm/RH% and 0 pm/RH% in the RH range of 50%–90% and temperature sensitivities of 9.6 pm/°C and 9.8 pm/°C were obtained by the two peaks shift, respectively. We testified that the simultaneous measurement of RH and temperature can be achieved by the sensitivity matrix method. Furthermore, the proposed sensor possesses remarkable stability and excellent repeatability. Such a cost-effective, integrated, easily fabricated, and reflection power detection-based humidity sensor promises great application prospects in the fields of agriculture, food industry, biological field, and other production activities.