Quasi-distributed fiber Bragg grating humidity sensor based on MXene/PI composite film

In this work, we propose a fibre Bragg grating (FBG)–based quasi-distributed humidity sensor, in which humidity-sensing grating and temperature-compensation grating are integrated on a single optical fibre, enabling simultaneous measurement and effective decoupling of relative humidity and temperature. The humidity-sensitive coating employs a PI/MXene/PI triple-layer composite architecture, wherein the PI layers are responsible for moisture absorption and efficient transfer of the resulting strain to the underlying FBG, while the MXene nanosheets furnish abundant hydrophilic sites and interlayer nanochannels that facilitate rapid water molecule diffusion. Experimental results demonstrate that the proposed sensing structure exhibits an excellent linear response over the range of 17–85%RH, with humidification/dehumidification sensitivities of 5.10/5.05pm/%RH, a low humidity hysteresis of 0.98%RH, and a response time of 7.58s. The incorporation of a dedicated temperature-compensation grating effectively suppresses thermal drift, thereby enhancing the overall accuracy and reliability of the humidity measurement. Moreover, the compact FBG architecture is inherently compatible with array deployment and multi-point multiplexing, rendering the proposed sensor highly suitable for multiparameter real-time monitoring in applications such as environmental sensing and fuel cell system management.