Humidity Sensor Based on Fiber BraggGratingCoated With DifferentPore-FoamingAgentDopedPolyimides

Several novel relative-humidity sensors based on fiber Bragg grating and various pore-foaming agent doped polyimide coating are proposed and demonstrated. Sensing characteristics of lithium chloride, acetone and methyl alcohol doped polyimide coated sensors were investigated, and all sensors show good stability and linear response during the experiment. The corresponding sensitivities are 1.71, 0.53, and 0.63 pm/%RH, respectively. Compared with the polyimide coated sensor (0.62 pm/%RH), the humidity sensor based on additive of lithium chloride can significantly enhance the sensitivity (2.76 times). Moreover, the proposed humidity sensors display linear response under different temperatures, which make it easier for the temperature compensation. Therefore, humidity sensor based on lithium chloride doped polymer sensor is promising to detect humidity fluctuation in some special facilities.