Fabry-Perot Hygrometer with a Thin Film Gelatin Sensor

Here we present the optical Fabry-Perot interferometer (FP) modified to work as a hygrometer. A gelatin thin film inserted between the mirrors of the FP behaves as the transductor. The thin film absorbs/desorbs water molecules and in this way the the thickness and refractive index will change. The interference pattern given by the FP, which consists of concentric rings, is affected by these changes and this variation can be used to infer the changes in relative humidity.