International audienceIn this paper, a new sensor system for relative humidity measurements based on a SnO2 sputtering deposition on a microstructure (MOF) low-finesse Fabry-Pérot sensing head is presented and characterized. The interrogation of the sensing head is carried out by monitoring the fast Fourier transform phase variations of the FP interference frequency. This method is independent of the signal amplitude and also avoids the necessity of tracking the wavelength evolution in the spectrum; moreover, it is applicable networks that require narrow band sensors, allowing high multiplexation rates. The sensor is operated within a wide humidity range (20%–90% relative humidity) with a maximum sensitivity achieved of 0.14rad/%. The system uses an optical interrogator as unique active element which presents a cost-effective feature