A Temperature‐Insensitive Relative Humidity Sensor by using Polarization Maintaining Fiber‐Based Sagnac Interferometer

ABSTRACT A relative humidity sensor based on two polarization maintaining fibers (PMFs) Sagnac interferometer with temperature compensation is presented by utilizing polyvinyl alcohol (PVA) as the sensitive cladding film. The proposed sensor is created through coating a thin layer of PVA onto a PMF from which a portion of the cladding is etched. PVA‐coated PMF is for air relative humidity measurement and the other section PMF is for temperature compensation. The results show that the dip wavelength of the transmission spectrum shifts with the relative humidity with a high sensitivity of 111.5 pm/%RH. Meanwhile the sensor is insensitive to environmental temperature change with thermal‐dependent coefficient of 7.2 pm/°C. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2305–2307, 2013