High birefringence fiber loop mirror with polymer coating used as humidity sensor

A relative humidity sensor based on polarization maintaining fiber (PMF) loop mirror is presented. The proposed sensors are created through coating a thin layer of polyvinyl alcohol (PVA), whose refractive index varies as a function of humidity level, onto a polarization maintaining fiber, from which a portion of the cladding is removed. The relative humidity optical fiber sensor is tested with different surrounding humidity level, showing a linear response to parameter. The sensitivity of the relative humidity measurement of 0.98 nm/%RH in the range from 20%-80% RH is experimentally achieved.