Relative humidity sensor based on side-polished fiber optic

This work presents a family of passive optical sensors to detect relative humidity in air. All sensors are based on side-polished optical fiber covered by a polymeric film, doped, in some cases, with cobalt chloride. When the optical fiber is laterally polished, access is gained to the evanescent field of the guided wave. If the film covering the polished part of the fiber changes optically with the magnitude to be sensed, transmitted optical power can be changed significantly. This basic idea has been extensively tested in this work for single-mode and multimode standard communication fibers. For the covering with polymeric films two different compositions have been tested by themselves and doped with a classic hygroscopic material that changes its color (CoCl ₂). All the cases studied show a coherent picture of the system useful for commercial sensor developments