Optical fiber based on humidity sensor with improved sensitivity for monitoring applications

Abstract An optical fiber humidity sensor combined with a new type of moisture-sensitive material is proposed and experimentally demonstrated. The structure of the sensor is based on two single-mode fibers (SMFs) spliced on two sides of a no core fiber (NCF) and coated with a calcium alginate (CaAlg) hydrogel film. The NCF is regarded as the fiber core, and the CaAlg hydrogel film is regarded as the cladding. Through the etching of the fiber core and coating with film of the same thickness, an evanescent field is created to enable the sensitivity of the sensor to reach the highest value of 0.3774 dBm/%RH from the initial 0.0254 dBm/%RH. This operation allows the sensor to increase sensitivity while keeping the response time constant. The sensor was verified as being successfully applicable for monitoring the humidity of an indoor environment for an entire day (24 h). Owing to its excellent stability, repeatability, and time response, the sensor has certain competitiveness in the field of medical storage and humidity monitoring of cultural relics.