A relative humidity sensor based on open-cavity Fabry-Perot interferometer by fiber capillary splicing

A relative humidity (RH) sensor based on optical fiber Fabry-Perot interferometer (FPI) with open cavity is proposed and demonstrated, which is manufactured by cutting the fiber capillary (FC) with inclined end and splicing it with the flat end of another FC by overlapping method. Polyvinyl alcohol (PVA) film is coated on the flat end of one FC. The proposed sensor is tested under the conditions of 180 μm cavity length, 45 μm hole size and 15 μm film thickness. The results show that the sensitivity is about 0.70 nm/%RH within the range of 35 %RH ∼ 85 %RH. The proposed sensor has the merits of high sensitivity, fast response time, and high stability.