Monitoring relative humidity using a Mach-Zehnder interferometer (MZI) senor based upon a photonic crystal fiber (PCF) coated with polyvinyl alcohol (PVA)

A relative humidity (RH) sensor is reported based upon a photonic crystal fiber (PCF) – Mach-Zehnder interferometer (MZI) with a polyvinyl alcohol (PVA) coating. The structure for sensing was prepared by fusing photonic crystal fiber to two single-mode fibers (SMFs) and completely collapsing the air holes of photonic crystal fiber in the fusion area to act as the beam splitter and coupler. By a lifting method, two to four layers of polyvinyl alcohol films were coated upon the photonic crystal fiber to characterize the influence of its thickness upon the sensitivity of the device for relative humidity. The experimental results show that the maximum sensitivity of this relative humidity sensor is 51.9 pm/% when the photonic crystal fiber surface is coated with three layers of polyvinyl alcohol film.