Fiber Optic Humidity Sensor Based on Self-Assembled Polyelectrolyte Multilayers

摘要

Polyelectrolyte multilayers were self-assembled onto planar glass substrates and midtimode optic fibers . The multilayer thin films deposited on glass substrates were characterized by using UV-vis spectroscopy andX- ray photoelectron spectroscopy. The multilayer thin films containing hydrophilic side-groups possessed are affinity for water molecules. The adsorption and desorption of free water vapor gave rise to the changes in the refractiveindex and in the reflectance of the thin films. A multilayer thin film based fiber optic humidity sensor with an LEDlight source of 0.85 μm was designed. Under certain conditions, the reflected light intensity of the thin film sensor was a function of the humidity of air. About 30 bilayers was optimal for the multilayer thin film sensor working at wavelength of 0.85μm. This sensor can work over almost the whole relative humidity range with very goodsensitivity.