Fiber-optic sensor for humidity.

A novel fiber-optic humidity sensor is described. It is based on reversible sorption of water from the ambient atmosphere in a porous thin-film interferometer that sits on the tip of a fiber. The sorbed water changes the refractive index of the thin films and thus the reflectivity of the interferometer; the resulting modulation of the reflected intensity is detected. The sensor is insensitive to electromagnetic interference and aggressive chemicals and is extremely small (micrometers).