An optical waveguide humidity detector

An optical waveguide humidity detector is described that is reliable and inexpensive. It utilizes a cobalt chloride/poly(vinyl pyrrolidone) film on the surface of a thin walled glass capillary waveguide, and monitors the absorption change at 660 nm as the waveguide is exposed to H2O(g). The humidity response is an S-shaped curve with the inflection point between 65% and 80% RH; location of inflection point is correlated with CoCl2 and PVP concentration in the film. The effects of reagent concentration and film thickness on detector response are described.