A sum parameter sensor for water quality

An integrated optical grating coupler incorporated in an optical waveguide is used to monitor water quality. The primary measured parameter is the phase velocity of a selected guided mode. Upon exposure to a water sample, the device responds extremely rapidly to contaminants. The response is a sum parameter comprising contributions from the refractive index of the bulk sample, dissolved and suspended species which can adsorb at the surface of the waveguide, and small ions which can penetrate into the waveguiding layer. The waveguide surface can be readily modified in order to confer a particular sensitivity profile to contaminants of interest.