An integrated optic chemical sensor has been developed to monitor benzene, toluene, ethylbenzene and xylene (BTEX) in water. The sensor uses planar waveguide interferometry, where the evanescent field associated with a guided wave probes the refractive index changes immediately above the waveguide surface. Currently, up to thirteen interferometers are fabricated on a 1 $MUL 2 cm glass chip. One arm of each interferometer is coated with a chemically interactive film, and the other arm is buried under an inert layer of silicon dioxide (SiO$-2$/). The interference pattern formed by combining the guided waves from the two arms is read by a linear photodiode array, and onboard electronics convert the raw optical intensities into analyte concentrations. The sensor is packaged in a 1.5 inch diameter, 18 inch long stainless steel housing suitable for use in monitoring wells of with cone penetrometers. It is plug-and-play compatible with E-SMART$+TM$/ monitoring networks.
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