Integrated optical enlarged-field interferometer used as a chemical sensor

A new intrinsic optical gas sensor is presented; it is based on an integrated planar waveguide designed as a Mach-Zehnder interferometer with tapers. Gas and vapours are detected when the refractive index changes following absorption of the organic molecules into the thin heteropolysiloxane polymer (DPMS) film deposited on the measurement arm of the interferometer. The performance of the device is presented in the case of the detection of hydrocarbon vapours in dehydrated air; the observed responses follow the order hexane > butane > propane. By using the classical model based on the thermodynamic aspects of the vapour-polymer interactions, a relation between the distribution coefficient of the vapour and its boiling point can be established.