OPTICAL RESTRICTIONS ON THE QUANTITATIVE USE OF GRATING COUPLER SENSORS (GCS)

Studies on in situ hydration and ex situ wet-etching experiments with single mode SiO2-TiO2 waveguides are presented. The controlled process parameters, i.e., resonance angles of incidence of coherent light of different polarization states, are first modelled using the grating eq uation in order to obtain the effective refractive indices N. The resu lts indicate that N of the basic TE and TM modes change with a strict linear dependence. Modelling the N values using the three-layer planar -waveguide model results in a characteristic dependence of the model p arameters, i.e., thickness and refractive index of the waveguiding fil m, which are determined by the experimentally derived gradients of the N values. As a consequence, refractive index and thickness of thin di electric films no longer fulfil the requirements of their proper defin itions.