CHEMOMETRIC EVALUATION OF THE MULTIPLE-MODE RESPONSE OF AN ION-DIFFUSED PLANAR OPTICAL WAVE-GUIDE TO LIQUID-PHASE ANALYTES

An ion-diffused planar optical waveguide was fabricated by exposing a soda-lime silica glass substrate with etched surface gratings to a AgNO3 melt solution. The ion-diffused waveguide exhibited multiple mode output which was imaged with a photodiode array detector. The waveguide response to modulations in cover solution composition was tested for a series of model chemical systems emphasizing the distinction between surface-active and surface-inactive species. Model systems were defined to test the waveguide response to changes in solution refractive index and absorbance and the important case of simultaneous changes in refractive index and absorbance. Chemometrics were applied to the analysis of the resulting multiple mode response data to characterize waveguide response components and to provide for multivariate calibration. The ion-diffused waveguide response to refractive index and absorbance changes is sufficiently different as to allow a PLS calibration to predict both components in mixture solutions. The waveguide response to surface-active analytes exhibited a large sensitivity enhancement relative to analytes which did not interact with the waveguide surface.