Two novel integrated optical sensor types for measuring chemical concentrations, based on chemically induced changes of modal field profiles

Two novel principles of sensing chemical concentrations by integrated optical sensors are presented. Both sensors are of the refractive type implying that a change of chemical concentration manifests itself as a change of the refractive index of a material located within the field profile of a guided mode. In contrast to common practice it is not the induced change of the effective refractive index Neff, but the change of the modal field profiles that is utilized for sensing, and here the changes of the refractive index finally show up as changes of the attenuation of a propagating mode. In the segmented waveguide sensor (SWS) the dependence of the modal transfer at the transition between two adjacent channel segments on the refractive index distributions of both segments is exploited while the second one relies on changes of the modal absorption as a result of a change of the penetration of the modal field into an absorptive region.

Sensitivity and resolution-potential of both principles have been analyzed theoretically also taking into account the properties of peripheral equipment. Based on structures producible with SiON technology a SWS with a refractive index resolution of 5×10-7 can be easily designed. In an implementation of the second principle suited for immuno-sensing, a resolution in the thickness of the immuno-layer better than 10-4 nm is shown to be theoretically feasible. A SWS sensor has been realized; theoretically and experimentally obtained performance corresponds well to each other.