Difference interferometer with new phase-measurement method as integrated-optical refractometer, humidity sensor and biosensor

The object of the present paper is to report on new versions of the difference interferometer which have been sucessfully used for refractometric measurements and for humidity-and biosensing, i.e., for real-time monitoring of the adsorption of proteins and of affinity-and immunoreactions. The basic principle of the difference interferometers is as follows: the TE0 and TM0 modes in a planar (or rib) waveguide are coherently excited and propagate on a common path and interact with the sample. The polarization-dependent interaction induces a time-dependent phase difference Delta<(Phi)over tilde>(t) between the TE0 and TM0 modes, which is measured as the interferometer's response. We have developed different methods to measure the phase difference a Delta<(Phi)over tilde>(t). The new methods have some advantages and can be expected to be easily extendable to multichannel (multianalyte) sensing. In the reported experiments we use not only SiO2-TiO2 but also Si3N4 films as high-refractive-index waveguides on oxidized silicon wafers as substrates.