GRATING COUPLERS AS CHEMICAL SENSORS - A NEW OPTICAL CONFIGURATION

An optical configuration is proposed that allows the determination of the coupling angle of an integrated optical grating coupler by means of a very simple set-up. The sensor head is small and no moving parts are required. A convergent (or divergent) light beam is directed onto the grating. The intensity distribution of the light reflected by the sample is analysed. Because of the coupling into the waveguide, at the coupling angle a dark line occurs in the reflected beam. The position of this line, which may be evaluated with a photodetector array, is a measure of the effective refractive index of the waveguide. From this, the quantity to be measured is derived.