SENSITIVITY OF INTEGRATED OPTICAL GRATING AND PRISM COUPLERS AS (BIO)CHEMICAL SENSORS

Grating and prism couplers on planar waveguides coated with a thin chemoresponsive coating are proposed and analysed as chemical and biochemical sensors, for example, as immunosensors. They respond to the formation of a sub-monomolecular adlayer by adsorption, chemisorption, binding of the analyte to the coating or to induced changes in the coating's refractive index. The theory of the sensor sensitivity is discussed. Very high sensitivity are obtained with thin monomode waveguides if the difference n//F-n//S between the refractive indices of the waveguides film F and the substrate S has a high value, e. g. , n//F-n//S greater than equivalent to 0. 3. With 100-200 nm thick SiO//2-TiO//2 waveguiding films on glass substrates, changes in thickness greater than equivalent to 0. 04 nm of an adsorbed or bound protein layer and changes in refractive index greater than equivalent to 2 multiplied by 10** minus **5 can be measured.