an integrated optical sensor for , for example , a chemical sensor has an optical waveguide having at least two coupling regions , which are separated by at least one measurement region . a first wave is excited in the waveguide by the first coupling region and passes through the measurement region and the second coupling region . a second wave is excited in the second coupling region and subsequently interferes with the first wave . here , the reduction in amplitude of the first wave by the second coupling region is less than 95 %.