Optical waveguide absorption sensor using a single coupling prism.

We propose an optical waveguide sensor that uses a leaky guided mode for measuring absorption of liquid samples. The sensor is composed of a single coupling prism on which a cladding layer and a waveguide layer are deposited. The guided mode generates dips in the reflectance spectrum; the depths of the dips depend on the extinction coefficient of a sample facing the layer. The sensitivity of the sensor is controlled by the thickness of the cladding layer. A simple theoretical model has been developed to analyze the behaviors of the sensor. In experiments we obtained sensitivity 17 times higher than that obtained by the conventional attenuated total reflection method.