Abstract: An optical detector for use in liquid chromatography systems or capillary electrophoresis systems comprises an optically transparent detector body through which an analyte channel extends, a fluid containing the analyte being adapted to be guided through said analyte channel. In order to increase the detection sensitivity, the light path between a light source introducing light and an optoelectric sensor element of the liquid chromatography system or capillary electrophoresis system is constructed as a Bragg waveguide structure extending at least along a sublength of said analyte channel essentially in the channel direction.