Buried optical channel waveguides integrated with a fluidic channel network on a planar microdevice are presented. The waveguides were fabricated using silica-on-silicon technology with the goal to replace bulk optical elements and facilitate various optical detection techniques for miniaturized total analysis systems or lab-on-a-chip systems. Waveguide structures with core layers doped with germanium were employed for fluorescence measurements, while waveguides with nitrogen-only doped core layers were used for absorbance measurements. By the elimination of germanium oxygen deficiency centers transmission of light down to 210 nm was possible, allowing absorbance measurements in the mid and far UV region (210 to 280 nm), which is the region where a large number of different molecules absorb light. Robust, alignment-free microdevices, which can easily be hooked up to a number of light sources and detectors, were used for fluorescence measurements of two dyes, fluorescein and Bodipy, and absorbance measurements of a stress-reducing drug, propranolol. The lowest detected concentrations were 250 pM for fluorescein, 100 nM for Bodipy and 12 μM for propranolol.