For development and optimization of the combustion process in engines it is vital to get time-resolved information about fuel concentrations and temperatures in the area of ignition. Fluorescence spectroscopy is an approved method for this task. Special tracer substances are added to the fuel and excited by UV-laser pulses. The goal is to work in close-to-production engines without geometric modifications. The influence of the optical sensor on the combus-tion process must be minimal. For this reason the combustion chamber is accessed by a modified spark plug that fulfills its ignition function and has integrated microoptics, additionally. Two functions must be provided by these optics: (i) the spatially defined excitation of the tracer substances and (ii) the detection of the emitted fluorescence light. The design is optimized for maximal detection efficiency and accounts for the requirements of the environment at high temperature and pressure. Another challenge is the high UV intensity needed for ex-citation. To simplify the handling of the sensor its interface to the outside optics is imple-mented by UV transmitting fibers. The design and its realization in a prototype are presented.