For the purpose of structure and temperature monitoring of Ariane launchers, a new fiber optic sensor interrogation system is developed by our institute. It is based on a monolithic, modulated-grating laser diode that is capable of switching between any two output wavelengths within less than ten nanoseconds. This makes the system very versatile since different sensors within the connected measurement channels can be read out in arbitrary sequence. Therefore sampling rates of single sensors can be adapted according to their application independently. The connection between spectral and time domain during read out of sensors is clarified. Performance optimization due to “Time of Flight” measurement and its consequences for different sample sequences are described. Issues that occur because of switching between different output wavelenghts during operation of the system are described in detail and solutions based on software algorithms are presented.