Calibration of the optical propagation time of an optoelectronic oscillator for sensing applications

The oscillation frequency of an optoelectronic oscillator (OEO) depends on the global loop propagation time whose most important contribution comes from the optical fiber loop. However the fiber loop effective refractive index depends on temperature and because of the long length of the loop this effect can have a significant influence on the oscillation frequency. That can be a drawback if the OEO is used for sensing application based precisely on frequency variations detection. In this paper, a method is proposed for a real time calibration of the oscillation frequency drift by using a vector network analyzer (VNA). By this way, it is possible to separate the effect of temperature changes and the effects of the sensing part placed in the OEO; the resolution of the system is improved by this new technique.