Thermal stability of optical add/drop gratings for WDM systems

One important application for fiber Bragg gratings is add/drop multiplexing for wavelength-division multiplexing (WDM) systems. This application puts a very stringent requirement on the grating rejection bandwidth and its spectral profile. Standards for these components also require that the grating characteristics be stable for up to 25 years at normal operating temperatures. It has been established that the decay rate of UV-induced refractive index change depends strongly on the temperature that the grating is exposed to. However, a relationship between the decay rate and the temperature found for one type of grating does not necessarily apply to other types of gratings. The fact that different decay rates are reported in different studies for apparently similar gratings indicates that the index decay depends strongly on the fiber material property and the inscribing techniques. This report presents the thermal reliability of add/drop gratings developed for WDM systems