Growth characteristics of fiber gratings

The physical mechanism responsible for UV-induced index of refraction change in the core of optical fiber is not well understood. We have conducted a series of measurements to characterize this effect for continuous-wave (CW) UV exposure and contrast these results with those for pulsed UV exposure. We have measured the growth rate of Bragg gratings in germanium-doped, germanium-boron-codoped, and hydrogen-loaded optical fiber. The measurements were made by observing the grating reflectance at various times during exposure to CW 244 nm light. We have also measured the change in blue fluorescence during exposure to UV light for these same fibers. Finally, we measured the effect of annealing the gratings at a variety of temperatures and compared this behavior for the different fiber types. We compare our measurements with the predictions of competing theories of the origin of photoinduced refractive index change