Radiation sensitivity of Bragg gratings written with femtosecond IR lasers
The radiation sensitivity of Bragg gratings written with a femtosecond IR laser was measured for the first time. Type I-IR and type II-IR gratings were written into hydrogen loaded as well as unloaded fibers of distinctly different radiation sensitivity with the intention to find extremely radiation resistant gratings for temperature or stress measurements in radiation environments, as well as very radiation sensitive ones for radiation dose measurements. With a highly radiation-hard F-doped fiber we found a radiation-induced wavelength shift between about 3 and 7 pm after a dose of 100 kGy. These are the lowest shifts observed so far. In such fibers it is very difficult to write gratings with an UV laser. However, gratings made of the highly radiation-sensitive fibers only showed shifts of about the same size as those made of the quite radiation-insensitive Corning SMF-28e fiber. This was already observed with UV laser gratings written in such fibers.