Abstract: UV photosensitivity of a germanosilicate fiber was studied experimentally. The mechanisms of photosensitivity in non-hydrogen loaded fibers and hydrogen-loaded fibers
were discussed respectively. The explanation of the processes of the refractive index changes was presented. Experimental results show that refractive index changes of the non-hydrogen-loaded fibers are about 10^-4. However, the refractive index changes of
the hydrogen-loaded fibers are about 10^-3 which is one order more than that of the non-hydrogen-loaded fibers. The difference of the curves of the
refractive index changes between the two types of fibers shows that the mechanisms of photosensitivity in the two types of fibers are different.

Key words: photosensitivity, hydrogen loading, germanosilicate fiber