Strong photosensitive gratings in tin-doped phosphosilicate optical fibers

Strong photosensitive gratings of both type I and II have been demonstrated in germanium-free tin-doped phosphosilicate fibers. An index change of ~1.2 x 10(-3) has been achieved in 40 s of exposure. The fibers have strong absorption (~0.8 dB/microm) at the writing wavelength of ~248 nm because of tin doping. This is the f irst time to our knowledge that such strong gratings have been written in a phosphorous-containing silica fiber without low-temperature hydrogenation and that type II gratings have been written in a germanium-free fiber. The tin-doping technique can be used to write gratings in rare-earth-doped phosphosilicate fibers and to produce low-N.A. fibers for mass production of strong single-pulse type II gratings during fiber pulling.