Influence of H2 loading on the performance of a cladding-mode-suppression photosensitive fiber

Cladding mode coupling loss below 0.1 dB for a 30 dB fiber Bragg grating are reported for a wide range of H2 treatment pressure up to 1500 psi. Extension of the photosensitive region into the clading was used for reducing the cladding mode coupling. It is shown that to take proper advantage of this, one must use a wider laser scan beam. Otherwise, the cladding mode coupling loss may increase as the H2 pressure treatment is raised. The benefit of a properly matched photosensitivity obtained by matching the Ge concentration in the core and cladding regions is also highlighted. The fiber was also designed to match a standard single-mode fiber in order to lower the average splicing loss below 0.03 dB and the attenuation to about 0.2 dB/km at 1550 nm.