V. Grubsky, D. S. Starodubov, and J. Feinberg, "Mechanisms of Index Change Induced by Near-UV Light In Hydrogen-Loaded Fibers," in Bragg Gratings, Photosensitivity, and Poling in Glass Fibers and Waveguides: Applications and Fundamentals, Technical Digest Series (Optica Publishing Group, 1997), paper JMA.3.