Page 43 - Fiber Bragg Gratings

24 Chapter 2 Photosensitivity and Photosensitization of Optical Fibers

Figure 2.4: The growth dynamics of the refractive index change in 20 mol%
Ge: 1 mol% Sn. The three data are for A: pristine fiber, B: after annealing, and
C: under strain of 0.2%. The Type IIA grating begins after the initial erasure,
(from: Douay M., Xie W. X., Taunay T., Bernage P., Niay P., Cordier P., Poumellec
B., Dong L., Bayon J. R, Poignant H., and Delevaque E., "Densification involved
in the UV based photosensitivity of silica glasses and optical fibers," J. Lightwave
Technol. 15(8), 1329-1342, 1997. © IEEE 1997.)

approximately linear increase in the rate of growth of the UV-induced
average refractive index. The data has been interpreted from Ref. [48],
bearing in mind that the for the initial growth rate in low germanium
fibers, there is a time delay before the grating begins to grow.