Spatially resolved Raman study of self-organized χ^(2) gratings in optical fibers

Medium-range ordering in glass structures as a background of photosensitivity in silica fibers

“…A remarkable fact of an enormous enhancement of the fundamental 490 cm À1 SRS band and the appearance of an extremely intense combination bands originating, in part, from this ÔdefectÕ vibration was reported also [22]. Moreover, the 490 cm À1 band intensity was found to be affected by photoinduced changes in a silica network: this band arises during a photobleaching procedure in the fiber capable of the SHG effect [17]. A rather evident correlation between formation of color centers responsible for the SHG effect in a silica fiber and 490 cm À1 band intensity was revealed by using picosecond SRS excitation [12].…”

“…In contrast to the Ge-doped fiber sample discussed here, earlier we used a relatively weakly doped Ge-doped fiber where the fundamental SRS band included the 490 cm À1 band as a shoulder [12]. In other works, the 490 cm À1 ÔdefectÕ band in a silica core grew monotonically during the photobleaching procedure as the colour centers responsible for the SHG effect were annihilated [17]. Table 1 Anharmonicity constants of the silica tetrahedron and ÔdefectÕ vibrations, harmonic vibration frequencies, and halfwidths of fundamental SRS bands in silica fibers …”

“…Attempts have been made to establish the correlations between D 1 and D 2 band parameters and photoinduced rearrangements in a silica core [17,20,21], in particular in germanium-doped fibers [17,20] and single-mode pure silica fibers [21]. It is reasonable to compare the D 1 and D 2 band parameters obtained under similar experimental conditions.…”

Spectroscopic characterization of silica-based fibers using picosecond SRS technique

“…There were some attempts to establish the correlations between D 1 and D 2 band parameters and photoinduced rearrangements in a silica core 6,11,12 . Note, that apart the germania-doped fibers 6,11 a single-mode pure silica fiber was studied 12 also.…”

“…A remarkable fact of an enormous enhancement of the fundamental 490 cm -1 SRS band and the appearance of an extremely intense combination bands originated, in part, from this "defect" vibration (see, Fig.3). Moreover, the 490 cm -1 band intensity is affected by photoinduced changes in a silica network: this band arises during photobleaching procedure in a fiber, capable to the SHG effect 6 . A more apparant competition between colour center formation, responsible for the SHG effect in a silica fiber and 490 cm -1 band intensity was demonstrated using picosecond SRS excitation procedure 3 .…”