THE VIBRATIONAL-STATES OF PHOTOINDUCED DEFECTS IN SILICA FIBERS

The stimulated Raman scattering by silica network vibrations and defects in a core of monomode germania-doped silica optical fibers with photoinduced defects and second harmonic generation was investigated. It was shown that the stimulated Raman spectra in optical fibers with effective second harmonic generation contained the 440 and 490 cm-1 bands, attributed to vibrations of silica tetrahedra and to vibrations of 'native' defect groups, respectively, and a new intense band at 570 cm-1 also. When the second harmonic intensity increased, the 490 cm-1 band intensity diminished and the intensity of the 570 cm-1 band increased. It was proposed that the structure of photoinduced defects in a core of silica fiber are similar but not identical to one of the 'native' defects of silica glasses with a characteristic vibrational frequency of 606 cm-1.