Abstract

In this study, FTIR FPA (Focal Plan Array) detector was used to image the 'bond-stretching' vibration mode observed near σ = 1120 cm^-1 of highly Ge-doped graded index multimode optical fibers (GI-MMF). Next, as calibration curves between σ and the fictive temperature T_f are not available in the literature for highly Ge-doped glasses (above 7 w %), we have determined our own calibration curves from 1 to 30 w% in Ge. Then, we have applied these corrections to our σ measurements in GI-MMF in order to estimate, for the first time to our knowledge, the fictive temperature distribution within MMF cross section.