Abstract
In this paper, a Fourier transform infrared focal-plane-array detector
was used to image the “bond-stretching” vibration mode observed
near σ =1120 cm<sup>-1</sup> of highly Ge-doped graded-index multimode optical fibers (GI-MMFs).
We show that the distribution of the peak wavenumber σ is nonuniform across the core and cladding
of the MMF, i.e., σ is
smaller in the core due to the Ge-doping. Next, as calibration curves between σ and the fictive temperature T<sub>f</sub> are not available in the
literature for highly Ge-doped glasses (above 7w%), we have determined calibration
curves from 1w% to 30w% in Ge. Then, we have applied these corrections in
order to estimate, for the first time to our knowledge, the fictive-temperature
distribution within multimode-fiber cross section. Using these curves, we
show that T<sub>f</sub> is higher
at the fiber edges, presumably due to faster cooling. Furthermore, there
is also a T<sub>f</sub> increase
in the center of the core (i.e., higher Ge content).
© 2007 IEEE
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