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The choice of the number of spectral
points M required for the reconstruction process by layer-peeling is not
absolute but depends on the number of layers N (and is then inversely related
to the layer thickness). Fig. 3-27 presents the reconstructions of FBG1
performed with a 3 mm-layer thickness and a ratio M/N of 1, 2, 5 and 10, respectively. The
reconstruction is poor for M = N and fairly good for
M = 2N. For M/N higher than 5 or ten, the results are very close. For
very strong gratings, a ratio increase to 30 or 50 improves the reconstruction,
but not in a significantly way (Fig. 3-24).
Fig. 3-27 Reconstructed coupling coefficient amplitude (top) and local Bragg
wavelength (bottom) for the FBG1 performed with layers thickness of 3 mm and different
ratio M/N : 10 for the solid lines, 5 for the dashed lines, 2 for the
dashed-dotted lines and 1 for the dotted lines; the curves are translated for
clarity
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