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This section presents an overview of
the different methods used to retrieve the local parameters of a grating. A
large emphasis has been given to the layer-peeling method, which has been
employed in this work.
The retrieval of the grating parameters
distribution from the grating spectral response has been widely studied.
Several papers have been published where only the spectral amplitude or phase
was exploited. In this case, the grating distributions needs to be monotonic [3-7,
3-8] or a priori assumption needs to be postulated (for example a
gradient direction) [3-9]. As a consequence, only one parameter can be
retrieved. For weak gratings, the knowledge of the intensity and the phase of
the spectral response permits to reconstruct the grating profile via a Fourier
Transform [3-2, 3-10]; for strong gratings, a backscattering
technique is instead necessary [3-11, 3-12]. The layer-peeling
technique discussed hereafter is a backscattering technique, which is highly
efficient and not very sensitive to the measurement noise, when applied to the
complex impulse response. Some methods use an iterative process where at each
step a theoretical grating profile and its reflection or phase spectrum are
generated and compared with a measured spectrum [3-13 to 3-16].
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