...phase

The position of the white light fringe measured in opd in wide-band interferometry is roughly, to within a 2#2 factor, the phase of the image Fourier transform, i.e. the phase of the complex visibility.

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...Visibility

More precisely, visibility moduli are straightforewardly measured by interferometers, a more indirect procedure is used for measurements of visibility phases, what is measured is the sum of three phases for a three-telescope loop which is called phase closure, this special technique was designed to cancel out additionnal phase errors, see references thereafter in the paper.

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