| http://www.w3.org/ns/prov#value | - A device according to one of claims 1, 2 or 3, wherein the wavelength diffracted by a first grating differs from the wavelength closest to the first one, diffracted by another grating, by a value substantially equal to 2d1, where d1 is a distance between the first wavelength or which the diffraction by the first grating is the maximum and a neighboring wavelength for which the diffraction by the s
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