Grating-type optical filter with apodised spectral response

Device adapted to have an optical wave travel through it and to filter that wave in terms of wavelength, in which an optical parameter of the device varies along the path of the wave in such a manner that the device has a series of sections (S−10-S10, 500, 600) each constituted by a pair of two successive segments, one in which the values of the optical parameter are less than an average value and the other in which the values of the optical parameter are greater than the average value, characterised in that the device has at least one zone of more than two sections (S−10-S10, 500, 600) in which the sections (S−10-S10, 500, 600) have lengths alternately less than the greater than an average length (M) of the sections in that zone (S−10-S10, 500, 600), in such a manner that in that zone each section having a length less than the average length is immediately followed by a section having a length greater than the average length and each section having a length greater than the average length is immediately followed by a section having a length less than the average length.