Tunable add/drop optical device for injecting or extracting (add/drop) at least a selected optical channel or carrier wavelength in or from a set of multiplexed channels or carriers of different wavelengths comprising a plurality of directional couplers (AD1... AD6) and a plurality of phase-shift stages (SF1...SF5) alternately connected in cascade, wherein each phase-shift stage defines a certain optical path length difference ( DELTA L1... DELTA L5) between two distinct optical paths of the stage. The tuning is performed modifying the refraction index of one path of said phase shift stages by means of Joule effect heating strips (L1... L5) or by means of metallic field plates adapted to receive a signal suitable to modify the electric field intensity. The first two phase-shift stages of said plurality of phase-shift stages have differences of length of optical paths different from each other and in a preestablished ratio while the remaining phase-shift stages have differences of length of optical paths identical. It is thus possible to provide a device having an exceptionally flat cross response characteristic, substantially free of ripple due to an inevitable truncation of the Fourier expansion series.