A device and method for the spectrally-designed and controlled attenuation of a light signal, including an attenuation structure which may be placed in the proximity of a waveguide's core and which comprises a base material system containing non-uniformities having optical properties that are different from those of the host. These non-uniformities may have various natures, geometrical forms and sizes and may be created, doped or otherwise introduced in the base material system to obtain externally controllable optical properties of the whole composite material providing a broadband spectral performance.