An optical device includes an optical splitter having an input port, a first output port, a second output port and a resonant structure including at least a
resonator, the optical splitter being adapted to receive at the input port a WDM optical
signal and to output at the first and second output ports, respectively, a first and a second portion of the optical
signal, the second portion including the channels
lying on a sub-grid of
optical frequencies spaced by an integer multiple of the WDM frequency spacing; an optical combiner having a first input port, a second input port, an output port and adapted to receive at the first and second input ports, respectively, the first and the second portions and adapted to output them at said output port; a first
optical path optically connecting the first output port of the optical splitter to the first input port of the optical combiner so as to propagate the first portion; a second
optical path optically connecting the second output port of the optical splitter to the second input port of the optical combiner so as to propagate the second portion; and an
optical filter optically coupled to the second
optical path, wherein the optical combiner includes at least one resonant structure including at least a
resonator.