iwg 610 a pwg 620 a damp 630 a det rdr 640 which are placed inside a cavity that is formed by the rint 650 and the frc 660 the pwg 620 may be discarded so that the rint 650 faces directly the damp 630 the iwg 610 can be either a passive waveguide if there is a photonic integrated solution for the onu or a fiber optic waveguide which includes then also means of fiber to waveguide coupling electrical interfaces 632 a b and 642 a b connect to electrodes 631 a b and 641 a b to provide the drive and bias for the damp 630 and the det rdr 640 the detected high frequency data signal of the downstream may be obtained from the electrical interface 642 a b in addition a phase shifting section phs 670 is placed inside the cavity to tune the spectral comb function of the cdd 600 in its shift of spectral maxima and minima this phs 670 can be from any suitable type and introduces e g a thermo optical or electro optical phase shift and will be in principle from smaller dimensions than the damp 630 according to its physical realization the electrodes 671 a b may also be heaters in the case of a thermo optical device an electrical interface 672 a b.