A spectral transfer method for producing a useful optical signal that has a spectrum in comb shape in a useful spectral interval, from a source optical signal that has a source spectrum also in comb shape but in another spectral interval, referred to as the source spectrum interval, and which does not have any overlap with the useful spectral interval, comprising simultaneously injecting the source optical signal and a laser radiation into a non-linear optical waveguide, and collecting, at an output of the non-linear optical waveguide, the useful optical signal as resulting from a four-wave mixture that is produced between the source optical signal and the laser radiation during simultaneous propagations of said source optical signal and of said laser radiation in said non-linear optical waveguide, characterised in that a frequency of the laser radiation is selected such that the source spectral interval is intermediate between the frequency of the laser radiation and the useful spectral interval, when the source spectral interval and the useful spectral interval are expressed in frequency values, so that the source optical signal has an energy source function for a modulation instability that is effective for said source optical signal during the propagation of said source optical signal in the non-linear optical waveguide, said modulation instability resulting from an interaction between a Kerr effect and at least one dispersion effect, parameters of the non-linear optical waveguide being selected so that a coefficient of a fourth-order derivative term with respect to time, which exists in a propagation equation of the non-linear optical waveguide, said propagation equation being effective for an envelope of the source optical signal, is negative, and so that a coefficient of a second-order derivative term with respect to time, which also exists in said propagation equation of the non-linear optical waveguide effective for the envelope of the source optical signal, is also negative, and in that the frequency of the laser radiation is also selected such that said laser radiation stimulates said modulation instability effective for the source optical signal, and the useful optical signal resulting from the fourth-wave mixture produced by the stimulated modulation instability. comprising simultaneously injecting the source optical signal and a laser radiation into a non-linear optical waveguide, and collecting, at an output of the non-linear optical waveguide, the useful optical signal as resulting from a four-wave mixture that is produced between the source optical signal and the laser radiation during simultaneous propagations of said source optical signal and of said laser radiation in said non-linear optical waveguide, characterised in that a frequency of the laser radiation is selected such that the source spectral interval is intermediate between the frequency of the laser radiation and the useful spectral interval, when the source spectral interval and the useful spectral interval are expressed in frequency values, so that the source optical signal has an energy source function for a modulation instability that is effective for said source optical signal during the propagation of said source optical signal in the non-linear optical waveguide, said modulation instability resulting from an interaction between a Kerr effect and at least one dispersion effect, parameters of the non-linear optical waveguide being selected so that a coefficient of a fourth-order derivative term with respect to time, which exists in a propagation equation of the non-linear optical waveguide, said propagation equation being effective for an envelope of the source optical signal, is negative, and so that a coefficient of a second-order derivative term with respect to time, which also exists in said propagation equation of the non-linear optical waveguide effective for the envelope of the source optical signal, is also negative, and in that the frequency of the laser radiation is also selected such that said laser radiation stimulates said modulation instability effective for the source optical signal, and the useful optical signal resulting from the fourth-wave mixture produced by the stimulated modulation instability.