Synchronization device for synchronizing a plurality of multiplexed optical signals after transmission through a plurality of wavelength division multiplexing channels (Cj) along an optical line, the said optical signals comprising data packets aimed at being detected separately and inter-packet gaps, the duration of a data packet and an inter-packet gap corresponding to the duration of a time slot, the said synchronization device comprising: - a plurality of delay lines having distinct fixed delays, - characterised by a wavelength selective switch configured to: - receive the said plurality of multiplexed optical signals, - demultiplex the said plurality of received multiplexed optical signals and, - distribute the demultiplexed optical signals toward the said plurality of delay lines according to a temporal shift of the demultiplexed optical signals with respect to the start of the next period of a periodic temporal reference corresponding to the duration of a time slot, a demultiplexed optical signal being transmitted to a delay line having the closest fixed delay with respect to the temporal shift of the said optical demultiplexed optical signal, and wherein the number of delay lines is determined according to the required accuracy for the synchronization of the optical signals wherein the synchronization device also comprises a plurality of optical circulators, the number of which corresponds to the number of delay lines, located between the wavelength selective switch and the plurality of delay lines, the said delay lines being looped on the said optical circulators so that the synchronized optical signals at the output of the delay lines are sent back to the wavelength selective switch to be multiplexed and wherein the wavelength selective switch is also configured to multiplex the demultiplexed synchronized optical signals received from the plurality of delay lines. - a plurality of delay lines having distinct fixed delays, - characterised by a wavelength selective switch configured to: - receive the said plurality of multiplexed optical signals, - demultiplex the said plurality of received multiplexed optical signals and, - distribute the demultiplexed optical signals toward the said plurality of delay lines according to a temporal shift of the demultiplexed optical signals with respect to the start of the next period of a periodic temporal reference corresponding to the duration of a time slot, a demultiplexed optical signal being transmitted to a delay line having the closest fixed delay with respect to the temporal shift of the said optical demultiplexed optical signal, and wherein the number of delay lines is determined according to the required accuracy for the synchronization of the optical signals wherein the synchronization device also comprises a plurality of optical circulators, the number of which corresponds to the number of delay lines, located between the wavelength selective switch and the plurality of delay lines, the said delay lines being looped on the said optical circulators so that the synchronized optical signals at the output of the delay lines are sent back to the wavelength selective switch to be multiplexed and wherein the wavelength selective switch is also configured to multiplex the demultiplexed synchronized optical signals received from the plurality of delay lines. - receive the said plurality of multiplexed optical signals, - demultiplex the said plurality of received multiplexed optical signals and, - distribute the demultiplexed optical signals toward the said plurality of delay lines according to a temporal shift of the demultiplexed optical signals with respect to the start of the next period of a periodic temporal reference corresponding to the duration of a time slot, a demultiplexed optical signal being transmitted to a delay line having the closest fixed delay with respect to the temporal shift of the said optical demultiplexed optical signal,