An arrayed-waveguide grating (AWG) is provided in a tunable mode-locked laser resonator where when a clock signal corresponding to a predetermined wavelength is input, the arrayed-waveguide grating (AWG) generates an output signal having an oscillation wavelength which has an arbitrary wavelength interval independent of the wavelength of said clock signal and a different propagation delay for each wavelength. Furthermore, a transmitter and a wavelength converter is provided that uses a tunable mode-locked laser where the frequency of the clock signal determines the wavelength and where a transmitted data signal at a fixed data rate is generated by setting the clock signal frequency sufficiently higher than the data rate. Furthermore, a wavelength converter and wavelength router is provided that uses said tunable mode-locked laser and in which the output wavelength is determined by extracting said clock signal from the input data signal. Furthermore, a transmission system is provided that uses said transmitter and/or said wavelength converter, and a receiver that recovers the envelope of said transmitted data signal.