A multi-wavelength laser, comprising N wavelength-tunable lasers, N beam splitters, a phase modulator, and N-1 frequency difference detection apparatuses, wherein N is a positive integer not less than 2; a first wavelength-tunable laser is configured to: generate a first laser signal, and send the first laser signal to a first beam splitter in the N beam splitters, wherein the N wavelength-tunable lasers comprise the first wavelength-tunable laser; the first beam splitter is configured to: split the first laser signal into at least two beams of first laser signals, and send a first beam of first laser signal to the phase modulator,; the phase modulator is configured to: modulate the first beam of first laser signal to generate a multi-wavelength optical signal, and send the multi-wavelength optical signal to a first frequency difference detection apparatus, wherein the N-1 frequency difference detection apparatuses comprise the first frequency difference detection apparatus, and frequency spacings between adjacent wavelengths in the multi-wavelength optical signal are the same; a second wavelength-tunable laser is configured to: generate a second laser signal, and send the second laser signal to a second beam splitter in the N beam splitters, wherein the N wavelength-tunable lasers comprise the second wavelength-tunable laser; the second beam splitter is configured to: split the second laser signal into at least two beams of second laser signals, and send a first beam of second laser signal to the first frequency difference detection apparatus, wherein a second beam of second laser signal is another output signal of the multi-wavelength laser; and the first frequency difference detection apparatus is configured to: obtain a first control signal based on the multi-wavelength optical signal and the first beam of second laser signal, and send the first control signal to the second wavelength-tunable laser, wherein the first control signal is used to tune an output wavelength of the second wavelength-tunable laser, characterised in that a second beam of the first laser signal is an output signal of the multi-wavelength laser. a first wavelength-tunable laser is configured to: generate a first laser signal, and send the first laser signal to a first beam splitter in the N beam splitters, wherein the N wavelength-tunable lasers comprise the first wavelength-tunable laser; the first beam splitter is configured to: split the first laser signal into at least two beams of first laser signals, and send a first beam of first laser signal to the phase modulator,; the phase modulator is configured to: modulate the first beam of first laser signal to generate a multi-wavelength optical signal, and send the multi-wavelength optical signal to a first frequency difference detection apparatus, wherein the N-1 frequency difference detection apparatuses comprise the first frequency difference detection apparatus, and frequency spacings between adjacent wavelengths in the multi-wavelength optical signal are the same; a second wavelength-tunable laser is configured to: generate a second laser signal, and send the second laser signal to a second beam splitter in the N beam splitters, wherein the N wavelength-tunable lasers comprise the second wavelength-tunable laser; the second beam splitter is configured to: split the second laser signal into at least two beams of second laser signals, and send a first beam of second laser signal to the first frequency difference detection apparatus, wherein a second beam of second laser signal is another output signal of the multi-wavelength laser; and the first frequency difference detection apparatus is configured to: obtain a first control signal based on the multi-wavelength optical signal and the first beam of second laser signal, and send the first control signal to the second wavelength-tunable laser, wherein the first control signal is used to tune an output wavelength of the second wavelength-tunable laser, characterised in that a second beam of the first laser signal is an output signal of the multi-wavelength laser.