A Fabry-Perot laser generates a mode-locked channel having the same wavelength as that of light injected into the laser. The laser includes a semiconductor substrate and a lower cladding layer formed on the substrate. An active layer is formed on the lower cladding layer and has a band gap distribution that continuously varies in a longitudinal direction of the substrate. The laser further includes an upper cladding layer formed on the active layer and the lower cladding layer.