Abstract: It is the object of the invention to provide a WDM optical transmitter, in which levels of optical signals transmitted therefrom is increased and equalized. Optical amplifiers, which are provided with rare metal doped optical fibers and laser diodes for pumping them, are respectively connected with the output ports of light sources. The gains of the optical fiber amplifiers are so controlled that levels of the optical signals at the output port of a coupler, which multiplexes the output powers of the optical fiber amplifiers, are equalized.

Abstract: Disclosed is a light source for wavelength division multiplexing communications which has: a unit for outputting light with a wavelength band having a constant width; a unit for dividing the light into first dividied light and second divided light; at least one selective wavelength blocking unit which blocks selectively light with a specific wavelength of the first divided light to output light that the light with a specific wavelength is removed; a unit for conducting such a phase control that the phase difference between the selectively-wevelength-blocked light and the second divided light is 180.degree. to each other and for outputting first phase-controlled light and second phase-controlled light; and a coupling for coupling the first phase-controlled light and the second phase-controlled light to output coupled light.