A multiple wavelength laser source comprises a loop mirror formed by a loop of active fiber and a 3-dB coupler, the fiber being connected between two ports of the coupler, two pump means for injecting pump energy into the active fiber so as to propagate in opposite directions therein, and a plurality of wavelength-selective reflection devices, e.g. gratings, coupled to at least one of the other ports of the coupler. Each grating reflects back into the loop light at a certain wavelength and transmits light of other wavelengths the selected wavelength, and transmits a second portion to an output port. The selected wavelengths of the plurality of reflection devices are different. The plurality of reflection devices may be in series between the coupler and the output port, or in parallel, each coupled to the corresponding port of the 3-dB coupler by a second coupler. Preferably, the first and second portions each comprise about 50 per cent.