Abstract: A multiplexer device includes a plurality of optical fibers. One of the end faces of each of the fibers is arranged in a common plane. The fibers include a first optical fiber for conducting several light signals of different wavelengths and at least two second optical fibers, each of which conduct a light signal in a single waveband. The device also includes a wavelength-selective element (33) and a lens system (51, 53) which is arranged between the wavelength-selective element and the common plane. In order to minimize the number of components of the device and to facilitate adjustment during assembly, the lens system is formed by a plane parallel, transparent plate (51) which bears against the end faces (9, 11) of the optical fibres as well as by a lens (53) having the shape of a flattened sphere whose plane surface rests on the plate.