Abstract: The demultiplexer comprises: a) an inlet wave-guide (1); b) a plurality of outlet wave-guides (5.sub.i); c) an assembly (3) of adjacent integrated wave-guides functioning in the form of a phase network; d) a mode-expanding wave-guide (12) arranged at the inlet of the inlet connector (2) and connected to the inlet wave-guides (1); and e) a plurality of mode-reducing wave-guides (16.sub.i) arranged at the outlet of the outlet connector (4) and connected in each case to one of the outlet wave-guides (5.sub.i). The mode-expanding guide (12) and the aforementioned mode-reducing guides (16.sub.i) are of identical geometry with a width that varies linearly in accordance with their length, whereby the width of the aforementioned expanding and reducing guides at their connection to the associated connector is defined in order to optimize the width of the band passing through a channel while limiting the cross-talk between the outlet channels (5.sub.i) to a pre-determined level.