Abstract: An optical waveguide device comprises at least one Y-junction integrated on a planar substrate. The junction comprises a first (1), a second (3) and a third (4) optical waveguide extending on the said substrate, and a transition portion (2), in which the second and third waveguides branch from the first waveguide, comprising a truncation (5) of predetermined width. At the position of the truncation, the width of the first waveguide is less than the sum of widths of the second waveguide, the third waveguide and the truncation. The first optical waveguide extends into the transition portion up to the bifurcation with its width essentially constant.