Abstract: Digital optical telecommunications use optical semiconductor components which contain a transition area for the expansion of the mode field of a light wave, in order to reduce coupling losses when coupling an optical fiber or an optical waveguide of a supporting plate. An optical semiconductor component (BE1; BE2) contains a deep ridged waveguide (RIDGE) with a cover layer (DS), which are arranged on a substrate (SUB). The ridged waveguide (RIDGE) has a first (MQW) and a second (BULK) waveguide core. The first waveguide core (MQW) contains one or several optically active semiconductor layers. In a first transition area (UB1), the layer thickness of the second waveguide core (BULK) decreases along a longitudinal direction (L) of the ridged waveguide (RIDGE). This causes a light wave being conducted in the optical semiconductor component (BE1; BE2) to divert into the semiconductor material of the cover layer (DS) and the substrate (SUB) surrounding the waveguide core, thereby expanding its mode field.