Optical structures useful in splitters, couplers, combiners, and switches are provided. An example optical structure has a Y-branch configuration that includes a linear taper segment and two branching waveguides. A straight section extends between the linear taper segment and the two branching waveguides to reduce losses during splitting/combining operation. The straight section may be used in Y-branch configurations having a blunt section, as well as configurations without a blunt section. Straight sections formed of a single segment and of multiple segments are shown, and the straight sections may be formed of substantially parallel outer walls or fanning-out outer walls. Further, in some embodiments, the branching waveguides form acute angles at the boundaries with the straight segment.