A mode-matched waveguide Y-junction with balanced or unbalanced splitting comprises an input waveguide, expanding from an input end to an output end, for expanding the input beam of light along a longitudinal axis; first and second output waveguides extending from the output end of the input waveguide separated by a gap. Ideally, each of the first and second output waveguides includes an initial section capable of supporting a fundamental super mode, and having an inner wall substantially parallel to the longitudinal axis, and a mode splitting section extending from the initial section at an acute angle to the longitudinal axis.