An optical waveguide power divider which uses a two-dimensional slab waveguide. An input confined to one arm propagates to a point where synchronism between two closely adjacent guides is abruptly introduced by introducing an overlay with a fast taper. The coupled guides are here sufficiently synchronous and close together that the symmetrical and asymmetrical normal modes of the coupled structure will be excited, each with 1/2 of the input power. Synchronism is then slowly removed by tapering the overlay to zero so that mode "a" selects arm #1 while mode "b" selects arm #2. These latter changes are adiabatic, i.e., slow enough tAfter synchronism has been removed, the two arms may be spatially separated to split the power into two directions.