An optical waveguide device, power coupler, a star coupler, a MMI coupler, an arrayed waveguide grating (AWG) or an Echelle grating, having at least one free space region with a plurality of optical waveguides coupled as inputs and separated by channels having a angled bottom portion, the channels monotonically decreasing in size or shape in a direction toward the free space region and optically coupling with adjacent waveguides at the interface region between the optical waveguides and the free space region so that insertion loss at the interface region is substantially reduced.