A digital optical switch and a method for digital optical modulation are disclosed. The digital optical switch is comprised of an optical waveguide having an input control region, a connection region, and a separation region, and a generator which generates a smoothly varying electric field in an input control region of said optical waveguide and a substantially constant electric field in said separation region of said optical waveguide. The optical waveguide may be either an x-shaped optical waveguide or a y-shaped optical waveguide.