An apparatus and associated method for altering the propagation constant of a region of equalizing propagation constant in an optical waveguide. The method comprising positioning an electrode of a prescribed electrode shape proximate the waveguide. An altered region of equalizing propagation constant is projected into the waveguide that corresponds, in shape, to the prescribed electrode shape by applying a voltage to the shaped electrode. The propagation constant of the region of equalizing propagation constant is controlled by varying the voltage.