An optical modulator includes a substrate having an electrooptic effect, an optical waveguide having first and second cascading portions in the substrate, and transmitting an optical field, a first coplanar strip electrode having a first part over the first cascading portion and second and third parts extending beyond the first cascading portion, wherein the first part is approximately perpendicular to the second and third parts and has a width substantially the same as the first cascading portion, a second coplanar strip electrode having a first part over the second cascading portion and second and third parts to extend beyond the second cascading portion, and the first part being approximately perpendicular to the second and third parts, and a voltage source supplying a voltage to the first coplanar strip electrode, wherein the second coplanar strip electrode is grounded and is symmetrical to the first coplanar strip electrode.