A low-voltage optical modulator includes a substrate, a waveguide, a first pair of electrodes, and a second pair of electrodes. The waveguide is diffused into the top surface of the substrate, into a major branch and a parallel modulating branch. A structure of the first and second pair of electrodes are same. The first pair of electrodes includes a first and a second electrode parallel to each other. The first electrode is formed on the modulating branch and the second electrode is opposite to the modulating branch and away from the major branch. The second pair of electrodes includes parallel third and fourth electrodes. The third electrode is formed on the major branch. The fourth electrode is opposite to the major branch and away from the modulating branch.