The present invention relates to an optical modulator including an optical waveguide, and at least one CPW-to-CPS transition. The CPW segments include a hot electrode; and a ground plane disposed on each side of the hot electrode, and they share a ground plane. The CPS segment extends along an interaction length of the modulator. In one embodiment, two driving signals are applied so that the modulator operates as a dual-drive modulator. In another embodiment, a domain-inverted region is formed in a substrate of the dual-drive modulator to overlap with one arm of the optical waveguide (MZI) and invert a sign of a phase shift induced in that arm. Finally, a fixed chirp can be introduced into the dual-drive modulator by asymmetrically positioning the interferometer arms into gaps of the CPW segments with respect to the hot electrode, and by employing unequal width gaps in the CPW segments.