Abstract: An optoelectronic modulator modulates an optical signal in response to an electromagnetic signal. The optoelectronic modulator includes a waveguide for conveying the optical signal, where the waveguide has an associated width, core thickness, and waveguide-electrode separation, and includes a optical index of refraction with respect to the optical signal and a microwave index of refraction with respect to the electromagnetic signal; and where the microwave index of refraction substantially matches the optical index of refraction for velocity-matching the optical signal and the electromagnetic signal through the waveguide. The waveguide may be disposed on an n-type doped substrate, may include a quantum well region disposed on the substrate, and may have a predetermined width for providing the matching of refractive indices.