This works is focused in the design and optimization of electro-optic modulators. In this aim, there is a first part exposing the related issues and specifically the coplanar waveguide as the base of these modulators. The second part consists on the development of closed-form expressions for the characterization of the coplanar waveguide. These expressions will be needed in order to calculate the modulator parameters. In the last part the design and optimization rules in terms of bandwidth and the required voltage are proposed, by means of graphic methods, together with several examples.