Optical modulation in silicon photonics is performed either via the plasma dispersion effect, or by thermal means. Both are relatively slow processes when utilized in large (multi micron) waveguide structures. However, modulators based on the plasma dispersion effect become much faster in smaller waveguides, but coupling to such waveguides is then inefficient. In this paper we discuss both the operation of small waveguide modulators and a potentially more efficient means of coupling to such waveguides. A number of design parameters of the modulators are discussed including the optimum configuration of a three terminal p-i-n diode around a rib waveguide, and the optimization of both the power efficiency and the operating speed of the device. Operating speed is theoretically increased by as much as 7400% with respect to devices in the literature. The problem of coupling to these waveguides is addressed via gratings. All work is theoretical, but sets the groundwork for subsequent fabrication.