Silicon has been proven to be a viable material for passive and active optoelectronic applications in the infrared region ((lambda) greater than 1.2 micrometer) of the electromagnetic spectrum. To date, light has been guided, modulated and switched in silicon. In this paper, novel silicon modulators incorporated into a rib waveguide will be discussed. The modulators are based upon transverse p-i-n structures, utilizing the plasma dispersion effect to produce the desired refractive index change in an optical rib waveguide. Although the devices measure several microns in cross sectional dimensions, they support a single optical mode, thereby simplifying fabrication and allowing efficient coupling to other single mode devices such as optical fibers. The modulators have been modeled extensively using the SILVACO semiconductor device simulator. SILVACO has been employed to optimize the overlap between the injected free carriers and the propagating optical mode. Both the dc and switching characteristics of the modulators have been evaluated. The device performance is encouraging. One of the devices studied requires a driving current of 2.8 mA to achieve a (pi) radian phase shift, corresponding to a current density of 112 A/cm2. Additionally the 10 - 90% rise and fall times are 29 ns and 4 ns respectively. We believe this to be the lowest predicted driving current or current density for modulators in silicon-on-insulator (SOI), although clearly experimental confirmation is required. Potential applications for silicon based optoelectronic devices include optical transmitters, optical receivers and optical sensor devices.