A silicon-based optical modulator exhibiting improved modulation efficiency and control of “chirp” (i.e., time-varying optical phase) is provided by separately biasing a selected, first region of the modulating device (e.g., the polysilicon region, defined as the common node). In particular, the common node is biased to shift the voltage swing of the silicon-based optical modulator into its accumulation region, which exhibits a larger change in phase as a function of applied voltage (larger OMA) and improved extinction ratio. The response in the accumulation region is also relatively linear, allowing for the chirp to be more easily controlled. The electrical modulation input signal (and its inverse) are applied as separate inputs to the second region (e.g., the SOI region) of each arm of the modulator.