The present invention provides silicon based thin-film structures that can be used to form high frequency optical modulators. Devices of the invention are formed as layered structures that have a thin-film dielectric layer, such as silicon dioxide, sandwiched between silicon layers. The silicon layers have high free carrier mobility. In one aspect of the invention a single crystal silicon material is bonded to a thin-film dielectric material to form a silicon-insulator-silicon thin-film structure for an optical modulator.