Due to its great achievements over the last few years, silicon photonics is now a focused topic in many conferences and forums. Among the key photonic blocks, an optical modulator based on a silicon substrate is one of the most attractive issues for scientists and engineers. According to the reported state-of-art experimental results, silicon based optical modulators have perfect operation speed (no less than 50 Gbit/s), low power consumption (no more than 40 fJ/bit) and small footprint (no more than 100 mm2). Till now, the most recent tested data rate reaches 60 Gbit/s. More research and development focuse on higher energy efficiency and higher integration density, which are required by optical communication, optical interconnect and optical sensing, to build information infrastructures with ultra-large bandwidth, much high density and very-big data.