This paper reviews recent progress in silicon photonics and compares it with other optical device platforms. The key components for optical communication systems, including arrayed waveguide gratings, optical switches, modulators and optical functional devices fabricated on silicon photonics platforms are explained. The integration of III-V compounds, lithium niobate, polymers, phase change and other functional materials are necessary to strengthen silicon photonics platforms. These are also reviewed, and the feasibilities are discussed. Finally, I express my personal view as to the best research direction for silicon photonics.