Silicon photonics technology is expected to be key to high-performance, low-power photonic networks. It is also expected that using Si photonics technology will make it possible to integrate photonic key components, such as optical waveguides, optical switches, polarization rotators, light emitters, and optical gain on Si chip C-MOS devices. We propose approaches to fabricating these key components on Si wafers. That is, we introduce some key technologies; (a) all-optical switching in a Si nanowire waveguide, (b) a Si waveguide polarization rotator, (c) material synthesis and waveguide formation of rare earth-doped SiOx thin-films for Si-based light emitters, and (d) a technique for fabricating nano-structured III-V semiconductors, such as Sb-based quantum dot structures, on Si wafers. We also propose a concept for applying Si photonics, i.e., a way to use Si photonics in information and communications technology (ICT).