Si photonics provides a low-cost volume-manufacturing of high-performance integrated photonic devices by taking advantage of well-matured process technology in Si CMOS industry. An optical modulator is one of the key active components in Si photonics. However, important figure-of-merit (FOM) of VπL (voltage × device length for π phase shift) and loss is still not sufficiently small due to intrinsic material properties. Recently, one of the breakthroughs would be hybridization of high-mobility material (III-V, Ge, etc.) and Si to enhance free carrier effects. Here, I would like to introduce simulation study for growth-based III-V/Si hybrid optical modulator, which can be realized imec’s selective epitaxy growth technique. Then, I will also discuss a little about waveguide platform for Mid-IR photonics, which we are currently developing at KIST.