We developed a high speed and high efficiency of MOS (metal-oxide-semiconductor) capacitor type and depletion type Si optical modulators (Si-MODs) with a pn junction by applying a p-type-doped strained SiGe layer which was stacked on the lateral pn junction type Si-MOD. We designed the optimum Si-MOD structures and demonstrated a high modulation efficiency of 0.16Vcm for MOS capacitor type Si-MOD. We also demonstrated high modulation efficiency of 0.67 Vcm for depletion type Si optical modulator with a p-type-doped strained SiGe layer, which is about 50% more efficient than that of Si-MOD with a lateral pn junction. We studied a high speed and high efficiency of vertically-illuminated p-i-n Ge photodetector (Ge-PD) with Ge thickness of 1800 nm. We developed a vertical p-i-n structure of Ge-PD and demonstrated high-responsivity of 0.8-0.9 A/W and high-speed of 25 Gbps at 1.3 μm wavelength.