The demand of bandwidth capacity has increased exponentially in recent years due to the rise of high-speed Internet. For low-cost Metropolitan Area Network (WAN), operating wavelength at 1.3 µm is chosen due to its low dispersive nature in the silica optical fibers, thus avoiding the need for costly dispersion compensators. Quantum dots (QDs), a self-assembly of coherently strained and defect-free three-dimensional nano-islands, are deemed as the new generation of active material. This is because one can expect better device performances due to the delta-like carrier density of states associated with the three-dimensional (3D) confinement. The most promising QD material system for 1.3 µm operation is that of InAs QDs. This book, therefore, report the study of InAs QDs for 1.3 µm electro-absorption modulators. In particular, it provides the theoretical calculations, epitaxial growth, devices fabrication and performances characterization. The materials and knowledge covered in this book are especially useful to professionals in the optoelectronics fields, and researchers who are considering the use of QD systems for optoelectronic devices.