Currently, light waves are ready to come into boxes of computers in high-performance computing systems like data centers and super computers to realize intra-box optical interconnects. For inter-box optical interconnects, light waves have successfully been introduced by OE modules, in which discrete bulk-chip OE/electronic devices are assembled using the flip-chip-bonding-based packaging technology. OE modules, however, are not applicable to intra-box optical interconnects, because intra-box interconnects involve “short line distances of the cm–mm order” and “large line counts of hundreds-thousands.” This causes optics excess, namely, excess components, materials, spaces, fabrication efforts for packaging, and design efforts. The optics excess raises sizes and costs of intra-box optical interconnects enormously when they are built using conventional OE modules. This book proposes the concept of self-organized 3D integrated optical interconnects and the strategy to reduce optics excess in intra-box optical interconnects.