The central question for Chap. 6 is how to connect optical multimode waveguides without interruption. Such systems are needed in device communication for the bus coupling of 3D-Opto-MID. A novel coupling concept (AOBC: asymmetrical optical bus coupler) is presented in this chapter. By coupling two cores at the side surfaces, it is possible to realize a bidirectional connection. The most important innovation of the presented principle is the possibility of asymmetric coupling, depending on the coupling direction. This makes it possible to couple less power from the bus into the module than vice versa. This ensures that enough optical power remains in the bus to provide the signal for all connected modules. On the other hand, it ensures that a module signal can also be reliably detected. This functionality is missing in known principles and has so far prevented purely optical bus systems from gaining acceptance in extended structures.