Even though 3D memory stacking can help mitigate the memory bandwidth problem, when it comes to off-chip communication,the pin limitations, the energy cost of electrical signaling, and the non-scalability of chip-length global wires are still significant bandwidth impediments. Recent developments in silicon nanophotonica technology have the potential to meet the off-chip communication bandwidth requirements at acceptable power levels. With the heterogeneous integration capability that 3D technology offers, one can integrate optical die together with CMOS processor dies. For example, HP Labs proposed the Corona architecture [25], which is a 3D manycore architecture that uses nanophotonics communication for both inter-core communication and off-stack communication to memory or I/O devices. A photonic crossbar fully interconnects its 256 low-power multithreaded cores at 20 terabyte per second bandwidth, with much lower power consumption.