At the International Solid-State Circuits Conference next February IBM, Intel, NEC and other leading semiconductor companies and researchers plan to discuss ideas how to make mainstream products with optical chip-to-chip interconnects
Optical chip-to-chip interconnections is not a completely new topic for the industry and efforts in the area of optical backplane technology have been underway for several years. Recently, these efforts have led to discussions regarding the role of embedded optics for chip-to-chip communication on printed circuit boards. Since bandwidth and capabilities of optical chip-to-chip interconnections are believed to be extreme, a consensus appears to be emerging that PCB interconnects for mainframes and high-end servers will leverage silicon photonics and similar tech. But will these approaches ever go mainstream?
During a session organized by Broadcom, IBM, Intel, Stanford University, NEC and others, the companies plan to review the latest in optical interconnect-related circuit design, the prospects for optics use in mainstream I/O applications, and to provide comparison to copper-based solutions and associated roadmaps.
IBM CMOS integrated silicon nanophotonics
Given the fact that there is no industry-wide consensus on how to implement on-chip optical interconnections, it is too early to talk about protocols, data rates or details of implementations. For example, a year ago IBM introduced CMOS Integrated Silicon Nanophotonics technology that combines electrical and optical devices on a single chip. The new IBM technology can be produced on the front-end of a standard CMOS manufacturing line and requires no new or special tooling. With this approach, silicon transistors can share the same silicon layer with silicon nanophotonics devices. According to IBM, the new technology adds just a few more processing modules to a standard CMOS fabrication flow, to enable a variety of silicon nanophotonics components, such as: modulators, germanium photodetectors and ultra-compact wavelength-division multiplexers to be integrated with high-performance analog and digital CMOS circuitry. As a result, single-chip optical communications transceivers can now be manufactured in a standard CMOS foundry, rather than assembled from multiple parts made with expensive compound semiconductor technology. By contrast, Intel proposes to make chips using the latest process technology on contemporary manufacturing foundries and then add all the necessary elements needed for optical interconnections.
With PCI Express 4.0 approaching 16Gb/s per lane speed on copper and various companies working on even faster technologies, it is clear that the prospects of on-chip optics lie many years down the road. Still, optical interconnections are inevitable as bandwidth requirements increase in all applications and exascale-class supercomputers are likely to demand ultra-fast interconnections by the end of the decade.