Issue link: https://iconnect007.uberflip.com/i/1330321
JANUARY 2021 I PCB007 MAGAZINE 81 expected to increase to 16 Gbps by Gen 4.0. Figure 1 shows the internet and IP traffic demand trends. The IBM optical transmission roadmap is designed to meet this coming future need. For "cloud computing," the IBM Roadmap (Figure 2) shows the past progression of global networking, to metro/local networking, continuing down to rack-board-module and then chip. To accomplish these higher speeds above 10 Gbps, optical connections seem to be the solu- tion. The growth of optical interconnect cabling for IBM super computers, grew from 5,000 fi- ber cables in 2006 to more than 540,000 for the P775 in 2011. The next machine, Blue Water, will have over 5 million fiber-optic cables [3] . In these last two implementations, instead of the fiber terminating at the PCB card edge, the Ag- ilent and Avago MicroPODTM optical connec- tor actually extends onto the central-processor module (as seen in Figure 18). The competition between electrons and pho- tons (copper versus waveguide) is now down to the last 100 meters. Looking at a roadmap from the Terabus Program [4] , the number of op- tical lines is increasing, along with the densi- ty of those lines, and correspondingly, the cost and power is coming down as well. Current- ly, the focus is on board-to-board channels of <1 meter, <10m for the "intra-system," and <100m for the "inter-system." Electrons Versus Photons Why the focus on photonics? It's probably because Gene Rodenberry told us that was the technology of the USS Enterprise on Star Trek back in 1966! But aside from science fiction, the photon has inherent advantages over the elec- tron. First, it does not generate magnetic fields, nor is it affected by a magnetic field, which is a big advantage in noise reduction. A second advantage is its density. It is much smaller and more compact than electrical cables. Third, in- dividual tracks (waveguides) and connectors can be packed closer together without generat- ing noise or crosstalk. These advantages are ex- pressed by IBM's Optical Roadmap (Figure 3) [5] . Figure 2. Breakdown of optical interconnects based on distance and structure. Terabus Program focuses on the "board" levels. (Source: ITRS)