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82 PCB007 MAGAZINE I JANUARY 2021 In 2006, their supercomputers used a single optical cable at the card edge, and multiple optical fibers to the card edge and across the board to individual connectors at the proces- sors (Figure 3d—MicroPODs). Reportedly de- ployed in the 2015 timeframe were integrated optical waveguides on the card and backplane with optical connectors and sockets. The pre- dictions were that by 2020, optical intercon- nections would be on the chip and between cores and memory, as well as board and back- plane. For the foreseeable future, systems will be a mixture of electrical circuits with high-speed optical and slower electrical data busses. This architecture is seen in Figure 4 [6] . In the far fu- ture, the actual circuit elements may be pho- tonic computing, memory, encryption and analysis as well as data distribution, effective- ly realizing the predictions of science fiction writers. Photonics and Waveguides While an electrical signal can be multiplexed on a single wire or trace, many laser frequen- cies can be multiplexed on a single waveguide. This results in a 1,000X increase in informa- tion handling while not being influenced by magnetic and electrical fields like electronic signals. The integrated optical board and backplanes are predicted to have a steady growth over the years. The predicted growth forecast by Elec- troniCast is that by 2020, the value of rigid and flex photonic boards will be $3,965 mil- lion. The need to route long-line optical signals in an efficient manner and at lower cost has created the interest in integrated optical wave- guides and methods of optical routing. The current method of signal routing is to convert the optical signal to an electronic signal, inter- rogate it, switch it to its next destination, and then convert it back to an optical signal. All of this forms what the industry calls "Terabit Routers" and can require up to 42 large, com- plex multilayers. With integrated optics, this can probably be done by one or two unique PCB assemblies. The "board-to-board" opto- electronic system will probably look like the il- lustration in Figure 4. It has to be considered that the design pro- cess is of the same importance within the val- Figure 3. IBM Optical Interconnect Roadmap. (Source: IBM [4] )