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FEATURE OPTICAL COMPONENTS


CFP2-ACO analogue coherent optical modules using indium phosphide. Doerr believes the opportunities for silicon


photonics will improve as more and more channels are integrated on a device, and with closer integration with the electronics – either co- packaged or using a 3D stack. For coherent designs, Doerr expects to see


further reductions in the size, cost and power consumption using silicon photonics, making it competitive with other optical transceiver technologies for distances as short as 2km. ‘You can use high order modulation formats such


as 256-QAM and achieve very high spectral efficiency,’ said Doerr. Using such a modulation scheme would require fewer overall lasers to achieve significant transport capacities, improving the cost-per-bit performance for applications such as data centre interconnect.


Disruptive technology Will silicon photonics displace other technologies? Tat’s the billion-dollar question in the industry right now. But views are mixed as to whether silicon photonics is genuinely disruptive. ‘If you look at the origins of what a disruptive technology is, it is a technology that works in one


field that but then it performs so well, it crosses the boundary into other areas,’ said Reed. Silicon photonics was initially regarded as a short-reach technology, but once the performance of its modulators started to increase drastically, the technology crossed the boundary into long-haul research, he notes. ‘Tat is the definition of a disruptive technology,’ he observed. Rickman also believes silicon photonics is


disruptive: ‘It is a paradigm shiſt; it is not a linear improvement.’ But he argues it has to have the right features and be used in the right way when addressing systems design. Instead of viewing silicon photonics as a


‘Band-Aid’ for semiconductors to delay the ending of Moore’s law, the key is to know the capabilities of silicon photonics and electronic ICs, and to organise them in a way that overcomes the ‘exhaustion of Moore’s law and the input/output problems’, he says. Acacia’s Christopher Doerr agrees. ‘I don’t think


we have hit the limitation at all,’ he said. ‘As we integrate more channels, being disruptive will be undeniable.’ Others do not view silicon photonics as


disruptive, however. ‘Te theory of disruption is that new technologies always come from the low


end, and then end up dominating the market,’ said Kozlov, ‘whereas silicon photonics, like optical integration more generally, is entering the market at the high-end.’ But Kozlov acknowledges that the technology


has performance disadvantages, compared to traditional technologies such as indium phosphide and gallium arsenide, and its optical performance is continually improving. ‘Tat may still be consistent with the theory of technological disruption,’ he noted. ‘I don’t know about disruptive; it is a word that is


used too much,’ commented Mario Paniccia. Silicon photonics is a technology that opens up a lot of new possibilities, as well as a new cost structure and the ability to produce components in volume. But it doesn’t solve every problem, he says. Optical players very much focus on cost. For


markets such as the large-scale data centre, it is all about achieving the required performance at the right cost. Paniccia thus expects silicon photonics, indium phosphide and VCSELs all to co-exist. ‘It is all about practical decisions based on price, performance and good-enough solutions,’ he concluded.l


Roy Rubenstein is a freelance science writer based in Israel, and author of Gazettabyte.com


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