Winter 2018 Optical Connections Magazine



looks to the FUTURE

O ften considered the limiting factor in today’s high-speed optical networks, electro-optical conversion technology is the subject of much research and development, whether in the materials of choice or functionality variations like multiplexing and polarising of the signals. At the same time, the recurring issues of reducing footprint and energy demand while boosting performance must also be considered. Leveraging advanced CMOS processing designs and reduction in design complexity, coherent optical solutions are now moving from long haul to metro and even shorter reach optical interfaces. Looking forward, the industry is working to standardise coherent solutions for even shorter reach interfaces. Acacia Communications, based in Maynard, Mass, US, which develops high- speed coherent optical interconnect products, has recently introduced several new compact high-capacity module solutions based on integrated photonics and digital host interfaces. At ECOC 2018 in Rome, Acacia demonstrated its AC1200 coherent module with dual- core design, which enable 1.2 Tbps error-free transmission over fibre with 600 Gbps per wavelength. This level of performance requires DSP and optics technology with both high bandwidth and high performance. Furthermore, its CFP2-DCO pluggable module supports four times the faceplate density of CFP- DCO. Acacia explained that there are a number of design advantages to its silicon photonics approach; a wide thermal operating range and highly integrated photonics. “Advances in CMOS technology have enabled increased DSP capabilities at lower power. This has allowed DSPs for coherent modulation to support higher speeds and increasing

Whether by improved device performance or new developments in parallel transmission, advanced electrical-optical conversion is the key to more effective networking, writes Matthew Peach.

complex modulation schemes,” says Christian Rasmussen, founder and vice president of digital signal processing and optics. “Also advances in mixed-signal analogue/digital components such as analogue-to-digital converters and digital-to-analogue converters have enabled optical coherent higher baud rate transmission. As coherent optics moves to smaller pluggable form factors, integrated packaging becomes very important.” He explained, “As intra-data centre speeds increase, we may see the need for coherent transmission increasing within the data centre and low-power coherent DSPs may become even more impactful in this situation. This capability could have the potential of reducing the number of

the optical-electrical interface. Coherent technology is gradually pushing further and further into the edge of the carrier infrastructure or the data centre interconnect. As we push this technology towards the edge, which is really a way to maximise bandwidth on those long- haul sub-links, we now have to be able to pack that type of performance into smaller and smaller form factors.” He added, “The key enablers for Oclaro to do this are the integration in indium phosphide of very efficient narrow linewidth lasers that can be tuned across the whole wavelength range combined with the high-efficiency modulators so that you can do the phase modulation that is required for coherent transmission. That’s the first part but, of course, next to that is one of the most

repeater nodes in a network, reducing CAPEX, OPEX and power levels from these installations.” Yves LeMaitre, chief strategy officer for Oclaro, outlined his company’s continued preference for indium phosphide-based technologies. He said, “The primary area of interest is around the implementation of coherent technology, which is a perfect example of position on electro- optical developments and his company’s

Fig1 shows the approximate 40% annual reduction in power/ cost/size for coherent optical technology.


| ISSUE 15 | Q4 2018

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