MATTHEW PEACH LONG-HAUL
are also seeing some of the data centre interconnect applications also coming up in 2019-2020.” CHALLENGES So, what are some of the main challenges facing operators who want to deliver long-haul solutions across continental distances? A basic problem at the physical layer is fibre exhaust, where there may not be enough fibre already laid down over such long a distance. This means that maximising spectral efficiency becomes a priority: how much bandwidth can be crammed onto a single fibre when the capacity is limited. Aiya added, “Can an operator put 10 or 20 Tbps on a single fibre? Spectral efficiency is key because that translates to the cost of delivery. Overall, performance is key as operators want to achieve longer-haul distances.” He ranked what he sees as the most important long-haul optical challenges to solve, starting with spectral efficiency, followed by: performance; achieving a universal platform (standards); power demand reduction; and signal density. ‘COLOURLESS, DIRECTIONLESS CONTENTIONLESS’ Lumentum provides optical products across data communication and telecommunication segments. It also provides photonic products such as commercial lasers for manufacturing, inspection, and life-science applications. Brian Smith works in Transport Product & Technology Strategy, at Lumentum. Considering his company’s approach to the long-haul sector, he told Optical Connections, “We see this market strongly favouring colourless, directionless contentionless (CDC) ROADM technology to support high-capacity core networks. CDC gives operators the maximum flexibility and capacity utilisation without suffering from wavelength blockages.” Today’s CDC deployments use MCSs (multi-cast switches) for the add-drop structure. These are adequate for the time being but are inherently very high loss, and require costly high power EDFA arrays to mitigate this loss in the node. Smith then described Lumentum’s strategy for dealing with the mushrooming growth of network traffic, “Looking ahead, network traffic is roughly doubling every two years but spectral efficiency is saturated, so total bandwidth needs to increase at the same rate as traffic growth. Coherent interface rates will continue to increase through the adoption of higher baud rates and eventually multi-carrier superchannels, providing efficiencies in ROADM node architectures. Higher baud rates and adoption of multi-carrier super channels drive higher channel bandwidth. Some of its key optical transceiver products include CFP, CFP2, CFP4, QSFP, QSFP28, SFP, SFP+, and XFP configurations.
A bigger percentage, probably about 80-90% of the long-haul market is in the window between 1000km to 3000km distance.
PRANAY AIYA VP OF PRODUCT MARKETING & APPLICATIONS ENGINEERING, INPHI SOLUTIONS
Today’s coherent signals have nominally constant power across their spectrum, so as channel bandwidth increases, the total power of the channel increases proportionally. As channel bandwidth scales, EDFA arrays associated with the multicast switch must support significantly more total power, which limits the maximum channel bandwidth that the MCS can practically accommodate.” He concluded, “Contentionless WSS add/drop modules have inherently lower loss compared to MCS; in many cases, the EDFA arrays can be eliminated. This saves on cost, power and ensures that the expanding channel bandwidth of evolving coherent transmission can be supported. Additionally, Contentionless MxN WSS has the added benefit of per channel filtering, improving performance and relaxing requirements on the optical transceivers.” As optical networks are transitioning from 100G to flexible transmission rates scaling up to 600G to support hyper-connected architectures, new flexible multi-rate optical transmission devices and software are needed. A notable recent example is the recently-announced Microchip Technology-Acacia Communications collaboration. Microchip Technology, through its subsidiary, Microsemi, and Acacia are supporting this transition with the demonstrated interoperability between Microchip’s DIGI-G5 Optical Transport Network (OTN) processor and Acacia’s AC1200 Coherent Module. The objective of the companies’ collaboration is to enable what they call “the industry’s first flexible rate system architectures with an established ecosystem to support the market’s transition to 200G, 400G, 600G and flexible rate OTN networks built with new Flexible Ethernet (FlexE) and OTUCn protocols.” The partners commented at the start of 2019, “By helping enable the market’s transition from 100G to flexible transmission system architectures, service providers could deploy higher bandwidth Ethernet connectivity at a faster rate and at a lower cost with Optical Internetworking Forum’s (OIF) FlexE protocol.” Babak Samimi, VP of Microchip’s FLEXIBLE TRANSMISSION UP TO 600G
Communications business, commented, “DIGI-G5 allows our optical transport system partners to deliver terabit-class OTN switching line cards at 50 percent less power per port while enabling flexible rate ports and protocols up to 600G. Demonstrating interworking of the DIGI-G5 with Acacia’s AC1200 coherent module highlights that the ecosystem is ready to support the market.” Benny Mikkelsen, CTO of Acacia, added, “In addition to high capacity and density, our AC1200 module introduces several key features designed to enable network operators to optimise capacity, reach and spectral efficiency —making flexible transmission solutions up to 600G a reality.” ‘REVOLUTIONARY’ MINI- MODULATORS Another key element of the higher- efficiency long-haul toolkit, the modulator, is undergoing a technology revolution. Now an international team of researchers have shrunk the dimensions of the lithium niobate (LiNbO3) optical modulator by factor of 100. Researchers from City University of Hong Kong (CityU), Harvard University and Nokia Bell Labs have fabricated a tiny on-chip lithium niobate modulator, an essential component for long-haul transmission, which is not only smaller it is also much more efficient than conventional LiNbO3 devices. The optoelectronic device will enable significantly faster data transmission but at a much lower cost, said the international team in a recent Nature journal article, commenting, “This technology is set to revolutionise the optical communications industry.” Dr. Wang Cheng, Assistant Professor in the Department of Electronic Engineering at CityU, Hong Kong, commented, “In the future, we will be able to put the CMOS right next to the modulator, so they can be more integrated, with less power consumption. The electrical amplifier will no longer be needed.” Thanks to the advanced nano fabrication approaches developed by the team, this modulator can be tiny in size while transmitting data at rates up to 210 Gbit/s, with about 10 times lower optical losses than existing modulators.”
20
| ISSUE 16 | Q1 2019
www.opticalconnectionsnews.com
Made with FlippingBook - Online magazine maker