Winter 2018 Optical Connections Magazine

ISSUE 15 | Q4 2018


THE LIGHTON FTTH test & measurement tools KEEPING



ELECTRO-OPTICS The future of the interface



Submarine tech goes terrestrial

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Industry News

John Williamson Putting FTTH to the Test

12 David Wang 14 Matthew Peach

Welcome to the last issue of Optical Connections of 2018. The end of the year is often a time for reflection, however new developments in optical communications in 2018 means the industry is keenly looking forward to the coming 12 months as progress and innovation continue in a variety of technologies and markets. Progress certainly came this year in the form of FTTH roll-outs, particularly across Europe, reaching almost 90% of households in some countries. However, keeping that fibre up and running will be a challenge for operators who will require a completely new set of tools to maintain those networks, given the fragility of fibre when compared to copper. Veteran technology journalist John Williamson takes a look at the test and measurement equipment needed to keep the light on. At the other end of the network, Antony Savvas looks at the latest developments in silicon photonics and the expected wide-scale adoption of photonic integrated circuits. In a similar vein, Matthew Peach examines the latest developments in the all-important electro-optical interface as new products begin to reach the market. In the data centre, the power consumption and physical footprint of transceivers are becoming critical issues. Optical Connections speaks to Brad Booth, chair of the COBO (Consortium for On- Board Optics) and principal network architect for Azure hardware at Microsoft, about the work the organisation is doing to develop low-power transceivers with a small, standardised footprint. On the subject of data centres, Wave2Wave’s founder and CEO David Wang, looks at the development of optical switching technologies and ways of automating the physical layer using robotics to automate data centre switching. New thinking and radical developments are also being applied to the long-distance cable industry. Corning’s market and technology development managers Dr. Hao Dong, and Dr. Sergejs Makovejs, explain how optical transmission technologies developed for submarine cables are being applied to terrestrial fibre networks. Of course, while all of these developments are completely changing the face of networks and the ways they operate, the software operating systems that make work more efficiently and offer new business models and opportunities need to evolve to keep pace. Optical connections spoke to Nokia’s senior marketing manager Scott Larrigan about the thinking behind the company’s newly-launched WaveSuite software which offers a unique, hierarchical approach to distributing optical capacity. 2018 has been a great year for the industry with an even more exciting time ahead, and Optical Connections will continue to bring you all the latest news and developments as we move into a new era of optical communication. In the meantime, The Optical Connections team would like to wish all our readers, advertisers and supporters a happy and prosperous 2019. Optical innovation to race ahead in 2019

 Breaking the Fibre Barrier

 Electro-Optical Interfacing Looks to the Future

16 Peter Dykes

 The Graphene Revolution

18 Dr. Hao Dong, and Dr. Sergejs Makovejs Advanced Submarine Technology Goes Terrestrial 20 Brad Booth  COBO: Transforming Transceiver Design 23 Peter Dykes  Transforming Optical Transport Delivery 25 Peter Dykes Quantum Security 26 Peter Dykes

 Innovation and Discussion at ECOC 2018

28 Christian Rookes

 Next Generation FTTX PON In China

30 Antony Savvas

New Opportunities in Silicon Photonics

33 Peter Dykes 34 Event Focus 36 Product Focus

FTTH Expo Preview

Peter Dykes Contributing Editor, Optical Connections




Optical Connections is published by NEXUS MEDIA EVENTS LTD

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ISSUE 15 | Q4 2018

“What are the latest opportunities in silicon photonics?”


Antony Savvas – see page 30

LightCounting values cloud 200/400 GbE Optics at $6.2 billion in 2023

Altice Europe N.V. has agreed to sell a minority stake of 49.99% in its French SFR FTTH operation for €1.8 billion. The buyer is Allianz Capital Partners, AXA Investment Managers - Real Assets, acting on behalf of its clients OMERS. The cash, along with access to cheap lines of credit, will be used to expand the Altice France/SFR fibre infrastructure. With 5 million homes to be passed (including 1 million homes built by year-end) and more to be franchised or acquired, SFR FTTH is the largest alternative FTTH infrastructure wholesale According to its latest global forecast for optical components and modules, LightCounting expects that sales of 200 GbE, 2×200 GbE and 400 GbE optics will expand the cloud/ datacentre market segment from $2.3 billion in 2018 to more than $6.8 billion in 2023. The company also believes the cloud pulled the optical transceiver market out of a ditch last year, and it is projected to limit the optical transceiver market’s decline in 2018 to less than 3%. The analyst firm had projected slightly higher sales of optics to the cloud in 2018, but rapid price declines of 40 GbE and 100 GbE transceivers limited sales growth. Google started deployments of 2×200 GbE optical transceivers in 2018 and its plans for next year are consistent with LightCounting’s forecast. Other cloud companies are exploring options of either staying with 100 GbE for another two-to-three years, or of possibly using 200 GbE or 400 GbE in a breakout

deal represents the first transaction of this type in Europe and the creation of one of the largest European FTTH wholesalers in Europe. It will also create the only nationwide infrastructure challenger to the incumbent with a very strong competitive position on its footprint, and accelerate the deployment of FTTH in medium and low dense areas in France. SFR FTTH complements Altice France’s other fixed infrastructure assets: a fully modernised and fully owned FTTB network covering 9 million homes delivering up to 1Gbits/s, and a fully-owned FTTH network. only 18% of the ports will use transponder modules made by companies like Acacia or Oclaro. Converting this to sales opportunity, the market for coherent modules is projected to reach $680 million in 2019, but it would have reached $3,750 million if all coherent ports used transponder modules. The company predicts that market share of coherent transponders will increase from 18% in 2019 to about 35% in 2023. The company also reckons that there are signs that a new cycle of DWDM system upgrades is starting now. Suppliers are reporting strong sales of pump lasers for applications in fibre amplifiers since the second half of 2017. Sales of WSS modules used in ROADMs are up sharply in 2018. All these products are usually deployed in the early stages of upgrade cycles and these should be followed by a pick-up in sales of DWDM transponders and line cards. LightCounting’s conclusion: this is very likely to happen in 2019.

partners and committing large resources to build the leading FTTH wholesaler in Europe,” said Altice Founder Patrick Drahi. “With this transformational transaction, and the various tower sales and partnerships announced earlier this year, Altice Europe has been able to crystallise €8 billion of infrastructure value and obtain cash proceeds of €4 billion in total in a few months. Through these transactions, Altice France and Altice Europe will deleverage and will have access to new and cheaper liquidity to invest in its fibre infrastructure.” Altice points out that the US-made products to ZTE added more confusion to the market and reduced the annual sales of optics to ZTE by 20% to 30%. Numerous projects were delayed in 2018, not just in China, but worldwide because of the ZTE ban and because of uncertainty related to China- US trade war. LightCounting believes the DWDM module market has room to grow. It expects that 130,000 coherent modules will be shipped in 2019, but the total number of coherent 100/200/400G ports will reach 710,000. This means that 82% of the ports will be built by system vendors (like Ciena or Huawei) and

operator in France. SFR FTTH will sell wholesale services to all operators at the same terms and conditions, including SFR as customer, with no minimum volume commitments. Altice France will sell technical services to SFR FTTH for the construction, the subscriber connection and the maintenance of its FTTH network. The plan is for SFR FTTH to deploy fibre massively in the next four years, with at least 1 million homes passed per year. “I am very pleased that three of the most renowned infrastructure investors in the world are becoming our configuration to maximise switch radix. The decline in sales of telecom optical components and modules in 2017-2018 was mostly due to weaker than expected sales of optics to Huawei and ZTE. Suppliers of optical components and modules first reported sharp drops in sales to these customers in March of 2017 which was related to excess inventory accumulated by Huawei and ZTE in 2016. Most of the excess inventory was depleted by the end of 2017, but suppliers continue to report slower than expected business with these Chinese customers. The April 2018 ban on sales of

Altice sells half stake in French fibre wholesale operation for €1.8bn


| ISSUE 15 | Q4 2018


Infinera’s fibre-deep access solution redefines speed and simplicity for cable operators


Infinera, a developer of Intelligent Transport Networks, has launched what it is calling “a low-cost packet-optical aggregation and transport solution purpose-built to accelerate and simplify the delivery of high-speed, low-latency services in access networks”. The new 1.6 terabit High- Density Ethernet Aggregator (HDEA) enables network operators to cost-efficiently address key operational and service deployment challenges in fibre-deep access environments, including Distributed Access Architectures in cable networks and 5G Radio Access Network (RAN) transport infrastructure. “The rapid pace of migration from 1G to 10G connectivity in access networks will create economic and operational Optical transceiver and component vendor Precision OT, has launched Lightseer, a machine learning-powered software- defined networking (SDN) application designed to monitor and analyse the physical layer of an optical software-defined network. The company claims the new product is the first software of its kind that can provide network administrators with real-time data all the way down to transceivers and individual optical links. “At Precision OT, we believe software-defined networks and white box technologies will aid in the operability of 5G networks, metro ethernet, hybrid fibre-coax networks and more,” says Todd Davis, CEO of Precision OT. “By covering all aspects of real-time optical monitoring and being compatible with a wide variety of white box

challenges for operators, and nowhere is this more evident than in the move to DAA within cable access networks,” commented Heidi Adams, Senior Research Director, IP & Optical Networks, at analyst IHS- Markit. “Space constraints, power efficiency, and cable management are all key concerns when introducing large-scale aggregation into hub-site locations. Infinera’s new HDEA platform tackles these challenges head-on.” The new HDEA, part of Infinera’s XTM Series, is an access-optimised packet- optical aggregator that integrates optical transport capabilities, Metro Ethernet Forum Carrier Ethernet 2.0-compliant Layer 2 Ethernet functionality and programmable software control, including direct access via OpenFlow. networking equipment, Lightseer meets the demand to ease logistical complexity and improve network intelligence.” Key features of Precision OT’s proprietary application include real-time optical monitoring showing the state and integrity of the complete optical network; wavelength density monitoring for CWDM/DWDM networks; compatibility with a large variety of white box networking equipment equipment; live management and configuration of optics deployed in the software- defined network (inventory, tuning, etc.) and machine learning for predictive analytics to forecast optical failures and anomalies before they cause network downtime. and off-the-shelf SDN controllers; integration with legacy networking

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ISSUE 15 | Q4 2018

The FTTH market is reliant on test and management tools


JohnWilliamson – see page 8

World-first Optical Fibre Transmits At Over 1 Petabps

A world-first optical fibre has been developed in Australia that can transmit data at 1.2 Petabps. This is 12 million times quicker than the country’s fastest National Broadband Network (NBN) connection. The dramatic improvement scientists from the Macquarie University Photonics Research Centre, a fibre jointly developed by Hokkaido University and Fujikura Ltd, and the transmission system developed by the National Institute of Information and Communications Technology Japan (NICT). The fibre researchers note that Internet data use is increasing exponentially, due to developments such as on-demand streaming and artificial intelligence, and we are fast approaching the limits of existing communications networks. They add that research into new types of optical fibre that can transmit ultra-large volumes of data have to date The Ethernet Alliance (EA) has announced its next Ethernet Higher Speed Networking Plugfest for port data rates ranging from 25 Gbits/s to 400 Gbits/s. The week-long event – beginning December. 3, 2018, at the University of New Hampshire InterOperability Laboratory (UNH-IOL) in Durham, NH – is designed to allow EA members, equipment manufacturers, test and measurement professionals, etc. to test and improve interoperability of their solutions. In addition, members of the 100G Lambda Multisource Agreement (MSA) Group also are invited to attend the plugfest, under terms in speed was enabled by a coupler developed by

said Dr Simon Gross from the Macquarie Photonics Research Centre. “This technology promises a solution to the bottleneck created by existing optical fibres. For the first time, we have created a realistic and useable-sized fibre which is resilient and can transport huge amounts of data. It also represents a big cost saving over installing the 12 standard optical fibres you would need to transport the same volume of data.” super-fast, ultra-broadband communications.” “Present-day optical communications are heading towards a ‘capacity crunch’ as they fail to keep up with the ever-increasing demands of Big Data,” Ren said. “What we’ve managed to do is accurately transmit data via light at its highest capacity in a way that will allow us to massively increase our bandwidth.” Current optical communications use only a fraction of light’s actual capacity by carrying data on the colour spectrum. New broadband technologies under development use the oscillation of light waves to encode data and increase bandwidth.”

significant cost-savings over other types of fibres. The fibre has applications in transmitting data between datacentres, metropolitan networks, or undersea communications cables, with the ability to smoothly accommodate traffic for big data and 5G services. “The world’s insatiable demand for data means that we are approaching a ‘capacity crunch’ and need to find new ways to transport ever-larger volumes,”

resulted in thick fibres that are vulnerable to damage from bending and pulling. The four-core, three- mode fibre developed by Hokkaido University and Fujikura Ltd is almost the same width as existing standard optical fibres but can transmit 12 times as much data per second. Its narrower diameter means it is less prone to damage and can easily be cabled and connected using existing equipment, resulting in of a new memorandum of understanding (MoU) between that industry consortium and the EA. “With so much technology development underway and transpiring on different timeframes, industry is more and more often demanding opportunities for trustworthy interoperability testing for their solutions. This is a role for which the Ethernet Alliance has grown globally respected,” said Dave Chalupsky, Plugfest Chair and Board Member, Ethernet Alliance, and Network Product Architect, Intel Corporation. “Ethernet is amid significant and historic growth, with so many new standards activities coming out over the last two years and still rolling out.”

RMIT optical breakthrough to allow 100x faster internet

Ethernet networking interoperability testing speeds up

A new form of “twisted” light, developed at RMIT, Melbourne Australia, can encode more data and process it much faster than conventional fibre optics. The developers say that their “twisted light beams” could lead to an Internet that is 100 times faster than today’s typical standard. A detailed paper on this world-first nanophotonic device has just been published in Nature Communications. Dr Haoran Ren from RMIT’s School of Science, Melbourne, Australia, who was co-lead author of the paper, said the tiny nanophotonic device they have built for reading twisted light is the “missing key required to unlock


| ISSUE 15 | Q4 2018


Room temperature quantum repeater advance

but it is way longer than what has previously been achieved with atoms at room temperature”, reported Karsten Dideriksen, PhD student on the project. The Niels Bohr Institute technique itself consists of a small glass container, filled with Cæsium atoms, in which the researchers are able to load, store and retrieve single photons from the quantum states necessary for the repeater. This technique improves the life span of the quantum states at room temperature by a hundred times. Simplicity is key, as one has to imagine this technology, once developed to its full potential, spread out across the globe as quantum repeaters in our information networks. The immediate use-case is storage for secure quantum information networks, but other options such as generation of on- demand single photons for quantum computing are on the table.

Researchers at the Niels Bohr Institute, University of Copenhagen, have recently succeeded in boosting the storage time of quantum information. The development used a small glass container filled with room temperature atoms, and marked an important step towards a secure quantum encoded distribution network and the realisation of real-world quantum repeaters. The researchers note that storage time comes into the quantum communications equation, as it actually takes some time for the information to travel in fibres. The delicate quantum entanglement has to be stored, waiting its turn to travel through the optical fibre. Accordingly, it makes very good sense to aim for a system that operates at room temperature, because of the scale of such networks. If quantum repeaters have to be deployed for


of the quantum state at room temperature to about a quarter of a millisecond. In this period of time the light can travel roughly 50 km in the fibre. “So, 50 km – it is still not very far, if you want to send regional quantum information,

approximately every 10 km of communication line, the benefits of a simple setup, working at room temperature, are tremendous.

The researchers at the Niels Bohr Institute have managed to boost this crucial lifespan

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ISSUE 15 | Q4 2018



Whichever way it’s presented, continuing FTTH market development is critically reliant on the availability and use of cutting-edge network test and measurement tools and solutions, writes John Williamson .

Y ou can slice and dice the FTTH opportunity in a number of ways. For example, Zion Market Research reckons the global FTTH/B network equipment market, using different flavours of PON, was worth around US$16,128.11 million in 2017 and could reach approximately US$28,882.24 million in 2024. Again, Broadbandtrends LLC believes that fixed broadband subscribers worldwide might number 859 million by the end of 2022, with nearly half of these being FTTH users. Douglas Clague, solutions marketing manager, Fiber Test Systems, Viavi Solutions, says that the reality is that it costs more to acquire a new FTTH subscriber versus retaining an existing one and, in addition, ARPU is fairly fixed and typically stays at the same level - or declines - in the years after subscriber install. He also observes that service provider business models rely on being able to retain customers for a minimum period of time, say an average two to three years, in order to recoup customer install costs, including ONT/CPE hardware costs, recover some network build costs and actually start generating positive revenue. “Poor service install/ turn-up or early life fails are the Achilles

heel that can lead to customers cancelling or churning, and can be some of the easiest things to avoid through good PON build procedures that include test and certification, plus simple basic things like connector inspection as part of installs,” he declares. As noted by Olivier Tremblay-Lavoie, Exfo team manager, Portfolio Marketing, the scale, high cost and long lead times of major FTTH projects puts a premium on the test component: “The testing aspect of this is not the largest part but it is a very important part if you want to get it right the first time.” THE PAINES OF GLASS Fibre is famously a less forgiving medium than copper, a circumstance reflected in

the possibilities for deployment glitches and system outages and the challenges associated with the optical network T&M function. Tremblay-Lavoie says that in any type of fibre network around 80% of fault issues are caused by connectors being dirty, contaminated by grease or oil, or by defects on the fibre end-face. “Connector inspection is universal and is something that should be carried out automatically, almost as an instinct throughout all phases of the networks lifecycle - build, activation and installs, maintenance and troubleshooting,” adds Clague. “The network is only as good as its weakest connection.” Tools such as Fibre Inspection Probes (FIBs) and Optical Time Domain

The network is only as good as its weakest connection



| ISSUE 15 | Q4 2018


ISSUE 15 | Q4 2018


GOING FORWARD So what does the future hold for FTTH T&M? It depends who you ask. In the frame, according to Cole, are advances in OTDR technology allowing for greater dynamic range and resolution, and improvements in how test processes are managed using cloud platforms for distributing jobs and collecting results directly from the field. “Keep an eye on fibrescopes as advancements in camera technology have made video inspection more meaningful and economical,” he further suggests. An example is AFL’s DFS1 Digital FiberScope supporting magnified video inspection of optical fibre connector end-faces during fibre optic cable and connector installation and maintenance. The migration from current GPON and EPON to newer PON types such as XGS-PON and NG-PON2, and the co-existence of established and new, will raise some FTTH test issues. “A requirement will be to detect which type of technology is on the network and adapt to that,” ventures Audet. According to Clague, one challenge is that the newer standards like NG- PONs, and especially the P2P services being looked at for business applications or 5G front/backhaul, use longer wavelengths up to and around 1,625 nm where macro-bending of fibres and the associated attenuation of power levels becomes a real problem. “So, what we see as a future requirement, but realistically a requirement for today, is including 1,625 nm in the testing and certification tools and Methods Of Procedure when certifying network build in order to remove future OpEx costs related to finding and fixing macro-bend issues.” The increased availability and use of multi-function test solutions is one of Messina’s suggestions for the future. “We expect this trend will increase with the deployment of next generation 5G networks, where mobile backhaul and fronthaul will require a large redefinition and deployment of higher speeds, with fibre and Ethernet/CPRI/eCPRI/RoE synchronisation testing at the same time,” he calculates. And while not strictly speaking a test development topic, Viavi definitely sees the building and validating of business cases for the use of fibre monitoring solutions in PON as a future business development. “Of course, good ROI for fibre monitoring systems can only be achieved by using it during multiple phases of the network lifecycle,” reasons Clague. “As an embedded tool for build certification, then to identify customer connection to the network during installs in order to trigger service activation, and then the more traditional use of monitoring tools for identifying network outages and pinpoint fault locations to improve Mean Time To Repair.”

Reflectometers (OTDR) are relevant here. Fibre also has a lower tolerance than copper for bending, with the prospect of light going out of the required range and loss of some of the signal if the tolerance is exceeded. Alessandro Messina, EMEA marketing director, IP Network Division, Anritsu points out that this requires the capability to not just detect broken fibres in the access network, but also identify bent fibres through the application of simultaneous double trace, or two different wavelengths, analysis. Some FTTH/B implementations adopt a Point-to-Point (P2P) architecture, others are Point-to-Multipoint (P2MP). In the case of P2MP test complexities increase with the issue of splitter losses. AFL EMEA marketing manager Nicholas Cole remarks that the introduction of splitters makes OTDR testing much more complex due to the large point of loss introduced by those devices. “Each 50% split is equal to a 3dB reduction in power which adds a minimum of 15 dB to networks containing a 1:32 split commonly found in a GPON,” he states. “Legacy OTDRs do not like short links

requirement to correctly identify each fibre at the users’ end,” says Messina.

LABOUR PAINS In parallel with the inherent challenges presented by working with fibre and optical technology, experts say there has been a shortage of suitably skilled technicians able to install and test that technology. “The people in the field deploying the fibre and handling it sometimes have a limited background in fibre testing,” observes Tremblay-Lavoie. “There’s a lot of staffing issues. There’s a lot of training and education required.” One response of the fibre test industry to skills shortages is to add intelligence to remove complexity and to automate test solutions. In this context, Messina instances his company’s Fiber Visualizer, a tool that allows full automatic OTDR testing, where the user is driven step by step and the resulting trace is also automatically analysed to show the events, recognise them, and provide the pass or failed results. One of Viavi’s solutions for reducing the complexity of OTDR operations is the Smart Link Mapper (SLM). This

The people in the field deploying the fibre … sometimes have a limited background in fibre testing


with high loss events as they are unable to achieve enough dynamic range whilst maintaining resolution. Equipment vendors have overcome this by designing OTDRs with sophisticated algorithms utilising multi-pulse and automated test modes.” There’s also a customer service issue. “For example, if you are serving 16 customers, and one has a fault, you can’t take the entire network down to troubleshoot that one,” comments Francis Audet, CTO Advisor at Exfo. Audet reckons P2P test may not be a walk in the park either if the connection mixes fibre and, say, vectoring/ bonding over copper technologies, an arrangement necessitating the assessment of different operating parameters. Other problems may arise from the requirement to be able to track and check all fibres when end-to-end testing from the central office to the home. “This includes big challenges because of the distance, the splitting points, and the

takes an OTDR trace and simplifies it to a series of icons representing the fibre link under test. An approach to skills shortages followed by Exfo and others is to exploit better process automation. Exfo’s TestFlow product is a cloud-based process automation and compliance solution. It is designed to simplify tasks for field technicians by breaking down complex test procedures into a step- by-step automated sequence that gives access to the right test parameters and procedures, in turn certifying that network construction and installation jobs are completed correctly and to the right specifications/thresholds. Yet another response is for test houses to become more engaged with network builders or service providers in establishing the initial test methods and procedures to be applied. This, as remarked by Tremblay- Lavoie, might extend to proposing adjustments to network planning or design where the test approach might be judged weak or inappropriate to the particular network or architecture.


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ISSUE 15 | Q4 2018


Automating The Physical Layer Breaking the Fibre Barrier:

How to automate physical connectivity in fibre networks without undue impairment of optical characteristics. Robotics may be the answer to a 20-year-old problem, writes David Wang , founder & CEO, Wave2Wave Solution

C loud computing, demand for bandwidth. Thanks to the introduction of edge computing, IOT and Big Data, there is also much more fluidity as to where data resides. To meet these demands, network operators are looking for software-defined reconfigurability, fast and low-cost provision of services, improved energy efficiency, and better scalability. Software Defined Networking is a key component for a carrier to improve their network efficiency and utilisation whilst accelerating services through automation and even self- service capability for their end users. Whilst SDN is delivering great benefits and driving multi-layer optimisation across the networks, often the last piece of the automated process is sending an email to the field engineer to visit the site to make any necessary physical network changes, which marks the end of the automated process. This can introduce delays in provisioning from days to weeks or even months. The physical layer, consisting of the actual optical fibres, not only underpins the entire network, it also links access networks and provides data centre interconnects. Historically, it has been largely resistant to software definition and automation. A human operator is still required to add or remove a network connection, manually interlinking fibres on a patch panel in order to create the required network topography. The entire process is slow, from requisition to execution of service. It is also prone to error, with adjacent services at risk of disturbance during the staggering amounts of video streaming, and ever-increasing wireless communications have created an insatiable

reconfiguration of frequently jumbled patch panels. Over the years many optical switching technologies have been put forward to address the challenge without achieving any significant uptake, including 2D MEMS (Micro-Electrical-Mechanical Systems), thermo-optic, and liquid crystal. All three of these technologies have scalability constraints, with port count restricted to 32x32 for reasonable switch insertion loss. Large port count optical switches do exist, but have their own limitations and drawbacks. Using multiple 3D MEMS optical switches, larger port count switches can be built. However, the optical losses of different connections in a 3D MEMS optical switch are intrinsically different, resulting in a relatively large insertion loss spread (up to 3-4dB) and the total optical loss quickly becoming unbearable for many applications.

with lens collimators and arranged into 2D arrays facing each other. Every fibre collimator is mounted to a 2D Piezo actuator which controls the collimator beam pointing in free space. To make a connection between an input fibre port and an output fibre port, the 2D Piezo actuator steers the input fibre collimator to point its beam to the destination collimator. With proper fibre collimator design, low insertion loss of ~0.4dB can be achieved. However, the path lengths of different fibre to fibre connections vary. The collimators can only be optimised for one given pathlength, thus an insertion loss variation exists across different connections. Non-uniformity of the fibre collimators also widens the loss spread. As a result, commercial switches using direct beam steering are specified with a 1.2dB typical loss and a 2.2dB maximum loss. Switching can be relatively fast, approximately 20ms. However, similar to 3D MEMS optical switches, there is no locking mechanism for the established connections and, therefore, it is not suitable for mission-critical applications. Fibre coupling using direct beam steering in theory can support both


One optical switching technology with commercial success is direct collimator steering. As shown in Figure 1, both the input and output fibres are terminated

Figure 1: Conceptual view of a collimator steering based optical switch


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single mode (SMF) and multimode fibre (MMF). However, high-order off-axis modes of MMF cannot be collimated as perfectly as the fundamental mode. Consequently, the loss of MMF switches is typically higher, and the switch port- count is smaller than with SMF switches. Silicon photonics technology, as illustrated in Figure 2, is creating new opportunities for fast optical circuit switching - silicon photonic switches have been demonstrated with microsecond and even nanosecond switching times. Unfortunately, accumulated losses limit the port count of these switches (≤8×8). Combining MEMS actuated vertical adiabatic couplers as switching elements in conjunction with a 2D silicon waveguide matrix, a scalable silicon photonic waveguide optical PROGRESS THROUGH SILICON PHOTONICS

connect fabric exist, such technologies fail to meet the requirements of emerging IT applications because of limited scalability resulting from fabrication limits, performance issues, insertion loss, and switching time.


Given the limitations of existing optical switching technologies, robotic optical networking is an innovative way to physically change the connectivity of a network without undue impairment of its optical characteristics. Robotic fibre switches (see Figure 3) have been developed that can make large cross-connect fabrics with low insertion losses and robust connections. The matrix design of the robotic fibre switch with cross-bar switching completely prevents fibre from entangling. The robotic fibre switch can pick up the connector pair and make a connection within 20 seconds or less. Because every connection in a robotic switch is made using LC connector- like mating, low optical loss is achieved independent of the switching path. The lowest optical insertion loss recorded so far was an average of 0.17dB, with a standard deviation of only 0.07dB. In addition, it is possible to scale up the switches to support 16K duplex ports with less than 1dB optical loss. A fibre cloud with half a million duplex ports can be supported with <1.5dB optical loss. With LC ferrules, the same design supports both SMF and MMF. The robots are shared among hundreds of fibre ports; hence the cost of the switch can

Figure 3: Illustration of a robotic matrix optical switch design

be relatively low. Once a connection is made by the robots, the connectors are locked on the metal matrix passively, resulting in extremely secure and reliable optical connections even under extreme conditions. A robotic based optical cross-connect provides significantly improved optical performance, is easily integrated into an SDN Controller and research demonstrates that an agile physical layer can improve the cost savings of multi- layer optimisation from a 19 percent to a 34 percent cost saving. With the deployment of optical fibre ever-increasing in response to today’s digital demands, effective automation of the physical layer is crucial. Robotic fibre switching is a cost- effective, technically compliant solution and may be the answer to a 20-year- old problem – how to automate the physical connectivity in fibre networks without undue impairment of its optical characteristics.

Figure 2: Schematic of a silicon photonic MEMS matrix switch

switch can be made that overcomes the cumulative losses. Switches with a size larger than 100×100 are theoretically possible and a 50×50 silicon photonic switch, monolithically integrated on a 7.6×7.6mm2 chip, already has been successfully demonstrated with an on- chip insertion loss of 8.5dB. Although promising, challenges still exist for digital silicon photonic MEMS switching. Due to large mode size mismatch between the fibre and the silicon waveguides, low loss coupling

between the fibres and the silicon chip is still a problem,

especially where 10s or even 100s of fibres are involved. In addition, silicon photonic MEMS switches with polarisation diversity are yet to be demonstrated. Consequently, while various optical switching

technologies for large size photonic cross-


ISSUE 15 | Q4 2018



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.


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sophisticated digital signal processors to be able to interpret and decode and do all of the signal processing at the electrical level and for that we are using the Acacia’s DSP products.” SMALLER FORM FACTORS LeMaitre agrees that the well- documented trend of optics and electronics elements becoming more compact and power efficient is driving the revision of modulation formats into new dimensions. “We have to be able to do this in conjunction with key developments in electronics such as the transition to 7nm digital signal processing in order to be able to increase performance while allowing it to be packed into smaller and smaller form factors,” he said. “Our job at Oclaro is to try to deliver the best photonics engines for these and then find the right partners that can give us the electronics sitting next to it. We do not develop the electronics so we have to rely on the industry and the DSP suppliers. Our part is based on using InP but there are other ways to do it; for example, there are other groups working on silicon photonics.” OPTICAL INTERNETWORKING Optical Connections interviewed the OIF (Optical Internetworking Forum) about its involvement in the development of electro-optical interface technologies. The OIF, which this year celebrates 20 years of activities, promotes the development and deployment of interoperable systems through international implementation agreements for optical networking products and component technologies. 100Gbps lambdas and therefore the industry will benefit from a 100Gbps electrical interface definition that enables industry interoperability while providing the simplest implementation of an optical transceiver function. Our CEI-112G projects are in the process of defining electrical channel definitions for die-to-die, host-to-module, chip- to-chip and backplane interoperable implementations.” The Forum commented, “Next generation optics will operate at

Some of the OIF’s current development projects that are addressing the industry’s optical and interface needs include the following: The High Baud Bandwidth Coherent Driver Modulator project prioritises RF performance over size by defining a small form factor component integrating a high performance, polarisation multiplexed quadrature modulator plus the RF drive functions for the high baud-rate and low modem implementation penalty segment of the coherent market. The Integrated Coherent Transmit- Receive Optical Sub Assembly project combines previous OIF efforts to define The primary area of interest is around the implementation of coherent technology integrated photonic components for both transmit and receive functions into a single package suitable for the next generation of high-density optical modules and onboard optics. The 400ZR project is an OIF optical project designed to specify a digital coherent module interface targeted at short reach DWDM links that enables interoperable, cost effective 400Gb/s implementations. Instead of specifying new technologies, the project provides a lighter version of a long haul, 400Gb coherent link. REVOLUTIONARY RESEARCH Focusing on the importance of the electro-optical interface, a research team comprising members from City University of Hong Kong, Harvard YVES LEMAITRE CHIEF STRATEGY OFFICER, OCLARO

University, Ma, US, and Nokia Bell Labs have fabricated an on-chip lithium niobate modulator that is smaller, more efficient and enables faster data transmission than previously available. The research project, entitled “Integrated lithium niobate electro- optic modulators operating at CMOS-compatible voltages,” was first announced in Nature journal in autumn 2018. The technology is said by its developers to be “set to revolutionise the industry.” This electro-optic modulator measures just 10 to 20mm long and its surface area is about 100 times smaller than traditional devices. It is also highly efficient, having higher data transmission speed with data bandwidth tripling from 35 GHz to 100 GHz, but with less energy consumption and ultra-low optical losses. Existing and commonly used lithium niobate modulators require a relatively high drive voltage of 3V to 5V, which is significantly higher than 1V, the voltage typically provided by CMOS circuitry. This requires a complementary electrical amplifier, which makes the whole device bulky, expensive and energy hungry. Project leader 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 Gbps, with about 10 times lower optical losses than existing modulators. This revolutionary invention is now on its way to commercialisation. Dr. Wang believes that those who look for modulators with the best performance to transmit data over long distances will be among the first to get in touch with this infrastructure for photonics. CONCLUSION Whether the physics of construction materials will ultimately limit E-O modulator performance to a matter of terabits per second, other innovations are likely to enable greater speeds, particularly the innovation of parallelism. Oclaro’s Yves LeMaitre concluded, “Probably the next step in my view is that a lot of the developments will be about parallel solutions until there is the next serial technology breakthrough. Somebody smarter than me will come up with the next serial step. 1 Tbps seems possible in terms of existing electro- optical technologies but beyond that, at the moment the only way seems to be to go parallel so I think we will continue with progress via a series of serial and parallel developments.”

Oclaro is focused on EO developments based on an indium phosphide platform


ISSUE 15 | Q4 2018

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