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OFC/NFOEC Organizers

Optical Communications in 2012 Progress in optical

communications is being

driven by an explosion of new

applications and services. This

article describes the current

state of the fi eld as seen by the

organizers of the upcoming

OFC/NFOEC conference.

1047-6938/12/01/42/6-$15.00 OSA

January 2012 | 43

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fter a long period of malaise brought on by the collapse of the tech bubble and recent turmoil in the global fi nancial markets, optical communication has

returned to the familiar territory of rapid business cycles modulating a background of growth. As we approach the theoretical capacity of optical fi ber in inter-city links, we will soon be

using technology that seemed impossible fi ve years ago. We are struggling to meet the band-width demands in access networks at the required cost. Meanwhile, for many countries, getting broadband communications to nearly all homes is the goal. e optical layer in networks is gaining intelligence that will facilitate greater effi ciency and enhance services. However, it also results in greater complexity in network operations.

e distinction between customer and carrier is blurring. is years OFC/NFOEC (Opti-cal Fiber Conference/National Fiber Optics Engineers Conference) in Los Angeles, Calif., U.S.A., from 4-8 March will feature a plenary talk by Googles Milo Medin, who will discuss his companys experiences in optical networking. A signifi cant fraction of all optical links are used for back-plane connections in data centers and in high-performance computers because the compactness and capacity of optical communication has become indispensible in the design of large data-handling systems. Greg Papadopoulos will deliver a plenary talk discussing the design of an exascale computer.

e recent earthquake and tsunami disaster in Japan reminded us that sophisticated hard-ware and softwareand all the glorious services they enablecan be quickly brought to a halt, leaving face-to-face conversation as the only option for communication. A plenary talk by Isao Sugino of Japans Ministry of Internal Aff airs and Communications will discuss the damage and the restoration of service in Japan as well as some of the many lessons that were learned about disaster recovery and disaster-resistant design.

is article is organized to provide highlights of all aspects of optical networks. It will start with networks, then look at applications and services, and conclude with components. e discussion is a collection of contributions from the organizers of OFC/NFOEC, which is the largest forum on optical communications. For more information about the conference, visit www.ofcnfoec.org.

Access networksFiber to the x (FTTx, where x can be home, premises, business, curb, etc.) has been deployed in many countries around the world, especially in East Asia and North America. Time division multiplexing (TDM) passive optical networks (PONs) such as ITU-T-standardized Gigabit PON (GPON) or IEEE-standardized 1G Ethernet PON (EPON) has been deployed widely in these regions. Subscriber numbers are rapidly increasing as the deployed technology becomes more cost-eff ective by incorporating advances in the endpoint electronics as well as the outside-plant optical components and processes.

In many countries, providers want to evolve to next-generation access platforms such as 10G PON1, next-generation PON2, 10G-EPON or wave-division multiplexing (WDM) systems. ere is much interest among optical engineers in fi guring out which platform to deploy; this will be explored in one of the conference workshops. Soon to be released commercially are XG-PON and 10G-EPON, which have smooth migration scenarios and good backward compatibil-ity and coexistence with the deployed PON.

Farther in the future are 100G-class PONs with fl exible bandwidth allocation, such as WDM-stacked TDM-PONs and orthogonal frequency-division multiplexed PONs with advanced modulation formats that use recent digital signal processing technology. e use of large-capacity

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PONs, wide-area PONs and large-split PONs is expected to reduce the opera-tors capital expenditure and operating expense. It is important to achieve a large optical budgetthrough, for example, burst-mode amplification or cost-effective coherent detection techniques.

We anticipate that the fiber-optic community will be tremendously interested in next-generation mobile backhaul networks. As mobile applica-tions explode, and the density of mobile base stations increases to approach that of PON optical network units, the use of high capacity PONs for mobile back-haul becomes attractive. That will drive research into synchronizing techniques and achieving low delay for access net-works, and it will also lead to the conver-gence of wired and wireless services.

Among the important issues to be addressed in invited talks are how to adequately monitor and protect PONs and to reduce power consumption in networks. The conference will also include reports on the status of fiber to the premises in Africa and South Amer-ica; recent experiences and plans going forward in Germany and the United States; and an update on Chinas experi-ence. Workshops will explore mobile backhaul and green networking. Other topics to be explored include the drivers of the explosion in bandwidth needs from residential and business subscrib-ers, the architecture options within the home to enable Gigabit bandwidths, and business applications for PONs.

Beyond 100 terabits/secondAt last years OFC/NFOEC, meeting participants demonstrated 100-Tbit/s fiber transmission capacity. But its unclear where we will go from here: Further incremental improvements in error-correcting codes, fiber loss and core area, and perhaps usable bandwidth are unlikely to provide even a tenfold increase in capacity. Yet traffic growth trends suggest that this expansion will be needed within 5 to 10 years. The beyond-100-Tb/s symposium will con-sider technologies and techniques that may allow a solution to this dilemma.

innovations in services, including recent enhancements in private-line connectiv-ity between data centers and large enter-prise sites, Internet connectivity, mobile communications and video delivery. The expanded use of cloud technologies, which allow customers to acquire and discard resources instantly, has been facilitated by network virtualizationas George Rouskas will discuss during a conference tutorial.

Recent core transport technology advances include deployment of multi-degree reconfigurable optical add/drop multiplexer (ROADM) technologies to realize large-scale all-optical core networks. The offloading of traffic from the transport layer (higher) to the opti-cal layer (lower) can reduce expensive optical-electrical/electrical-optical (OE/EO) conversions and minimize power consumption. Packet-aware trans-port that uses optical channel data unit (ODU) cross-connect systems has also been developed to allow more flexible sub-lambda level grooming.

The imminent standardization of flexible-grid WDM systems will allow for spectral efficiency to be enhanced due to the allocation of channel bandwidth in order to match data-transport demands. It will also allow for grooming at the optical level. At a conference workshop, speakers and attendees will discuss this hot topic and its impact on system performance as well as networking, transmission and component technolo-gies. Equipment and component vendors and network operators will deliver their visions of the future and highlight the challenges of new technologies, which will include flexible and automated recon-figuration, failure detection and recovery, network upgradeability, ease of network planning, control and management, and overall cost and power efficiency.

Datacom and computercomIn the summer of 2011, the U.S. Depart-ment of Energy issued a Request for Information to find out more about whether various suppliers could build an exa-scale (1018 operations per second) supercomputer within the next decade.

Widespread adoption of single-mode optics in data centers may be driven by increases in WDM capability, extended reach and the prospect of optically switched networks.

Spatial multiplexing, with and with-out multiple-input multiple-output (MIMO) signal processing, seems to be a promising solution to this problem, as demonstrated by the 2011 reports of two independent 100-Tbit/s class 7-core fiber systems. The symposium will include a discussion of the theoretical limitations on capacity and techniques for bringing the benefit of optical amplification to spatially multiplexed systems.

Digital transmissionTransport capacity scaling and the utmost flexibility of the network are at the heart of concurrent optical transmis-sion systems research. Topics include digi-tal signal processing, increased spectral efficiency transmission, enhanced impair-ment mitigation and spatial multiplexing using MIMO techniques. Researchers are reporting exciting results on higher-order quadrature amplitude modulation, software-defined transponders, forward error correction, polarization-dependent transmission impairments, free-space communications through the turbulent atmosphere, parametric processing and quantum communications, all of which will be subjects of invited talks at the conference. In-depth tutorials by Sebas-tien Bigo and Sander Jansen will review coherent long-haul fiber transmission and advanced multi-carrier modulation.

Core networksCore transport networks are continu-ally evolving in response to relentless traffic increases, economic pressures and

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The request explicitly calls for advances in optical technologies that will be required to support a 3.2-Tb/s bidirec-tional processor module input/output at power efficiencies of only a few pJ/bit.

The challenges presented by these aggressive targets highlight on a grand scale key trends in the data communica-tions and computer interconnects field: the drive toward ever-higher speeds while power and the cost of optical links are simultaneously reduced. A tuto-rial by Alan Benner will illustrate the system design challenges associated with these ambitious specifications for optics in supercomputers. Beyond high-end computing systems, data centers are also becoming increasingly more intercon-nected in order to maximize perfor-mance and reconfigurabilitya trend that also motivates the development of new architectures and underpinning optical technologies.

Widespread adoption of single-mode optics in data centers may be driven by increases in WDM capabil-ity, extended reach and the prospect of optically switched networks. Until then, multi-mode optics continues to be a successful incumbent technology. These issuesand the role of optics in data centerswill be examined in a work-shop with a panel of industry experts and a tutorial by Amin Vahdat of The Univer-sity of California San Diego/Google.

Optical network applications and services

Societys continuing need for bandwidth is driving new services into networks. In addition, services and networks are becoming more dynamic, and they need to support multi-layer demands, neces-sitating that more work be done on the control plane and that new requirements be added.

Thus, it is critical that the research community keep an eye on the new services and optical needs that are emerging, including cloud services, distributed computing and low-cost wireless backhaul. Two invited talks at the conference will focus on some very

Market Watch and the Service Provider SummitThe Market Watch program at the con-ference presents an ecosystem view, link-ing the complex relationships between carriers, system vendors and component suppliers. In addition to discussing the latest technology, the speakers will describe the drivers of market demand, product uptake and roadmaps. A state of the industry panel will provide an overview. Two application-centric panels will focus on high-speed access: PON and mobile broadband. The two technology-centric panels will look at what is enabled by advanced integrated photonics and 100G transmission, respectively, across applications ranging from supercomputers, data centers, and inter-office and core networks.

The Service Provider Summit at OFC/NFOEC is a forum that enables leading service providers to share their vision with their peers and to engage with the research and vendor communi-ties. In a keynote address, Stuart Elby will describe Verizons target network architecture based on the needs of cloud computing as a service. Then, a panel will discuss efforts to flatten hierarchi-cal network architectures in order to reduce cost. Operators from around the world will compare their perspectives and experiences based on their different circumstances. A second panel will look at what the role of the network could or should become in the future, given the rise of social media as a dominant application set.

FiberA massive global interest is focused on bypassing the capacity limits of current fibers by developing radically new forms of transmission fiberin particular multicore and multimode fibers for spatial division multiplexing. This could increase significantly the number of information channels in a single strand of fiber, requiring new approaches to fiber design, fabrication and character-ization. Ji Wang will present a tutorial on current and emerging approaches to

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high-tech emerging services. A tutorial on OpenFlow will help to explore some of what this might mean to network designers in terms of bandwidth and new requirements.

Service/data center providers and equipment suppliers alike are looking at ways to efficiently deploy their equipment so that it will be ready for new services. At the same time, they want to prevent the scenario in which a glut of expensive equipment is sitting in wait. Optimizing multi-layer networks is a challenge, with many ways of making the layers work and blending packet technologies and optical technologies together.

Finding ways to best support these networks and meet the service needs is very dependent on the mix of services, the costs of the interfaces and equip-ment, and the view of how the future will evolve. Some competing methods include packet-aware layer 1 networks, optical transport network (OTN) switching, generalized multi-protocol label switching (GMPLS)-based control planes, etc. The tradeoffs of the various designs, and each carriers view of their drivers and economics is key to helping equipment suppliers and component suppliers do the right development for the future. At this years conference, China Telecomm, Korea Telecomm, AT&T and Telefonica will all share their network drivers and designs in a series of invited talks.

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Evgeny Dianov will deliver a tutorial on doped amplifiers operating outside the C and L bands.

Optical devices for switching, filtering and signal compensationSilicon photonics became a hot topic a few years ago, when researchers real-ized that passive optical devices could be made with the ubiquitous complementary metal-oxide semiconductor processing. Today, the technology is poised to have a large impact on optical interconnects by providing low cost, high data rates and low power consumption. Recent progress in optical devices and systems is enabling cost-effective, agile ROADM archi-tectures for optical networks, working towards gridless ROADM.

Researchers have made much progress in developing advanced format modu-lators by using thin-film polymers, as well as hybrid configurations with silica planar lightwave circuits (PLCs) and LiNbO3 (LN) phase modulators. At the conference, Gianlorenzo Masini will review silicon photonic transceivers for optical interconnects, and the progress

fiber fabrication, and Vincent Lecouche will do likewise on fiber characterization techniques with an emphasis on installed cables. Spatial-division multiplexing issues will also be covered in a work-shop and special symposium.

A more near-term approach to increasing fiber capacity is to reduce nonlinearity by increasing the mode area, as discussed by Marianne Bigot-Astruc. An alternative is to attempt to reduce both nonlinearity and loss with hollow-core photonic band gap fibers (PBGFs), as described by Fran-cesco Poletti. Solid-core PBGF variants continue to be incorporated in device applications due to the in-line filtering, dispersion and nonlinearity control they offer; this will be reviewed by Thomas Alkeskjold. Researchers are also intense-ly interested in fibers that use non-silica glasses and/or that incorporate addi-tional materials into their structure. They offer a host of new opportunities in telecommunications, sensors and lasers. Jean Luc Adam will describe recent progress in chalcogenide fibers, while Ayman Abouraddy discusses the incredible advances that have been made in multimaterial fibers and their most exciting applications.

Fiber and waveguide devicesThe economic rationale of multi-mode and multi-core systems relies on their amplifiers. These amplifiers must offer adequate performance at a cost lower than the multiple single-mode amplifiers they replace. Therefore, they are a critical focus of research.

Researchers are very interested in amplifiers that operate outside the gain bandwidth of erbium-doped silica as well as phase-sensitive amplifiers and alternative approaches to increasing fiber capacity. Recent experimental results suggest that the latter may provide a modest improvement in system per-formance. Peter Andrekson, Radan Slavik, Colin McKinstrie and Bill Kuo will discuss different aspects of these amplifiers and parametric amplifiers in general. Peter Krummrich will discuss multi-mode/multi-mode amplifiers, and

that has been made towards commer-cialization. Roel Baets will talk about various silicon photonics integration platforms, while Jean-marc Fedeli will review the latest developments in silicon photonics devices and integration.

Tom Koch will do an exhaustive review of III-V and silicon photonics in a tutorial. A workshop will assess the impact of silicon photonics on network architecture. Tom Strasser will explore approaches for gridless ROADMs, while Toshio Watanabe will discuss silica-based PLC transponder aggregators for color-less, direction-less, and contention-less ROADMs. Takashi Goh will address flexible format modulators using PLC LN hybrid technology, and Raluca Dinus will discuss new approaches, including small form-factor, thin-film polymer modula-tors for telecom applications.

PlasmonicsThe exciting field of plasmonics may provide a solution for next-generation chip-scale optical interconnects. This rela-tively new discipline has been progressing rapidly. It relies on the propagation of electromagnetic waves along a metal-dielectric interface. It offers strong mode confinement with, in principle, high pho-tonic integration densities and low energy consumption. Exascale processors will require optical interconnects with unprec-edented metrics in these properties.

The conference will explore this technology in a symposium. Pioneers of the field will discuss challenges and opportunities across all relevant aspects of plasmonic interconnects, spanning from plasmonic circuit fabrication up to system-level applications. Sergey Bozhevolnyi will present an overview of plasmonic waveguide platforms and their prospects for applications in the datacom industry. Anatolyi Zayats will review the field of active plasmonics for compen-sating the high plasmonic propagation losses and enabling the manipulation of plasmons. Marc Brongersma will discuss the fundamental principles of plasmons, outlining their potential to act as the next-generation interconnect platform. Finally, Jung Jin Ju will review the data

(Top) The end of a hollow-core photonic band-gap fiber. (Bottom) Details of the structure, which, when compared to solid-core fibers, offers the possibility of lower loss, lower nonlinearity and lower effective index, providing lower transmission delay.

Courtesy of Marco Petrovich, Southampton University

20 m

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transmission characteristics of long-range plasmonic waveguides.

Optoelectronic devices and photonic integration

Each of the following factors is driving the development of photonic integration circuits (PICs) for core networks: the trend toward phase-dependent modula-tion formats and increasing capacity, the anticipated rise of 400G and the need for a small footprint. New generations of optoelectronic devices and PICs offer flexibility in wavelength, bandwidth and modulation formats. Photonic integration is becoming increasingly important in short-reach applications because data-cen-ter operators rely on optics to transport huge amounts of data. Microprocessor manufacturers may soon follow suit.

There is rapidly growing interest in components that are adapted to the new multi-core or spatial-mode multiplexing schemes. As always, we see continuous improvement in the energy consumption, speed and package density of existing concepts. Rajeev Ram will provide an overview of the newest developments in silicon photonic integrated circuits, while Di Lang will focus on the integration of optical sources into silicon. A workshop will examine the challenges of packag-ing and assembly of PICs, a crucial topic ignored too often by chip researchers.

PICs, whether hybrid or mono-lithic, and whether they are based on silicon, InP or a polymercan only be as good as the components that are being integrated. The conference will feature reports on improvements in such well-known concepts as vertical-cavity surface-emitting lasers (M.C. Amann), high-power photo-diodes (Jin-Wee Shi) or polymer modulators (Alan Willner), as well as very early stage concepts such as nanolasers (Constance Chang-Hasnain, Shun Lien Chuang).

Transmission subsystems and network elementsIncreasing data rates and capacities as well as ever more complex modulation formats are placing severe demands on

however, there has been a concentrated effort to develop compact, integrated, nonlinear optical waveguides to take their place. The growing prevalence of efficient, multilevel modulation formats is both a challenge and an opportunity for optical signal processing systems.

Recent demonstrations of phase-sensitive optical amplification to reduce impairment from optical amplifier noise and demonstrations of optical regenera-tion of phase-modulated signals have generated extreme interest in all-optical processing. The increasing demand for high-bandwidth wireless communica-tion is motivating the greater use of millimeter-wave communication bands in the range of 60 to 100 GHz.

Optical fiber technologies are being explored to meet the challenges of generating, modulating, transmit-ting, processing and detecting these mm-wave signals. The conference will feature invited talks devoted to non-linear optical processing systems in optical fiber and silicon waveguides as well as a workshop seeking to address which material system will prove to be the best for nonlinear signal process-ing. Another workshop will consider future applications for all-optical signal processing in multi-level systems. The invited program will also include con-tent on optical sampling, microwave photonic filtering and optical tech-niques for mm-wave generation.

This article is just a snapshot of the state of optical communications in the autumn of 2011. The field is advancing so rapidly that new advances will be made by the time this article appears in print. To stay up to date, be sure to reg-ister for OFC/NFOEC 2012 conference in March. Visit www.ofcnfoec.org for more information. Well see you there! t

Contributors include Nikola Alic, Solomon Assefa, Keren Bergman, Yun Chung, Mehran Esfandiari, Hans-Martin Foisel, Scott Hamilton, Robert Jopson (virgin@alcatel-lucent.com), Karen Liu, Ed Murphy, Thomas Murphy, Vincent O'Byrne, David Plant, Nikos Pleros, Steve Plote, David Richardson, Ken-ichi Sato, Martin Schell, Clint Schow, Vishnu

Shukla, Robert Tkach, Kathy Tse, Peter Winzer and Naoto Yoshimoto.

The growing prevalence of efficient, multilevel modulation formats is both a challenge and an opportunity for optical signal processing systems.

Member

underlying technologies. Clock recovery and jitter tolerance are critical, analog-to-digital/digital-to-analog conversion technology is being pushed beyond the state-of-the-art, and multilevel modula-tion formats have become important as signal-to-noise ratios are squeezed, as has post-detection spectral shaping in the electrical domain.

The conference will include invited talks on each of these underlying tech-nologies by Han Sun, Markus Weber, S. Chandrasekhar and Gabriella Bosco, respectively. In addition, Maurice OSullivan will discuss methods for reaching 400G/1T on a single chan-nel based on high spectral efficiency and enabling subsystem concepts. Data centers will require new optical sub-systems; this topic will be addressed by Casimir DeCusatis. In tutorials, Stephan ten Brink, Andreas Leven and Bogdan Szafraniec will discuss two extremely important technologieserror correc-tion and performance monitoring. Power consumption, an increasingly important metric, will be addressed in a workshop that discusses the feasibility of a 3-Watt, 100G transponder.

Optical processing and analog subsystemsAs data rates increase in optical net-works, the cost per channel of OE and EO conversion increases while that of all-optical processing remains more or less constant. This has generated interest in the latter technology. Nonlinear fiber has provided the best performance for signal processing in the past. Recently,