BT makes plans for continued traffic growth in its core
Part 1
Kevin Smith: “A lot of the work we are doing with the trials have demonstrated we can scale our networks gracefully rather than there being a brick wall of a problem.”
BT is confident that its core network will accommodate the expected IP traffic growth for the next decade. Traffic in BT’s core is growing at between 35 and 40 percent annually, compared to the global average growth rate of 20 to 30 percent. BT attributes the higher growth to the rollout of fibre-based broadband across the UK.
The telco is deploying 100-gigabit wavelengths in high-traffic areas of its network. “These are key sites where we're running out of wavelengths such that we need to implement higher-speed ones,” says Kevin Smith, research leader for BT’s transport networks. The operator is now trialling 200-gigabit wavelengths using polarisation multiplexing, 16-quadrature amplitude modulation (PM-16QAM).
Adopting higher-order modulation increases capacity and spectral efficiency but at the expense of a loss in system performance which can be significant.
Systems vendors use polarisation-multiplexed, quadrature phase-shift keying (PM-QPSK) for 100-gigabit wavelengths. Moving to PM-16QAM doubles the bits on the wavelength but the received data has less tolerance to noise. The result is a 6-decibel loss compared to PM-QPSK, such that the transmission distance drops to a quarter. If PM-QPSK spans a 4,000km link, using PM-16QAM the reach on the same link is only 1,000km.
The transmitted capacity can also be increased by using pulse-shaping at the transmitter to cram a wavelength into a narrower channel. BT’s existing optical network uses fixed 50GHz-wide channels. But in a recent network trial with Huawei, a 3 terabit super-channel was transmitted over a 360km link using a flexible grid.
The super-channel comprised 15 channels, each carrying 200 gigabit using PM-16QAM. Using the flexible grid, each carrier occupied a 33.5GHz channel, increasing fibre capacity by a factor of 1.5 compared to a 50GHz fixed-grid. “For 16-QAM, it [33.5GHz] is pretty close to the limit,” says Smith.
Increasing the baud rate is the most structurally-efficient way to accommodate the high speed
Another way to boost the carrier’s data as well as reduce system cost is to up the signalling rate. Current optical transport systems use a 30Gbaud symbol rate. Here, two carriers each using PM-16QAM are needed to deliver 400 gigabit. Doubling the symbol rate to 60Gbaud enables a single 400 gigabit wavelength. Doubling the baud rate also halves a platform’s transponder count, reducing the overall cost-per-bit, and increases platform density.
“Increasing the baud rate is the most structurally-efficient way to accommodate the high speed,” says Smith. Going to 16QAM increases the data that is carried but at the expense of reach. By increasing the baud rate, reach can be extended while also keeping the modulation rate at a lower level, he says.
BT says it is seeing signs of such ‘flexrate’ transponders that can adapt modulation format and baud rate. “This is a very interesting area we can mine,” says Smith. The fundamental driver is about reducing cost but also giving BT more flexibility in its network, he says.
Traffic growth
Coping with traffic growth is a constant challenge, says BT.
“I’m not worried about a capacity crunch,” says Smith. “A lot of the work we are doing with the trials have demonstrated we can scale our networks gracefully rather than there being a brick wall of a problem.”
The operator is confident that 25 to 30 terabit of traffic can be squeezed into the C-band using flexgrid and narrower bands. Beyond that, BT says broadening the spectral window using additional spectral bands such as the L-band could boost a fibre’s capacity to 100 terabit. Vendors are already looking at extending the spectral window, says BT.
Sliceable transponders
BT is also part of longer-term research exploring an extension to the ‘flexrate' transponder, dubbed the sliceable bit rate variable transponder (S-BVT).
“It is very much early days but the idea is to put multiple modulators on the same big super transponder so that it can kick out super-channels that can be provisioned on demand,” says Andrew Lord, head of optical research at BT.
The large multi-terabit super-channel would be sent out and sliced further down the network by flexible grid wavelength-selective switches such that parts of the super-channel would end up at different destinations. “You don’t need all that capacity to go to one other node but you might need it to go to multiple nodes,” says Lord.
Such a sliceable transponder promises several benefits. One is an ability to keep repartitioning the multi-terabit slice based on demand. “It is a good thing if we see that kind of dynamics happening, but not fast dynamics,” says Lord. The repartitioning would more likely be occasional, adding extra capacity between nodes based on demand. Accordingly, the sliced multi-terabit super-channel would end up at fewer destinations over time.
The sliceable transponder concept also promises cost reduction through greater component integration.
BT stresses this is still early research but such a transponder could end up in the network in five years’ time.
Space-division multiplexing
Another research area that promises to increase significantly the overall capacity of a fibre is space-division multiplexing (SDM).
SDM promises to boost the capacity by a factor of between 10 and 100 through the adoption of parallel transmission paths. The simplest way to create such parallel paths is to bundle several standard single-mode fibres in a cable. But speciality fibre could also be used, either multi-core or multi-mode.
BT says it is not researching spatial multiplexing.
”I’m very much more interested in how we use the fibre we have already got,” says Lord. The priority is pushing channels together as close as possible and getting the 25 terabit figure higher, as well as exploring the L-band. “That is a much more practical way to go forward,” says Lord.
However, BT welcomes the research into SDM. “What it [SDM] is pushing into the industry is a knowledge about how to do integration and the expertise that comes out of that is still really valid,” says Lord. “As it is, I don’t see how it fits.”
Finisar adds silicon photonics to its technology toolkit
- Finisar revealed its in-house silicon photonics design capability at ECOC
- The company also showed its latest ROADM technologies: a dual wavelength-selective switch and a high-resolution optical channel monitor.
- Also shown was an optical amplifier that spans 400km fibre links
These two complementary technologies [VCSELs and silicon photonics] work well together as we think about the next-generation Ethernet applications.
Rafik Ward
Finisar demonstrated at ECOC its first optical design implemented using silicon photonics. The photonic integrated circuit (PIC) uses a silicon photonics modulator and receiver and was shown operating at 50 Gigabit-per-second.
The light source used with the PIC was a continuous wave distributed feedback (DFB) laser. One Finisar ECOC demonstration showed the eye diagram of the 50 Gig transmitter using non-return-to-zero (NRZ) signalling. Separately, a 40 Gig link using this technology was shown operating error-free over 12km of single mode fibre.
"Finisar, and its fab partner STMicroelectronics, surprised the market with the 50 Gig silicon photonics demonstration,” says Daryl Inniss, practice leader of components at Ovum.
"This, to our knowledge, was the first public demonstration of silicon photonics running at such a high speed," says Rafik Ward, vice president of marketing at Finisar. However, the demonstrations were solely to show the technology's potential. "We are not announcing any new products," he says.
Potential applications for the PIC include the future 50 Gig IEEE Ethernet standard, as well as a possible 40 Gig serial Ethernet standard. "Also next-generation 400 Gig Ethernet and 100 Gig Ethernet using 50 Gig lanes," says Ward. "All these things are being discussed within the IEEE."
Jerry Rawls, co-founder and chairman of Finisar, said in an interview a year ago that the company had not developed any silicon photonics-based products as the technology had not shown any compelling advantage compared to its existing optical technologies.
Now Finisar has decided to reveal its in-house design capability as the technology is at a suitable stage of development to show to the industry. It is also timely, says Ward, given the many topics and applications being discussed in the standards work.
The company sees silicon photonics as part of its technology toolkit available to its engineers as they tackle next-generation module designs.
Finisar unveiled a vertical-cavity surface-emitting laser (VCSEL) operating at 40 Gig at the OFC show held in March. The 40 Gig VCSEL demonstration also used NRZ signalling. IBM has also published a technical paper that used Finisar's VCSEL technology operating at 50 Gbps.
"What we are trying to do is come up with solutions where we can enable a common architecture between the short wave and the long wave optical modules," says Ward. "These two complementary technologies [VCSELs and silicon photonics] work well together as we think about the next-generation Ethernet applications."
Cisco Systems, also a silicon photonics proponent, was quoted in the accompanying Finisar ECOC press release as being 'excited' to see Finisar advancing the development of silicon photonics technology. "Cisco is our biggest customer," says Ward. "We see this as a significant endorsement from a very large user of optical modules." Cisco acquired silicon photonics start-up Lightwire for $271 million in March 2012.
ROADM technologies
Finisar also demonstrated two products for reconfigurable optical add/ drop multiplexers (ROADM): a dual configuration wavelength-selective switch (WSS) and an optical channel monitor (OCM).
The dual-configuration WSS is suited to route-and-select ROADM architectures.
Two architectures are used for ROADMs: broadcast-and-select and route-and-select. With broadcast-and-select, incoming channels are routed in the various directions using a passive splitter that in effect makes copies of the incoming signal. To route signals in the outgoing direction, a 1xN WSS is used. However, due to the optical losses of the splitters, such an architecture is used for low node-degree applications. For higher-degree nodes, the optical loss becomes a barrier, such that a WSS is also used for the incoming signals, resulting in the route-and-select architecture. A dual-configuration WSS thus benefits a route-and-select ROADM design.
Finisar's WSS module is sufficiently slim that it occupies a single-chassis slot, unlike existing designs that require two. "It enables system designers to free up slots for other applications such as transponder line cards inside their chassis," says Ward.
The dual WSS modules support flexible grid and come in 2x1x20, 2x1x9 and 2x8x12 configurations. "There are some architectures being discussed for add/ drop that would utilise the WSS in that [2x8x12] configuration," says Ward.
The ECOC demonstrations included different traffic patterns passing through the WSS, as well as attenuation control and the management of super-channels.
Finisar also showed an accompanying high-resolution OCM that also occupies a single-chassis slot. The OCM can resolve the spectral power of channels as narrow as 6.25GHz. The OCM, a single-channel device, can scan a fibre's C-band in 200ms.
A rule of thumb is that an OCM is used for each WSS. A customer often monitors channels on a single fibre, says Ward, and must pick which fibres to monitor. The OCM is typically connected to each fibre or to an optical switch to scan multiple fibres.
"People are looking to use the spectrum in a fibre in a much more optimised way," says Ward. The advent of flexible grid and super-channels requires a much tighter packing of channels. "So, being able to see and identify all of the key elements of these channels and manage them is going to become more and more difficult," he says, with the issue growing in importance as operators move to line speeds greater than 100 Gig.
Finisar also used the ECOC show to demonstrate repeater-less transmission using an amplifier that can span 400km of fibre. Such an amplifier is used in harsh environments where it is difficult to build amplifier huts. The amplifier can also be used for certain submarine applications known as 'festooning' where the cable follows a coastline and returns to land each time amplification is required. Using such a long-span amplifier reduces the overall hops back to the coast.
ClariPhy samples a 200 Gigabit coherent DSP-ASIC
The CL20010 is the first of ClariPhy's LightSpeed-II family of coherent digital signal processing ASICs (DSP-ASICs), manufactured using a 28nm CMOS process. "We believe it is the first 28nm standard product, and leaps ahead of the current generation [DSP-ASIC] devices," says Paul Voois, co-founder and chief strategy officer at ClariPhy.
Paul Voois
ClariPhy has been shipping its 40 Gigabit coherent CL4010 LightSpeed chip since September 2011. Customers using the device include optical module makers Oclaro, NEC and JDSU. "We continue to go into new deployments but it is true that the 40 Gig market is not growing like the 100 Gig market," says Voois.
With the CL20010, Clariphy now joins NTT Electronics (NEL) as a merchant supplier of high-speed coherent silicon. Clariphy has said that the LightSpeed-II devices will address metro, long-haul and submarine.
No longer do the integrators need to buy a separate transmit multiplexer chip
Using an advanced 28nm CMOS process enables greater on-chip integration. The CL20010 includes the transmit and receive DSPs, soft-decision forward error correction, and mixed signal analogue-to-digital and digital-to-analogue converters. "No longer do the integrators need to buy a separate transmit multiplexer chip," says Voois.
The LightSpeed-II silicon also features an on-chip Optical Transport Network (OTN) framer/ mapper and a general-purpose processor. The general purpose processor enables the chip to be more network aware - for example, the state of a link - and support software-defined networking (SDN) in the WAN.
The LightSpeed-II ICs support three modulation schemes - polarisation-multiplexed, bipolar phase-shift keying (PM-BPSK), quadrature phase-shift keying (PM-QPSK) and 16-quadrature amplitude modulation (PM-16-QAM). Using PM-16-QAM, the CL20010 can support 200 Gigabit traffic. "I believe that is also a first for merchant silicon," says Voois.
Having an on-chip framer enables the transmission of two 100 Gigabit clients signals as a 200 Gigabit OTN signal. In turn, combining two CL20010 devices enables a 400 Gig flexible-grid super-channel to be transmitted. The on-chip transmit DSP enables the CL20010 to support flexible grid, with the dual carrier 400 Gigabit super-channel occupying 75GHz rather than 100GHz. The CL20010 can achieve a reach of 3,500km at 100 Gig, and over 600km at 200 and 400 Gig.
ClariPhy has not announced the power consumption of its chips but says that it is also targeting the metro pluggable market. Given that a CFP coherent module consumes up to 32W and that the optics alone consume 12W, a LightSpeed-II metro DSP-ASIC will likely consume 18-20W.
Merchant market
Many of the leading optical transport equipment makers, such as Alcatel-Lucent, Ciena, Cisco Systems, Huawei and Infinera, use their own coherent DSP-ASICs. More recently, Acacia Communications announced a CFP 100 Gig coherent pluggable module that uses its internally developed DSP-ASIC.
Some of the OEMs will continue to develop internal technology but even they can't cover all possible applications
ClariPhy says that despite the bulk of the 100 Gigabit coherent ports shipped use internally developed designs, there are signs that the market is moving towards adopting merchant silicon. "It doesn't happen all at once," says Voois. "Some of the OEMs will continue to develop internal technology but even they can't cover all possible applications."
He cites coherent silicon for metro networks as an example. Equipment makers are focussed on DSP-ASIC designs that satisfy the most demanding, ultra-long-haul network applications. But such high-performance, high-power chips are not suited for the more cost-conscious, low-power and compact metro requirements.
"Our committed customer base includes a nice spectrum of applications and integration types: OEMs and module vendors; metro, long haul and submarine," says Voois.
General availability of the CL20010 is expected later this year. The company will also be demonstrating the device at OFC 2014.
OFC/NFOEC 2013 industry reflections - Final part
Gazettabyte spoke with Jörg-Peter Elbers, vice president, advanced technology at ADVA Optical Networking about the state of the optical industry following the recent OFC/NFOEC exhibition.
"There were many people in the OFC workshops talking about getting rid of pluggability and the cages and getting the stuff mounted on the printed circuit board instead, as a cheaper, more scalable approach"
Jörg-Peter Elbers, ADVA Optical Networking
Q: What was noteworthy at the show?
A: There were three big themes and a couple of additional ones that were evolutionary. The headlines I heard most were software-defined networking (SDN), Network Functions Virtualisation (NFV) and silicon photonics.
Other themes include what needs to be done for next-generation data centres to drive greater capacity interconnect and switching, and how do we go beyond 100 Gig and whether flexible grid is required or not?
The consensus is that flex grid is needed if we want to go to 400 Gig and one Terabit. Flex grid gives us the capability to form bigger pipes and get those chunks of signals through the network. But equally it allows not only one interface to transport 400 Gig or 1 Terabit as one chunk of spectrum, but also the possibility to slice and dice the signal so that it can use holes in the network, similar to what radio does.
With the radio spectrum, you allocate slices to establish a communication link. In optics, you have the optical fibre spectrum and you want to get the capacity between Point A and Point B. You look at the spectrum, where the holes [spectrum gaps] are, and then shape the signal - think of it as software-defined optics - to fit into those holes.
There is a lot of SDN activity. People are thinking about what it means, and there were lots of announcements, experiments and demonstrations.
At the same time as OFC/NFOEC, the Open Networking Foundation agreed to found an optical transport work group to come up with OpenFlow extensions for optical transport connectivity. At the show, people were looking into use cases, the respective technology and what is required to make this happen.
SDN starts at the packet layer but there is value in providing big pipes for bandwidth-on-demand. Clearly with cloud computing and cloud data centres, people are moving from a localised model to a cloud one, and this adds merit to the bandwidth-on-demand scenario.
This is probably the biggest use case for extending SDN into the optical domain through an interface that can be virtualised and shared by multiple tenants.
"This is not the end of III-V photonics. There are many III-V players, vertically integrated, that have shown that they can integrate and get compact, high-quality circuits"
Network Functions Virtualisation: Why was that discussed at OFC?
At first glance, it was not obvious. But looking at it in more detail, much of the infrastructure over which those network functions run is optical.
Just take one Network Functions Virtualisation example: the mobile backhaul space. If you look at LTE/ LTE Advanced, there is clearly a push to put in more fibre and more optical infrastructure.
At the same time, you still have a bandwidth crunch. It is very difficult to have enough bandwidth to the antenna to support all the users and give them the quality of experience they expect.
Putting networking functions such as cacheing at a cell site, deeper within the network, and managing a virtualised session there, is an interesting trend that operators are looking at, and which we, with our partnership with Saguna Networks, have shown a solution for.
Virtualising network functions such as cacheing, firewalling and wide area network (WAN) optimisation are higher layer functions. But as you do that, the network infrastructure needs to adapt dynamically.
You need orchestration that combines the control and the co-ordination of the networking functions. This is more IT infrastructure - server-based blades and open-source software.
Then you have SDN underneath, supporting changes in the traffic flow with reconfiguration of the network infrastructure.
There was much discussion about the CFP2 and Cisco's own silicon photonics-based CPAK. Was this the main silicon photonics story at the show?
There is much interest in silicon photonics not only for short reach optical interconnects but more generally, as an alternative to III-V photonics for integrated optical functions.
For light sources and amplification, you still need indium phosphide and you need to think about how to combine the two. But people have shown that even in the core network you can get decent performance at 100 Gig coherent using silicon photonics.
This is an interesting development because such a solution could potentially lower cost, simplify thermal management, and from a fab access and manufacturing perspective, it could be simpler going to a global foundry.
But a word of caution: there is big hype here too. This is not the end of III-V photonics. There are many III-V players, vertically integrated, that have shown that they can integrate and get compact, high-quality circuits.
You mentioned interconnect in the data centre as one evolving theme. What did you mean?
The capacities inside the data centre are growing much faster than the WAN interconnects. That is not surprising because people are trying to do as much as possible in the data centre because WAN interconnect is expensive.
People are looking increasingly at how to integrate the optics and the server hardware more closely. This is moving beyond the concept of pluggables all the way to mounted optics on the board or even on-chip to achieve more density, less power and less cost.
There were many people in the OFC workshops talking about getting rid of pluggability and the cages and getting the stuff mounted on the printed circuit board instead, as a cheaper, more scalable approach.
"Right now we are running 28 Gig on a single wavelength. Clearly with speeds increasing and with these kind of developments [PAM-8, discrete multi-tone], you see that this is not the end"
What did you learn at the show?
There wasn't anything that was radically new. But there were some significant silicon photonics demonstrations. That was the most exciting part for me although I'm not sure I can discuss the demos [due to confidentiality].
Another area we are interested in revolves around the ongoing IEEE work on short reach 100 Gigabit serial interfaces. The original objective was 2km but they have now honed in on 500m.
PAM-8 - pulse amplitude modulation with eight levels - is one of the proposed solutions; another is discrete multi-tone (DMT). [With DMT] using a set of electrical sub-carriers and doing adaptive bit loading means that even with bandwidth-limited components, you can transmit over the required distances. There was a demo at the exhibition from Fujitsu Labs showing DMT over 2km using a 10 Gig transmitter and receiver.
This is of interest to us as we have a 100 Gigabit direct detection dense WDM solution today and are working on the product evolution.
We use the existing [component/ module] ecosystem for our current direct detect solution. These developments bring up some interesting new thoughts for our next generation.
So you can go beyond 100 Gigabit direct detection?
Right now we are running 28 Gig on a single wavelength. Clearly with speeds increasing and with these kind of developments [PAM-8, DMT], you see that this is not the end.
Part 1: Software-defined networking: A network game-changer, click here
Part 2: OFC/NFOEC 2013 industry reflections, click here
Part 3: OFC/NFOEC 2013 industry reflections, click here
Part 4: OFC/NFOEC industry reflections, click here
OFC/NFOEC 2013 product round-up - Part 2
Second and final part
- Custom add/drop integrated platform and a dual 1x20 WSS module
- Coherent receiver with integrated variable optical attenuator
- 100/200 Gigabit coherent CFP and 100 Gigabit CFP2 roadmaps
- Mid-board parallel optics - from 150 to over 600 Gigabit.
- 10 Gigabit EPON triplexer
Add/drop platform and wavelength-selective switches
Oclaro announced an add/drop routing platform for next-generation reconfigurable optical add/drop multiplexers (ROADMs). The platform, which supports colourless, directionless, contentionless (CDC) and flexible grid ROADMs, can be tailored to a system vendor's requirements and includes such functions as cross-connect switching, arrayed amplifiers and optical channel monitors.
"If we make the whole thing [add/drop platform], we can integrate in a much better way"
Per Hansen, Oclaro
After working with system vendors on various line card designs, Oclaro realised there are significant benefits to engineering the complete design.
"You end up with a controller controlling other controllers, and boxes that get bolted on top of each other; a fairly unattractive solution," says Per Hansen, vice president of product marketing, optical networks solutions at Oclaro. "If we make the whole thing, we can integrate in a much better way."
The increasingly complex nature of the add/drop card is due to the dynamic features now required. "You have support for CDC and even flexible grid," says Hansen. "You want to have many more features so that you can control it remotely in software."
A consequence of the add/drop's complexity and automation is a need for more amplifiers. "It is a sign that the optics is getting mature; you are integrating more functionality within your equipment and as you do that, you have losses and you need to put amplifiers into your circuits," says Hansen.
Oclaro continues to expand its amplifier component portfolio. At OFC/NFOEC, the company announced dual-chip uncooled pump lasers in the 10-pin butterfly package multi-source agreement (MSA) it announced at ECOC 2012.
"We have two 500mW uncooled pumps in a single package with two fibres, each pump being independently controlled," says Robert Blum, director of product marketing for Oclaro's photonic components unit.
The package occupies half the space and consumes less than half the power compared to two standard discrete thermo-electrically cooled pumps. The dual-chip pump lasers will be available as samples in July 2013.
Oclaro gets requests to design 4- and 8-degree nodes; with four- and eight-degree signifying the number of fibre pairs emanating from a node.
"Depending on what features customers want in terms of amplifiers and optical channel monitors, we can design these all the way down to single-slot cards," says Hansen. Vendors can then upgrade their platforms with enhanced switching and flexibility while using the same form factor card.
Meanwhile, Finisar demonstrated at OFC/NFOEC a module containing two 1x20 liquid-crystal-on-silicon-based wavelength-selective switches (WSSes). The module supports CDC and flexible grid ROADMs. "This two-port module supports the next-generation route-and-select [ROADM] architecture; one [WSS] on the add side and one on the drop side," says Rafik Ward, vice president of marketing at Finisar.
100Gbps line side components
NeoPhotonics has added two products to its 100 Gigabit-per-second (Gbps) coherent transport product line.
The first is an coherent receiver that integrates a variable optical attenuator (VOA). The VOA sits in front of the receiver to screen the dynamic range of the incoming signal. "This is even more important in coherent systems as coherent is different to direct detection in that you do not have to optically filter the channels coming in," says Ferris Lipscomb, vice president of marketing at NeoPhotonics.
"That is the power of photonic integration: you do a new chip with an extra feature and it goes in the same package."
Ferris Lipscomb, NeoPhotonics
In a traditional system, he says, a drop port goes through an arrayed waveguide grating which filters out the other channels. "But with coherent you can tune it like a heterodyne radio," says Lipscomb. "You have a local oscillator that you 'beat' against the signal so that the beat frequency for the channel you are tuned to will be within the bandwidth of the receiver but the beat frequency of the adjacent channel will be outside the bandwidth of the receiver."
It is possible to do colourless ROADM drops where many channels are dropped, and using the local oscillator, the channel of interest is selected. "This means that the power coming in can be more varied than in a traditional case," says Lipscomb, depending on how many other channels are present. Since there can be up to 80 channels falling on the detector, the VOA is needed to control the dynamic range of the signal to protect the receiver.
"Because we use photonic integration to make our integrated coherent receiver, we can put the VOA directly on the chip," says Lipscomb. "That is the power of photonic integration: you do a new chip with an extra feature and it goes in the same package."
The VOA integrated coherent receiver is sampling and will be generally available in the third quarter of 2013.
NeoPhotonics also announced a narrow linewidth tunable laser for coherent systems in a micro integrated tunable laser assembly (micro-ITLA). This is the follow-on, more compact version of the Optical Internetworking Forum's (OIF) ITLA form factor for coherent designs.
While the device is sampling now, Lipscomb points out that is it for next-generation designs such that it is too early for any great demand.
Sumitomo Electric Industries and ClariPhy Communications demonstrated 100Gbps coherent CFP technology at OFC/NFOEC.
ClariPhy has implemented system-on-chip (SoC) analogue-to-digital (ADC) and digital-to-analogue (DAC) converter blocks in 28nm CMOS while Sumitomo has indium phosphide modulator and driver technology as well as an integrated coherent receiver, and an ITLA.
The SoC technology is able to support 100Gbps and 200Gbps using QPSK and 16-QAM formats. The companies say that their collaboration will result in a pluggable CFP module for 100Gbps coherent being available this year.
Market research firm, Ovum, points out that the announcement marks a change in strategy for Sumitomo as it enters the long-distance transmission business.
In another development, Oclaro detailed integrated tunable transmitter and coherent receiver components that promise to enable 100 Gigabit coherent modules in the CFP2 form factor.
The company has combined three functions within the transmitter. It has developed a monolithic tunable laser that does not require an external cavity. "The tunable laser has a high-enough output power that you can tap off a portion of the signal and use it as the local oscillator [for the receiver]," says Blum. Oclaro has also developed a discrete indium-phosphide modulator co-packaged with the laser.
The CFP2 100Gbps coherent pluggable module is likely to have a reach of 80-1,000km, suited to metro and metro regional networks. It will also be used alongside next-generation digital signal processing (DSP) ASICs that will use a more advanced CMOS process resulting in a much lower power consumption .
To be able to meet the 12W power consumption upper limit of the CFP2, the DSP-ASIC will reside on the line card, external to the module. A CFP, however, with its upper power limit of 32W will be able to integrate the DSP-ASIC.
Oclaro expects such an CFP2 module to be available from mid-2014 but there are several hurdles to be overcome.
One is that the next-generation DSP-ASICs will not be available till next year. Another is getting the optics and associated electronics ready. "One challenge is the analogue connector to interface the optics and the DSP," says Blum.
Achieving the CFP2 12W power consumption limit is non-trivial too. "We have data that the transmitter already has a low enough power dissipation," says Blum.
Board-mounted optics
Finisar demonstrated its board-mounted optical assembly (BOA) running at 28Gbps-per-channel. When Finisar first detailed the VCSEL-based parallel optics engine, it operated at 10Gbps.
The mid-board optics, being aimed at linking chassis and board-to-board interconnect, can be used in several configurations: 24 transmit channels, 24 receive channels or as a transceiver - 12 transmit and 12 receive. When operated at full rate, the resulting data rate is 672Gbps (24x28Gbps) simplex.
The BOA is protocol-agnostic operating at several speeds ranging from 10Gbps to 28Gbps. For example 25Gbps supports Ethernet lanes for 100Gbps while 28Gbps is used for Optical Transport Network (OTN) and Fibre Channel. Overall the mid-board optics supports Ethernet, PCI Express, Serial Attached SCSI (SAS), Infiniband, Fibre Channel and proprietary protocols. Finisar has started shipping BOA samples.
Avago detailed samples of higher-speed Atlas optical engine devices based on its 12-channel MicroPod and MiniPod designs. The company has extended the channel speed from 10Gbps to 12.5Gbps and to 14Gbps, giving a total bandwidth of 150Gbps and 168Gbps, respectively.
"There is enough of a market demand for applications up to 12.5Gbps that justifies a separate part number," says Sharon Hall, product line manager for embedded optics at Avago Technologies.
The 12x12.5Gbps optical engines can be used for 100GBASE-SR10 (10x10Gbps) as well as quad data rate (QDR) Infiniband. The extra capacity supports Optical Transport Network (OTN) with its associated overhead bits for telecom. There are also ASIC designs that require 12.5Gbps interfaces to maximise system bandwidth.
The 12x14Gbps supports the Fourteen Data Rate (FDR) Infiniband standard and addresses system vendors that want yet more bandwidth.
The Atlas optical engines support channel data rates from 1Gbps. The 12x12.5Gbps devices have a reach of 100m while for the 12x14Gbps devices it is 50m.
Hall points out that while there is much interest in 25Gbps channel rates, the total system cost can be expensive due to the immaturity of the ICs: "It is going to take a little bit of time." Offering a 14Gbps-per-channel rate can keep the overall system cost lower while meeting bandwidth requirements, she says.
10 Gig EPON
Operators want to increase the split ratio - the number of end users supported by a passive optical network - to lower the overall cost.
A PON reach of 20km is another important requirement to operators, to make best use of their central offices housing the optical line terminal (OLT) that serves PON subscribers.
To meet both requirements, the 10G-EPON has a PRX40 specification standard which has a sufficiently high optical link budget. Finisar has announced a 10G-EPON OLT triplexer optical sub-assembly (OSA) that can be used within an XFP module among others that meets the PRX40 specification.
The OSA triplexer supports 10Gbps and 1G downstream (to the user) and 1Gbps upstream. The two downstream rates are needed as not all subscribers on a PON will transition to a 10G-EPON optical network unit (ONU).
To meet the standard, a triplexer design typically uses an externally modulated laser. Finisar has met the specification using a less complex directly modulated laser. The result is a 10G-EPON triplexer supporting a split ratio of 1:64 and higher, and that meets the 20km reach requirement.
Finisar will sell the OSA to PON transceiver makers with production starting first quarter, 2014. Up till now the company has used its designs for its own PON transceivers.
See also:
OFC/NFOEC 2013 product round-up - Part 1, click here
OFC/NFOEC 2013 industry reflections - Part 3
Joe Berthold, vice president of network architecture, Ciena
The two topics that received the most attention, judging from session attendance and discussion in the hallways, were silicon photonics and software-defined networking (SDN). I predict that next year those who wish to capitalise on this popularity wave will be submitting papers on SDN-enabled silicon photonics.
More seriously, though, there remains vigorous debate about the relative importance of III-V integrated optics and silicon photonics, and I look forward to seeing how this evolves in the marketplace.
"Some of the SDN-related talks from the global research and education community were very good. They have been pioneers in making high capacity optical networks dynamic, and we have much to learn from them as they have several years experience building and operating SDNs, even before the term existed."
With respect to SDN and service providers, it is going to be several years before we see a true, SDN-enabled network as there are many other issues that need to be addressed.
This is one of the reasons Ciena is taking a lead role in the Open Networking Foundation's investigation of applying OpenFlow or the like at the optical layers. I thought some of the SDN-related talks from the global research and education community were very good. They have been pioneers in making high capacity optical networks dynamic, and we have much to learn from them as they have several years experience building and operating SDNs, even before the term existed.
"One of the most interesting commercial developments to watch in the coming years related to 100 Gig is the work that has begun on pluggable coherent analogue optical modules"
There was also quite a bit of buzz about 100 Gig deployments. It was nice to hear one of the industry analysts refer to 2013 as the year of 100 Gig as this is an area where Ciena has been quite successful.
I did not see or hear of any dramatic advances reported at the conference. What I did see, in talks and on the show floor, was a broad base of technology development that will lead to increased system density and lower cost and power.
On the client side, many companies showed 100 Gig CFP2 modules, and there was quite a bit of talk and demonstrations of technology building blocks that will lead to even smaller size.
Another optical networking topic that means many different things to different people was flexible grids and flexible transmission formats. From speaking with a number of network operators, it seems there is an appreciation for the future-proofing benefit of flexible grid ROADMs, but a recognition that the spectral efficiency gains to be had are quite limited, especially in a ROADM mesh network. So they are emerging as a nice-to-have feature but not a must-have-at-any-price feature.
Another 'flex' concept is flex-transceivers. The flavour of flex-transceivers that seem by most I spoke with to be practical are those that maintain a fixed baud rate but vary modulation format, say from BPSK to QPSK, 8PSK, 16QAM and perhaps beyond, to fit different distance applications.
I think one of the most interesting commercial developments to watch in the coming years related to 100 Gig is the work that has begun on pluggable coherent analogue optical modules, likely to emerge in a CFP2 form factor. I view this as a major next step the industry will take to reduce the cost and increase the density of coherent interfaces on switches and transmission systems.
The OIF did the industry a great service in pulling together a set of interoperable building blocks that form the photonic foundation of 100 Gig solutions today. The next step is to integrate these pieces and place them in a pluggable module. There is yet no formal project with this goal, but discussions are underway.
Watch this space...
Karen Liu, principal analyst components, Ovum.
There was a real sense of openness to new directions even as a lot of short-term activity continues to focus on getting 100 Gig to full maturity. Instead of pitching their favourite directions, some people actually solicited more ideas.
"One trend to watch is the battle between VCSELs and silicon photonics"
Directions that seemed promising but unformed last year got a bit firmed up. Connections are being made from the application down to the device technology. What had been wacky ideas previously are being taken seriously:
- Optical circuit switching looks like it will have a place in conjunction with Ethernet switching.
- Spatial division multiplexing is the hot research topic. I like the work that Bell Labs is doing, particularly where the add/drop increment ties together multiple cores of the same wavelength so compensation algorithms can take advantage of similar environmental history. This is moving past the physics, to thinking about network architecture.
- Monolithic integration of electronics with photonics. Early stages still and primarily around the drivers. But as this is motivated by power consumption, it seems like a solid direction that will have legs.
One trend to watch is the battle between VCSELs (vertical-cavity surface-emitting lasers) and silicon photonics. Conventional wisdom was that VCSELS were for multi-mode and silicon photonics for single-mode but both have crossed over into the other's space.
Martin Guy, vice-president of product management and technology Teraxion
There were several noteworthy developments. In particular, silicon photonics has started to show its promises as new products are introduced:
- Cisco announced its 100 Gig CPAK transceiver following the Lightwire acquisition
- Kotura showed its 100 Gig WDM QSFP package with only 3.5 W of power consumption.
- Luxtera demonstrated a 100 Gig QSFP package using four fibre pairs, each [fibre] carrying 25Gbps.
- Teraxion introduced its small form factor coherent receiver based on silicon photonics
Silicon photonics was also largely discussed at the technical conference and very impressive results were demonstrated. Most notably, Cisco and Alcatel-Lucent presented results on silicon photonic modulators for metro and long-haul coherent systems with performance comparable to lithium niobate.
Tunable laser technologies on silicon photonics were also presented by companies such as Skorpios and Aurrion during the post-deadline sessions.
"Cisco and Alcatel-Lucent presented results on silicon photonic modulators for metro and long-haul coherent systems with performance comparable to lithium niobate."
All those new silicon photonics technologies could eventually become key building blocks of future highly-integrated transceivers.
Pluggable coherent modules will be a big market opportunity and it is all about density and low power consumption.
At the show, Oclaro demonstrated key milestones to bring to market a CFP2 coherent module by mid-2014 while this product is on the roadmap of all other major transceiver vendors.
From Teraxion’s perspective, our recent acquisition of Cogo Optronics Canada for high-speed modulators is directly in line with this market trend at the modules level where performance, size and low power consumption are key requirements.
Paul Brooks, product line manager for high-speed test solutions, JDSU
The growing confidence in second-generation 100 Gig CFP2s was evident at the show. Many companies, including JDSU, demonstrated robust second-generation 100 Gig modules which will drive confidence across the whole 100 Gig ecosystem to allow cost efficient 100 Gig clients. Our ONT CFP2 test solution was well received and we spent a lot of time demonstrating the features that will enable successful CFP2 deployment.
"Many companies are openly discussing 400 Gig and beyond, the bandwidth demand is there but considerable technology challenges need to be address"
One thing enforced at the show is the continued importance of innovation in test and measurement solutions required by our customers as we move to 100 Gig+ systems.
Many companies are openly discussing 400 Gig and beyond, the bandwidth demand is there but considerable technology challenges need to be address. The intellectual horsepower present at the show allows fruitful and engaging discussions on key topics.
See also:
Part 1: Software-defined networking: A network game-changer, click here
Part 2: OFC/NFOEC industry reflections, click here
Part 4: OFC/NFOEC industry reflections, click here
Part 5: OFC/NFEC 2013 industry reflections, click here
Ciena: Changing bandwidth on the fly
Ciena has announced its latest coherent chipset that will be the foundation for its future optical transmission offerings. The chipset, dubbed WaveLogic 3, will extend the performance of its 100 Gigabit links while introducing transmission flexibility that will trade capacity with reach.
Feature: Beyond 100 Gigabit - Part 1
"We are going to be deployed, [with WaveLogic 3] running live traffic in many customers’ networks by the end of the year"
Michael Adams, Ciena
"This is changing bandwidth modulation on the fly," says Ron Kline, principal analyst, network infrastructure group at market research firm, Ovum. “The capability will allow users to dynamically optimise wavelengths to match application performance requirements.”
WaveLogic 3 is Ciena's third-generation coherent chipset that introduces several firsts for the company.
- The chipset supports single-carrier 100 Gigabit-per-second (Gbps) transmission in a 50GHz channel.
- The chipset includes a transmit digital signal processor (DSP) - which can adapt the modulation schemes as well as shape the pulses to increase spectral efficiency. The coherent transmitter DSP is the first announced in the industry.
- WaveLogic 3's second chip, the coherent receiver DSP, also includes soft-decision forward error correction (SD-FEC). SD-FEC is important for high-capacity metro and regional, not just long-haul and trans-Pacific routes, says Ciena.
The two-ASIC chipset is implemented using a 32nm CMOS process. According to Ciena, the receiver DSP chip, which compensates for channel impairments, measures 18 mm sq. and is capable of 75 Tera-operations a second.
Ciena says the chipset supports three modulation formats: dual-polarisation bipolar phase-shift keying (DP-BPSK), quadrature phase-shift keying (DP-QPSK) and 16-QAM (quadrature amplitude modulation). Using a single carrier, these equate to 50Gbps, 100Gbps and 200Gbps data rates. Going to 16-QAM may increase the data rate to 200Gbps but it comes at a cost: a loss in spectral efficiency and in reach.
"This software programmability is critical for today's dynamic, cloud-centric networks," says Michael Adams, Ciena’s vice president of product & technology marketing.
WaveLogic 3 has also been designed to scale to 400Gbps. "This is the first programmable coherent technology scalable to 400 Gig," says Adams. "For 400 Gig, we would be using a dual-carrier, dual-polarisation 16-QAM that would use multiple [WaveLogic 3] chipsets."
Performance
Ciena stresses that this is a technology not a product announcement. But it is willing to detail that in a terrestrial network, a single carrier 100Gbps link using WaveLogic 3 can achieve a reach of 2,500+ km. "These refer to a full-fill [wavelengths in the C-Band] and average fibre," says Adams. "This is not a hero test with one wavelength and special [low-loss] fibre.”
Metro to trans-Pacific: The different reaches and distances over terrestrial and submarine using Ciena's WaveLogic 3. SC stands for single carrier. Source: Ciena/ Gazettabyte
When the modulation is changed to BPSK, the reach is effectively doubled. And Ciena expects a 9,000-10,000km reach on submarine links.
The same single-carrier 50GHz channel reverting to 16-QAM can transmit a 200Gbps signal over distances of 750-1,000km. "A modulation change [to 16-QAM] and adding a second 100 Gigabit Ethernet transceiver and immediately you get an economic improvement," says Adams.
For 400Gbps, two carriers, each 16-QAM, are needed and the distances achieved are 'metro regional', says Ciena.
The transmit DSP also can implement spectral shaping. According to Ciena, by shaping the signals sent, a 20-30% bandwidth improvement (capacity increase) can be achieved. However that feature will only be fully exploited once networks deploy flexible grid ROADMs.
At OFC/NFOEC. Ciena will be showing a prototype card that will demonstrate the modulation going from BPSK to QPSK to 16-QAM. "We are going to be deployed, running live traffic in many customers’ networks by the end of the year," says Adams.
Analysis
Sterling Perrin, senior analyst, Heavy Reading
Heavy Reading believes Ciena's WaveLogic 3 is an impressive development, compared to its current WaveLogic 2 and to other available coherent chipsets. But Perrin thinks the most significant WaveLogic 3 development is Ciena’s single-carrier 100Gbps debut.
Until now, Ciena has used two carriers within a 50GHz, each carrying 50Gbps of data.
"The dual carrier approach gave Ciena a first-to-market advantage at 100Gbps, but we have seen the vendor lose ground as Alcatel-Lucent rolled out its single carrier 100Gbps system," says Perrin in a Heavy Reading research note. "We believe that Alcatel-Lucent was the market leader in 100Gbps transport in 2011."
Other suppliers, including Cisco Systems and Huawei, have also announced single-carrier 100Gbps, and more single-wavelength 100Gbps announcements will come throughout 2012.
Heavy Reading believes the ability to scale to 400Gbps is important, as is the use of multiple carriers (or super-channels). But 400 Gigabit and 1 Terabit transport are still years away and 100Gbps transport will be the core networking technology for a long time yet.
"The vendors with the best 100G systems will be best-positioned to capture share over the next five years, we believe," says Perrin.
Ron Kline, principal analyst for Ovum’s network infrastructure group.
For Ron Kline, Ciena's announcement was less of a surprise. Ciena showcased WaveLogic 3's to analysts late last year. The challenge with such a technology announcement is understanding the capabilities and how it will be rolled out and used within a product, he says.
"Ciena's WaveLogic 3 is the basis for 400 Gig," says Kline. "They are not out there saying 'we have 400 Gig'." Instead, what the company is stressing is the degree of added capacity, intelligence and flexibility that WaveLogic 3 will deliver. That said, Ciena does have trials planned for 400 Gig this year, he says.
What is noteworthy, says Ovum, is that 400Gbps is within Ciena's grasp whereas there are still some vendors yet to record revenues for 100Gbps.
"Product differentiation has changed - it used to be about coherent," says Kline. "But now that nearly all vendors have coherent, differentiation is going to be determined by who has the best coherent technology."