NeoPhotonics samples its first CFP-DCO products
The company has announced two such CFP Digital Coherent Optics (CFP-DCO) modules: a 100 gigabit-per-second (Gbps) module and a dual-rate 100Gbps and 200Gbps one.
“Our rationale [for entering the CFP-DCO market] is we have all the optical components and the [merchant coherent] DSPs are now becoming available,” says Ferris Lipscomb (pictured), vice president of marketing at NeoPhotonics. “It is possible to make this product without developing your own custom DSP, with all the expense that entails.”
-DCO versus -ACO
The pluggable transceiver line-side market is split between Digital Coherent Optics and Analog Coherent Optics (ACO) modules.
Optical module makers are already supplying the more compact CFP2 Analog Coherent Optics (CFP2-ACO) transceivers. The CFP2-ACO integrates the optics only, with the accompanying coherent DSP-ASIC chip residing on the line card. The CFP2-ACO suits system vendors that have their own custom DSP-ASICs and can offer differentiated, higher-transmission performance while choosing the optics in a compact pluggable module from several suppliers.
In contrast, the CFP-DCO suits more standard deployments, and for those end-customers that do not want to be locked into a single vendor and a proprietary DSP. The -DCO is also easier to deploy. In China, currently undertaking large-scale 100-gigabit optical transport deployments, operators want a module that can be deployed in the field by a relatively unskilled technician. Deploying an ACO requires an engineer to perform the calibration due to the analogue interface between the module and the DSP, says NeoPhotonics.
The DCO also suits those systems vendors that do not have their own DSP and do not want to source a merchant coherent DSP and implement the analogue integration on the line card.
Our rationale [for entering the CFP-DCO market] is we have all the optical components and the [merchant coherent] DSPs are now becoming available
One platform, two products
The two announced ClearLight CFP-DCO products are a 100 gigabit-per-second (Gbps) module implemented using polarisation multiplexing, quadrature phase-shift keying modulation (PM-QPSK), and a module that supports both 100Gbps and 200Gbps using PM-QPSK and 16 quadrature amplitude modulation (PM-16QAM), respectively.
The two modules share the same optics and DSP-ASIC. Where they differ is in the software loaded onto the DSP and the host interface used. The lower-speed module has a 4 by 25-gigabit interface whereas the 200-gigabit CFP-DCO uses an 8 by 25-gigabit-wide interface. “The 100-gigabit CFP-DCO plugs into existing client-side slots whereas the 200-gigabit CFPs have to plug into custom designed equipment slots,” says Lipscomb.
The 100-gigabit CFP-DCO has a reach of 1,000km plus and has a power consumption under 24W. Lipscomb points out that the actual specs including the power consumption are negotiated on a customer-by-customer basis. The 200-gigabit CFP-DCO has a reach of 500km.
NeoPhotonics says it is using a latest-generation 16nm CMOS merchant DSP. NTT Electronics (NEL) and Clariphy have both announced 16nm CMOS coherent DSPs.
“We are designing to be able to second-source the DSP,” says Lipscomb. “There are currently only two merchant suppliers but there are others that have developments but are not yet at the point where they would be in the market.”
The CFP-DCO modules also support flexible grid that can fit a carrier within the narrower 37.5GHz channel to increase overall transmission capacity sent across a fibre’s C-band.
NeoPhotonics’s 100Gbps CFP-DCO is already sampling and it expected to be generally available in mid-2017, while the 200Gbps CFP-DCO is expected to be available one-quarter later.
“For 200-gigabit, you need to have customers building slots,” says Lipscomb. “For 100-gigabit, there are lots of slots available that you can plug into; 200-gigabits will take a little bit longer.”
NeoPhotonics’ CFP-DCO delivers the line rate used by the Voyager white box packet optical switch being developed as part of the Telecom Infra Project backed by Facebook and ten operators including Deutsche Telekom and SK Telecom. But the one-rack-unit Voyager packet optical platform uses four 5"x7" modules not pluggable CFP-DCOs to achieve the total line rate of 800Gbps.
Roadmap
NeoPhotonics is developing coherent module designs that will use higher baud rates than the standard 32-35 gigabaud (Gbaud), such as 45Gbaud and 64Gbaud.
The company also plans to develop a CFP2-DCO. Such a module is expected around 2018 once lower-power DSP-ASICs become available that can fit within the 12W power envelope of the CFP2. Such merchant DSP-ASICs will likely be implemented in a more advanced CMOS process such as 12nm or even 7nm.
Acacia Communications is already sampling a CFP2-DCO. Acacia designs its own silicon photonics-based optics and the coherent DSP-ASIC.
NeoPhotonics is also considered future -ACO designs beyond the CFP2 such as the CFP8, the 400-gigabit OSFP form factor and even the CFP4. “We are studying it but we don't know yet which directions things are going to go,” says Lipscomb.
Corrected on Dec 22nd. The Voyager box does not use pluggable CFP-DCO modules.
Ciena brings data analytics to optical networking
- Ciena's WaveLogic Ai coherent DSP-ASIC makes real-time measurements, enabling operators to analyse and adapt their networks.
- The DSP-ASIC supports 100-gigabit to 400-gigabit wavelengths in 50-gigabit increments.
- The WaveLogic Ai will be used in Ciena’s systems from 2Q 2017.
Ciena has unveiled its latest generation coherent DSP-ASIC. The device, dubbed WaveLogic Ai, follows Ciena’s WaveLogic 3 family of coherent chips which was first announced in 2012. The Ai naming scheme reflects the company's belief that its latest chipset represents a significant advancement in coherent DSP-ASIC functionality.
Helen XenosThe WaveLogic Ai is Ciena's first DSP-ASIC to support two baud rates, 35 gigabaud for fixed-grid optical networks and 56 gigabaud for flexible-grid ones. The design also uses advanced modulation schemes to optimise the data transmission over a given link.
Perhaps the most significant development, however, is the real-time network monitoring offered by the coherent DSP-ASIC. The data will allow operators to fine-tune transmissions to adapt to changing networking conditions.
“We do believe we are taking that first step towards a more automated network and even laying the foundation for the vision of a self-driving network,” says Helen Xenos, director, portfolio solutions marketing at Ciena.
All those assumptions of the past [based on static traffic] aren't holding true anymore
Network Analytics
Conservative margins are used when designing links due to a lack of accurate data regarding the optical network's status. This curtails the transmission capacity that can be sent since a relatively large link margin is used. In turn, cloud services and new applications mean networks are being exercised in increasingly dynamic ways. “The business environment has changed a little bit,” says Joe Cumello, vice president, portfolio marketing at Ciena. “All those assumptions of the past [based on static traffic] aren't holding true anymore.”
Ciena is being asked by more and more operators to provide information as to what is happening within their networks. Operators want real-time data that they can feed to analytics software to make network optimisation decisions. "Imagine a network where, instead of those rigid assumptions in place, run on manual spreadsheets, the network is making decisions on its own," says Cumello.
WaveLogic Ai performs real-time analysis, making available network measurements data every 10ms. The data can be fed through application programming interfaces to analytics software whose output is used by operators to adapt their networks.
Joe Cumello
The network parameters collected include the transmitter and receiver optical power, polarisation channel and chromatic dispersion conditions, error rates and transmission latency. In addition, the DSP-ASIC separates the linear and non-linear noise components of the signal-to-noise ratio. An operator will thus see what the network margin is and allow links to operate more closely to the limit, improving transmissions by exploiting the WaveLogic Ai's 50-gigabit transmission increments.
"Maybe there are only a few wavelengths in the network such that the capacity can be cranked up to 300 gigabits. But as more and more wavelengths are added, if you have the tools, you can tell the operator to adjust,” says Xenos. “This helps them get to the next level; something that has not been available before.”
WaveLogic Ai
The WaveLogic Ai's lower baud rate - 35 gigabaud - is a common symbol rate used by optical transmission systems today. The baud rate is suited to existing fixed-grid networks based on 50GHz-wide channels. At 35 gigabaud, the WaveLogic Ai supports data rates from 100 to 250 gigabits-per-second (Gbps).
The second, higher 56 gigabaud rate enables 400Gbps single-wavelength transmissions and supports data rates of 100 to 400Gbps in increments of 50Gbps.
Using 35 gigabaud and polarisation multiplexing, 16-ary quadrature amplitude modulation (PM-16QAM), a 200-gigabit wavelength has a reach is 1,000km.
With 35-gigabaud and 16-QAM, effectively 8 bits per symbol are sent.
In contrast, 5 bits per symbol are used with the faster 56 gigabaud symbol rate. Here, a more complex modulation scheme is used based on multi-dimensional coding. Multi-dimensional formats add additional dimensions to the four commonly used based on real and imaginary signal components and the two polarisations of light. The higher dimension formats may use more than one time slot, or sub-carriers in the frequency domain, or even use both techniques.
For the WaveLogic Ai, the 200-gigabit wavelength at 56 gigabaud achieves a reach of 3,000km, a threefold improvement compared to using a 35 gigabaud symbol rate. The additional reach occurs because fewer constellation points are required at 56 gigabaud compared to 16-QAM at 35 gigabaud, resulting in a greater Euclidean distance between the constellation points. "That means there is a higher signal-to-noise ratio and you can go a farther distance," says Xenos. "The way of getting to these different types of constellations is using a higher complexity modulation and multi-dimensional coding."
We do believe we are taking that first step towards a more automated network and even laying the foundation for the vision of a self-driving network
The increasingly sophisticated schemes used at 56 gigabaud also marks a new development whereby Ciena no longer spells out the particular modulation scheme used for a given optical channel rate. At 56 gigabaud, the symbol rate varies between 4 and 10 bits per symbol, says Ciena.
The optical channel widths at 56 gigabaud are wider than the fixed grid 50GHz. "Any time you go over 35 gigabaud, you will not fit [a wavelength] in a 50GHz band," says Xenos.
The particular channel width at 56 gigabaud depends on whether a super-channel is being sent or a mesh architecture is used whereby channels of differing widths are added and dropped at network nodes. Since wavelengths making up a super-channel go to a single destination, the channels can be packed more closely, with each channel occupying 60GHz. For the mesh architecture, guard bands are required either side of the wavelength such that a 75GHz optical channel width is used.
The WaveLogic Ai enables submarine links of 14,000km at 100Gbps, 3,000km links at 200Gbps (as detailed), 1,000km at 300Gbps and 300km at 400Gbps.
Hardware details
The WaveLogic Ai is implemented using a 28nm semiconductor process known as fully-depleted silicon-on-insulator (FD-SOI). "This has much lower power than a 16nm or 18nm FinFET CMOS process," says Xenos. (See Fully-depleted SOI vs FinFET)
Using FD-SOI more than halves the power consumption compared to Ciena’s existing WaveLogic 3 coherent devices. "We did some network modelling using either the WaveLogic 3 Extreme or the WaveLogic 3 Nano, depending on what the network requirements were," says Xenos. "Overall, it [the WaveLogic Ai] was driving down [power consumption] more than 50 percent." The WaveLogic 3 Extreme is Ciena's current flagship coherent DSP-ASIC while the Nano is tailored for 100-gigabit metro rates.
Other Ai features include support for 400 Gigabit Ethernet and Flexible Ethernet formats. Flexible Ethernet is designed to support Ethernet MAC rates independent of the Ethernet physical layer rate being used. Flexible Ethernet will enable Ciena to match the client signals as required to fill up the variable line rates.
Further information:
SOI Industry Consortium, click here
STMicroelectronics White Paper on FD-SOI, click here
Other coherent DSP-ASIC announcements in 2016
Infinera's Infinite Capacity Engine, click here
Nokia's PSE-2, click here
Enabling coherent optics down to 2km short-reach links
Interview 5: Chris Doerr
Chris Doerr admits he was a relative latecomer to silicon photonics. But after making his first silicon photonics chip, he was hooked. Nearly a decade later and Doerr is associate vice president of integrated photonics at Acacia Communications. The company uses silicon photonics for its long-distance optical coherent transceivers.
Chris Doerr in the lab
Acacia Communications made headlines in May after completing an initial public offering (IPO), raising approximately $105 million for the company. Technology company IPOs have become a rarity and are not always successful. On its first day of trading, Acacia’s shares opened at $29 per share and closed just under $31.
Although investors may not have understood the subtleties of silicon photonics or coherent DSP-ASICs for that matter, they noted that Acacia has been profitable since 2013. But as becomes clear in talking to Doerr, silicon photonics plays an important role in the company’s coherent transceiver design, and its full potential for coherent has still to be realised.
Bell Labs
Doerr was at Bell Labs for 17 years before joining Acacia in 2011. He spent the majority of his time at Bell Labs making first indium phosphide-based optical devices and then also planar lightwave circuits. One of his bosses at Bell Labs was Y.K. Chen. Chen had arranged a silicon photonics foundry run and asked Doerr if he wanted to submit a design.
What hooked Doerr was silicon photonics’ high yields. He could assume every device was good, whereas when making complex indium phosphide designs, he would have to test maybe five or six devices before finding a working one. And because the yields were high, he could focus more on the design aspects. “Then you could start to make very complex designs - devices with many elements - with confidence,” he says.
Another benefit was that the performance of the silicon photonic circuit matched closely its simulation results. “Indium phosphide is so complex,” he says. “You have to worry about the composition effects and the etching is not that precise.” With silicon, in contrast, the dimensions and the refractive index are known with precision. “You can simulate and design very precisely, which made it [the whole process] richer,” says Doerr.
Silicon photonics is a disruptive technology because of its ability to integrate so many things together and still be high yield and get the raw performance
After that first wafer run, Doerr continued to design both planar lightwave circuits and indium phosphide components at Bell Labs. But soon it was solely silicon photonics ICs.
Doerr views Acacia’s volume production of an integrated coherent transceiver - the transmit and receive optics on the one chip - with a performance that matches discrete optical designs, as one of silicon photonics’ most notable achievements to date.
With a discrete component coherent design, you can use the best of each material, he explains, whereas with an integrated design, compromises are inevitable. “You can’t optimise the layer structure; each component has to share the wafer structure,” he says. Yet with silicon photonics, the design space is so powerful and high-yielding, that these compromises are readily overcome.
Doerr also describes a key moment when he realised the potential of silicon photonics for volume manufacturing.
He was reading an academic paper on grating couplers, a structure used to couple fibres to waveguides. “You can only make that in silicon photonics because you need a high vertical [refractive] index contrast,” he says. Technically, a grating coupler can also be made in indium phosphide but the material has to be cut from under the waveguide; this leaves the waveguide suspended in air.
When he first heard of grating couplers he assumed the coupling efficiency would be of the order of a few percent whereas in practice it is closer to 85 percent. “That is when I realised it is a very powerful concept,” he says.
Integration is key
Doerr pauses before giving measured answers to questions about silicon photonics. Nor does his enthusiasm for silicon photonics blinker him to the challenges it faces. However, his optimism regarding the technology’s future is clear.
“Silicon photonics is a disruptive technology because of its ability to integrate so many things together and still be high yield and get the raw performance,” he says. In the industry, silicon photonics has proven itself for such applications as metro telecommunications but it faces significant competition from established technologies such as indium phosphide. It will require more channels to be integrated for the full potential of silicon photonics as a disruption technology to emerge, says Doerr.
Silicon photonics also has an advantage on indium phosphide in that it can be integrated with electronic ICs using 2.5D and 3D packaging, saving cost, footprint, and power. “If you are in the same material system then such system-in-package is easier,” he says. Also, silicon photonic integrated circuits do not require temperature control, unlike indium phosphide modulators, which saves power.
Areas of focus
One silicon photonics issue is the need for an external laser. For coherent transceivers, it is better to separate the laser from the high-speed optics due to the fact that the coherent DSP-ASIC and the photonic chips are hot and the laser requires temperature control.
For applications such as very short reach links, silicon photonics needs a laser source and while there are many options to integrate the laser to the chip, a clear winning approach has yet to emerge. “Until a really low cost solution is found, it precludes silicon from competing with really low-cost solutions like VCSELs for very short reach applications,” he says.
Silicon photonic chip volumes are still many orders of magnitude fewer than those of electronic ICs. But Acacia says foundries already have silicon photonics lines running, and as these foundries ramp volumes, costs, production times, and node-sizes will continually improve.
Opportunities
The adoption of silicon photonics will increase significantly as more and more functions are integrated onto devices. For coherent designs, Doerr can foresee silicon photonics further reducing the size, cost and power consumption, making them competitive with other optical transceiver technologies for distances as short as 2km.
“You can use high-order formats such as 256-QAM and achieve very high spectral efficiency,” says Doerr. Using such a modulation scheme would require fewer overall lasers to achieve significant transport capacities, improving the cost-per-bit performance for applications such as data centre interconnect. “Fibre is expensive so the more you can squeeze down a fibre, the better,” he says.
Doerr also highlights other opportunities for silicon photonics, beyond communications. Medical applications is one such area. He cites a post-deadline paper at OFC 2016 from Acacia on optical coherent tomography which has similarities with the coherent technology used in telecom.
Longer term, he sees silicon photonics enabling optical input/ output (I/O) between chips. As further evolutionary improvements are achieved, he can see lasers being used externally to the chip to power such I/O. “That could become very high volume,” he says.
However, he expects 3D stacking of chips to take hold first. “That is the easier way,” he says.
OIF document aims to spur line-side innovation
The CFP2-ACO. Source: OIF
The pluggable CFP2-ACO houses the coherent optics, known as the analogue front end. The components include the tuneable lasers, modulation, coherent receiver, and the associated electronics - the drivers and the trans-impedance amplifier. The Implementation Agreement also includes the CFP2-ACO's high-speed electrical interface connecting the optics to the coherent DSP chip that sits on the line card.
One historical issue involving the design of innovative optical components into systems has been their long development time, says Ian Betty of Ciena, and OIF board member and editor of the CFP2-ACO Implementation Agreement. The lengthy development time made it risky for systems vendors to adopt such components as part of their optical transport designs. Now, with the CFP2-ACO, much of that risk is removed; system vendors can choose from a range of CFP2-ACO suppliers based on the module's performance and price.
Implementation Agreement
Much of the two-year effort developing the Implementation Agreement involved defining the management interface to the optical module. "This is different from our historical management interfaces," says Betty. "This is much more bare metal control of components."
For 7x5-inch and 4x5-inch MSA transponders, the management interface is focused on system-level parameters, whereas for the CFP2-ACO, lower-level optical parameters are accessible given the module's analogue transmission and receive signals.
"A lot of the management is to interrogate information about power levels, or adjusting transfer functions with pre-emphasis, or adjusting drive levels on drivers internal to the device, or asking for information: 'Have you received my RF signal?'," says Betty. "It is very much a lower-level interface because you have separated between the DSP and the optical interface."
The Implementation Agreement's definitions for the CFP2-ACO are also deliberately abstract. The optical technology used is not stated, nor is the module's data rate. "The module has no information associated with the system level - if it is 16-QAM or QPSK [modulation] or what the dispersion is," says Betty.
This is a strength, he says, as it makes the module independent of a data rate and gives it a larger market because any coherent ASIC can make use of this analogue front end. "It lets the optics guys innovate, which is what they are good at," says Betty.
Innovation
The CFP2-ACO is starting to be adopted in a variety of platforms. Arista Networks has added a CFP2-ACO line card to its 7500 data centre switches while several optical transport vendors are using the module for their data centre interconnect platforms.
One obvious way optical designers can innovate is by adding flexible modulation formats to the CFP2-ACO. Coriant's Groove G30 data centre interconnect platform uses CFP2-ACOs that support polarisation-multiplexed, quadrature phase-shift keying (PM-QPSK), polarisation-multiplexed, 8-state quadrature amplitude modulation (PM-8QAM) and PM-16QAM, delivering 100, 150 and 200 gigabit-per-second transmission, respectively. Coriant says the CFP2-ACOs it uses are silicon photonics and indium phosphide based.
Cisco Systems uses CFP2-ACO modules for its first data centre interconnect product, the NCS 1002. The system can use a CFP2-ACO with a higher baud rate to deliver 250 gigabit-per-second using a single carrier and PM-16QAM.
Ian BettyThe CFP2-ACO enables a much higher density line-side solution than other available form factors. The Groove G30, for example, fits eight such modules on one rack-unit line card. "That is the key enabler that -ACOs give," says Betty.
And being agnostic to a particular DSP, the CFP2-ACO enlarges the total addressable market. Betty hopes that by being able to sell the CFP2-ACO to multiple systems vendors, the line-side optical module players can drive down cost.
Roadmap
Betty says that the CFP2-ACO may offer the best route to greater overall line side capacity rather than moving to a smaller form factor module in future. He points out that in the last decade, the power consumption of the optics has gone down from some 16W to 12W. He does not foresee the power consumption coming down further to the 6W region that would be needed to enable a CFP4-ACO. "The size [of the CFP4] with all the technology available is very doable," says Betty. "But there is not an obvious way to make it [the optics] 6W."
The key issue is the analogue interface which determines what baud rate and what modulation or level of constellation can be put through a module. "The easiest way to lump all that together is with an implementation penalty for the optical front end," says Betty. "If you make the module smaller, you might have a higher implementation penalty, and with this penalty, you might not be able to put a higher constellation through it."
In other words, there are design trade-offs: the data rates supported by the CFP2 modules may achieve a higher overall line-side rate than more, smaller modules, each supporting a lower maximum data rate due to a higher implementation penalty.
"What gets you the ultimate maximum density of data rate through a given volume?" says Betty. "It is not necessarily obvious that making it smaller is better."
Could a CFP2-ACO support 32-QAM and 64-QAM? "The technical answer is what is the implementation penalty of the module?" says Betty. This is something that the industry will answer in time.
"This isn't the same as client optics where there is a spec, you do the spec and there are no brownie points for doing better than the spec, so all you can compete on is cost," says Betty. "Here, you can take your optical innovation and compete on cost, and you can also compete by having lower implementation penalties."
Coriant's 134 terabit data centre interconnect platform
“We have several customers that have either purpose-built data centre interconnect networks or have data centre interconnect as a key application riding on top of their metro or long-haul networks,” says Jean-Charles Fahmy, vice president of cloud and data centre at Coriant.
Jean-Charles Fahmy
Each card in the platform is one rack unit (1RU) high and has a total capacity of 3.2 terabit-per-second, while the full G30 rack supports 42 such cards for a total platform capacity of 134 terabits. The G30's power consumption equates to 0.45W-per-gigabit.
The card supports up to 1.6 terabit line-side capacity and up to 1.6 terabit of client side interfaces. The card can hold eight silicon photonics-based CFP2-ACO (analogue coherent optics) line-side pluggables. For the client-side optics, 16, 100 gigabit QSFP28 modules can be used or 20 QSFP+ modules that support 40 or 4x10 gigabit rates.
Silicon photonics
Each CFP2-ACO supports 100, 150 or 200 gigabit transmission depending on the modulation scheme used. For 100 gigabit line rates, dual-polarisation, quadrature phase-shift keying (DP-QPSK) is used, while dual-polarisation, 8 quadrature amplitude modulation (DP-8-QAM) is used for 150 gigabit, and DP-16-QAM for 200 gigabit.
A total of 128 wavelengths can be packed into the C-band equating to 25.6 terabit when using DP-16-QAM.
It [the data centre interconnect] is a dynamic competitive market and in some ways customer categories are blurring. Cloud and content providers are becoming network operators, telcos have their own data centre assets, and all are competing for customer value
Coriant claims the platform can achieve 1,000 km using DP-16-QAM, 2,000 km using 8-QAM and up to 4,000 km using DP-QPSK. That said, the equipment maker points out that the bulk of applications require distances of a few hundred kilometers or less.
This is the first detailed CFP2-ACO module that supports all three modulation formats. Coriant says it has worked closely with its strategic partners and that it is using more than one CFP2-ACO supplier.
Acacia is one silicon photonics player that announced at OFC 2015 a chip that supports 100, 150 and 200 gigabit rates however it has not detailed a CFP2-ACO product yet. Acacia would not comment whether it is supplying modules for the G30 or whether it has used its silicon photonics chip in a CFP2-ACO. The company did say it is providing its silicon photonics products to a variety of customers.
“Coriant has been active in engaging the evolving ecosystem of silicon photonics,” says Fahmy. “We have also built some in-house capability in this domain.” Silicon photonics technology as part of the Groove G30 is a combination of Coriant’s own in-house designs and its partnering with companies as part of this ecosystem, says Fahmy: “We feel that this is one of the key competitive advantages we have.”
The company would not disclose the degree to which the CFP2-ACO coherent transceiver is silicon photonics-based. And when asked if the different CFP2-ACOs supplied are all silicon photonics-based, Fahmy answered that Coriant’s supply chain offers a range of options.
Oclaro would not comment as to whether it is supplying Coriant but did say its indium-phosphide CFP2-ACO has a linear interface that supports such modulation formats as BPSK, QPSK, 8-QAM and 16-QAM.
So what exactly does silicon photonics contribute?
“Silicon photonics offers the opportunity to craft system architectures that perhaps would not have been possible before, at cost points that perhaps may not have been possible before,” says Fahmy.
Modular design
Coriant has used a modular design for its 1RU card, enabling data centre operators to grow their system based on demand and save on up-front costs. For example, Coriant uses ‘sleds’, trays that slide onto the card that host different combinations of CFP2-ACOs, coherent DSP functionality and client-side interface options.
“This modular architecture allows pay-as-you-grow and, as we like to say, power-as-you-grow,” says Fahmy. “It also allows a simple sparing strategy.”
The Groove G30 uses a merchant-supplied coherent DSP-ASIC. In 2011, NSN invested in ClariPhy the DSP-ASIC supplier, and Coriant was founded from the optical networking arm of NSN. The company will noy say the ratio of DSP-ASICs to CFP2-ACOs used but it is possible that four DSP-ASICs serve the eight CFP2-ACOs, equating to two CFP2-ACOs and a DSP-ASIC per sled.
“Web-scale customers will most probably start with a fully loaded system, while smaller cloud players or even telcos may want to start with a few 10 or 40 gigabit interfaces and grow [capacity] as required,” says Fahmy.
Open interfaces
Coriant has designed the G30 with two software environments in mind. “The platform has a full set of open interfaces allowing the product to be integrated into a data centre software-defined networking (SDN) environment,” says Bill Kautz, Coriant’s director of product solutions. “We have also integrated the G30 into Coriant’s network management and control software: the TNMS network management and the Transcend SDN controller.”
Coriant also describes the G30 as a disaggregated transponder/ muxponder platform. The platform does not support dense WDM line functions such as optical multiplexing, ROADMs, amplifiers or dispersion compensation modules. Accordingly, Groove is designed to interoperate with Coriant’s line-system options.
Groove can also be used as a source of alien wavelengths over third-party line systems, says Fahmy. The latter is a key requirement of customers that want to use their existing line systems.
“It [the data centre interconnect] is a dynamic competitive market and in some ways customer categories are blurring,” says Fahmy. “Cloud and content providers are becoming network operators, telcos have their own data centre assets, and all are competing for customer value.”
Further information
IHS hosted a recent webinar with Coriant, Cisco and Oclaro on 100 gigabit metro evolution, click here
OFC 2015 digest: Part 1
- Several vendors announced CFP2 analogue coherent optics
- 5x7-inch coherent MSAs: from 40 Gig submarine and ultra-long haul to 400 Gig metro
- Dual micro-ITLAs, dual modulators and dual ICRs as vendors prepare for 400 Gig
- WDM-PON demonstration from ADVA Optical Networking and Oclaro
- More compact and modular ROADM building blocks
JDSU also showed a dual-carrier coherent lithium niobate modulator capable of 400 Gig for long-reach applications. The company is also sampling a dual 100 Gig micro-ICR also for multiple sub-channel applications.
Avago announced a micro-ITLA device using its external cavity laser that has a line-width less than 100kHz. The micro-ITLA is suited for 100 Gig PM-QPSK and 200 Gig 16-QAM modulation formats and supports a flex-grid or gridless architecture.
Verizon readies its metro for next-generation P-OTS
Verizon is preparing its metro network to carry significant amounts of 100 Gigabit traffic and has detailed its next-generation packet-optical transport system (P-OTS) requirements. The operator says technological advances in 100 Gig transmission and new P-OTS platforms - some yet to be announced - will help bring large scale 100 Gig deployments in the metro in the next year or so.
Glenn Wellbrock
The operator says P-OTS will be used for its metro and regional networks for spans of 400-600km. "That is where we have very dense networks," says Glenn Wellbrock, director of optical transport network architecture and design at Verizon. "The amount of 100 Gig is going to be substantially higher than it was in long haul."
Verizon announced in April that it had selected Fujitsu and Coriant for a 100 Gig metro upgrade. The operator has already deployed Fujitsu's FlashWave 9500 and the Coriant 7100 (formerly Tellabs 7100) P-OTS platforms. "The announcement [in April] is to put 100 Gig channels in that embedded base," says Wellbrock.
The operator has 4,000 reconfigurable optical add/ drop multiplexers (ROADMs) across its metro networks worldwide and all support 100 Gig channels. But the networks are not tailored for high-speed transmission and hence the cost of 100 Gig remains high. For example, dispersion compensation fibre, and Erbium-doped fibre amplifiers (EDFA) rather than hybrid EDFA-Raman are used for the existing links. "It [the network] is not optimised for 100 Gig but will support it, and we are using [100 Gig] on an as-needed basis," says Wellbrock.
The metro platform will be similar to those used for Verizon's 100 Gig long-haul in that it will be coherent-based and use advanced, colourless, directionless, contentionless and flexible-grid ROADMs. "But all in a package that fits in the metro, with a much lower cost, better density and not such a long reach," says Wellbrock.
The amount of 100 Gig is going to be substantially higher than it was in long haul
One development that will reduce system cost is the advent of the CFP2-based line-side optical module; another is the emergence of third- or fourth-generation coherent DSP-ASICs. "We are getting to the point where we feel it is ready for the metro," says Wellbrock. "Can we get it to be cost-competitive? We feel that a lot of the platforms are coming along."
The latest P-OTS platforms feature enhanced packet capabilities, supporting carrier Ethernet, multi-protocol label switching - transport profile (MPLS-TP), and high-capacity packet and Optical Transport Network (OTN) switching. Recently announced P-OTS platforms suited to Verizon's metro request-for-proposal include Cisco Systems' Network Convergence System (NCS) 4000 and Coriant's mTera. Verizon says it expects other vendors to introduce platforms in the next year.
Verizon still has over 250,000 SONET elements in its network. Many are small and reside in the access network but SONET also exists in its metro and regional networks. The operator is keen to replace the legacy technology but with such a huge number of installed network elements, this will not happen overnight.
Verizon's strategy is to terminate the aggregated SONET traffic at its edge central offices so that it only has to deal with large Ethernet and OTN flows at the network node. "We plan to terminate the SONET, peel out the packets and send them in a packet-optimised fashion," says Wellbrock. In effect, SONET is to be stopped from an infrastructure point of view, he says, by converting the traffic for transport over OTN and Ethernet.
SDN and multi-layer optimisation
The P-OTS platform, with its integrated functionality spanning layer-0 to layer-2, will have a role in multi-layer optimisation. The goal of multi-layer optimisation is to transport services on the most suitable networking layer, typically the lowest, most economical layer possible. Software-defined networking (SDN) will be used to oversee such multi-layer optimisation.
However, P-OTS, unlike servers used in the data centre, are specialist rather than generic platforms. "Optical stuff is not generic hardware," says Wellbrock. Each P-OTS platform is vendor-proprietary. What can be done, he says, is to use 'domain controllers'. Each vendor's platform will have its own domain controller, above which will sit the SDN controller. Using this arrangement, the vendor's own portion of the network can be operated generically by an SDN controller, while benefitting from the particular attributes of each vendor's platform using the domain controller.
There is always frustration; we always want to move faster than things are coming about
Verizon's view is that there will be a hierarchy of domain and SDN controllers."We assume there are going to be multiple layers of abstraction for SDN," says Wellbrock. There will be no one, overriding controller with knowledge of all the networking layers: from layer-0 to layer-3. Even layer-0 - the optical layer - has become dynamic with the addition of colourless, directionless, contentionless and flexible-grid ROADM features, says Wellbrock.
Instead, as part of these abstraction layers, there will be one domain that will control all the transport, and another that is all-IP. Some software element above these controllers will then inform the optical and IP domains how best to implement service tasks such as interconnecting two data centres, for example. The transport controller will then inform each layer its particular task. "Now I want layer-0 to do that, and that is my Ciena box; I need layer-1 to do this and that happens to be a Cyan box; and we need MPLS transport to do this, and that could be Juniper," says Wellbrock, pointing out that in this example, three vendor-domains are involved, each with its own domain controller.
Is Verizon happy with the SDN progress being made by the P-OTS vendors?
"There is always frustration; we always want to move faster than things are coming about," says Wellbrock. "The issue, though, is that there is nothing I see that is a showstopper."
Merits and challenges of optical transmission at 64 Gbaud
u2t Photonics announced recently a balanced detector that supports 64Gbaud. This promises coherent transmission systems with double the data rate. But even if the remaining components - the modulator and DSP-ASIC capable of operating at 64Gbaud - were available, would such an approach make sense?
Gazettabyte asked system vendors Transmode and Ciena for their views.
Transmode:
Transmode points out that 100 Gigabit dual-polarisation, quadrature phase-shift keying (DP-QPSK) using coherent detection has several attractive characteristics as a modulation format.
It can be used in the same grid as 10 Gigabit-per-second (Gbps) and 40Gbps signals in the C-band. It also has a similar reach as 10Gbps by achieving a comparable optical signal-to-noise ratio (OSNR). Moreover, it has superior tolerance to chromatic dispersion and polarisation mode dispersion (PMD), enabling easier network design, especially with meshed networking.
The IEEE has started work standardising the follow-on speed of 400 Gigabit. "This is a reasonable step since it will be possible to design optical transmission systems at 400 Gig with reasonable performance and cost," says Ulf Persson, director of network architecture in Transmode's CTO office.
Moving to 100Gbps was a large technology jump that involved advanced technologies such as high-speed analogue-to-digital (A/D) converters and advanced digital signal processing, says Transmode. But it kept the complexity within the optical transceivers which could be used with current optical networks. It also enabled new network designs due to the advanced chromatic dispersion and PMD compensations made possible by the coherent technology and the DSP-ASIC.
For 400Gbps, the transition will be simpler. "Going from 100 Gig to 400 Gig will re-use a lot of the technologies used for 100 Gig coherent," says Magnus Olson, director of hardware engineering.
So even if there will be some challenges with higher-speed components, the main challenge will move from the optical transceivers to the network, he says. That is because whatever modulation format is selected for 400Gbps, it will not be possible to fit that signal into current networks keeping both the current channel plan and the reach.
"From an industry point of view, a metro-centric cost reduction of 100Gbps coherent is currently more important than increasing the bit rate to 400Gbps"
"If you choose a 400 Gigabit single carrier modulation format that fits into a 50 Gig channel spacing, the optical performance will be rather poor, resulting in shorter transmission distances," says Persson. Choosing a modulation format that has a reasonable optical performance will require a wider passband. Inevitably there will be a tradeoff between these two parameters, he says.
This will likely lead to different modulation formats being used at 400 Gig, depending on the network application targeted. Several modulation formats are being investigated, says Transmode, but the two most discussed are:
- 4x100Gbps super-channels modulated with DP-QPSK. This is the same as today's modulation format with the same optical performance as 100Gbps, and requires a channel width of 150GHz.
- 2x200Gbps super-channels, modulated with DP-16-QAM. This will have a passband of about 75GHz. It is also possible to put each of the two channels in separate 50GHz-spaced channels and use existing networks The effective bandwidth will then be 100GHz for a 400GHz signal. However, the OSNR performance for this format is about 5-6 dB worse than the 100Gbps super-channels. That equates to about a quarter of the reach at 100Gbps.
As a result, 100Gbps super-channels are more suited to long distance systems while 200Gbps super-channels are applicable to metro/ regional systems.
Since 200Gbps super-channels can use standard 50GHz spacing, they can be used in existing metro networks carrying a mix of traffic including 10Gbps and 40Gbps light paths.
"Both 400 Gig alternatives mentioned have a baud rate of about 32 Gig and therefore do not require a 64 Gbaud photo detector," says Olson. "If you want to go to a single channel 400G with 16-QAM or 32-QAM modulation, you will get 64Gbaud or 51Gbaud rate and then you will need the 64 Gig detector."
The single channel formats, however, have worse OSNR performance than 200Gbps super-channels, about 10-12 dB worse than 100Gbps, says Transmode, and have a similar spectral efficiency as 200Gbps super-channels. "So it is not the most likely candidates for 400 Gig," says Olson. "It is therefore unclear for us if this detector will have a use in 400 Gigabit transmission in the near future."
Transmode points out that the state-of-the-art bit rate has traditionally been limited by the available optics. This has kept the baud rate low by using higher order modulation formats that support more bits per symbol to enable existing, affordable technology to be used.
"But the price you have to pay, as you can not fool physics, is shorter reach due to the OSNR penalty," says Persson.
Now the challenges associated with the DSP-ASIC development will be equally important as the optics to further boost capacity.
The bundling of optical carriers into super-channels is an approach that scales well beyond what can be accomplished with improved optics. "Again, we have to pay the price, in this case eating greater portions of the spectrum," says Persson.
Improving the bandwidth of the balanced detector to the extent done by u2t is a very impressive achievement. But it will not make it alone into new products, modulators and a faster DSP-ASIC will also be required.
"From an industry point of view, a metro-centric cost reduction of 100Gbps coherent is currently more important than increasing the bit rate to 400Gbps," says Olson. "When 100 Gig coherent costs less than 10x10 Gig, both in dollars and watts, the technology will have matured to again allow for scaling the bit rate, using technology that suits the application best."
Ciena:
How the optical performance changes going from 32Gbaud to 64Gbaud depends largely on how well the DSP-ASIC can mitigate the dispersion penalties that get worse with speed as the duration of a symbol narrows.
BPSK goes twice as far as QPSK which goes about 4.5 times as far as 16-QAM
"I would also expect a higher sensitivity would be needed also, so another fundamental impact," says Joe Berthold, vice president of network architecture at Ciena. "We have quite a bit or margin with the WaveLogic 3 [DSP-ASIC] for many popular network link distances, so it may not be a big deal."
With a good implementation of a coherent transmission system, the reach is primarily a function of the modulation format. BPSK goes twice as far as QPSK which goes about 4.5 times as far as 16-QAM, says Berthold.
"On fibres without enough dispersion, a higher baud rate will go 25 percent further than the same modulation format at half of that baud rate, due to the nonlinear propagation effects," says Berthold. This is the opposite of what occurred at 10 Gigabit incoherent. On fibres with plenty of local dispersion, the difference becomes marginal, approximately 0.05 dB, according to Ciena.
Regarding how spectral efficiency changes with symbol rate, doubling the baud rate doubles the spectral occupancy, says Berthold, so the benefit of upping the baud rate is that fewer components are needed for a super-channel.
"Of course if the cost of the higher speed components are higher this benefit could be eroded," he says. "So the 200 Gbps signal using DP-QPSK at 64 Gbaud would nominally require 75GHz of spectrum given spectral shaping that we have available in WaveLogic 3, but only require one laser."
Does Ciena have an view as to when 64Gbaud systems will be deployed in the network?
Berthold says this hard to answer. "It depends on expectations that all elements of the signal path, from modulators and detectors to A/D converters, to DSP circuitry, all work at twice the speed, and you get this speedup for free, or almost."
The question has two parts, he says: When could it be done? And when will it provide a significant cost advantage? "As CMOS geometries narrow, components get faster, but mask sets get much more expensive," says Berthold.
100 Gigabit and packet optical loom large in the metro
"One hundred Gig metro has become critical in terms of new [operator] wins"
Michael Adams, Ciena
Ciena says operator interest in 100 Gigabit for the metro has been growing significantly.
"One hundred Gig metro has become critical in terms of new [operator] wins," says Michael Adams, vice president of product and technical marketing at Ciena. "Another request is integrated packet switching and OTN (Optical Transport Network) switching to fill those 100 Gig pipes."
The operator CenturyLink announced recently it had selected Ciena's 6500 packet optical transport platform for its network spanning 50 metropolitan regions.
The win is viewed by Ciena as significant given CenturyLink is the third largest telecommunications company in the US and has a global network. "We have already deployed Singapore, London and Hong Kong, and a few select US metropolitans and we are rolling that out across the country," says Adams.
Ciena says CenturyLink wants to offer 1, 10 and 100 Gigabit Ethernet (GbE) services. "In terms of the RFP (request for proposal) process with CenturyLink for next generation metro, the 100 Gigabit wavelength service was key and an important part of the [vendor] selection process."
The vendor offers different line cards based on its WaveLogic 3 coherent chipset depending on a metro or long haul network's specifications. "We firmly believe that 100 Gig coherent in the metro is going to be the way the market moves," says Adams.
At the recent OFC/NFOEC show, Ciena demonstrated WaveLogic 3 based production cards moving between several modulation formats, from binary phase-shift keying (BPSK) to quadrature PSK (QPSK) to 16-QAM (quadrature amplitude modulation).
Ciena showed a 16-QAM-based 400 Gig circuit using two, 200 Gig carriers. "With a flexible grid ROADM, the two [carriers] are pushed together into a spectral grid much less than 100GHz [wide]," says Adams.
The WaveLogic 3 features a transmit digital signal processor (DSP) as well as the receive DSP. "The transmit DSP is key to be able to move the frequencies to much less than 100GHz of spectrum in order to get greater than 20 Terabits [capacity] per fibre," says Adams. "With 88 wavelengths at 100 Gig that is 8.8 Terabits, and with 16-QAM that doubles to 17.6Tbps; we expect at least a [further] 20 percent uplift with the transmit DSP and gridless."
Adams says the company will soon detail the reach performance of its 400 Gig technology using 16-QAM.
It is still early in the market regarding operator demand for 400 Gig transmission. "2013 is the year for 100 Gig but customers always want to know that your platform can deliver the next thing," says Adams. "In the metro regional distances, we believe we can get a 50 percent improvement in economics using 16-QAM." That is because WaveLogic 3 can transmit 100GbE or 10x10GbE in a 50GHz channel, or double that - 2x100GbE or 20x10GbE - using 16-QAM modulation.
The system vendor is also one of AT&T's domain programme suppliers. Ciena will not expand on the partnership beyond saying there is close collaboration between the two. "We give them a lot of insight on roadmaps and on technology; they have a lot of opportunity to say where they would like their partner to be investing," says Adams.
Ciena came top in terms of innovation and leadership in a recent Heavy Reading survey of over 100 operators regarding metro packet-optical. Ciena was rated first, followed by Cisco Systems, Alcatel-Lucent and Huawei. "Our solid packet switching [on the 6500] is why CenturyLink chose us," says Adams.