The many paths to 400 gigabits
The race is on to deliver 400-gigabit optical interfaces in time for the next-generation of data centre switches expected in late 2018.
The industry largely agrees that a four-wavelength 400-gigabit optical interface is most desirable yet alternative designs are also being developed.
Optical module makers must consider such factors as technical risk, time-to-market and cost when choosing which design to back.
Rafik Ward, FinisarUntil now, the industry has sought a consensus on interfaces, making use of such standards bodies as the IEEE to serve the telecom operators.
Now, the volumes of modules used by the internet giants are such that they dictate their own solutions. And the business case for module makers is sufficiently attractive that they are willing to comply.
Another challenge at 400 gigabits is that there is no consensus regarding what pluggable form factor to use.
“There is probably more technical risk in 400 gigabits than any of the historical data-rate jumps we have seen,” says Rafik Ward, vice president of marketing at Finisar.
Shrinking timeframes
One-hundred-gigabit interfaces are now firmly established in the marketplace. It took several generations to achieve the desired module design. First, the CFP module was used, followed by the CFP2. The industry then faced a choice between the CFP4 and the QSFP28 form factors. The QSFP28 ended up winning because the 100-gigabit module met the price, density and performance expectations of the big users - the large-scale data centre players, says Paul Brooks, director of strategy for lab and production at Viavi Solutions.
“The QSFP28 is driving huge volumes, orders of magnitude more than we see with the other form factors,” he says.
There is probably more technical risk in 400 gigabits than any of the historical data-rate jumps we have seen
It was the telcos that initially drove 100-gigabit interfaces, as with all the previous interface speeds. Telcos have rigorous optical and physical media device requirements such that the first 100-gigabit design was the 10km 100GBASE-LR4 interface, used to connect IP routers and dense wavelength-division multiplexing (DWDM) equipment.
Paul Brooks, Viavi Solutions
But 100 gigabits is also the first main interface speed influenced by the internet giants. “One-hundred-gigabit volumes didn’t take that inflection point until we saw the PSM4 and CWDM4 [transceiver designs],” says Brooks. The PSM4 and CWDM4 are not IEEE specification but multi-source agreements (MSAs) driven by the industry.
The large-scale data centre players are now at the forefront driving 400 gigabits. They don’t want to wait for three generations of modules before they get their hands on an optimised design. They want the end design from the start.
“There was a lot of value in having iterations at 100 gigabits before we got to the high-volume form factor,” says Ward. “It will be more challenging with the compressed timeframe for 400 gigabits.”
Datacom traffic is driven by machine-to-machine communication whereas telecom is driven by consumer demand. Machine-to-machine has twice the growth rate.
Data centre needs
Brandon Collins, CTO of Lumentum, explains that the urgency of the large-scale data centre players for 400 gigabits is due to their more pressing capacity requirements compared to the telcos.
Brandon Collings, LumentumDatacom traffic is driven by machine-to-machine communication whereas telecom is driven by consumer demand. “Machine-to-machine has twice the growth rate,” says Collins. “The expectation in the market - and everything in the market aligns with this - is that the datacom guys will be adopting in volume much sooner than the telecom guys.”
The data centre players require 400-gigabit interfaces for the next-generation 6.4- and 12.8-terabit top-of-rack switches in the data centre.
“The reason why the top-of-rack switch is going to need 400-gigabit uplinks is because server speeds are going to go from 25 gigabits to 50 gigabits,” says Adam Carter, chief commercial operator for Oclaro.
A top-of-rack switch’s downlinks connect to the servers while the uplinks interface to larger ‘spine’ switches. For a 36-port switch, if four to six ports are reserved for uplinks and the remaining ports are at 50 gigabits-per-second (Gbps), 100-gigabit uplinks cannot accommodate all the traffic.
The 6.4-terabit and 12.8-terabit switches are expected towards the end of next year. These switches will be based on silicon such as Broadcom’s Tomahawk-III, start-up Innovium’s Teralynx and Mellanox’s Spectrum-2. All three silicon design examples use 50-gigabit electrical signalling implemented using 4-level pulse-amplitude modulation (PAM-4).
PAM-4, a higher order modulation scheme, used for the electrical and optical client interfaces is another challenge at 400-gigabit. The use of PAM-4 requires a slight increase in bandwidth, says Brooks, and introduces a loss that requires compensation using forward error correction (FEC). “Four-hundred-gigabits is the first Ethernet technology where you always have FEC on,” he says.
CFP8
The modules being proposed for 400-gigabit interfaces include the CFP8, the Octal Small Form Factor (OSFP) and the double-density QSFP (QSFP-DD) pluggable modules. COBO, the interoperable on-board optics standard, will also support 400-gigabit interfaces.
The QSFP-DD is designed to be backward compatible with the QSFP and QSFP28 pluggables while the OSFP is a new form factor.
At OFC earlier this year, several companies showcased 400-gigabit CFP8-based designs.
NeoPhotonics detailed a CFP8 implementing 400GBASE-LR8, the IEEE 802.3bs Task Force’s 10km specification that uses eight wavelengths, each at 50-gigabit PAM4. Finisar announced two CFP8 transceivers: the 2km 400GBASE-FR8 and the 10km 400GBASE-LR8. Oclaro also announced two CFP8 designs: the 10km 400GBASE-LR8 and an even longer reach 40km version.
The 400-gigabit CFP8 is aimed at traditional telecom applications such as linking routers and transport equipment.
NeoPhotonics’ CFP8 is not yet in production and the company says it is not seeing a present need. “There is probably a short window before it gets replaced by the QSFP-DD or, on the telecom side, the OSFP,” says Ferris Lipscomb, vice president of marketing at NeoPhotonics.
Finisar expects its 400-gigabit CFP8 products by the year-end, while Oclaro is sampling its 10km 400-gigabit CFP8.
But the large-scale data centre players are not interested in the CFP8 which they see as too bulky for the data centre. Instead, Amazon, Facebook, and equipment vendor Cisco Systems are backing the higher-density QSFP-DD, while Google and Arista Networks are proponents of the OSFP.
“The data centre players don’t need IEEE standardisation, they need the lowest cost and the most compact form factor,” says Lumentum’s Collings.
QSFP-DD and OSFP
To achieve 400 gigabits, the QSFP-DD has twice the number of electrical lanes of the QSFP, going from four to eight, while each lane’s speed is doubled to 56Gbps using PAM-4.
“Time and time again we have heard with the QSFP-DD that plugging in legacy modules is a key benefit of that technology,” says Scott Sommers, group product manager at Molex and a co-chair of the QSFP-DD MSA. The power envelope of the QSFP-DD is some 12W.
Yasunori Nagakubo, Fujitsu Optical ComponentsYasunori Nagakubo, director of marketing at Fujitsu Optical Components also highlights the high-density merits of the QSFP-DD. Up to 36 ports can fit on the front panel of a one-rack-unit (1RU) box, enabling a throughput of 14.4 terabits.
In contrast, the OSFP has been designed with a fresh sheet of paper. The form factor has a larger volume and surface area compared to the QSFP-DD and, accordingly, has a power envelope of some 16W. Up to 32 OSFP ports can fit on a 1RU front panel.
“The QSFP-DD is a natural evolution of the QSFP and is used for switch-to-switch interconnect inside the data centre,” says Robert Blum, director of strategic marketing and business development at Intel’s silicon photonics product division. He views the OSFP as being a more ambitious design. “Obviously, you have a lot of overlap in terms of applications,” says Blum. “But the OSFP is trying to address a wider segment such as coherent and also be future proofed for 800 gigabits.”
“A lot of people are trying to make everything fit inside a QSFP-DD but, after all, the OSFP is still a bigger form factor which is easier for different components to fit in,” says Winston Way, CTO, systems at NeoPhotonics. Should a 400-gigabit design meet the more constrained volume and power requirements of the QSFP-DD, the design will also work in an OSFP.
The consensus among the module makers is that neither the QSFP-DD nor the OSFP can be ignored and they plan to back both.
This [400 gigabits] may be the last hurrah for face-plate pluggables
“We have been in this discussion with both camps for quite some time and are supporting both,” says Collings. What will determine their relative success will be time-to-market issues and which switch vendors produces the switch with the selected form factors and how their switches sell. “Presumably, switches are bought on other things than which pluggable they elected to use,” says Collings.
Is having two form factors an issue for Microsoft?
“Yes and no,” says Brad Booth, principal network architect for Microsoft’s Azure Infrastructure and chair of the COBO initiative. “I understand why the QSFP-DD exists and why the OSFP exists, and both are the same reason why we started COBO.”
COBO will support 400-gigabit interfaces and also 800 gigabits by combining two modules side-by-side.
Booth believes that 400-gigabit pluggable module designs face significant power consumption challenges: “I’ve been privy to data that says this is not as easy as many people believe.”
Brad Booth, MicrosoftIf it were only 400-gigabit speeds, it is a question of choosing one of the two pluggable modules and running with it, he says. But for future Ethernet speeds, whether it is 800 gigabits or 1.6 terabits, the design must be able to meet the thermal environment and electrical requirements.
“I do not get that feeling when I look at anything that is a face-plate pluggable,” says Booth. “This [400 gigabits] may be the last hurrah for face-plate pluggables.”
Formats
There are several 400-gigabit interface specifications at different stages of development.
The IEEE’s 802.3bs 400 Gigabit Ethernet Task Force has defined four 400 Gigabit specifications: a multi-mode fibre design and three single-mode interfaces.
The 100m 400GBASE-SR16 uses 16 multi-mode fibres, each at 25Gbps. The -SR16 has a high fibre count but future 400-gigabit multi-mode designs are likely to be optimised. One approach is an eight-fibre design, each at 50Gbps. And a four-fibre design could be developed with each fibre using coarse wavelength-division multiplexing (CWDM) carrying four 25-gigabit wavelengths.
The expectation is that at OFC 2018 next March, many companies will be demonstrating their 400-gigabit module designs including four-wavelength ones
The three single-mode IEEE specifications are the 500m 400GBASE-DR4 which uses four single-mode fibres, each conveying a 100-gigabit wavelength, and the 2km 400GBASE-FR8 and 10km 400GBASE-LR8 that multiplex eight wavelengths onto a single-mode fibre, each wavelength carrying a 50-gigabit PAM-4 signal.
The 2km and 10km IEEE specifications use a LAN-WDM spacing scheme and that requires tight wavelength control and hence laser cooling. The standards also use the IEEE CDAUI-8 electrical interface that supports eight 50-gigabit PAM-4 signals. The -FR8 and -LR8 standards are the first 400-gigabit specifications being implemented using the CFP8 module.
A new initiative, the CWDM8 MSA, has been announced to implement an alternative eight-wavelength design based on CWDM such that laser cooling is not required. And while CWDM8 will also use the CDAUI-8 electrical interface, the signals sent across the fibre are 50-gigabit non-return-to-zero (NRZ). A retimer chip is required to convert the input 50-gigabit PAM-4 electrical signals into 50-gigabit NRZ before being sent optically.
Robert Blum, IntelProponents of the CWDM8 MSA see it as a pragmatic solution that offers a low-risk, timely way to deliver 400-gigabit interfaces.
“When we looked at what is available and how to do an optical interface, there was no good solution that would allow us to meet those timelines, fit the power budget of the QSFP-DD and be at the cost points required for data centre deployment,” says Intel’s Blum. Intel is one of 11 founding companies backing the new MSA.
A disadvantage of the MSA is that it requires eight lasers instead of four, adding to the module’s overall cost.
“Making lasers at eight different wavelengths is not a trivial thing,” says Vivek Rajgarhia, senior vice president and general manager, lightwave at Macom.
This is what the 100G Lambda MSA aims to address with its four 100-gigabit wavelength design over duplex fibre. This can be seen as a four-wavelength CWDM complement to the IEEE’s 400GBASE-DR4 500m specification.
Vivek Rajgarhia, Macom
The first 400-gigabit standard the MSA is developing is the 400G-FR4, a 2km link that uses a CDAUI-8 interface and an internal PAM4 chip to create the 100-gigabit PAM-4 signals that are optically multiplexed onto a fibre.
The large-scale data centre players are the main drivers of four-wavelength 400-gigabit designs. Indeed, two large-scale data centre operators, Microsoft and Alibaba, have joined the 100G Lambda MSA.
“People think that because I work at Microsoft, I don’t talk to people at Google and Facebook,” says Booth. “We may not agree but we do talk.
“My point to them was that we need a CWDM4 version of 400 gigabits; the LAN-WDM eight-wavelength is a non-starter for all of us,” says Booth. “If you talk to any of the big end users, they will tell you it is a non-starter. They are waiting for the FR4.”
“Everyone wants 400 gigabit - 4x100-gigabit, that is what they are looking for,” says Rajgarhia.
If companies adopt other solutions it is purely a time-to-market consideration. “If they are going for intermediate solutions, as soon as there is 400 gigabits based on 100-gigabit serial, there is no need for them, whether it is 200-gigabit or 8x50-gigabit modules,” says Rajgarhia.
At the recent ECOC 2017 show, Macom demonstrated a 100-gigabit single-wavelength solution based on its silicon photonics optics and its 100-gigabit PAM-4 DSP chip. MultiPhy also announced a 100-gigabit PAM-4 chip at the show and companies are already testing its silicon.
The expectation is that at OFC 2018 next March, many companies will be demonstrating their 400-gigabit module designs including four-wavelength ones.
Fujitsu Optical Components says it will have a working four-wavelength 400-gigabit module demonstration at the show. “Fujitsu Optical Components favours a 4x100-gigabit solution for 400 gigabits instead of the alternative eight-wavelength solutions,” says Nagakubo. “We believe that eight-wavelength solutions will be short lived until the 4x100-gigabit design becomes available.”
The roadmap is slipping and slipping because the QSFP-DD is hard, very hard
Challenges and risk
“Everyone understands that, ultimately, the end game is the QSFP-DD but how do we get there?” says Viavi’s Brooks.
He describes as significant the challenges involved in developing a four-wavelength 400-gigabit design. These include signal integrity issues, the optics for 100-gigabit single wavelengths, the PAM-4 DSP, the connectors and the ‘insanely hot and hard’ thermal issues.
“All these problems need to be solved before you can get the QSFP-DD to a wider market,” says Brooks. “The roadmap is slipping and slipping because the QSFP-DD is hard, very hard.”
Lumentum’s Collins says quite a bit of investment has been made to reduce the cost of existing 100-gigabit CWDM4 designs and this investment will continue. “That same technology is basically all you need for 400 gigabits if you can increase the bandwidth to get 50 gigabaud and you are using a technology that is fairly linear so you can switch from NRZ to PAM-4 modulation.”
In other words, extending to a 400-gigabit four-wavelength design becomes an engineering matter if the technology platform that is used can scale.
Microsoft’s Booth is also optimistic. He does not see any challenges that suggest that the industry will fail to deliver the 400-gigabit modules that the large-scale data centre players require: “I feel very confident that the ecosystem will be built out for what we need.”
Module companies backing the most technically-challenging four-wavelength designs face the largest risk, yet also the greatest reward if they deliver by the end of 2018 and into 2019. Any slippage and the players backing alternative designs will benefit.
How the 400-gigabit market transpires will be ‘very interesting’, says Finisar’s Ward: “It will be clear who executes and who does not.”
Oclaro’s 400-gigabit plans
Adam Carter, Oclaro’s chief commercial officer, discusses the company’s 400-gigabit and higher-speed coherent optical transmission plans and the 400-gigabit client-side pluggable opportunity.
Oclaro showcased its first coherent module that uses Ciena’s WaveLogic Ai digital signal processor at the ECOC show held recently in Gothenburg.
Adam CarterOclaro is one of three optical module makers, the others being Lumentum and NeoPhotonics, that signed an agreement with Ciena earlier this year to use the system vendor’s DSP technology and know-how to bring coherent modules to market. The first product resulting from the collaboration is a 5x7-inch board-mounted module that supports 400-gigabits on a single-wavelength.
The first WaveLogic Ai-based modules are already being tested at several of Oclaro’s customers’ labs. “They [the module samples] are very preliminary,” says Adam Carter, the chief commercial officer at Oclaro. “The really important timeframe is when we get towards the new year because then we will have beta samples.”
DSP developments
The coherent module is a Ciena design and Carter admits there isn’t going to be much differentiation between the three module makers’ products.
“We have some of the key components that sit inside that module and the idea is, over time, we would design in the rest of the componentry that we make that isn’t already in there,” says Carter. “But it is still going to be the same spec between the three suppliers.”
The collaboration with the module makers helps Ciena promote its coherent DSP to a wider market and in particular China, a market where its systems are not deployed.
Over time, the scope for differentiation between the three module makers will grow. “It [the deal] gives us access to another DSP chip for potential future applications,” says Carter.
Here, Oclaro will be the design authority, procuring the DSP chip for Ciena before adding its own optics. “So, for example, for the [OIF’s] 400G ZR, we would ask Ciena to develop a chip to a certain spec and then put our optical sub-assemblies around it,” says Carter. “This is where we do believe we can differentiate.”
Oclaro also unveiled at ECOC an integrated coherent transmitter and an intradyne coherent receiver optical sub-assemblies using its indium phosphide technology that operate at up to 64 gigabaud (Gbaud).
We expect to see 64Gbaud optical systems being trialed in 2018 with production systems following at the end of next year
A 64Gbaud symbol rate enables a 400-gigabit wavelength using 16-ary quadrature amplitude modulation (16-QAM) and a 600-gigabit wavelength using 64-QAM.
Certain customers want such optical sub-assemblies for their line card designs and Oclaro will also use the building blocks for its own modules. The devices will be available this quarter. “We expect to see 64Gbaud optical systems being trialed in 2018 with production systems following at the end of next year and the beginning of 2019,” says Carter.
Oclaro also announced that its lithium niobate modulator supporting 400-gigabit single wavelengths is now in volume production. “Certain customers do have their preferences when it comes to first designs and particularly for long-reach systems,” says Carter. “Lithium niobate seems to be the one people go with.”
400-gigabit form factors
Oclaro did not make any announcements regarding 400-gigabit client-side modules at ECOC. At the OFC show held earlier this year, it detailed two CFP8-based 400-gigabit designs based on eight wavelengths with reaches of 10km and 40km.
“We are sampling the 400-gigabit 10km product right now,” says Carter. “The product is being tested at the system level and will go through various qualification runs.”
The 40km CFP8 product is further out. There are customers interested in such a module as they have requirements to link IP routers that are more than 10km apart.
Carter describes the CFP8 400-gigabit modules as first-generation products. The CFP8 is similar in size to the CFP2 pluggable module and that is too large for the large-scale data centre players. They want higher aggregate bandwidth and greater front panel densities for their switches and are looking such form factors as the double-density QSFP (QSFP-DD) and the Octal Small Form Factor pluggable (OSFP).
The OSFP is a fresh design, has a larger power envelope - some 15W compared to the 12W of the QSFP-DD - and has a roadmap that supports 800-gigabit data rates. In contrast, the QSFP-DD is backward compatible with the QSFP, an attractive feature for many vendors.
But it is not only a module’s power envelope that is an issue for 400-gigabit designs but also whether a one-rack-unit box can be sufficiently cooled when fully populated to avoid thermal runaway. Some 36 QSFP-DDs can fit on the front panel compared to 32 OSFPs.
Carter stresses both form factors can’t be dismissed for 400-gigabit: “Everyone is pursuing designs that are suitable for both.” Oclaro is not an advocate of either form factor given it provides optical sub-assemblies suitable for both.
The industry really wants four-channels. When you use more lasers, you are adding more cost.
Optical formats
Oclaro’s core technology is indium phosphide and, as such, its focusses on single-mode fibre designs.
The single mode options for 400 gigabits are split between eight-wavelength designs such as the IEEE 802.3bs 2km 400GBASE-FR8 and 10km 400GBASE-LR8 and the newly announced CWDM8 MSA, and four-wavelength specifications - the 500m IEEE 802.3bs parallel fibre 400GBASE-DR4 and the 2km 100G Lambda MSA 400G-FR4 that is under development. Oclaro is a founding member of the 100 Gigabit Lambda MSA but has not joined the CWDM8 MSA.
"The industry really wants four channels," says Carter. "When you use more lasers, you are adding more cost." It is also not trivial fitting eight lasers into a CFP8 never mind into the smaller QSFP-DD and OSFP modules.
“There might be some that have the technology to do the eight-channel part and there might be customers that will use that,” says Carter. “But most of the discussions we’ve been having are around four channels.”
Challenges
The industry’s goal is to have 400-gigabit QSFP-DD and OSFP module in production by the end of next year and into 2019. “There is still some risk but everybody is driving to meet that schedule,” says Carter.
Oclaro says first samples of 100-gigabit PAM-4 chips needed for 100-gigabit single wavelengths are now in the labs. Module makers can thus add their optical sub-assemblies to the chips and start testing system performance. Four-channel PAM-4 chips will be needed for the 400-gigabit module products.
Carter also acknowledges that any further delay in four-wavelength designs could open the door for other 400-gigabit solutions and even interim 200-gigabit designs.
“As a transceiver supplier and an optical component supplier you are always aware of that,” he says. “You have to have backup plans if that comes off.”
The OIF’s 400ZR coherent interface starts to take shape
Part 2: Coherent developments
The Optical Internetworking Forum’s (OIF) group tasked with developing two styles of 400-gigabit coherent interface is now concentrating its efforts on one of the two.
When first announced last November, the 400ZR project planned to define a dense wavelength-division multiplexing (DWDM) 400-gigabit interface and a single wavelength one. Now the work is concentrating on the DWDM interface, with the single-channel interface deemed secondary.
Karl Gass"It [the single channel] appears to be a very small percentage of what the fielded units would be,” says Karl Gass of Qorvo and the OIF Physical and Link Layer working group vice chair, optical, the group responsible for the 400ZR work.
The likelihood is that the resulting optical module will serve both applications. “Realistically, probably both [interfaces] will use a tunable laser because the goal is to have the same hardware,” says Gass.
The resulting module may also only have a reach of 80km, shorter than the original goal of up to 120km, due to the challenging optical link budget.
Origins and status
The 400ZR project began after Microsoft and other large-scale data centre players such as Google and Facebook approached the OIF to develop an interoperable 400-gigabit coherent interface they could then buy from multiple optical module makers.
The internet content providers’ interest in an 80km-plus link is to connect premises across the metro. “Eighty kilometres is the magic number from a latency standpoint so that multiple buildings can look like a single mega data centre,” says Nathan Tracy of TE Connectivity and the OIF’s vice president of marketing.
Since then, traditional service providers have shown an interest in 400ZR for their metro needs. The telcos’ requirements are different to the data centre players, causing the group to tweak the channel requirements. This is the current focus of the work, with the OIF collaborating with the ITU.
The catch is how much can we strip everything down and still meet a large percentage of the use cases
“The ITU does a lot of work on channels and they have a channel measurement methodology,” says Gass. “They are working with us as we try to do some division of labour.”
The group will choose a forward error correction (FEC) scheme once there is common agreement on the channel. “Imagine all those [coherent] DSP makers in the same room, each one recommending a different FEC,” says Gass. “We are all trying to figure out how to compare the FEC schemes on a level playing field.”
Meeting the link budget is challenging, says Gass, which is why the link might end up being 80km only. “The catch is how much can we strip everything down and still meet a large percentage of the use cases.”
The cloud is the biggest voice in the universe
400ZR form factors
Once the FEC is chosen, the power envelope will be fine-tuned and then the discussion will move to form factors. The OIF says it is still too early to discuss whether the project will select a particular form factor. Potential candidates include the OSFP MSA and the CFP8.
Nathan TracyThe industry assumption is that the 80km-plus 400ZR digital coherent optics module will consume around 15W, requiring a very low-power coherent DSP that will be made using 7nm CMOS.
“There is strong support across the industry for this project, evidenced by the fact that project calls are happening more frequently to make the progress happen,” says Tracy.
Why the urgency? “The cloud is the biggest voice in the universe,” says Tracy. To support the move of data and applications to the cloud, the infrastructure has to evolve, leading to the data centre players linking smaller locations spread across the metro.
“At the same time, the next-gen speed that is going to be used in these data centres - and therefore outside the data centres - is 400 gigabit,” says Tracy.
Talking markets: Oclaro on 100 gigabits and beyond
Oclaro’s chief commercial officer, Adam Carter, discusses the 100-gigabit market, optical module trends, silicon photonics, and why this is a good time to be an optical component maker.
Oclaro has started its first quarter 2017 fiscal results as it ended fiscal year 2016 with another record quarter. The company reported revenues of $136 million in the quarter ending in September, 8 percent sequential growth and the company's fifth consecutive quarter of 7 percent or greater revenue growth.
Adam CarterA large part of Oclaro’s growth was due to strong demand for 100 gigabits across the company’s optical module and component portfolio.
The company has been supplying 100-gigabit client-side optics using the CFP, CFP2 and CFP4 pluggable form factors for a while. “What we saw in June was the first real production ramp of our CFP2-ACO [coherent] module,” says Adam Carter, chief commercial officer at Oclaro. “We have transferred all that manufacturing over to Asia now.”
The CFP2-ACO is being used predominantly for data centre interconnect applications. But Oclaro has also seen first orders from system vendors that are supplying US communications service provider Verizon for its metro buildout.
The company is also seeing strong demand for components from China. “The China market for 100 gigabits has really grown in the last year and we expect it to be pretty stable going forward,” says Carter. LightCounting Market Research in its latest optical market forecast report highlights the importance of China’s 100-gigabit market. China’s massive deployments of FTTx and wireless front haul optics fuelled growth in 2011 to 2015, says LightCounting, but this year it is demand for 100-gigabit dense wavelength-division multiplexing and 100 Gigabit Ethernet optics that is increasing China’s share of the global market.
The China market for 100 gigabits has really grown in the last year and we expect it to be pretty stable going forward
QSFP28 modules
Oclaro is also providing 100-gigabit QSFP28 pluggables for the data centre, in particular, the 100-gigabit PSM4 parallel single-mode module and the 100-gigabit CWDM4 based on wavelength-division multiplexing technology.
2016 was expected to be the year these 100-gigabit optical modules for the data centre would take off. “It has not contributed a huge amount to date but it will start kicking in now,” says Carter. “We always signalled that it would pick up around June.”
One reason why it has taken time for the market for the 100-gigabit QSFP28 modules to take off is the investment needed to ramp manufacturing capacity to meet the demand. “The sheer volume of these modules that will be needed for one of these new big data centres is vast,” says Carter. “Everyone uses similar [manufacturing] equipment and goes to the same suppliers, so bringing in extra capacity has long lead times as well.”
Once a large-scale data centre is fully equipped and powered, it generates instant profit for an Internet content provider. “This is very rapid adoption; the instant monetisation of capital expenditure,” says Carter. “This is a very different scenario from where we were five to ten years ago with the telecom service providers."
Data centre servers and their increasing interface speed to leaf switches are what will drive module rates beyond 100 gigabits, says Carter. Ten Gigabit Ethernet links will be followed by 25 and 50 Gigabit Ethernet. “The lifecycle you have seen at the lower speeds [1 Gigabit and 10 Gigabit] is definitely being shrunk,” says Carter.
Such new speeds will spur 400-gigabit links between the data centre's leaf and spine switches, and between the spine switches. “Two hundred Gigabit Ethernet may be an intermediate step but I’m not sure if that is going to be a big volume or a niche for first movers,” says Carter.
400 gigabit CFP8
Oclaro showed a prototype 400-gigabit module in a CFP8 module at the recent ECOC show in September. The demonstrator is an 8-by-50 gigabit design using 25 gigabaud optics and PAM-4 modulation. The module implements the 400Gbase-LR8 10km standard using eight 1310nm distributed feedback lasers, each with an integrated electro-absorption modulator. The design also uses two 4-wide photo-detector arrays.
“We are using the four lasers we use for the CWDM4 100-gigabit design and we can show we have the other four [wavelength] lasers as well,” says Carter.
Carter says IP core routers will be the main application for the 400Gbase-LR8 module. The company is not yet saying when the 400-gigabit CFP8 module will be generally available.
We can definitely see the CFP2-ACO could support 400 gigabits and above
Coherent
Oclaro is already working with equipment customers to increase the line-side interface density on the front panel of their equipment.
The Optical Internetworking Forum (OIF) has already started work on the CFP8-ACO that will be able to support up to four wavelengths, each supporting up to 400 gigabits. But Carter says Oclaro is working with customers to see how the line-side capacity of the CFP2-ACO can be advanced. “We can definitely see the CFP2-ACO could support 400 gigabits and above,” says Carter. “We are working with customers as to what that looks like and what the schedule will be.”
And there are two other pluggable form factors smaller than the CFP2: the CFP4 and the QSFP28. “Will you get 400 gigabits in a QSFP28? Time will tell, although there is still more work to be done around the technology building blocks,” says Carter.
Vendors are seeking the highest aggregate front panel density, he says: “The higher aggregate bandwidth we are hearing about is 2 terabits but there is a need to potentially going to 3.2 and 4.8 terabits.”
Silicon photonics
Oclaro says it continues to watch closely silicon photonics and to question whether it is a technology that can be brought in-house. But issues remain. “This industry has always used different technologies and everything still needs light to work which means the basic III-V [compound semiconductor] lasers,” says Carter.
“Producing silicon photonics chips versus producing packaged products that meet various industry standards and specifications are still pretty challenging to do in high volume,” says Carter. And integration can be done using either silicon photonics or indium phosphide. “My feeling is that the technologies will co-exist,” says Carter.
Ranovus shows 200 gigabit direct detection at ECOC
Ranovus has announced it first direct-detection optical products for applications including data centre interconnect.
Saeid AramidehThe start-up has announced two products to coincide with this week’s ECOC show being held in Dusseldorf, Germany.
One product is a 200 gigabit-per-second (Gbps) dense wavelength-division multiplexing (WDM) CFP2 pluggable optical module that spans distances up to 130km. Ranovus will also sell the 200Gbps transmitter and receiver optical engines that can be integrated by vendors onto a host line card.
The dense WDM direct-detection solution from Ranovus is being positioned as a cheaper, lower-power alternative to coherent optics used for high-capacity metro and long-haul optical transport. Using such technology, service providers can link their data centre buildings distributed across a metro area.
The cost [of the CFP2 direct detection] proves in much better than coherent
“The power consumption [of the direct-detection design] is well within the envelope of what the CFP2 power budget is,” says Saeid Aramideh, a Ranovus co-founder and chief marketing. The CFP2 module's power envelop is rated at 12W and while there are pluggable CFP2-ACO modules now available, a coherent DSP-ASIC is required to work alongside the module.
“The cost [of the CFP2 direct detection] proves in much better than coherent does,” says Aramideh, although he points out that for distances greater than 120km, the economics change.
The 200Gbps CFP2 module uses four wavelengths, each at 50Gbps. Ranovus is using 25Gbps optics with 4-level pulse-amplitude modulation (PAM-4) technology provided by fabless chip company Broadcom to achieve the 50Gbps channels. Up to 96, 50 Gbps channels can be fitted in the C-band to achieve a total transmission bandwidth of 4.8 terabits.
Ranovus is demonstrating at ECOC eight wavelengths being sent over 100km of fibre. The link uses a standard erbium-doped fibre amplifier and the forward-error correction scheme built into PAM-4.
Technologies
Ranovus has developed several key technologies for its proprietary optical interconnect products. These include a multi-wavelength quantum dot laser, a silicon photonics based ring-resonator modulator, an optical receiver, and the associated driver and receiver electronics.
The quantum dot technology implements what is known as a comb laser, producing multiple laser outputs at wavelengths and grid spacings that are defined during fabrication. For the CFP2, the laser produces four wavelengths spaced 50GHz apart.
For the 200Gbps optical engine transmitter, the laser outputs are fed to four silicon photonics ring-resonator modulators to produce the four output wavelengths, while at the receiver there is an equivalent bank of tuned ring resonators that delivers the wavelengths to the photo-detectors. Ranovus has developed several receiver designs, with the lower channel count version being silicon photonics based.
The quantum dot technology implements what is known as a comb laser, producing multiple laser outputs at wavelengths and grid spacings that are defined during fabrication.
The use of ring resonators - effectively filters - at the receiver means that no multiplexer or demultiplexer is needed within the optical module.
“At some point before you go to the fibre, there is a multiplexer because you are multiplexing up to 96 channels in the C-band,” says Aramideh. “But that multiplexer is not needed inside the module.”
Company plans
The startup has raised $35 million in investment funding to date. Aramideh says the start-up is not seeking a further funding round but he does not rule it out.
The most recent funding round, for $24 million, was in 2014. At the time the company was planning to release its first product - a QSFP28 100-Gigabit OpenOptics module - in 2015. Ranovus along with Mellanox Technologies are co-founders of the dense WDM OpenOptics multi-source agreement that supports client side interface speeds at 100Gbps, 400Gbps and terabit speeds.
However, the company realised that 100-gigabit links within the data centre were being served by the coarse WDM CWDM4 and CLR4 module standards, and it chose instead to focus on the data centre interconnect market using its direct detection technology.
Ranovus has also been working with ADVA Optical Networking with it data centre interconnect technology. Last year, ADVA Optical Networking announced its FSP 3000 CloudConnect data centre interconnect platform that can span both the C- and L-bands.
Also planned by Ranovus is a 400-gigabit CFP8 module - which could be a four or eight channel design - for the data centre interconnect market.
Meanwhile, the CFP2 direct-detection module and the optical engine will be generally available from December.