Is traffic aggregation the next role for coherent?
Ciena and Infinera have each demonstrated the transmission of 800-gigabit wavelengths over near-1,000km distances, continuing coherent's marked progress. But what next for coherent now that high-end optical transmission is approaching the theoretical limit? Can coherent compete over shorter spans and will it find new uses?
Part 1: XR Optics
“I’m going to be a bit of a historian here,” says Dave Welch, when asked about the future of coherent.
Interest in coherent started with the idea of using electronics rather than optics to tackle dispersion in fibre. Using electronics for dispersion compensation made optical link engineering simpler.
Dave Welch
Coherent then evolved as a way to improve spectral efficiency and reduce the cost of sending traffic, measured in gigabit-per-dollar.
“By moving up the QAM (quadrature amplitude modulation) scale, you got both these benefits,” says Welch, the chief innovation officer at Infinera.
Improving the economics of traffic transmission still drives coherent. Coherent transmission offers predictable performance over a range of distances while non-coherent optics links have limited spans.
But coherent comes at a cost. The receiver needs a local oscillator - a laser source - and a coherent digital signal processor (DSP).
Infinera believes coherent is now entering a phase that will add value to networking. “This is less about coherent and more about the processor that sits within that DSP,” says Welch.
Aggregation
Infinera is developing technology - dubbed XR Optics - that uses coherent for traffic aggregate in the optical domain.
The 'XR’ label is a play on 400ZR, the 400-gigabit pluggable optics coherent standard. XR will enable point-to-point spans like ZR optics but also point-to-multipoint links.
Infinera, working with network operators, has been assessing XR optics’ role in the network. The studies highlight how traffic aggregation dictates networking costs.
“If you aggregate traffic in the optical realm and avoid going through a digital conversion to aggregate information, your network costs plummet,” says Welch.
Are there network developments that are ripe for such optical aggregation?
“The expansion of bandwidth demand at the network edge,” says Rob Shore, Infinera’s senior vice president of marketing. “It is growing, and it is growing unpredictably.”
XR Optics
XR optics uses coherent technology and Nyquist sub-carriers. Instead of a laser generating a single carrier, pulse-shaping at the optical transmitter is used to create multiple carriers, dubbed Nyquist sub-carriers.
The sub-carriers carry the same information as a single carrier but each one has a lower symbol rate. The lower symbol rate improves tolerance to non-linear fibre effects and enables the use of lower-speed electronics. This benefits long-distance transmissions.
But sub-carriers also enable traffic aggregation. Traffic is fanned out over the Nyquist sub-carriers. This enables modules with different capacities to communicate, using the sub-carrier as a basic data rate. For example, a 25-gigabit single sub-carrier XR module and a 100-gigabit XR module based on four sub-carriers can talk to a 400-gigabit module that supports 16.
It means that optics is no longer limited to a fixed point-to-point link but can support point-to-multipoint links where capacities can be changed adaptively.
“You are not using coherent to improve performance but to increase flexibility and allow dynamic reconfigurability,” says Shore.
Rob Shore
XR optics makes an intermediate-stage aggregation switch redundant since the higher-capacity XR coherent module aggregates the traffic from the lower-capacity edge modules.
The result is a 70 per cent reduction in networking costs: the transceiver count is halved and platforms can be removed from the network.
XR Optics starts to make economic sense at 10-gigabit data rates, says Shore. “It depends on the rest of the architecture and how much of it you can drive out,” he says. “For 25-gigabit data rates, it becomes a virtual no-brainer.”
There may be the coherent ‘tax’ associated with XR Optics but it removes so much networking cost that it proves itself much earlier than a 400ZR module, says Shore.
Applications
First uses of XR Optics will include 5G and distributed access architecture (DAA) whereby cable operators bring fibre closer to the network edge.
XR Optics will likely be adopted in two phases. The first is traditional point-to-point links, just as with 400ZR pluggables.
“For mobile backhaul, what is fascinating is that XR Optics dramatically reduces the expense of your router upgrade cost,” says Welch. “With the ZR model I have to upgrade every router on that ring; in XR I only have to upgrade the routers needing more bandwidth.”
Phase two will be for point-to-multipoint aggregation networks: 5G, followed by cable operators as they expand their fibre footprint.
Aggregation also takes place in the data centre, has coherent a role there?
“The intra-data centre application [of XR Optics] is intriguing in how much you can change in that environment but it is far from proven,” says Welch.
Coherent for point-to-point links will not be used inside the data centre as it doesn’t add value but configurable point-to-multiple links do have merit.
“It is less about coherent and more about the management of how content is sent to various locations in a point-to-multiple or multipoint-to-multipoint way,” says Welch. “That is where the game can be had.”
Uptake
Infinera is working with leading mobile operators regarding using XR Optics for optical aggregation. Infinera is talking to their network architects and technologists at this stage, says Shore.
Given how bandwidth at the network edge is set to expand, operators are keen to explore approaches that promise cost savings. “The people that build mobile networks or cable have told us they need help,” says Shore.
Infinera is developing the coherent DSPs for XR Optics and has teamed with optical module makers Lumentum and II-VI. Other unnamed partners have also joined Infinera to bring the technology to market.
The company will detail its pluggable module strategy including XR Optics and ZR+ later this year.
Infinera’s ICE6 sends 800 gigabits over a 950km link
Infinera has demonstrated the coherent transmission of an 800-gigabit signal across a 950km span of an operational network.
Infinera used its Infinite Capacity Engine 6 (ICE6), comprising an indium-phosphide photonic integrated circuit (PIC) and its FlexCoherent 6 coherent digital signal processor (DSP).
The ICE6 supports 1.6 terabits of traffic: two channels, each supporting up to 800-gigabit of data.
The trial, conducted over an unnamed operator’s network in North America, sent the 800-gigabit signal as an alien wavelength over a third-party line-system carrying live traffic.
“We have proved not only the state of our 800-gigabit with ICE6 but also the distances it can achieve,” says Robert Shore, senior vice president of marketing at Infinera.
800G trials
Several systems vendors have undertaken 800-gigabit optical trials.
Ciena detailed two demonstrations using its WaveLogic 5 Extreme (WL5e). One was an interoperability trial involving Verizon and Juniper Networks while the second connected two data centres belonging to the operator, Southern Cross Cable, to confirm the deployment of the WL5e cards in a live network environment.
Neither Ciena trial was designed to demonstrated WL5e’s limit of optical performance. Accordingly, no distances were quoted although both links were sub-100km, according to Ciena.
Meanwhile, Huawei has trialled its 800-gigabit technology in the networks of operators Turkcell and China Mobile.
The motivation for vendors to increase the speed of line-side optical transceivers is to reduce the cost of data transport. “One laser generating more data,” says Shore. “But it is not just high-speed transmissions, it is high-speed transmissions over distance.”
Infinera’s first 800-gigabit demonstration involved the ICE6 sending the signal over 800km of Corning’s TXF low-loss fibre.
“We did the demo on that fibre and we realised we had a ton of margin left over after completing the 800-gigabit circuit,” says Shore. The company then looked for a suitable network trial using standard optical fibre.
Infinera used a third-party’s optical line system to highlight that the 950km reach wasn’t due to a combination of the ICE6 module and the company’s own line system.
“What we have shown is that you can take any link anywhere, use anyone’s line system, carrying any kind of traffic, drop in the ICE6 and get 800-gigabit connections over 950km,” says Shore.
ICE 6
Infinera attributes the ICE6’s optical performance to its advanced coherent toolkit and the fact that the company has both photonics and coherent DSP technology, enabling their co-design to optimise the system’s performance.
One toolkit technique is Nyquist sub-carriers. Here, data is sent using several Nyquist sub-carriers across the channel instead of modulating the data onto a single carrier. The ICE6 is Infinera’s second-generation design to use sub-carriers, the first being ICE4, that doubles the number from four to eight.
The benefit of using sub-carriers is that high data rates can be achieved while the baud rate used for each one is much lower. And a lower baud rate is more tolerant to non-linear channel impairments during optical transmission.
Sub-carriers also improve spectral efficiency as the channels have sharper edges and can be packed tightly.
Infinera applies probabilistic constellation shaping to each sub-carrier, allowing fine-tuning of the data each carries. As a result, more data can be sent on the inner sub-carriers and less on the outer two outer sub-carrier where signal recovering is harder.
The sweet spot for sub-carriers is a symbol rate of 8-11 gigabaud (GBd). For the Infinera trial, eight sub-carriers were used, each at 12GBd, for an overall symbol rate of 96GBd.
“While it is best to stay as close to 8-11GBd, the coding gain you get as you go from 11GBd to 12GBd per sub-carrier is greater than the increased non-linear penalties,” says Shore.
Another feature of the coherent DSP is its use of soft-decision forward-error correction (SD-FEC) gain sharing. By sharing the FEC codes, processing resources can be shifted to one of the PIC’s two optical channels that needs it the most.
The result is that some of the strength of the stronger signal can be traded to bolster the weaker one, extending its reach or potentially allowing a higher modulation scheme to be used.
Applications
Linking data centres is one application where the ICE6 will be used. Another is sub-sea optical transmission involving spans that can be thousands of kilometres long, requiring lower modulation schemes and lower data rates.
“It’s not just cost-per-bit and power-per-bit, it is also spectral efficiency,” says Shore. “And a higher-performing optical signal can maintain a higher modulation rate over longer distances as well.”
Infinera says that at 600 gigabits-per-second (Gbps), link distances will be “significantly better” than 1,600km. The company is exploring suitable links to quantify ICE6’s reach at 600Gbps.
The ICE6 is packaged in a 5×7-inch optical module. Infinera’s Groove series will first adopt the ICE6 followed by the XTC platforms, part of the DTN-X series. First network deployments will occur in the second half of this year.
Infinera is also selling the ICE6 5×7-inch module to interested parties.
XR Optics
Infinera is not addressing the 400ZR coherent pluggable module market. The 400ZR is the OIF-defined 400-gigabit coherent standard developed to connect equipment in data centres up to 120km apart.
Infinera is, however, eyeing the emerging ZR+ opportunity using XR Optics. ZR+ is not a standard but it extends the features of 400ZR.
XR Optics is the brainchild of Infinera that is based on coherent sub-carriers. All the sub-carriers can be sent to the same destination for point-to-point links, but they can also be sent to different locations to allow for point-to-multipoint communications. Such an arrangement allows for traffic aggregation.
“You can steer all the sub-carriers coming out of an XR transceiver to the same destination to get a 400-gigabit point-to-point link to compete with ZR+,” says Shore. “And because we are using sub-carriers instead of a single carrier, we expect to get significantly better performance.”
Infinera is developing the coherent DSPs for XR Optics and has teamed up with optical module makers, Lumentum and II-VI.
Other unnamed partners have joined Infinera to bring the technology to market. Shore says that the partners include network operators that have contributed to the technology’s development.
Infinera planned to showcase XR Optics at the OFC conference and exhibition held recently in San Diego.
Shore says to expect XR Optics announcements in late summer, from Infinera and perhaps others. These will detail the XR Optics form factors and how they function as well as the products’ schedules.
Lumentum on ROADM growth, ZR+, and 800G
CTO interview: Brandon Collings
- The ROADM market is experiencing a period of sustained growth
- The Open ROADM MSA continues to advance and expand its scope
- ZR+ coherent modules will support some interoperability to avoid becoming siloed but optical performance differentiation remains key
Lumentum reckons the ROADM growth started some 18-24 months ago.
Brandon Collings gave a Market Focus talk at the recent ECOC show in Dublin, where he explained why it is a good time to be in the reconfigurable optical add-drop multiplexer (ROADM) business.
“Quantities are growing substantially and it is not one reason but a multitude of reasons,” says Collings. The CTO of Lumentum reckons the growth started some 18-24 months ago.
ROADM markets
Lumentum highlights three factors fuelling the demand for ROADM components.
The first is the emergence of markets such as China and India that previously did not use ROADMs.
“China has pretty universally adopted ROADMs going forward,” says Collings. Previously, Optical Transport Network (OTN) point-to-point links and large OTN switches have been used. But ongoing traffic growth means this solution alone is not sustainable, both in terms of the switch capacity and the number of optical transceivers required.
“The bandwidth needed for these OTN switches is scaling beyond the rational use of optical-electrical-optical (OEO) node configuration,” says Collings. “You need 50 to 300 terabits of OTN [switch capacity] surrounded by the equivalent amount of optical transceivers, and that is not economical.”
The Chinese service providers have adopted a hybrid ROADM and OTN network architecture. The ROADMs perform optical bypass – passing on lightpaths destined for other nodes in the network – to reduce the optical transceivers and OTN switch capacity needed.
The network operators in India, in contrast, are using ROADMs to cope with the many fibre cuts they experience. The ROADMs are used to restore the network by rerouting traffic around the faults.
A second market magnifier is how modern ROADM networks use more wavelength-selective switches (WSSes). Both colourless and directionless (CD) ROADMs, and colourless, directionless and contentionless (CDC) ROADMs use more WSSes per node (see diagram above).
Such ROADMs also use more advanced WSS designs. Using an MxN WSS for the multicast switch in a route-and-select CDC ROADM, for example, delivers system benefits especially when adding and dropping wider optical channels that are starting to be used. Collings says Lumentum’s own MxN WSS is now close to volume manufacturing.
The third factor fuelling ROADM growth is the ongoing demand for more capacity. “Every time you fill a fibre, you typically use another degree in your [ROADM] node and light up a second fibre to grow capacity,” says Collings.
Operators with limited fibre are exploiting the fibre’s spectrum by using the C-band and L-band to grow capacity. This, too, requires more WSSes per node.
“All of these growth factors are happening simultaneously,” says Collings.
Open ROADM MSA
Lumentum is also a member of the Open ROADM multi-source agreement (MSA) that has created a disaggregated design to enable interoperability between systems vendors’ ROADMs.
AT&T is deploying Open ROADM systems in its metro networks while the MSA members have begun work on Revision 6.0 of the standard.
“Open ROADM is maturing and increasing its span of interest,” says Collings.
At first glance, Lumentum’s membership is surprising given it supplies ROADM building-blocks to vendors that make the ROADM systems. Moreover, the Open ROADM standard views a ROADM as an enclosed system.
“The Open ROADM has set certain boundaries where it defines interfaces so that vendor A can talk to vendor B,” says Collings. “And it has set that boundary pretty much at the complete ROADM node.”
Yet Lumentum is an MSA member because part of the software involved in controlling the ROADM is within the node. “It is not just a hardware solution, it is hardware and a significant software solution to supply into that,” says Collings.
Pluggable optics is also a part of the Open ROADM MSA, another reason for Lumentum’s interest. “There is a general discussion about potentially making a boundary condition around pluggable optics as well,” he says.
Collings says the MSA continues to build the ecosystem and the management system to help others use Open ROADM, not just AT&T.
400ZR, OpenZR+ and ZR+
As a supplier of coherent optics and line-side modules, Lumentum is interested in the OIF’s 400ZR standard and what is referred to as ZR+.
ZR+ offers an extended set of features and enhance optical performance. Both 400ZR and ZR+ will be implemented using QSFP-DD and OSFP pluggable modules.
The 400ZR specification has been developed for a specific purpose: to deliver 400 Gigabit Ethernet for distances of at least 80km for data centre interconnect applications. But 400ZR is not suited for more demanding metro mesh and longer-distance metro-regional applications.
This is what ZR+ aims to address. However, ZR+, unlike 400ZR, is not a standard and is a broad term.
At ECOC, Acacia Communications and NTT Electronics detailed interoperability between their coherent DSPs using what they call ‘OpenZR+’. OpenZR+ uses Ethernet traffic like 400ZR but also supports the additional data rates of 100, 200 and 300 Gigabit Ethernet. OpenZR+ also borrows from the OpenROADM specification to enable module interoperability between vendors for data centre interconnect applications with reaches beyond 120km.
But ZR+ encompasses differentiated coherent designs that support 400 gigabits in a compact pluggable but also lower transmission rates that trade capacity for reach.
“So, yes, both classes of ‘ZR+’ are emerging,” says Collings.
OpenZR+ seeks interoperability in compact pluggables, as well as higher power, higher performance modes less focused on interoperability, while ZR+ includes proprietary, higher-power solutions. “That [ZR+] is an area where distance and capacity equal money, in terms of savings and value,” says Collings. “That is going to be an area of differentiation, as it has always been for coherent interfaces.”
Collings favours some standardisation around ZR+, to enable interchangeability among module vendors and avoid the creation of a siloed market.
“But I don’t think we are going to find ZR+ interfaces defined for interoperability because you will find yourself walking back on that differentiation in terms of value that the network operators are looking to extract,” says Collings. “They need every bit of distance they can get.”
Network operators want compact, cost-effective solutions that do ‘even more stuff’ than they are used to. “400ZR checks that box but for bigger, broader networks, operators want the same thing,” says Collings.
There is a continuum of possibilities here, he says: “It is high value from a network operator point of view and it’s a technology challenge for the likes of us and the [DSP] chip vendors.”
800G Pluggable MSA
Lumentum also recently joined the 800G Pluggable MSA that was announced at the CIOE show, held in Shenzhen in September.
“Like any client interface where Lumentum is a supplier of the underlying [laser] chips – whether DMLs, EMLs or VCSELs – we feel it is pretty important for us to be in the definition setting of the interface,” says Collings. “We want the interface to be aligned optimally to what the chip can do.”
Lumentum announced last year that it is exiting the client-side module business and therefore will be less involved in the module aspects of the interface work.
“Having moved out of the [client-side] module business, we’re finding an awful lot of customers interested in engaging with us on the chip level, much more than before,” says Collings.
Further information
For an Optical Connections article about OpenZR+, co-authored by Acacia, NTT Electronics, Lumentum, Juniper Networks and Fujitsu Optical Components, click here
Lumentum completes sale of certain datacom lines to CIG
Brandon Collings, CTO of Lumentum, talks CIG, 400ZR and 400ZR+, COBO, co-packaged optics and why silicon photonics is not going to change the world.
Lumentum has completed the sale of part of its datacom product lines to design and manufacturing company, Cambridge Industries Group.
The sale will lower the company's quarterly revenues by between $20 million to $25 million. Lumentum also said that it will stop selling datacom transceivers in the next year to 18 months.
The move highlights how fierce competition and diminishing margins from the sale of client-side modules is causing optical component companies to rethink their strategies.
Lumentum’s focus is now to supply its photonic chips to the module makers, including CIG. “From a value-add point of view, there is a lot more value in selling those chips than the modules,” says Brandon Collings, CTO of Lumentum.
400ZR and ZR+
Lumentum will continue to design and sell line-side coherent optical modules, however.
“With coherent, there is a lot of complexity and challenge in the module’s design and manufacture,” says Collings. “We believe we can extract the value we need to continue in that business.”
The emerging 400ZR and 400ZR+ are examples of such challenging coherent interfaces.
The 400ZR specification, developed by the Optical Internetworking Forum (OIF), is a 400-gigabit coherent interface with an 80km reach. The 400 gigabit-per-second (Gbps) line rate will be achieved using a 64-gigabaud symbol rate and a 16-QAM modulation scheme.
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“[400ZR] is not client-side. Sixty-four gigabaud is very hard to do in such an extremely compact form factor.
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Module makers will implement the 400ZR interface using client-side pluggable modules such as the QSFP-DD and the OSFP to enable data centre operators to add coherent interfaces directly to their switches.
But implementing 400ZR will be a challenge. “This is not client-side,” says Collings. “Sixty-four gigabaud is very hard to do in such an extremely compact form factor.”
First samples of 400ZR modules are expected by year-end.
The 400ZR+ interface, while not a specification, is a catch-all for a 400-gigabit coherent that exceeds the 400ZR specification. The 400ZR+ will be a multi-rate design that will support additional line rates of 300, 200 and 100Gbps. Such rates coupled with more advanced forward-error correction (FEC) schemes will enable the 400ZR+ to span much greater distances than 80km.
The 400ZR+ interface helps the developers of next-generation coherent DSP chips to recoup their investment by boosting the overall market their devices can address. “It is basically a way of saying I’m going to spend $50 million developing a coherent DSP, and the 400ZR market alone is not big enough for that investment,” says Collings.
Lumentum says there will be some additional functionality that will be possible to fit into a QSFP-DD such that at least one of the ZR+ modes will be supported. But given the QSFP-DD module’s compactness and power constraints, the ZR+ will also be implemented in the CFP2 form factor that has the headroom needed to fully exploit the coherent DSP’s capabilities to also address metro and regional networks.
400ZR+ modules are expected in volume by the end of 2020 or early 2021.
DSP economics
Lumentum will need to source a coherent DSP for its 400ZR/ ZR+ designs as it does not have its own coherent chip. At the recent OFC show held in San Diego, the talk was of new coherent DSP players entering the marketplace to take advantage of the 400ZR/ZR+ opportunity. Collings says he is aware of five DSP players but did not cite names.
NEL and Inphi are the two established suppliers of merchant coherent DSPs. Lumentum (Oclaro) has partnered with Acacia Communications to use its Meru DSP for Lumentum’s CFP2-DCO design, although it is questionable whether Acacia will license its DSP for 400ZR/ ZR+, at least initially.
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“God forbid if 10 or more players are doing this as no matter how you slice it, people will be losing [money]”
Lumentum and Oclaro also partnered with Ciena to use its WaveLogic Ai for a long-haul module. That leaves room for at least one more provider of a coherent DSP that could be a new entrant or an established system vendor that will license an internal design.
Collings points out that it makes no sense economically to have more than five players. If it takes $50 million to tape out a 7nm CMOS coherent DSP, the five players will invest a total of $250 million. And if the investment cost for the module, photonics and everything else is a comparable amount, that equates to $500 million being spent on the 400-gigabit coherent generation.
As for the opportunity, Collings talks of about a total of up to 500,000 ports a year by 2020. That equates to an investment return in the first year of $1,000 per device sold. “God forbid if 10 or more players are doing this as no matter how you slice it, people will be losing [money].”
Beyond Pluggables
The evolution of optics beyond pluggables was another topic under discussion at OFC.
The Consortium of On-Board Optics (COBO), the developerof an interoperable optical solution that embeds optics on the line card, had a stand at the show and a demonstration of its technology. In turn, co-packaged optics, the stage after COBO in the evolution of optical interfaces that will integrate the optics with the silicon in one package, is also now also on companies' agenda.
Collings explains that COBO came about because the industry thought on-board optics would be needed given the challenge of 400-gigabit pluggables meeting the interface density needed for 12.8-terabit switches . “I shared that opinion four to five years ago,” he says, adding that Lumentum is a member of COBO.
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“That problem is real. It is a matter of how far the current engineering can go before it becomes too painful.”
But 400-gigabit optics has been engineered to meet the required faceplate density, including ZR for coherent. As a result, COBO is less applicable. “That need to break the paradigm is a lot less,” he says.
That said, Collings says COBO has driven valuable industry discussion given that the data centre is heading in a direction where 32 ports of 800-gigabit interfaces will be needed to get data in and out of next-generation, 25-terabit switches.
“That problem is real,” says Collings. “It is a matter of how far the current engineering can go before it becomes too painful.” Scaling indefinitely what is done today is not an option, he says.
It is possible with the next generation of switch chip to simply use a two-rack-unit box with twice as many 400-gigabit modules. “That has already been done at the 100-gigabit generation that lasted longer because it doubled up the 100-gigabit port count,” he says.
“In the generation after that, you are now asking for stuff that looks very challenging with today’s technology,” he says. “And that is where co-packaging is focused, the 50-terabit switch generation.” Switches using such capacity silicon are expected in the next four years.
But this is where it gets tricky, as co-packaging not only presents significant technical challenges but also will change the supply chain and business models.
Collings points out that hyperscalars do not like making big pioneering investments in new technology, rather they favour buying commodity hardware. “They don’t like risk, they love competition, and they like a healthy ecosystem,” he says.
“There is a lot of talk from the technology direction of how we can solve this problem [using co-packaged optics] but I think on the business side, the riskside, the investment side is putting a lot of pressure on that actually happening,” says Collings. “Where it ends up I don’t honestly know.”
Silicon photonics
One trend evident at OFC was the growing adoption of silicon photonics by optical component companies.
Indeed, the market research firm, LightCounting, in a research note summarising OFC 2019, sees silicon photonics as a must-have technology given co-packaged optics is now clearly on the industry’s roadmap.
However, Collings stresses that Lumentum’s perspective remains unchanged regarding the technology.
“It’s a fabless exercise so we can participate in silicon photonics and, quite frankly, that is why a lot of other companies are participating because the barrier to entry is quite low,” says Collings. “Nevertheless, we look at silicon photonics as another tool in the toolbox: it has advantages in some areas, some significant disadvantages in others, and in some places, it is simply comparable.”
When looking at a design from a system perspective such as a module, other considerations come into play besides the cost of the silicon photonics chip itself. Collings cites the CFP2 coherent module. While the performance of its receiver is good using silicon photonics, the modulator is questionable. You also need a laser and a semiconductor optical amplifier to compensate for silicon photonics higher loss, he says,
The alternative is to use an indium phosphide-based design and that has its own design issues. “What we are finding when you look at the right level is that the two are the same or indium phosphide has the advantage,” says Collings. “And as we go faster, we are finding silicon is not really keeping up in bandwidth and performance.”
As a result, Lumentum is backing indium phosphide for coherent operating at 64 gigabaud.
“A lot of people are talking about silicon photonics because they can talk about it,” says Collings. “It’s not worthless, don’t get me wrong, but its success outside of Acacia has been niche, and Acacia is top notch at doing this stuff.”
Books in 2018 - Part 3
More books read in 2018, as recommended by Steve Alexander and Yves LeMaitre.
Steve Alexander, senior vice president and CTO, Ciena
I was standing in line at a Starbucks and was chatting with another person who asked what all these engineers were doing talking about networks of submarines. In fact, it was a nearby conference on submarine cables. The person said: “I thought that’s what satellites were for”.
I wanted to find a book I could point people to who think that satellites carry most of the international traffic when, in fact, it is the fibre-optic submarine cables that carry the vast majority of the world’s communications. I came up with The Undersea Network by Nicole Starosielski.
Our industry does such a good job at this that most people don’t even know such networks exist. It is like air; it is there and it works.
My youngest son read The Martian by Andy Weir after seeing the movie and he thought it was pretty good. I’ve always been a Sci-Fi fan but haven’t read much lately so it was nice to get back into it.
Yves LeMaitre, chief strategy officer at Lumentum
I am afraid I am guilty of spending far too much time streaming shows and sports to my laptop. The good thing is my TV stays off. However, I did manage to read several books this year. The three I would highlight - all non-fiction - have a focus on US history.
The first, Destiny of the Republic: A Tale of Madness, Medicine and the Murder of a President by Candice Millard, is about the presidency and assassination of James Garfield intertwined with several of the scientific inventions of the times.
Another title by Candice Millard that I recommend is The River of Doubt: Theodore Roosevelt’s Darkest Journey that details his exploration of the Amazon.
My third recommendation, The Devil in the White City: A Saga of Magic and Murder at the Fair that Changed America by Erik Larson, tells the story of the Chicago’s World Fair of 1893 combined with a serial killer story.
Reading about what are still relatively recent events highlights how much the world has changed in the last century while people’s aspirations and desires have not.
The life stories and achievements of Theodore Roosevelt, James Garfield and Daniel Burnham, the architect of the Chicago World’s Fair, should challenge us to expect more from our leadership, whether in the political, business or social arenas. We have become complacent in accepting mediocrity and lowering our standards.
Reading these stories should remind us that true leadership exists and is a rare quality that should be appreciated and recognised.
Relentless traffic growth leads to a ROADM rethink
Technology briefing: ROADMs
Lumentum has developed an optical switch to enable reconfigurable optical add-drop multiplexers (ROADMs) to cope with the traffic growth expected over the next decade.
The company’s MxN wavelength-selective switch (WSS) will replace the existing multicast switch used in colourless, directionless and contentionless ROADMs. The Lumentum TrueFlex 8x24 twin switch will enable networking nodes of 400-terabit capacity.
“This second-generation switch is what will take us into the 100 gigabaud and super-channel era of network scalability,” says Brandon Collings, CTO of Lumentum.
ROADMs
ROADMs sit at the mesh nodes in an optical network. Their function is to pass lightpaths destined for other nodes in the network - referred to as optical bypass - and enable the adding and dropping of wavelengths at the node. Such add/drops may be rerouted traffic or provisioned new services.
As network traffic continues to grow, so do the degrees of a ROADM and the ports of its sub-systems. The degree of a ROADM is defined to the number of connections or fibre pairs it can support. In the diagram, a ROADM of degree three is shown.
A multicast switch-based 3-degree CDC ROADM. Source Lumentum.
It is rare to encounter more than five or six fibre routes leaving any given mesh node in a network, says Lumentum. “But in those fibre routes there is typically a large number of fibres - 64 or 128,” says Collings. “Operators deploy a conduit of fibre between cities.”
When the C-band fills up, an operator will light another fibre pair, taking up another of the ROADM’s degrees. ROADMs built today have 16 degrees. And since a fibre’s C-band can occupy some 30 terabits of data, this is how 400-terabit mesh nodes will be achieved.
“That is a pretty big node but that is the end [of life] capacity,” says Collings. “I don’t think you will find a 400-terabit node today but we build our networks so that they get there, five to eight years from when they are deployed.”
This raises another issue: the length of time it takes for any generational change of a ROADM design to take hold in the network.
“When a new approach comes along, it takes a couple of years for everyone to figure out how they will use it,” says Collings. Then, once a decision is made, it takes another two years to deploy followed by five to eight years before the ROADM node is filled.
“Nothing happens quickly in this business,” says Collings. “But the upside, from a business point of view, is that as things are designed in, they have a long deployment cycle.”
Lumentum illustrates the point with its own products.
The company is seeing growing demand for its dual TrueFlex WSS deployed in route-and-select ROADM architectures. “But we are still seeing growth on the older broadcast-and-select architectures underpinned by singe 1x9 WSSes,” says James Goodchild, director, product line management for wavelength management products at Lumentum.
CDC ROADMs
A colourless, directionless and contentionless (CDC) ROADM uses a twin multicast switch for the wavelength add and drop functions. The input fibre to each degree’s WSS is connected to the output path WSS of each of the ROADM’s other degrees. The input WSS also connects to the drop multicast switch (see diagram above).
Using a WSS on the input path means that only wavelengths of interest are routed to the WSS’ output ports. Hence the ROADM’s reference as a route-and-select architecture.
Using a 1xN splitter array instead of a WSS for the input path results in a broadcast-and-select ROADM. Here, the input fibre’s wavelengths are broadcast to all the N output ports. The high optical loss associated with the splitters is the main reason why CDC ROADM designs have transitioned to the WSS-based route-and-select architecture.
This second-generation switch is what will take us into the 100 gigabaud and super-channel era of network scalability
However, there is still an optical loss issue to be contended with, introduced by the add or drop multicast switch. Accordingly, along with the twin multicast switch are two arrays of erbium-doped fibre amplifiers (EDFAs). One EDFA array is on the drop ports to the MxN multicast switch and the second amplifier array boosts the outputs of the add-path multicast switch before their transmission into the network.
The MxN multicast switch comprises 1xN splitter arrays, N being the number of add-drop ports, and Mx1 selection switches where M is the number of directions the ROADM supports. A typical multicast switch is 8x16: eight being the ROADM’s number of directions and 16 the drop-port count.
Each of the N splitter arrays sends the signals on a drop port to all the Mx1 selection switches where each one pulls off the channel to be dropped. Having a selection switch at each of the multicast switch’s N drop ports is what enables contentionless operation, the avoidance of a collision when the same wavelength is droppedat a node from different degree directions.
MxN switch
Lumentum’s decision to develop the MxN switch to replace the multicast switch follows its study to understand how optical transmission networks will evolve with continual traffic growth.
One development is the adoption of higher-baud-rate, higher-capacity coherent transmissions that require wider channel widths. A 400-gigabit wavelength requires a 75GHz channel compared to the standard 50GHz fixed grid used for 100- and 200-gigabit transmissions. Future transmission speeds of 800 gigabits will use two such channels or 150GHz of spectrum, while a 1 terabit signal is expected to occupy 300GHz of fibre spectrum. “This is how we anticipate coherent transmission evolving,” says Collings.
Moving to wider channels also benefits the ROADM’s cost. If operators continued to use 50GHz channels, the channel count would grow exponentially with the growth in traffic. In contrast, adopting wider channels means the add-drop port count grows only linearly with traffic. “Using wider channels, the advantage is you don't have to support 600 ports of add-drop in your ROADM networks,” says Collings.
But wider channels means greater amplification demands on the EDFA arrays, an issue that will only worsen over time.
Multicast switch-based designs don’t support the wider channels we know are coming
Losing the amp
Because the power spectral density is constant, the power in a channel increases proportionally with its width. For example, a 75GHz channel has 2dB more power compared to a 50GHz channel spacing, a 150GHz channel 5dB more while a 300GHz channel has an extra 8dB.
The EDFA array is engineered to handle the worst case power requirement that occurs when all 16 optical transceivers into the multicast switch go to the same ROADM degree. Here the EDFA must be able to boost all 16 channels.
For a multicast switch with 16 ports, 22dBm amplification is needed for a 150GHz channel which requires going from an uncooled pump design to a cooled pump one. Equally, 25dBm amplification is needed for 300GHz channels. And as the number of degrees grows, so do the demands on the amplification until no practical amplifier design is possible (see diagram).
The EDFA requirements to compensate for the optical loss of the multicast switch. The complexity of the EDFA design grows with the multicast switch's port count until it becomes insupportable. Source: Lumentum.
“This is not an issue today because we use very modest-sized channels and we engineer our systems to accommodate them,” says Collings. “But if you look forward, you realise they [multicast switch-based designs] don’t support the wider channels we know are coming.”
Using a WSS-based MxN switch solves this issue because, as with the input port WSS of a route-and-select architecture, the switch has a lower optical loss - under 8dB - compared to the 17dB of the splitter-based multicast switch.
The sub-8dB loss is below the threshold where amplification is needed: the optical signal is sufficiently strong at the drop port to be received, as are the added signals for transmission into the network. The resulting removal of the EDFAs simplifies greatly the complexity, size and cost of the CDC ROADM.
“The MxN is a WSS - it’s a router - so it sends all of the light in the direction it is supposed to go,” says Collings. “You can push through the MxN switch channels of any width and of any power because there is no amplifier that needs to be there and be designed appropriately."
The resulting second-generation CDC ROADM design is shown below.
Source: Lumentum
Lumentum's Goodchild says the 8x24 twin implementation of the MxN switch will be available in the first quarter of 2019.
“Certain systems vendors already have access to samples,” says Goodchild.
Further reading
2D WSSes, click here
ROADMs and their evolving amplification needs, click here
Oclaro showcases its pluggable CFP2-DCO at ECOC
Multi-sourcing CFP2-DCO modules, coherent digital signal processor (DSP) partnerships, new laser opportunities and the latest on Lumentum’s acquisition of Oclaro. A conversation with Oclaro’s chief strategy officer, Yves LeMaitre.
Oclaro demonstrated its CFP2 Digital Coherent Optics (CFP2-DCO) pluggable module working with Acacia Communications’ own CFP2-DCO at the recent European Conference on Optical Communication (ECOC), held in Rome.
Yves LeMaitreOclaro announced earlier this year that it would use Acacia’s Meru coherent DSP for a CFP2-DCO product.
The company also announced at ECOC the availability of a portfolio of single-mode lasers that operate over an extended temperature range.
“We see two new laser opportunities for us,” says LeMaitre. “The upgrade of the access networks and, concurrently, the deployment of 5G.”
Coherent pluggables
The CFP2-DCO is a dense wavelength-division multiplexing (DWDM) module that supports 100-gigabit and 200-gigabit data rates. With the CFP2-DCO design, the coherent DSP is integrated within the module, unlike the CFP2 Analog Coherent Optics (CFP2-ACO) where the DSP chip resides on the line card.
“A concern of the market is that there has been essentially only one source of CFP2-DCO for the last few years and it was Acacia,” says LeMaitre. “Now there will be a broader supply for people who want coherent pluggables.”
Oclaro has been selling a CFP2-ACO but the company could not address those systems vendors that do not have their own DSP yet want to use coherent pluggables. “Now we can leverage our optics and combine it with Acacia’s DSP and bring another source of the CFP2-DCO,” says LeMaitre.
Acacia’s Meru is a low-power DSP that supports 200 gigabit-per-second (Gbps) wavelengths using either 8-ary quadrature amplitude modulation (8-QAM) or 16-QAM. Using 8-QAM enhances the optical reach at 200 gigabit. Oclaro’s CFP2-DCO uses its indium phosphide-based optics whereas Acacia’s module uses the company’s silicon photonics technology.
Oclaro sees the deal with Acacia as a first step, given the coming generation of 400-gigabit coherent modules including the 400ZR.
Production of Oclaro’s CFP2-DCO will commence in early 2019.
WaveLogic Ai DSP
Oclaro, along with module makers Lumentum and NeoPhotonics, signed an agreement in 2017 with Ciena to use the equipment maker’s 400-gigabit WaveLogic Ai coherent DSP. Oclaro is now shipping the 400-gigabit optical module that uses the Ciena DSP.
“The market for these types of large 400-gigabit form-factor modules in fairly limited as it is already addressed by many of the network equipment manufacturers,” says LeMaitre. “It [the module] is targeted at a few customers and a few opportunities.”
When the agreement with the three module makers was announced, there was talk of Ciena developing coherent DSPs for emerging applications such as 400-gigabit pluggables. However, Ciena has since decided to bring its own coherent modules to the marketplace and Oclaro does not yet know if it will get access to Ciena’s future coherent DSPs.
“We remain very interested in working with Ciena if they give us access to a DSP that could fit into pluggable coherent solutions but we have no agreement on that,” says LeMaitre.
There is an expectation in terms of dollar-per-bit that 400-gigabit modules are not yet meeting
Access and 5G wireless
At ECOC, Oclaro announced the availability of extended-temperature 10-gigabit and 25-gigabit lasers for access network and 5G deployments. The company also detailed its electro-absorption modulated laser (EML) supporting single-wavelength 100-gigabit transmissions for the data centre.
LeMaitre says the latest laser opportunities stem from the expansion and speed upgrades of the access infrastructure as well as upcoming 5G deployments. “This is resulting in a new lease of life for single-mode lasers because of the faster speeds and increased distances,” he says. These distances range from 10-40km and even 80km.
The environmental conditions required for these applications means the lasers must operate over industrial temperature (I-Temp) ranges, from -40 to 85oC and even higher.
Oclaro’s 25-gigabit directly-modulated laser (DML) for 5G fronthaul and mid-haul applications operates at up to 95oC. This means the laser does not need a thermo-electric cooler, simplifying the module design and reducing its power consumption. The laser has also been operated at 50 gigabit-per-second (Gbps) using 4-level pulse-amplitude modulation (PAM-4).
LeMaitre says the architectures for 5G will vary depending on the density of deployments and the primary application such as broadband or the Internet of Things.
Oclaro also announced an extended temperature range DML for 10-gigabit passive optical networks such as XGS-PON and 10GE-PON. The laser, which operates at the 1270nm wavelength, is used at the optical network unit (ONU) at the premises. Oclaro is also developing new 10-gigabit EMLs for the downstream link, from the PON optical line terminal (OLT) to the ONU. Transmission distances for such PONs can be 20km.
The company recently expanded laser production at its Japan and UK facilities, while the 10- and 25-gigabit lasers are now being mass-produced.
400 Gigabit Ethernet
Oclaro was one of five companies that took part in a 100-gigabit single-wavelength interoperability demonstration organised by the Ethernet Alliance at the show. The other four were Applied Optoelectronics, InnoLight Technology, Source Photonics, and Sumitomo Electric Industries.
The company showed its EML operating at 50 gigabaud with PAM-4 in the 100-Gigabit QSFP28 module. The 50Gbaud EML can operate uncooled such that no thermo-electric cooler is needed.
Oclaro says it will soon start sampling a 400-gigabit QSFP-DD FR4 module. The 2km four-channel FR4 developed by the 100-Gigabit Single Lambda MSA will use four 50Gbaud lasers. Volume production of the FR4 module is expected from the second quarter of 2019.
LeMaitre says 400-gigabit modules for the data centre face two key challenges.
One is meeting the power consumption of the new form factor modules such as the QSFP-DD. The optics for a four-wavelength design consumes 3-4W while the accompanying PAM-4 digital signal processor can consume 7-8W. “A transceiver burning 10-12W might be an issue for large-scale deployments,” says LeMaitre. “There is a power issue here that needs to be fixed.”
The second challenge for 400-gigabit client-side is cost. The price of 100-gigabit modules has now come down considerably. “There is an expectation in terms of dollar-per-bit that 400-gigabit modules are not yet meeting,” says LeMaitre. If the DSPs have yet to meet the power needs while the cost of the new modules is not in line with the dollar-per-bit performance of 100-gigabit modules, then 400-gigabit modules will be delayed, he says.
Acquisition
Lumentum’s acquisition of Oclaro, announced in March, continues to progress.
LeMaitre says two of the main three hurdles have now been overcome: anti-trust clearance in the U.S. and gaining shareholder approval. What remains is achieving Chinese clearance via the State Authority for Market Regulation.
“Until the merger deal is closed, we have to continue to operate as two separate companies,” says LeMaitre. But that doesn't prevent the two firms planning for the day when the deal is completed. Issues being worked through include the new organisation, the geographic locations of the companies’ groups, and how the two firms will work together to build a combined financial model.
The deal is expected to close before the year-end.
Lumentum jolts the industry with Oclaro acquisition
Lumentum announced on Monday its plan to acquire Oclaro in a deal worth $1.8 billion.
The prospect of consolidation among optical component players has long been mooted yet the announcement provided the first big news jolt at the OFC show, being held in San Diego this week.
Alan Lowe“Combined, we will be an industry leader in telecom transmission and transport as well as 3D sensing,” said Alan Lowe, president and CEO of Lumentum, on an analyst call discussing the deal.
Lumentum says their joint revenues totalled $1.7 billion with a 39% gross margin over the last year. And $60 million in synergies are forecast in the second year after the deal closes, which is expected to happen later this year.
The $1.8 billion acquisition will comprise 56 percent cash and 44 percent Lumentum stock. Lumentum will also raise $550 million to help finance the deal.
“This is a big deal as it consolidates the telecom part of the component market,” says Daryl Inniss, business development manager at OFS Fitel and former market research analyst.
Background
Lowe said that ever since Lumentum became a standalone company three years ago, the firm concentrated on addressing the increase in optical communications demand that started in late 2015 and then last year on ramping the production of its 3D sensing components. “Execution on major M&As had to wait,” he said.
The company investigated potential acquisitions and evaluated several key technologies including silicon photonics and indium phosphide. This led to it alighting on Oclaro with its indium phosphide and photonic integrated circuit (PIC) expertise.
Lowe also highlighted Oclaro’s strategy of the last five years of first trimming its business lines and then successfully executing on delivering optical transmission products.
Oclaro’s CEO, Greg Dougherty, CEO of Oclaro, described how his company has focussed on delivering differentiated photonic chip products to various growing end markets. “This is a very good combination for both companies and for the industry,” said Dougherty.
There is no overabundance in [optical] chip designers worldwide and together we have the strongest chip designer team in the world
Business plans
Lumentum’s business includes telecom transport components, modules and sub-systems. Its products include reconfigurable optical add/drop multiplexers (ROADMs), pump lasers, optical amplifiers and submarine products. In the second half of 2017, Lumentum’s telecom revenue mix was split three quarters telecom transport with transmission products accounted for the remaining quarter. Other Lumentum businesses include industrial lasers and 3D sensing.
In contrast, Oclaro’s focus in solely transmission components and modules, with the revenue mix in its most recent quarter being 53 percent telecom line side and 47 percent datacom client-side products.
The combined R&D resources of the merged company will allow it to do a much better job at supporting datacom products using the new QSFP-DD and OSFP form factors. “Right now I’m guessing that Alan is spread thin and I know the Oclaro datacom team has been spread thin,” says Dougherty.
The acquisition will also pool the two companies’ fabrication facilities.
Lumentum has already moved its lithium niobate manufacturing to its main gallium arsenide and indium phosphide fab in San Jose, California. San Jose also hosts a separate planar lightwave circuit fab.
Oclaro, which is headquartered in San Jose, has three photonic chip fabrication sites: an indium phosphide laser fab for datacom in Japan that makes directly modulated lasers (DMLs) and electro-absorption modulated lasers (EMLs), an indium phosphide fab in the UK that manufactures coherent optical components and sub-assemblies, and a lithium niobate fab in Italy.
The acquisition will also bolster the company’s chip design resources. “There is no overabundance in [optical] chip designers worldwide and together we have the strongest chip designer team in the world,” says Dougherty.
Lumentum plans to assign some of the chip designers to tackle a burgeoning pipeline of 3D sensing product designs.
In 2017 Lumentum reported three customers that accounted for nearly half of its revenues, while Oclaro had four customers, each accounted for 10 percent or more of its sales, in 4Q 2017. Oclaro selected customers include the webscale players, Amazon, Google and Microsoft, as well as leading systems vendors such as Ciena, Cisco, Coriant, Huawei, Juniper, Nokia and ZTE.
Both Oclaro and Lumentum, along with Neophotonics, signed an agreement with Ciena a year ago to use its WaveLogic Ai DSP in their coherent module designs.
Lumentum plans to provide more deal details closer to its closure. Meanwhile, the two CEOs will continue to run their companies with Oclaro’s Dougherty remaining at least during the transition period.
Further information:
For the link to the acquisition presentation, click here.
Juniper Networks opens up the optical line system
Juniper Networks has responded to the demands of the large-scale data centre players with an open optical line system architecture.
Donyel Jones-WilliamsThe system vendor has created software external to its switch, IP router and optical transport platforms that centrally controls the optical layer.
Juniper has also announced a reconfigurable optical add-drop multiplexer (ROADM) - the TCX1000 - that is Lumentum’s own white box ROADM design. Juniper will offer the Lumentum white box as its own, part of its optical product portfolio.
The open line system architecture, including the TCX1000, is also being pitched to communications service providers that want an optical line system and prefer to deal with a single vendor.
“Juniper plans to address the optical layer with a combination of software and open hardware in the common optical layer,” says Andrew Schmitt, founder and lead analyst at Cignal AI. “This is the solution it will bring to customers rather than partnering with an optical vendor, which Juniper has tried several times without great success.”
Open line systems
An optical line system comprises terminal and transmission equipment and network management software. The terminal equipment refers to coherent optics hosted on platforms, while line elements such as filters, optical amplifiers and ROADMs make up the transmission equipment. Traditionally, a single vendor has provided all these elements with the network management software embedded within the vendor’s platforms.
An open optical line system refers to line equipment and the network management system from a vendor such as Nokia, Infinera or Ciena that allows the attachment of independent terminal equipment. An example would be the Telecom Infra Project’s Voyager box linked to a Nokia line system, says Schmitt.
The open line system can also be implemented as a disaggregated design. Here, says Schmitt, the control software would be acquired from a vendor such as Juniper, Fujitsu, or Ciena with the customer buying open ROADMs, amplifiers and filters from various vendors before connecting them. Open software interfaces are used to communicate with these components. And true to an open line system, any terminal equipment can be connected.
The advantage of an open disaggregated optical line system is that elements can be bought from various sources to avoid vendor lock-in. It also allows the best components to be acquired and upgraded as needed.
Meanwhile, disaggregating the management and control software from the optical line system and equipment appeals to the way the internet content providers architect and manage their large-scale data centres. This is what Juniper’s proNX Optical Director platform enables, the second part of its open line system announcement.
Juniper believes its design is an industry first in how it separates the control plane from the optical hardware.
“We have taken the concept of disaggregation and software-defined networking to separate the control plane out of the hardware,” says Donyel Jones-Williams, director of product marketing management at Juniper Networks. “Our control plane is no longer tied to physical hardware.”
Having an open line system supplied by one vendor gets you 90% of the way there
Disaggregated control benefits the optimisation of the open line system, and enables flexible updates without disrupting the service.
Cignal AI’s Schmitt says that the cloud and co-location players are already using open line systems just not disaggregated ones.
“Having an open line system supplied by one vendor gets you 90% of the way there,” says Schmitt. For him, a key question is what problem is being solved by taking this one step further and disaggregating the hardware.
Schmitt’s view is that an operator introduces a lot of complexity into the network for the marginal benefit of picking hardware suppliers independently. “And realistically they are still single-sourcing the software from a vendor like Juniper or Ciena,” says Schmitt.
Juniper now can offer an open line system, and if a customer wants a disaggregated one, it can build it. “I don’t think users will choose to do that,” says Schmitt. “But Juniper is in a great position to sell the right open line system technology to its customer base and this announcement is interesting and important because Juniper is clearly stating this is the path it plans to take.”
TCX1000 and proNX
Juniper’s open optical line system announcement is the latest development in its optical strategy since it acquired optical transport firm, BTI Systems, in 2016.
BTI’s acquisition provided Juniper with a line system for 100-gigabit transport. “The filters and ROADMs didn’t allow the system to scale to 200-gigabit and 400-gigabit line rates and to support super-channels and flexgrid,” says Jones-Williams.
With the TCX1000, Juniper now has a one-rack-unit 20-degree ROADM that is colourless, directionless and which supports flexgrid to enable 400-gigabit, 600-gigabit and even higher capacity optical channels in future. The TCX1000 supports up to 25.6 terabits-per-second per line.
A customer can also buy the white box ROADM from Lumentum directly, says Juniper. “It gives our customers freedom as to how they want to source their product,” says Jones-Williams.
Competition between vendors is now in the software domain. We no longer believe that there is differentiation in the optical line system hardware
Juniper’s management and control software, the ProNX Optical Director, has been architected using microservices. Microservices offers a way to architect applications using virtualisation technology. Each application is run in isolation based on the service they provide. This allows a service to run and scale independently while application programming interfaces (APIs) enable communication with other services.
Container technology is used to implement microservices. Containers use fewer hardware resources than virtual machines, an alternative approach to server virtualisation.
Source: Juniper Networks.
“It is built for data centre operators,” says Don Frey, principal analyst, routers and transport at the market research firm, Ovum. “Microservices makes the product more modular.”
Juniper believes the competition between vendors is now in the software domain. “We no longer believe that there is differentiation in the optical line system hardware,” says Jones-Williams.
Data centre operators are not concerned about line system interoperability, they are just trying to remove the blade lock-in so they can get the latest technology.
Market demands
Most links between data centres are point-to-point networks yet despite that, the internet content providers are interested in ROADMs, says Juniper. What they want is to simplify network design using the ROADM’s colourless and flexible grid attributes. A directionless ROADM is only needed for complex hub sites that require flexibility in moving wavelengths through a mesh network.
The strategy of the large-scale data centre operators is to split the optical system between an open line system and purpose-built blades. The split allows them to upgrade to the best blades or pluggable optics while leaving the core untouched. “The concept is similar to the open submarine cables as the speed of innovation in core systems is not the same as the line optics,” says Frey. “Data centre operators are not concerned about line system interoperability, they are just trying to remove the blade lock-in so they can get the latest technology.”
Juniper says there is also interest from communications service providers in the ROADM as part of their embrace of open initiatives such as the Open ROADM MSA. Frey says AT&T will make its first deployment of the Open ROADM before the year-end or in early 2018.
“There are a lot of synergies in terms of what we have announced and things like Open ROADM,” says Jones-Williams. “But we know that there are customers out there that just want a line system and they do not care if it is open or not.”
Juniper is already working with customers with its open line system as part of the development of its proNX software.
The branded ROADM and the proNX Optical Director will be generally available in early 2018.
ST makes its first PSM4 optical engine deliveries
What gives Benetti confidence is the demand he is seeing for 100-gigabit transceivers in the data centre. “From my visibility today, the tipping point is 2016,” says Benetti, group vice president and general manager, digital and mixed processes ASIC division at STMicroelectronics.
Flavio Benetti
Benetti and colleagues at ST have spent the last four years working to bring to market the silicon photonics technology that the chip company licensed from Luxtera.
The company has developed a 300mm-wafer silicon photonics production line at its fabrication plant in Crolles that is now up and running. ST also has its first silicon photonics product - a mid-reach PSM4 100-gigabit optical engine - and has just started its very first deliveries.
At the OFC show in March, ST said it had already delivered samples to one unnamed 'customer partner', possibly Luxtera, and Benetti showed a slide of the PSM4 chips as part of a Lumentum transceiver.
Another ST achievement Benetti highlights is the development of a complete supply chain for the technology. In addition to wafer production, ST has developed electro-optic wafer testing. This allows devices to be probed electrically and optically to select working designs before the wafer is diced. ST has also developed a process to 3D-bond chips.
“We have focussed on building an industrial environment, with a supply chain that can deliver hundreds of thousands and millions of devices,” says Benetti.
PSM4 and CWDM4
ST’s first product, the components for a 4x25 gigabit PSM4 transceiver, is a two-chip design.
One chip is the silicon photonics optical engine which integrates the PSM4’s four modulators, four detectors and the grating couplers used to interface the chip to the fibres. The second chip, fabricated using ST’s 55nm BiCMOS process, houses the transceiver’s associated electronics such as the drivers, and trans-impedance amplifiers.
The two chips are combined using 3D packaging. “The 3D packaging consists of the two dies, one copper-pillar bonded to the other,” says Benetti. “It is a dramatic simplification of the mounting process of an optical module.”
The company is also developing a 100-gigabit CWDM4 transceiver which unlike the PSM4 uses four 25-gigabit wavelengths on a single fibre.
The CWDM4 product will be developed using two designs. The first is an interim, hybrid solution that uses an external planar lightwave circuit-based multiplexer and demultiplexer, followed by an integrated silicon photonics design. The hybrid design is being developed and is expected in late 2017; the integrated silicon photonics design is due in 2018.
With the hybrid design, it is not just a question of adding a mux-demux to the PSM4 design. “The four channels are each carrying a different wavelength so there are some changes that need to be done to the PSM4,” says Benetti, adding that ST is working with partners that will provide the mux-demux and do the integration.
We need to have a 100-gigabit solution in high volume for the market, and the pricing pressure that is coming has convinced us that silicon photonics is the right thing to do
Opportunities
Despite the growing demand for 100-gigabit transceivers that ST is seeing, Benetti stresses that these are not 'mobile-phone wafer volumes'. “We are much more limited in terms of wafers,” he says. Accordingly, there is probably only room for one or two large fabs for silicon photonics globally, in his opinion.
So why is ST investing in a large production line? For Benetti, this is an obvious development for the company which has been a provider of electrical ICs for the optical module industry for years.
“ST has entered silicon photonics to provide our customers with a roadmap,” says Benetti. “We need to have a 100-gigabit solution in high volume for the market, and the pricing pressure that is coming has convinced us that silicon photonics is the right thing to do.”
It also offers chip players the possibility of increasing its revenues. “The optical engine integrates all the components that were in the old-fashioned modules so we can increase our revenues there,” he says.
ST is tracking developments for 200-gigabit and 400-gigabit links and is assessing whether there is enough of an opportunity to justify pursuing 200-gigabit interconnects.
For now though, it is seeing strong pricing pressure for 100-gigabit links for reaches of several hundred meters. “We do not think we can compete for very short reach distances,” says Benetti. “We will leave that to VCSELs until the technology can no longer follow.” As link speeds increase, the reach of VCSEL links diminishes. “We will see more room for silicon photonics but this is not the case in the short term,” says Benetti.
Market promise
People have been waiting for years for silicon photonics to become a reality, says Benetti. “My target is to demonstrate it [silicon photonics] is possible, that we are serious in delivering parts to the market in an industrial way and in volumes that have not been delivered before.”
To convince the market, it is not just showing the technological advantages of silicon photonics but the fact that there is a great simplification in constructing the optical module along with the ability to deliver devices in volume. “This is the point,” he says.
Benetti’s other role at ST is overseeing advanced networking ASICs. He argues that over the mid- to long-term, there needs to be a convergence between ASIC and optical connectivity.
“Look at a switch board, for example, you have a big ASIC or two in the middle and a bunch of optical modes on the side,” says Benetti. For him, the two technologies - photonics and ICs - are complementary and the industry’s challenge is to make the two live together in an efficient way.