Infinera's XR optics pluggable plans
Infinera’s coherent pluggables for XR optics will also address the company’s metro needs.
Coherent pluggables now dominate the metro market where embedded designs account for just a fifth of all ports, says Infinera.
“As we grow our metro business, we need our own pluggables if we want to be cost-competitive,” says Robert Shore, senior vice president of marketing at Infinera.
Infinera’s family of pluggables implementing the XR optics concept is dubbed ICE-XR.
XR optics splits a coherent optical signal into Nyquist sub-carriers, each carrying a data payload. Twenty-five gigabits will likely be the sub-carrier capacity chosen.
XR optics can be used for point-to-point links where all the sub-carriers go to the same destination. But the sub-carriers can also be steered to different destinations, similar to how breakout cables are used in the data centre.
With XR optics, a module can talk to several lower-speed ones in a point-to-multipoint arrangement. This enables optical feeds to be summed, ideal for traffic aggregation applications such as access and 5G.
Open XR Forum
Infinera detailed its ICE-XR pluggables during the OFC virtual conference and exhibition.
The event coincided with the launch of the Open XR Forum whose members include network operators, Verizon, Lumen Technologies (formerly CenturyLink), Windstream and Liberty Global.
Members of the Open XR Forum span sub-component makers, systems vendors like Infinera, and network operators. The day the Open XR Forum website was launched, Infinera received a dozen enquiries from interested parties.
The Open XR Forum will define standards for XR optics such as how the networks are managed, the form factors used, their speeds and power requirements.
“There are a lot of underlying operational aspects that need to be worked out,” says Shore.
XR optics will use a similar model to ZR+ coherent optics. ZR+ delivers enhanced transmission performance compared to the OIF’s 400ZR coherent standard. “ZR+ is not a standard but rather a set of open specifications that can be used by anyone to create a product, and that is exactly the approach we are taking with XR optics,” says Shore.
Over the last 18 months, Infinera has met with 150 network operators regarding XR optics. “We wanted to validate this is a worthwhile technology and that people wanted it,” says Shore.
There have also been 40 network operator trials of the technology by the end of July. BT has used the technology as part of a metro aggregation trial while Virgin Media and American Tower each tested XR optics over PON.
More members have joined the Open XR Forum and will be announced in the autumn.
ICE-XR
ICE-XR’s name combines two concepts.
The first, ICE, refers to the Infinite Capacity Engine, the optics and coherent digital signal processor (DSP) that is the basis for Infinera’s ICE4 and newer ICE6 coherent transmission designs. ICE4 was Infinera’s first product to use Nyquist sub-carriers.
“XR”, meanwhile, borrows from 400ZR. Here, the ‘X’ highlights that XR supports point-to-point coherent communications, like 400ZR, and point-to-multipoint.
“ICE-XR’s release will be timed in conjunction with the official ratification of the specifications from the Open XR Forum,” says Shore.
Infinera’s ICE-XR portfolio will include 100, 400, and 800-gigabit optical modules.
The 100-gigabit ICE-XR, based on four 25-gigabit sub-carriers, will be offered as QSFP-28, QSDP-DD and CFP2 form factors. The 400-gigabit and 800-gigabit variants, using 16 and 32 sub-carriers respectively, will be available as QSFP-DD and CFP2 modules.
The 100-gigabit and 400-gigabit ICE-XR modules will be released first in 2022.
The 400-gigabit ICE-XR will also double as Infinera’s ZR+ offering when used point-to-point.
Shore says its first ZR+ module will not support the oFEC forward-error correction (FEC) used by the OpenZR+ multi-source agreement (MSA).
“The performance hit you take to ensure multi-vendor interoperability is vastly outweighed by the benefits of the improved [optical] performance [using a proprietary FEC],” says Shore.
Merchant DSP suppliers and the systems vendors with in-house DSP designs all support proprietary FEC schemes that deliver far better performance than oFEC, says Shore.
Infinera is developing a monolithic photonic integrated circuit (PIC) for ICE-XR manufactured at its indium phosphide facility.“ICE-XR will increase the utilisation of our fabrication centre, especially when pluggables produce higher volumes compared to embedded [coherent designs],” says Shore.
Infinera says more than one coherent DSP will be needed for the ICE-XR product portfolio. The modules used have a range of power profiles. The QSFP-28 module will need to operate within 4-5W, for example, while the QSFP-DD implementing ZR+ will need to be below 20W. Developing one DSP to span such a power range is not possible.
Business model
The Open XR Forum’s specifications will enable vendors to develop their own XR optics implementations.
Infinera will also license aspects of its design including its coherent DSPs. The aim, says Shore, is to develop as broad an ecosystem as possible: “We want to make XR optics an industry movement.”
Shore stresses ZR+ interoperability is not a must for most applications. Typically, a vendor’s module will be used at both ends of a link to benefit from the ZR+’s custom features. But interoperability is a must for XR optics given its multi-rate nature. The different speed modules from different vendors must talk to each other.
“Because you have multi-generational and multi-rate designs, it becomes even more important to support multi-vendor interoperability,” says Shore. “It gives the network operators more choice, freedom and flexibility.”
XR optics for the data centre
Infinera says there are developments to use XR optics within the data centre.
As data rates between equipment rise, direct-detect optics will struggle to cope, says Shore. The hierarchical architectures used in data centres also lend themselves to a hub-and-spoke architecture of XR optics.
“This type of technology could fit very nicely into that environment once the capacity requirements get high enough,” says Shore.
For this to happen, power-efficient coherent designs are required. But first, XR optics will need to become established and demonstrate a compelling advantage in a point-to-multipoint configuration.
XR optics will also need to replace traditional direct-detect pluggables that continue to progress; 800-gigabit designs are appearing and 1.6-terabit designs were discussed at OFC. Co-packaged optics is another competing technology.
“You are not looking at the 2022-23 timeframe, but maybe 2025-26,” says Shore.
Covid-era shows
Infinera postponed its customer meetings that pre-covid would take place at OFC till after the show to avoid clashing with the online sessions. Once the meetings occurred, customers were given a tour of Infinera’s virtual OFC booth.
Infinera’s solutions marketing team also divided between them the OFC sessions of interest to attend. The team then ‘met’ daily to share their learnings.
“I do think that the world of in-person events has changed forever,” says Shore. Infinera attended 40 events in 2019. “We will probably do fewer than 20 [a year] going forward,” says Shore.
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.