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.
Windstream to add ICE6 as it stirs its optical network
Windstream has sent an 800-gigabit optical signal between the US cities of Phoenix and San Diego. The operator used Infinera’s Groove modular chassis fitted with its latest ICE6 infinite capacity engine for the trial.
Infinera reported in March sending an 800-gigabit signal 950km with another operator but this is the first time a customer, Windstream, is openly discussing a trial and the technology.
The bulk of Windstream’s traffic is sent using 100-gigabit wavelengths. Moving to 800-gigabit will reduce its optical transport costs.
Windstream will also be able to cram more digital traffic down its fibre. It sends 12 terabits and that could grow to 40 terabits.
Motivation
Windstream provides residential broadband, business and wholesale services in the US.
“We operate a national footprint for wholesale and enterprise services,” says Art Nichols, vice president of architecture and technology at Windstream. “The optical focus is for wholesale and enterprise.”
Art Nichols
The communications service provider has 160,000 miles of fibre, 3,700 points-of-presence (PoPs) and operates in 840 cities. “We are continually looking to expand that,” says Nichols. “Picking up new PoPs, on-ramps and landing spots to jump onto the long-haul network.”
If Windstream’s traffic is predominantly at 100-gigabit, it also has 200-gigabit wavelengths and introduced recently 400-gigabit signals. In April Windstream and Infinera trialled Gigabit Ethernet (GbE) client-side services using LR8 modules.
Windstream is interested in adopting 800-gigabit wavelengths to reduce transport costs. “To try to draw as much efficiency as you can, using as few lasers as you can, to push down the cost-per-bit,” says Nichols.
The operator is experiencing traffic growth at a 20-30 per cent compound annual growth rate that is eroding its revenue-per-bit.
Weekly traffic has also jumped a further 20 per cent during the COVID-19 pandemic. Video traffic is the main driver, with peak traffic hours starting earlier in the day and continuing into the evenings.
Sending more data on a wavelength reduces cost-per-bit and improves revenue-per-bit figures.
In addition to sending a 800-gigabit signal over 730km, the operator sent a 700-gigabit signal 1,460km. The two spans are representative of Windstream’s network.
“Eight hundred gigabits is an easier multiple - better to fit two 400GbE clients - but 700 gigabits has tons of applications,” says Nichols. “We are predominantly filling 100-gigabit orders today so being able to multiplex them is advantageous.”
Another reason to embrace the new technology is to fulfill wholesale orders in days not months. “The ability to turn around multi-terabit orders from webscale customers,” says Nichols. “That is increasingly expected of us.”
One reason order fulfilment is faster is that the programming interfaces of the equipment are exposed, allowing Windstream to connect its management software. “We instantiate services in a short turnaround,” says Nichols.
ICE6 technology
Infinera’s ICE6 uses a 1.6-terabit photonics integrated circuit (PIC) and its 7nm CMOS FlexCoherent 6 digital signal processor (DSP). The 1.6 terabits is achieved using two wavelengths, each able to carry up to 800 gigabits of traffic.
The ICE6 uses several techniques to achieve its optical performance. One is Nyquist sub-carriers where data is encoded onto several sub-carriers rather than modulating all the data onto a single carrier.
The benefit of sub-carriers is that high data rates are achieved despite the symbol rate of each sub-carrier being much lower. The lower symbol rate means the optical transmission is more tolerant to non-linear channel impairments. Sub-carriers also have sharper edges so can be squeezed together enabling more data in a given slice of spectrum.
Infinera also applies probabilistic constellation shaping to each sub-carrier, enabling just the right amount of data to be placed on each one.
The FlexCoherent 6 DSP also uses soft-decision forward-error correction (SD-FEC) gain sharing. The chip can redistribute processing to the optical channel that needs it the most.
Some of the strength of the stronger signal can be cashed in to strengthen the weaker one, extending its reach or potentially allowing more bits to be sent by enabling a higher modulation scheme to be used.
Windstream cannot quantify the cost-per-bit advantage using the ICE6. “We don’t have finalised pricing,” says Nichols. But he says the latest coherent technology has significantly better spectral efficiency.
Spectral efficiency can be increased in two ways, says Rob Shore, Infinera’s senior vice president of marketing.
One is to increase the modulation scheme and the other is to close the link and maintain the high modulation over longer spans. If the link can’t be closed, lowering the modulation scheme is required which reduces the bits carried and the spectral efficiency.
Windstream will be able to increase capacity per fibre by as much as 70 per cent compared to the earlier generation 400-gigabit coherent technology and by as much as 35 per cent compared to 600-gigabit coherent.
A total of 42.4 terabits can be sent over a fibre using 800-gigabit wavelengths, says Shore, but the symbol rate needs to be reduced to 84 gigabaud shortening the overall reach.
Trial learnings
The rate-reach performance of the ICE6 was central to the trial but what Windstream sought to answer was how the ICE6 would perform across its network.
“We paid really close attention to margins and noise isolation as indicators as to how it would work across the network,” says Nichols. “The exciting thing is that it is extremely applicable.”
Windstream is also upbeat about the technology’s optical performance.
“We have a fair amount of information as to what the latest optical engines are capable of,” says Nichols. “This trial gave us a good view of how the ICE6 performs and it turns out it has advantages in terms of rate-reach performance.”
Ciena, Huawei and Infinera all have 800-gigabit coherent technology. Nokia recently unveiled its PSE-V family of coherent devices that does not implement 800-gigabit wavelengths.
Michael Genovese, a financial analyst at MKM Partners, puts the ICE6 on a par with Ciena’s WaveLogic 5 that is already shipping to over 12 customers.
“We expect 800 gigabit to be a large and long cycle," says Genovese in a recent research note. “We think most of the important internet content providers, telcos and subsea consortia will adopt a duel-vendor strategy, benefitting Ciena and Infinera over time.”
Windstream will adopt Infinera’s ICE6 technology in the first half of 2021. First customers to adopt the ICE6 will be the internet content providers 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.
Acacia heralds the era of terabit-plus optical channels
Acacia Communications has unveiled the AC1200-SC2 that delivers 1.2 terabits over a single optical channel.
The SC2 (single chip, single channel) is an upgrade of Acacia’s high-end AC1200 module. The AC1200 too is a 1.2-terabit module but uses two optical channels, each transmitting a 600-gigabit wavelength. The SC2 sends 1.2 terabits using two sub-carriers that fit within a single 150GHz-wide channel.
Each line is a data rate. Shown is the scope of how the baud rate and the modulation scheme can be varied and its impact on channel width, reach and data rate. Source: ADVA.
“In the SC2, we take care of everything so the user configures a single channel that is easier to manage in their network,” says Tom Williams, vice president of marketing at Acacia.
1.2-terabit channel
Acacia unveiled the AC1200 at the ECOC show in 2017. With its introduction, Acacia gained an advantage over its system-vendor rivals in bringing a 1.2-terabit coherent module to market using 600-gigabit wavelengths. The module supports up to 64-ary quadrature amplitude modulation (64-QAM) and a symbol rate of 69 gigabaud (GBd).
Systems vendors such as Ciena, with its WaveLogic 5, and Infinera, with its Infinite Coherent Engine 6 (ICE6), responded with their next-generation coherent designs that use symbol rates approaching 100GBd and support an 800-gigabit wavelength.
Sell-side research analysts interpreted the coherent developments as Acacia having a window of opportunity to exploit the AC1200 until the systems vendors’ coherent designs come to market in the coming year. The analysts also noted how 400 Gigabit Ethernet client signals better fit in an 800-gigabit wavelength compared to a 600-gigabit wavelength.
Then, in July, Acacia’s status as a merchant coherent technology supplier changed with the announcement that Cisco Systems is to acquire the company for $2.6 billion. Now, Acacia has detailed the SC2 as its acquisition awaits completion.
AC1200-SC2
The SC2 uses the same form factor and electrical connector as the AC1200 module, simplifying the upgrading of system designs using the AC1200. However, the SC2 module uses a single fibre pair for its optical output whereas the AC1200 uses two pairs, one for each channel.
The SC2 module shares the same Pico coherent digital signal processor (DSP) and baud rates as the AC1200. The Pico DSP uses fractional quadrature amplitude modulation (QAM) and an adjustable baud rate.
Fractional QAM allows the tuning of the transmitted data rate by using a mix of adjacent modulation formats. For example, 8-QAM and 16-QAM are alternated, and the percentage of time each is used determining the resulting data rate. In turn, the baud rate can be increased to widen the signal’s spectrum, if the optical channel permits, such that using a lower modulation scheme may become possible, improving the reach (see diagram above).
The AC1200 uses 50GHz- and 75GHz-wide channels while the SC2 uses 50-150GHz channels. For 600-gigabit and 1.2-terabit transmissions, the widest channels are used: 75GHz for the AC1200, and 150GHz for the SC2. “But as you go down in data rate, you can address the transmission in multiple ways,” says Williams. “You can run a higher modulation scheme in a narrow channel or, with a wider channel, run a lower modulation scheme to go further.”
The result optical performance means that the SC2 can be used for multiple applications: from short-span data centre interconnect where the full 1.2-terabit capacity is sent using 64-QAM, to metro-regional and long-haul distances using 800-gigabit and 16-QAM, all the way to ultra-long-haul terrestrial and subsea links with 400-gigabitand quadrature phase-shift keying (QPSK) modulation.
The AC1200 and the SC2 have comparable optical performance in terms of spectral efficiency and reach. This is unsurprising given how both modules use the same Pico DSP, baud rates and modulation schemes.
The AC1200 uses two 75GHz channels, each carrying 600 gigabits, to send 1.2 terabits, while the SC2 uses two sub-carriers in a 150GHz channel. However, the SC2 has a slight advantage since no guard band is needed between the two channels as is required with the AC1200 (unless the AC1200 is sending a two-channel ‘superchannel’ whereby no dead zone is needed between the channels).
Acacia is not detailing how it generates the optical sub-carriers besides saying the change stems from the interface between the Pico DSP and its silicon photonics-based photonic integrated circuit (PIC). The company will also not say if the SC2 uses a new PIC design.
Operational benefits
The fact that the SC2 and AC1200 deliver the same reach and capacity may explain why Acacia downplays the argument that the company has again leapfrogged its rivals with the advent of a module that sends 1.2 terabits over a single channel.
Instead, Acacia stresses the system and operational benefits resulting from doubling the data transmitted per channel.
“The SC2 module allows the entire capacity to be managed as a single channel,” says Williams. “The original [AC1200] module is well-suited to brownfield networks operating with 50GHz or 75GHz spacing, while the SC2 offers advantages in greenfield network architectures that can use channel plans up to 150GHz.”
Using a higher-capacity channel requires fewer optical components and reconfigurable optical add/ drop multiplexer (ROADM) ports thereby reducing networking costs, says Williams.
Using 150GHz-wide channels also aligns with an emerging consensus among network operators regarding wavelength roadmaps. “Network operators want to operate on some standardised grid based on regular multiples [50GHz, 75GHz] because it avoids fragmentation,” says Williams.
Availability
Acacia is already providing the SC2 module to certain customers that are undertaking validation testing. The firm is ready to ramp production based on particular customer demand.
Acacia will also be demonstrating its latest module at this week’s ECOC show being held in Dublin.