Infinera’s ICE6 crosses the 100-gigabaud threshold
Coherent discourse 3
- The ICE6 Turbo can send two 800-gigabit wavelengths over network spans of 1,100-1,200km using a 100.4 gigabaud (GBd) symbol rate.
- The enhanced reach can reduce the optical transport equipment needed in a network by 25 to 30 per cent.
Infinera has enhanced the optical performance of its ICE6 coherent engine, increasing by up to 30 per cent the reach of its highest-capacity wavelength transmissions.
The ICE6 Turbo coherent optical engine can send 800-gigabit optical wavelengths over 1,100-1,200km compared to the ICE6’s reach of 700-800km.
ICE6 Turbo uses the same coherent digital signal processor (DSP) and optics as the ICE6 but operates at a higher symbol rate of 100.4GBd.
“This is the first time 800 gigabits can hit long-haul distances,” says Ron Johnson, general manager of Infinera’s optical systems & network solutions group.
Baud rates
Infinera’s ICE6 operates at 84-96GBd to transmit two wavelengths ranging from 200-800 gigabits. This gives a total capacity of 1.6 terabits, able to send 4×400 Gigabit Ethernet (GbE) or 16x100GbE channels, for example.
Infinera’s ICE6’s coherent DSP uses sub-carriers and their number and baud rates are tuned to the higher symbol rate.
The bit rate sent is defined using long-codeword probabilistic constellation shaping (LC-PAS) while Infinera also uses soft-decision FEC gain sharing between the DSP’s two channels.
The ICE6 Turbo adds several more operating modes to the DSP that exploit this higher baud rate, says Rob Shore, senior vice president of marketing at Infinera.
Reach
Infinera says that the ICE6 Turbo can also send two 600-gigabit wavelengths over 4,000km.
“This is almost every network in the world except sub-sea,” says Shore, adding that the enhanced reach will reduce the optical transport equipment needed in a network by 25 to 30 per cent.
“One thousand kilometres sending 2×800 gigabits or 4x400GbE is a powerful thing,” adds Johnson. “We’ll see a lot of traction with the content providers with this.”
Increasing symbol rate
Optical transport system designers continue to push the symbol rate. Acacia, part of Cisco, has announced its next 128GBd coherent engine while Infinera’s ICE6 Turbo now exceeds 100GBd.
Increasing the baud rate boosts the capacity of a single coherent transceiver while lowering the cost and power used to transport data. A higher baud rate can also send the same data further, as with the ICE6 Turbo.
“The original ICE6 device was targeted for 84GBd but it had that much overhead in the design to allow for these higher baud rate modes,” says Johnson. “We strived for 84GBd and technically we can go well beyond 100.4GBd.”
This is common, he adds.
The electronics of the coherent design – the silicon germanium modulator drivers, trans-impedance amplifiers, and analogue-to-digital and digital-to-analogue converters – are designed to perform at a certain level and are typically pushed harder and harder over time.
Baud rate versus parallel-channel designs
Shore believes that the industry is fast approaching the point where upping the symbol rate will no longer make sense. Instead, coherent engines will embrace parallel-channel designs.
Already upping the baud rate no longer improves spectral efficiency. “The industry has lost a vector in which we typically expect improvements generation by generation,” says Shore. “We now only have the vector of lowering cost-per-bit.”
At some point, coherent designs will use multiple DSP cores and wavelengths. What matters will be the capacity of the optical engine rather than the capacity of an individual wavelength, says Shore.
“We have had a lot of discussion about parallelism versus baud rate,” adds Johnson.
Already there is fragmentation with embedded and pluggable coherent optics designs. Embedded designs are optimised for high-performance spectral efficiency while for pluggables cost-per-bit is key.
This highlights that there is more than one optimisation approach, says Johnson: “We have got to develop multiple technologies to hit all those different optimisations.”
Infinera will use 5nm and 3nm CMOS for its future coherent DSPs, optimised for different parts of the network.
Infinera will keep pushing the baud rate but Johnson admits that at some point the cost-per-bit will start to rise.
“At present, it is not clear that doubling the baud rate again is the right answer,” says Johnson. “Maybe it is a combination of a little bit more [symbol rate] and parallelism, or it is moving to 200GBd.”
The key is to explore the options and deliver coherent technology consistently.
“If we put too much risk in one area and drive too hard, it has the potential to push our time-to-market out,” says Johnson.
The ICE6 Turbo will be showcased at the OFC show being held in San Diego in March.
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.
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.