Nokia buys Elenion for its expertise and partnerships
Nokia will become the latest systems vendor to bolster its silicon photonics expertise with the acquisition of Elenion Technologies.
The deal for Elenion, a privately-held company, is expected to be completed this quarter, subject to regulatory approval. No fee has been disclosed.
“If you look at the vertically-integrated [systems] vendors, they captured the lion’s share of the optical coherent marketplace,” says Kyle Hollasch, director of optical networking product marketing at Nokia. “But the coherent marketplace is shifting to pluggables and it is shifting to more integration; we can’t afford to be left behind.”
Elenion Technologies
Elenion started in mid-2014, with a focus of using silicon as a platform for photonics. “We consider ourselves more of a semiconductor company than an optics company,” says Larry Schwerin, CEO of Elenion.
Elenion makes photonic engines and chipsets and is not an optical module company. “We then use the embedded ecosystem to offer up solutions,” says Schwerin. “That is how we approach the marketplace.”
The company has developed a process design kit (PDK) for photonics and has built a library of circuits that it uses for its designs and custom solutions for customers.
A PDK is a semiconductor industry concept that allows circuit designers to develop complex integrated circuits without worrying about the underlying transistor physics. Adhering to the PDK ensures the circuit design is manufacturable at a chip fabrication plant (fab).
But developing a PDK for optics is tricky. How the PDK is designed and developed must be carefully thought through, as has the manufacturing process, says Elenion.
“We got started on a process and developed a library,” says Larry Schwerin, CEO of Elenion. “And we modelled ourselves on the hyperscale innovation cycle, priding ourselves that we could get down to less than three years for new products to come out.”
The “embedded ecosystem” Elenion refers to involves close relationships with companies such as Jabil to benefit from semiconductor assembly test and packaging techniques. Other partnerships include Molex and webscale player, Alibaba.
Elenion initially focussed on coherent optics, providing its CSTAR coherent device that supports 100- and 200-gigabit transmissions to Jabil for a CFP2-DCO pluggable module. Other customers also use the design, mostly for CFP2-DCO modules.
The company has now developed a third-generation coherent design, dubbed CSTAR ZR, for 400ZR optics. The optical engine can operate up to 600 gigabits-per-second (Gbps), says Elenion.
Elenion’s work with the cloud arm of Alibaba covers 400-gigabit DR4 client-side optics as well as an 800-gigabit design.
Alibaba Cloud has said the joint technology development with Elenion and Hisense Broadband covers all the production stages: the design, packaging and testing of the silicon photonics chip followed by the design, packaging, assembly and testing of the resulting optical module.
Bringing optics in-house
With the acquisition of Elenion, Nokia becomes the latest systems vendors to buy a silicon photonics specialist.
Cisco Systems acquired Lightwire in 2012 that enabled it to launch the CPAK, a 100-gigabit optical module, a year ahead of its rivals. Cisco went on another silicon photonics shopping spree more recently with the acquisition of Luxtera in 2019, and it is the process of acquiring leading merchant coherent player, Acacia Communications.
In 2013 Huawei bought the Belgium silicon photonics start-up, Caliopa, while Mellanox Technologies acquired silicon photonics firm, Kotura, although subsequently, it disbanded its silicon photonics arm.
Ciena bought the silicon-photonics arm of Teraxion in 2016 and, in the same year, Juniper bought silicon photonics start-up, Aurrion Technologies.
Markets
Nokia highlights several markets – 5G, cloud and data centres – where optics is undergoing rapid change and where the system vendor’s designs will benefit from Elenion’s expertise.
“5G is a pretty obvious one; a significant portion of our optical business over the last two years has been mobile front-haul,” says Nokia’s Hollasch. “And that is only going to become more significant with 5G.”
Front-haul is optics-dependent and requires new pluggable form factors supporting lower data rates such as 25Gbps and 100Gbps. “This is the new frontier for coherent,” says Hollasch.
Nokia is not looking to be an optical module provider, at least for now. “That one we are treading cautiously,” says Hollasch. “We, ourselves, are quite a massive customer [of optics] which gives us some built-in scale straight away but our go-to-market [strategy] is still to be determined.”
Not being a module provider, adds Schwerin, means that Nokia doesn’t have to come out with modules to capitalise on what Elenion has been doing.
Nokia says both silicon photonics and indium phosphide will play a role for its coherent optical designs. Nokia also has its own coherent digital signal processors (DSPs).
“There is an increasingly widening application space for silicon photonics,” says Hollasch. “Initially, silicon photonics was looked at for the data centre and then strictly for metro [networks]; I don’t think that is the case anymore.”
Why sell?
Schwerin says the company was pragmatic when it came to being sold. Elenion wasn’t looking to be acquired and the idea of a deal came from Nokia. But once the dialogue started, the deal took shape.
“The industry is in a tumultuous state and from a standpoint of scenario planning, there are multiple dynamics afoot,” says Schwerin.
As the company has grown and started working with larger players including webscales, their requirements have become more demanding.
“As you get more into bigs, they require big,” says Schwerin. “They want supply assurance, and network indemnification clauses come into play.” The need to innovate is also constant and that means continual investment.
“When you weigh it all up, this deal makes sense,” he says.
Schwerin laughs when asked what he plans to do next: “I know what my wife wants me to do.
“I will be going with this organisation for a short while at least,” he says. “You have to make sure things go well in the absorption process involving big companies and little companies.”
Coherent gets a boost with probabilistic shaping
Nokia has detailed its next-generation PSE-3 digital signal processor (DSP) family for coherent optical transmission.
The PSE-3s is the industry’s first announced coherent DSP that supports probabilistic constellation shaping, claims Nokia.
Probabilistic shaping is the latest in a series of techniques adopted to improve coherent optical transmission performance. These techniques include higher-order modulation, soft-decision forward error correction (SD-FEC), multi-dimensional coding, Nyquist filtering and higher baud rates.
Kyle Hollasch
“There is an element here that the last big gains have now been had,” says Kyle Hollasch, director of product marketing for optical networks at Nokia.
Probabilistic shaping is a signal-processing technique that squeezes the last bit of capacity out of a fibre’s spectrum, approaching what is known as the non-linear Shannon Limit.
“We are not saying we absolutely hit the Shannon Limit but we are extremely close: tenths of a decibel whereas most modern systems are a couple of decibels away from the theoretical maximum,” says Hollasch.
Satisfying requirements
Optical transport equipment vendors are continually challenged to meet the requirements of the telcos and the webscale players.
One issue is meeting the continual growth in IP traffic: telcos are experiencing 25 percent yearly traffic growth whereas for the webscale players it is 60 percent. Vendors must also ensure that their equipment keeps reducing the cost of transport when measured as the cost-per-bit.
Operators also want to automate their networks. Technologies such as flexible-grid, reconfigurable optical add/drop multiplexers (ROADMs), higher-order modulation and higher baud rates all add flexibility to the optical layer but at the expense of complexity.
There is an element here that the last big gains have now been had
“It is easy to say software-defined networking will hide all that complexity,” says Hollasch. “But hardware has an important role: to keep delivering capacity gains but also make the network simpler.”
Satisfying these demands is what Nokia set out to achieve when designing the PSE-3s.
Capacity and cost
Like the current PSE-2 coherent DSPs that Nokia launched in 2016, two chips make up the PSE-3 family: the super coherent PSE-3s and the low-power compact PSE-3c.
The PSE-3s is a 1.2-terabit chip that can drive two sets of optics, each capable of transmitting 100 to 600 gigabit wavelengths. This compares to the 500-gigabit PSE-2s that can drive two wavelengths, each up to 250Gbps.
The low-power PSE-3c also can transmit more traffic, 100 and 200-gigabit wavelengths, twice the capacity of the 100-gigabit PSE-2c.
Nokia has used a software model of two operators’ networks, one an North America and another in Germany, to assess the PSE-3s.
The PSE-3s’ probabilistic shaping delivers 70% more capacity while using a third fewer line cards when compared with existing commercial systems based on 100Gbps for long haul and 200Gbps for the metro. When the PSE-3s is compared with existing Nokia PSE-2s-based platforms on the same networks, a 25 percent capacity gain is achieved using a quarter fewer line cards.
Hollasch says that the capacity gain is 1.7x and not greater because 100-gigabit coherent technology used for long haul is already spectrally efficient. “But it is less so for shorter distances and you do get more capacity gains in the metro,” says Hollasch.
Probabilistic shaping
The 16nm CMOS PSE-3s supports a symbol rate of up to 67Gbaud. This compares to the 28nm CMOS PSE-2s that uses two symbol rates: 33Gbaud and 45Gbaud.
The PSE-3s’ higher baud rate results in a dense wavelength-division multiplexing (DWDM) channel width of 75GHz. Traditional fixed-grid channels are 50GHz wide. With 75GHz-wide channels, 64 lightpaths can fit within the C-band.
The PSE-3s uses one modulation format only: probabilistic shaping 64-ary quadrature amplitude modulation (PS-64QAM). This compares with the PSE-2s that supports six modulations ranging from binary phase-shift keying (BPSK) for the longest spans to 64-QAM for a 400-gigabit wavelength.
Using probabilistic shaping, one modulation format supports data rates from 200 to 600Gbps. For 100Gbps, the PSE-3s uses a lower baud rate in order to fit existing 50GHz-wide channels.
In current optical networks, all the constellation points of the various modulation formats are used with equal probability. BPSK has two constellation points while 64-QAM has 64. Probabilistic shaping does not give equal weighting to all the constellation points. Instead, it favours those with lower energy, represented by those points closer to the origin in a constellation graph. The only time all the constellation points are used is at the maximum data rate - 600Gbps for the PSE-3s.
Using the inner, lower energy constellation points more frequently than the outer points reduces the overall average energy and this improves the signal-to-noise ratio. That is because the symbol error rate at the receiver is dominated by the distance between neighbouring points on the constellation. Reducing the average energy still keeps the distance between the points the same, but since a constant signal power level is used for DWDM transmission, applying gain increases the distance between the constellation points.
“We separate these points further in space - the Euclidean distance between them,” says Hollasch. “That is where the shaping gain comes from.”
Changing the probabilistic shaping in response to feedback from the chip, from the network, we think that is a powerful innovation
Using probabilistic shaping delivers a maximum 1.53dB of improvement in a linear transmission channel. In practice, Nokia says it achieves 1dB. “One dB does not sound a lot but I call it the ultimate dB, the last dB in addition to all the other techniques,” he says.
By using few and fewer of the constellation points, or favouring those points closer to the origin, reduces the data that can be transported. This is how the data rate is reduced from the maximum 600Gbps to 200Gbps.
To implement probabilistic shaping, Nokia has developed an IP block for the chip called the distribution matcher. The matcher maps the input data stream as rates as high as 1.2 terabits-per-second onto the constellation points in a non-uniform way.
Theoretically, probabilistic shaping allows any chosen data rate to be used. But what dictates the actual data rate gradations is the granularity of the client signals. The Optical Internetworking Forum’s Flex Ethernet (FlexE) standard defines 25-gigabit increments and that will be the size of the line-side data rate increments.
Embracing a single modulation format and a 75GHz channel results in network operation benefits, says Hollasch: “It stops you having to worry and manage a complicated spectrum across a broad network.” And it also offers the prospect of network optimisation. “Changing the probabilistic shaping in response to feedback from the chip, from the network, we think that is a powerful innovation,” says Hollasch.
The reach performance of the PSE-3s using 62Gbaud and PS-64QAM. The reach performance of the PSE-2s is shown (where relevant) for comparison purposes.
Product plans
The first Nokia product to use the PSE-3 chips is the 1830 Photonic Service Interconnect-Modular, a 1 rack-unit compact modular platform favoured by the webscale players.
Nokia has designed two module-types or ‘sleds’ for the 1830 PSI-M pizza box. The first is a 400-gigabit sled that uses two sets of optics and two PSE-3c chips along with four 100-gigabit client-side interfaces. Four such 400-gigabit sleds fit within the platform to deliver a total of 1.6 terabits of line-side capacity.
In contrast, two double-width sleds fit within the platform using the PSE-3s. Each sled has one PSE-3 chip and two sets of optics, each capable of up to a 600-gigabit wavelength, and a dozen 100-gigabit interfaces. Here the line-side capacity is 2.4 terabits.
Nokia says the 400-gigabit sleds will be available in the first half of this year whereas the 1.2 terabit sleds will start shipping at the year-end or early 2019. The first samples of the PSE-3s are expected in the second half of 2018. Nokia will then migrate the PSE-3s to the rest of its optical transport platform portfolio.
So has coherent largely run its course?
“In terms of a major innovation in signal processing, probabilistic shaping is completing the coherent picture,” says Hollasch. There will be future coherent DSP chips based on more advanced process nodes than 16nm with symbol rates approaching 100GBaud. Higher data rates per wavelength will result but at the expense of a wider channel width. But once probabilistic shaping is deployed, further spectral efficiencies will be limited.
Nokia’s PSE-2s delivers 400 gigabit on a wavelength
Four hundred gigabit transmission over a single carrier is enabled using Nokia’s second-generation programmable Photonic Service Engine coherent processor, the PSE2, part of several upgrades to Nokia's flagship PSS 1830 family of packet-optical transport platforms.
Kyle Hollasch“One thing that is clear is that performance will have a key role to play in optics for a long time to come, including distance, capacity per fiber, and density,” says Sterling Perrin, senior analyst at Heavy Reading.
This limits the appeal of the so-called “white box” trend for many applications in optics, he says: “We will continue to see proprietary advances that boost performance in specific ways and which gain market traction with operators as a result”.
The 1830 Photonic Service Switch
The 1830 PSS family comprises dense wavelength-division multiplexing (DWDM) platforms and packet-OTN (Optical Transport Network) switches.
The DWDM platform includes line amplifiers, reconfigurable optical add-drop multiplexers (ROADMs), transponder and muxponder cards. The 1830 platforms span the PSS-4, -8, -16 and the largest and original -32, while the 1830 PSS packet-OTN switches include the PSS-36 and the PSS-64 platforms. The switches include their own coherent uplinks but can be linked to the 1830 DWDM platforms for their line amps and ROADMs.
The 1830 PSS upgrades include a 500-gigabit muxponder card for the DWDM platforms that feature the PSE2, new ROADM and line amplifiers that will support the L-band alongside the C-band to double fibre capacity, and the PSS-24x that complements the two existing OTN switch platforms.
100-gigabit as a service
In DWDM transmissions, 100-gigabit wavelengths are commonly used to transport multiplexed 10-gigabit signals. Nokia says it is now seeing increasing demand to transport 100-gigabit client signals.
“One hundred gigabit is becoming the new currency,” says Kyle Hollasch, director, optical marketing at Nokia. “No longer is the thinking of 100 gigabit just as a DWDM line rate but 100 gigabit as a service, being handed from a customer for transport over the network.”
Current PSS 1830 platform line cards support 50-gigabit, 100-gigabit and 200-gigabit coherent transmission using polarisation-multiplexed, binary phase-shift keying (PM-BPSK), quadrature phase-shift keying (PM-QPSK) and 16 quadrature amplitude modulation (PM-16QAM), respectively. Nokia now offers a 500-gigabit muxponder card that aggregates and transports 100-gigabit client signals. The 500-gigabit muxponder card has been available since the first quarter and already several hundred cards have been shipped.
“The challenge is not just to crank up capacity but to do so profitably,” says Hollasch. “Keeping the cost-per-bit down, the power consumption down while pushing towards the Shannon limit [of fibre] to carry more capacity.”
Source: Nokia
Modulation formats
The PSE2 family of coherent processors comprises two designs: the high-end super-coherent PSE-2s and the compact low-power PSE-2c.
Nokia joins the likes of Ciena and Infinera in developing several coherent ASICs, highlighting how optical transport requirements are best met using custom silicon. Infinera also announced its latest generation photonic integrated circuit that supports up to 2.4 terabits.
The high-end PSE-2s is a significant enhancement on the PSE coherent chipset first announced in 2012. Implemented using 28nm CMOS, the PSE-2s has a power consumption similar to the original PSE yet halves the power consumption-per-bit given its higher throughput.
The PSE-2s adds four modulation formats to the PSE’s existing three and supports two symbol rates: 32.5 gigabaud and 44.5 gigabaud. The modulation schemes and distances they enable are shown in the chart.
The 1.4 billion transistor PSE-2s has sufficient processing performance to support two coherent channels. Each channel can implement a different modulation format if desired, or the two can be tightly coupled to form a super-channel. The only exception is the 400-gigabit single wavelength format. Here the PSE-2s supports only one channel implemented using a 45 gigabaud symbol rate and PM-64QAM. The 400-gigabit wavelength has a relatively short 100-150km reach, but this suits data centre interconnect applications where links are short and maximising capacity is key.
Nokia recently conducted a lab experiment resulting in the sending of 31.2 terabits of data over 90km of standard single-mode fibre using 78, 400-gigabit channels spaced 50GHz apart across the C-band. "We were only limited by the available hardware from reaching 35 terabits," says Hollasch.
Using the 45-gigabaud rate and PM-16QAM enables two 250-gigabit channels. This is how the 500-gigabit muxponder card is achieved. The 250-gigabit wavelength has a reach of 900km, and this can be extended to 1,000km but at 200 gigabit by dropping to the 32-gigabaud symbol rate, as implemented with the current PSE chipset.
Nokia also offers 200 gigabit implemented using 45 gigabaud and 8-QAM. “The extra baud rate gets us [from 150 gigabit] to 200 gigabit; this is very valuable,” says Hollasch. The resulting reach is 2,000km and he expects this format to gain the most market traction.
The PSE-2s, like the PSE, also implements PM-QPSK and PM-BPSK but with reaches of 3,000-5,000km and 10,000km, respectively.
The PSE-2s introduces a fourth modulation format dubbed set-partition QPSK (SP-QPSK).
Standard QPSK uses amplitude and phase modulation resulting in a 4-point constellation. With SP-QPSK, only three out of the possible four constellation points are used for any given symbol. The downside of the approach is that a third fewer constellation points are used and hence less data is transported but the lost third can be restored using the higher 45-gigabaud symbol rate.
The benefit of SP-QPSK is its extended reach. “By properly mapping the sequence of symbols in time, you create a greater Euclidean distance between the symbol points,” says Hollasch. “What that gives you is gain.” This 2.5dB extra gain compared to PM-QPSK equates to a reach beyond 5,000km. “That is the territory most implementation are using BPSK and also addresses a lot of sub-sea applications,” says Hollasch. “Using SP-QPSK [at 100 gigabit] also means fewer carriers and hence, it is more spectrally efficient than [50-gigabit] BPSK.”
The PSE-2c
The second coherent DSP-ASIC in the new family is the PSE-2c compact, also implemented in 28nm CMOS, designed for smaller, low-power metro platforms and metro-regional reaches.
The PSE-2c supports a 100-gigabit line rate using PM-QPSK and will be used alongside the CFP2-ACO line-side pluggable module. The PSE-2c consumes a third of the power of the current PSE operating at 100 gigabit.
“We are putting the PSE2 [processors] in multiple form factors and multiple products,” says Hollasch.
The recent Infinera and Nokia announcements highlight the electronic processing versus photonic integration innovation dynamics, says Heavy Reading's Perrin. He notes how innovations in electronics are driving transmission across greater distances and greater capacities per fibre and finding applications in both long haul and metro networks as a result.
“Parallel photonic integration is a density play, but even Infinera’s ICE announcement is a combination of photonic integration and electronic processing advancements,” says Perrin. “In our view, electronic processing has taken a front seat in importance for addressing fibre capacity and transmission distance, which is why the need for parallel photonic integration in transport has not really spread beyond Infinera so far.”
The PSS-24x showing the 24, 400 gigabit line cards and 3 switch fabric cards, 2 that are used and one for redundancy. Source: Nokia
PSS-24x OTN switch
Nokia has also unveiled its latest 28nm CMOS Transport Switch Engine, a 2.4-terabit non-blocking OTN switch chip that is central to its latest PSS-24x switch platform. Two such chips are used on a fabric card to achieve 4.8 terabits, and three such cards are used in the PSS-24x, two active cards and a third for redundancy. The result is 9.6 terabits of switching capacity instead of the current platforms' 4 terabits, while power consumption is halved.
Nokia says it already has a roadmap to 48-terabits of switching capacity. “The current generation [24x] shipping in just a few months is 400-gigabit per slot,” says Hollasch. The 24 slots that fit within the half chassis results in 9.6 terabits of switching capacity. However, Nokia's platform roadmap will achieve 1 terabit-per-slot by 2018-19. The backplane is already designed to support such higher speeds, says Hollasch. This would enable 24 terabits of switching capacity per shelf and with two shelves in a bay, a total switching capacity of 48 terabits.
The transport switch engine chip switches OTN only. It is not designed as a packet and OTN switch. “A cell-based agnostic switching architecture comes with a power and density penalty,” explains Hollasch, adding that customers prefer the lowest possible power consumption and highest possible density.
The result is a centralised OTN switch fabric with line-card packet switching. Nokia will introduce packet switching line cards next year that will support 300 gigabit per card. Two such cards will be ‘pair-able’ to boost capacity to 600 gigabit but Hollasch stresses that the PSS-24x will not switch packets through its central fabric.
Doubling capacity with the L-band
By extending the 1830 PSS platform to include the L-band, up to 70 terabits of data can be supported on a fibre, says Hollasch.
Nokia has developed a line card that supports both C-band and L-band amplification that will be available around the fourth quarter of this year. The ROADM and 500-gigabit muxponder card for the L-band will be launched in 2017.
Once the amplification is available, operators can start future-proofing their networks. Then when the L-band ROADMs and muxponder cards become available, operators can pay as they grow; extending wavelengths into the L-band, once all 96 channels of the C-band are used, says Hollasch.