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From: FUBHO10/4/2017 9:02:59 PM
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Facebook to Build $1B Data Center in Virginia: Report

OCT 04, 2017
Company plans 1 million square feet in Phase I; location is 100...

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From: FUBHO10/5/2017 1:25:53 PM
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NeoPhotonics blames slow China demand for upcoming layoffs

October 5, 2017
Author Stephen Hardy
Editorial Director and Associate Publisher

Citing the fact that soft demand for its products in the China market has continued into the third quarter, NeoPhotonics Corp. (NYSE: NPTN) has announced restructuring efforts that include layoffs. Company management expects the restructuring to reduce quarterly operating expenses immediately and result in an approximately $2 million reduction when fully realized in the first quarter of 2018.

The company did not reveal how many employees will be affected. The restructuring also will include real estate consolidation, a write down of inventory for "certain programs and assets" and a write-down of idle assets. Reduction costs are expected to be approximately $4.8 million, with $4.2 million in asset-write off costs and $0.6 million in severance costs. NeoPhotonics predicts approximately $4.6 million of these costs will fall in the third quarter, with the rest incurred in the fourth quarter.

While reports suggest that optical transceiver sales overall began to climb in the second quarter of this year (see "Optical transceiver sales rebound in 2Q17: LightCounting"), that growth came despite continued weakness in demand from systems houses in China. That softness has yet to show signs of relenting, according to NeoPhotonics.

"Lacking a clear indication of increased demand in China in the third quarter, we initiated several operational changes with the goal of expediting our return to profitability, including implementing certain restructuring initiatives designed to align our business with the current demand environment and lowering manufacturing output to manage inventory levels," said Tim Jenks, chairman and CEO of NeoPhotonics. "In taking these actions, we have maintained our research and development focus on products for next-generation coherent systems, operating at 400 Gbps to beyond 1 Tbps, wherein our advanced hybrid photonic integration provides the highest value."

The restructuring announcement came as NeoPhotonics released preliminary results for the third quarter. The company expects to report revenue between $69 million to $71 million, with GAAP gross margin of approximately 10% to 13% and GAAP loss per share of $0.50 to $0.40, inclusive of the restructuring charges. These figures compare to previous guidance of $70 million to $76 million in revenue, GAAP gross margin of 23% to 26%, and GAAP net loss per share of $0.21 to $0.11.

Meanwhile, the company now expects non-GAAP gross margin will be in the range of 14% to 17% and non-GAAP loss per share in the range of $0.35 to $0.27. Previous guidance called for non-GAAP gross margin of 24% to 27% and non-GAAP loss of $0.17 to $0.07. In addition to the restructuring charges, non-GAAP gross margin and non-GAAP net loss will suffer from the decision to reduce production levels during the quarter because of the lack of visibility into future demand levels in China.

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From: FUBHO10/6/2017 12:32:18 AM
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Infinera Makes (Terabit) Waves at ECOC 2017 - Infinera

September 28, 2017

By Geoff Bennett
Director, Solutions and Technology

Last week the Infinera team, along with our mobile demonstration unit, the Infinera Express, attended the European Conference on Optical Communication (ECOC) 2017 exhibition and conference in Gothenburg, Sweden. The exhibition attracted 5,234 visitors, with 313 exhibiting companies from 27 countries and a record 3,189 people visiting the Market Focus sessions across the three days.

At the conference, Infinera achieved two industry-first milestones around advanced coherent technologies:
  • A demonstration of a 1024QAM (quadrature amplitude modulation) signal including constellation shaping.
  • A 100 gigabaud (GBaud), 32QAM single wavelength transmission.
As you can see from the figure below, Baud rate and modulation order are two of three possible axes of scaling for individual transponder capacity, and if 1024QAM was combined with 100 GBaud transmission the result would be a 1.5 terabit per second (Tb/s) data rate!

Figure 1: Three Axes of Scaling for Individual Transponder Capacity

At this point I will come clean. In an Optical Society of America webinar a few years ago, I explained that it would be “really hard” to implement a single wavelength with terabit data rates, and at the same time I explained that increasing the modulation order results in dramatically shorter optical reach. This is one reason why the parallel approach of super-channels for scaling transponder or appliance capacity has been phenomenally successful in the data center interconnect (DCI), long-haul and subsea markets. Super-channels allow us to combine lower-data-rate waves into a higher-data-rate optical channel that’s treated as a single entity from an operational point of view. Service providers can run bigger networks with smaller teams of engineers, and can respond to more dynamic changes in terabit-scale demand using unique architectural innovations such as Instant Network.

So why was increasing Baud rate so difficult a few years ago? Let’s delve a bit deeper into the technology options for scaling line card capacity:
  • Baud rate. The Baud rate of a wavelength is the rate at which modulation symbols are sent. The most common long-haul data rate today is 100 gigabits per second (Gb/s), using polarization-multiplexed quadrature phase-shift keying (PM-QPSK) modulation. The typical Baud rate is 32 GBaud, and PM-QPSK carries 4 bits per Baud. The additional data over 100 Gb/s is consumed by Optical Transport Network forward error correction. In general, the Baud rate is limited by the opto-electronics technology that is available. For several years 32 GBaud has been the most cost-effective Baud rate, but more recently this limit has been exceeded thanks to smaller feature sizes on the application-specific integrated circuits used in modern coherent systems. In other words, after reaching a plateau for several years, opto-electronics has moved to a higher rate, with 48 to 66 GBaud products on the horizon.
  • Modulation order. Another way to increase data rate is to carry more bits in each symbol. polarization-multiplexed binary phase-shift keying (PM-BPSK) carries 2 bits per symbol, PM-QPSK carries 4 bits, PM-8QAM carries 6 bits, and PM-16QAM carries 8 bits. Thus, a 32 GBaud, 16QAM wavelength will have a data rate of 200 Gb/s. There is a drawback to increasing modulation order, however, because the result is dramatically reduced reach. While PM-16QAM increases the data rate by a factor of two compared to PM-QPSK, it reduces reach by about 80 percent. However, PM-16QAM is a very important modulation technique where longer reach isn’t needed – such as the metro and DCI markets.
  • Infinera uniquely has access to a third axis of scalability: implementing multiple, parallel wavelengths on the same line card in order to create a coherent super-channel. We make this practical using our large-scale photonic integrated circuit (PIC) technology, but it also gives us a distinct advantage because we can focus development on one, two, or all three of these dimensions, depending on the current state of optical and electronic technologies.
Let’s look at our two post-deadline papers in more detail. In the first paper, Dr. Ryan Going of Infinera’s PIC team presented lab results for what we believe is the first reported demonstration of single-wavelength, 1 Tb/s data rates using 32QAM modulation at an astonishing 100 GBaud symbol rate. While opto-electronic power has definitely moved on since my OSA webinar a few years ago, a key capability that makes this very high Baud rate possible is the use of photonic integration. In simple terms, as Baud rates increase there is a very high value in being able to locate optical components as close together as possible, and the ultimate limit is for those components (i.e. laser, modulator, waveguides) to be integrated onto the same chip, using the same material – in this case indium phosphide. Silicon germanium drivers were also integrated into the package.

In the second paper. Dr. Robert Maher discussed the practicalities and consequences of extremely high order modulation – in this case up to 1024QAM at 66 GBaud, including advanced constellation-shaping algorithms. To understand the value of constellation shaping we need to imagine what a “symbol” actually means, and in this explanation, I will focus on a single polarization state – remember that in a real implementation there would be an X and Y version of each symbol, resulting in twice as many bits carried.Figure 2: Comparing 16QAM, 1024QAM, and a Shaped 1024QAM ConstellationIn Figure 2, we see a 16QAM constellation on the left, which consists of 16 symbols, with each symbol transporting four bits of information. Typically, each symbol has an equal chance of being transmitted through the system, so on average the amount of information being sent is 4 bits per symbol. For 1024QAM, shown in the center of Figure 2, there are 1024 independent symbols, each carrying 10 bits per symbol, assuming each symbol is given an equal chance of being transmitted through the system.

However, constellation shaping constrains the chances of certain symbols being transmitted in order to apply a form of “natural selection” in order to optimize the carrying capacity of the wavelength. This can be done because the lower-power symbols, closer to the origin, have a greater chance of being transmitted than the higher-power symbols. What this ultimately achieves is increased spacing between the symbols, thus making the shaped format less sensitive to noise. The trade-off is reduced transmission capacity, but the big advantage is that the noise tolerance can be adaptively tailored to match the signal-to-noise ratio of any given transmission link. In other words, Constellation Shaping allows us to maximize the data rate for the optical budget of a given fiber path (i.e. a given reach).

On the right of Figure 2 is the actual experimental result of constellation-shaped 66 GBaud 1024QAM presented by Dr. Maher at ECOC.

Note that the optical reach for 1024QAM will be relatively short – but it could find a sweet spot for the distances needed by DCI customers as they consume ever-increasing amounts of capacity.

From Demonstrations to Production NetworksThe two papers I’ve referred to are technology demonstrations – their purpose is to show what kind of technologies will become important in future products. We know, for example, that 400 Gb/s products are getting closer to shipping, and we also saw at ECOC technology demonstrations of 600 Gb/s per wavelengths taking place and participated in discussions of 800 Gb/s per wavelength. Infinera’s fifth-generation Infinite Capacity Engine (ICE5) is targeting 600 Gb/s per wavelength and ICE6, our sixth generation, is targeting at least 800 Gb/s per wavelength.

The optical reach for these higher data rates and for modulations like 1024QAM will be relatively short in terms of distance – but it will likely find a sweet spot for short-haul DCI customers as they consume ever-increasing amounts of capacity.

Infinera has also recently demonstrated some leadership at the other end of the distance spectrum – subsea. Recently Seaborn put their Seabras-1 subsea cable into production using Infinera’s commercially available XTS-3300 based on ICE4, the fourth generation of our Infinite Capacity Engine. On Sept 20, Infinera and Seaborn jointly announced that a new industry benchmark was set with 18.2 Tb/s over the 10,500+ km link using 8QAM and exceptionally tight channel spacing.


The innovative terabit wave capability test at ECOC is an indication of where single-wavelength access and metro solutions, as well as multi-wavelength sliceable super-channel technology for DCI, metro core, long-haul and subsea, could be heading in years to come. For Infinera this is a vital proof point of our ability to push the boundaries of the single-wavelength optical performance curve, but to also have the unique ability to combine multiple wavelengths in a single PIC-based module to deliver the benefits of super-channel scalability, namely service responsiveness and ease of operations, at the optimum price point for our customers. Infinera is commercially shipping ICE4 products today that are leading the market in terms of performance and ease of use. We are already demonstrating ICE5 and ICE6 test results, as well as showcasing technologies, like those shown at ECOC, that highlight the tremendous future scalability of coherent digital signal processors combined with photonic integrated circuits.

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To: FUBHO who wrote (3251)10/7/2017 12:47:37 PM
From: Tartuffe
1 Recommendation   of 3800
The Heavy Reading report Telco Optical Systems Beyond 100G, looks at how demand for optical transport has changed, how coherent optics is evolving and what the future holds for this established but dynamic technology. It examines advances in electronics that are pushing speeds faster, as well as the consequences for the standard optical grid spacing.Further, it looks at standardization efforts, including those led from the demand-side of the market, and compares the approaches and portfolios of 11 vendors of telco-focused optical systems.— Danny Dicks, Contributing Analyst, Heavy Reading

I think that Acacia's DSP and the move toward merchant silicone DSP's might be a very good thing for INFN and the ICE PICS platforms. That move might also facilitate the transition toward SDN by giving all the optical vendors a common starting point that would put everyone on the same page as far as interoperability is concerned. ASIC DSP's cost a lot of R&D money to develop,and produce and it is very inefficient and wasteful for every every vendor to develope and produce their own ASIC DSP's in limited volumes, not to mention the the interoperability issues (ASCIS as opposed to FPGA's have better performance, but need VOLUME to justify their development and production expense) ACACIA was out spending everyone and producing the best DSP which is why CEIN capitulated and made their DSP available to everyone in an attempt to recoup some of the costs. Having merchant silicone benefits everyone since all the optical vendors will not have the interoperability issues that are one of the biggest barriers to SDN's implementation. If the market moves to merchant silicone DSP's, the real competition can be over who can shape, transport, tune, manage and deliver in terms of performance, power consumption, capacity, configurability and ease of implementation etc. where INFN is leading IMO. This thesis, if true, brings ACIA onto the radar screen although INFN has made me gun shy about "following the technology" ... My thesis might be correct, but that is a pyrric victory if the portfolio suffers- The timing, demand cycles, execution and management might be more important, but I do think ACIA success might be good for INFN especially, and the industry as a whole, and may even be a very good investment. I thought I would float it here for feedback though- I also don't see anyone else willing to try and spend enough to keep up to compete with ACIA.....Huawei might steal the IP and produce it more cheaply, but other than that, I don't see anyone who would challenge their market share since the volumes might not justify multiple vendors.....

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To: Tartuffe who wrote (3252)10/7/2017 12:54:13 PM
   of 3800
It all depends how fast Infinera can come out with their own. If they are late with the next generations, they might not have a lot of choice. They are already using Acacia in XTM II which should be making the news right now, as it was due out end of Q3...

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From: FUBHO10/9/2017 1:02:10 PM
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Research & Education Networks: A Path Toward Cognitive Networking

October 11, 2017

11:00am to 12:00pm
Eastern Daylight Time

Level 3 and Infinera
Your Host

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From: FUBHO10/11/2017 3:51:45 PM
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CenturyLink pleads with FCC to approve Level 3 acquisition | FierceTelecom

CenturyLink is making a final push to get the FCC to approve its pending acquisition of Level 3 Communications, with hopes of closing it later this month. The FCC is the only regulator that has yet to sign off on the purchase.

To date, CenturyLink and Level 3’s proposed merger has gotten approvals from 19 states. It has also gained pre-closing notice filings in 14 other states.

At this point, CenturyLink and Level only need the final sign off from the California Public Utilities Commission (PUC), which is expected to approve the acquisition during their meeting later this week.

In September, a proposed decision to approve the acquisition was issued last month by Regina DeAngelis, the presiding Administrative Law Judge in California. The judge’s decision has been placed on the Consent Agenda for the California Public Utilities Commission’s next open meeting, scheduled for Thursday.

The California Administrative Law Judge proposed a decision that recognized the combination of CenturyLink and Level 3 was in the public interest.

Just last week, the deal was also approved by the Department of Justice with conditions that the two providers divest certain fiber assets in their respective regions.

Meanwhile, a U.S. District Court Judge executed the Asset Preservation Stipulation and Order filed jointly by the Division and the Applicants, clearing the applicants to complete the acquisition.

CenturyLink said in an FCC filing (PDF) that now it has gained these other approvals, the regulator should have all it needs to approve the acquisition.

“In light of these developments, and based on the record developed in this proceeding, the Applicants submit that the Transaction is in the public interest and thus urge the Commission to approve it forthwith,” CenturyLink said.

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From: FUBHO10/11/2017 4:02:47 PM
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FCC Restarts Approval Clock for CenturyLink & Level 3

By CAROL WILSON, Editor-at-large, 10/11/2017
CenturyLink's pending $34 billion purchase of Level 3 Communications is now apparently days away from completion, as the FCC has restarted its informal approval clock, now set to expire in the next two weeks.

The deal was announced a year ago, and both companies have since weathered stock price woes. The US Department of Justice weighed in a week ago, setting its conditions for the merger. Then the Federal Communications Commission (FCC) issued its letter Wednesday saying it had restarted its 180-day informal approval clock last Friday, making it likely that CenturyLink Inc.(NYSE: CTL) and Level 3 Communications Inc. (NYSE: LVLT) will finally be allowed to combine. (see DOJ Blesses CenturyLink, Level 3 Merger... With Conditions and CenturyLink Splashes $34B on Level 3 Buy.)

Merger plans are well underway at the companies, with management structures in place and a palpable eagerness to get started, especially in addressing the business services market, as indicated in off-the-record discussions with executives at both CenturyLink and Level 3.

CenturyLink also must get California state regulators' approval but that is expected later this week, after a state administrative law judge issued a decision that the merger was in the public interest.

The FCC letter notes that CenturyLink has "fulfilled their obligations to provide responsive information to the Commission in connection with its requests in this docket, and because most of the supplemental materials had been provided before then, we were able to complete our review of those materials on that date. Accordingly, we are restarting the informal 180-day clock as of Friday, October 6, 2017, making that date Day 170 of the Commission's review."

The first challenge for the combined company will be to convince Wall Street of its potential for success, an effort likely to start when CenturyLink announces its quarterly earnings on October 30. Both CenturyLink and Level 3 stocks are currently hovering above their 52-week lows. (See Investors Flee US Rural Incumbents and CenturyLink Posts Lackluster Q2.)

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To: FUBHO who wrote (3256)10/11/2017 4:10:12 PM
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Colt Preps AI-Enabled Network Management

THE HAGUE -- SDN NFV World Congress -- With its initial NFV architecture in place and helping to deliver on-demand services to its enterprise customers, Colt is now looking to tidy up its virtualization deployment and seek ways to automate its network management during 2018, according to a senior executive from the operator.

Mirko Voltolini, VP of technology and architecture at Colt Technology Services Group Ltd (London: COLT), cited automation as one of the key areas of innovation at the operator, which offers services to enterprise users primarily in Europe and Asia. Colt has created a new "AI-driven networking" project called Sentio with the aim of developing fully automated service management capabilities -- traffic flow classification, fault prediction, WAN path optimization, capacity management, security, intelligent bandwidth-on-demand, and more -- and service modification and restoration through the automated scaling of virtual network functions (VNFs).

A key element in this process would be an analytics engine based on machine learning and artificial intelligence (AI) capabilities that would feed information into Colt's network controllers.

Voltolini told Light Reading that there are some suitable existing tools in the market that could help the operator get started on the road to automation and that he had already held conversations with a few companies. Colt has also issued a request for information (RFI), and Voltolini said that the initial responses would be examined in the coming weeks.

He noted that Colt has deliberately not been too prescriptive about what it is seeking in terms of machine learning capabilities so as not to limit the responses from the vendor community and that the focus of the RFI has been on what Colt is hoping to ultimately achieve.

Voltolini isn't talking about specifics currently, or which companies stand out from his early information gathering, but it was notable here that IBM Corp. (NYSE: IBM), in partnership with Accanto Systems , is pushing its network management automation capabilities strongly and it's hard to imagine that the software giant won't feature in Colt’s initial considerations.

So with Project Sentio underway, does Voltolini see any value in the creation of an European Telecommunications Standards Institute (ETSI)group focused on automation? Absolutely, particularly for identifying the potential use cases, he noted. (See Automation Gets Its Own ETSI Group.)

Virtualization consolidation
Another key initiative for Colt in 2018 is the unification of its systems underpinning its initial virtualization efforts.

The operator is well known for being one of the early movers in terms of deploying SDN and NFV capabilities but its early initiatives have left it with a number of similar systems. (See How Colt Capitalized on SDN & NFV.)

"We have some inefficiencies in our current NFV set-up," noted Voltolini, that has resulted in an inefficient use of compute and networking infrastructure, operational complexity and a lengthy and complex process to bring additional VNFs on board.

So the operator is using blueprints from the ETSI NFV Industry Specification Group (ISG) to shift to common orchestration, VNF manager and Virtual Infrastructure Manager (VIM) layers, a move that will deliver cost efficiencies and reduced overheads and development cycles, as well as speeding up VNF onboarding and enabling the development of a single service catalog. Colt also expects this move will help it to introduce the automation it plans to introduce with Project Sentio.

Voltolini also noted during his presentation that Colt is further developing the SDN federation capabilities it has worked on with AT&T, Orange Business Services and the MEF and that it is also working on additional new bilateral SDN interconnections with partner network operators that it plans to announce soon. (See AT&T, Colt, Orange Team with SDOs on Global API Standards and MEF Proclaims Progress on Key LSO Interfaces.)

Colt is also working on the development of an Optical SDN service that will enable on-demand optical services in the same way it currently offers on-demand IP and Ethernet services. "Disaster recovery has emerged as one of the key use cases for such a service," Voltolini noted.

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From: FUBHO10/12/2017 2:05:42 AM
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Game-changing Technology for New Subsea Cables - Infinera

October 09, 2017

By Peter Zwinkels
Sr. Sales Account Director

The subsea cable market is booming with approximately $9.8 billion in new cables expected to enter service between 2016 and 2018 driven largely by the cloud. The deployment of a subsea cable of over 10,000 kilometers (km) in length can cost more than $500 million, with multiple investors typically financing the venture. Further, a subsea cable has relatively few fibers compared to a terrestrial network because each fiber requires its own repeaters spaced about every 80 km. Given that a single subsea cable usually houses only up to eight fiber pairs, you can probably guess what an investor is thinking: how can I maximize my return on investment with only a few fibers? The answer is simply to get as much revenue as possible out of the cable during its roughly 25-year lifespan. This means maximizing the capacity on the cable is critical. Thus, subsea cable operators are eager to deploy the fastest technology available for maximum capacity-reach performance, or more saliently, revenue-reach performance. In this blog let us look at the latest technology subsea cable operators can use to get the most potential from their cable.

In the late 1990s, 10 gigabits per second (10 Gb/s) and 16-channel dense wavelength-division multiplexing (DWDM) technology were used. These optical channels were intensity modulated, and their capacity-reach performance was directly impacted by chromatic and polarization dispersion. To achieve the capacity-reach necessary, the cable had to be meticulously compensated at periodic intervals with counter-dispersion characteristics that would produce a net zero dispersion effect for the channels over the length of the cable. The good thing was that such dispersion is linear and thus can be calculated and managed. Since the early 2000s, compensated fiber pairs with 10 Gb/s DWDM technology have been able to provide up to 960 Gb/s (96 channels of 10 Gb/s) of capacity. Given that subsea capacity demand growth is more than 45 percent year-over-year and 100 Gigabit Ethernet connectivity is dominant, these cable systems quickly run out of capacity. However, the good news is that the limitation is not the cable itself but the optical transport technology currently implemented. Upgrading these cables with the latest technology will add significant capacity and value to the subsea cable operator’s greatest asset.

From 10 Gb/s to 100 Gb/s Yields More than 10 Times the Capacity

The shift from 10 Gb/s to 100 Gb/s required a significant technology change, from intensity modulation of light to coherent modulation, which varies the light’s amplitude, phase and polarization in much the same way as in radio and wireline modems. One might think that going from 10 Gb/s to 100 Gb/s results in a tenfold improvement in a DWDM subsea cable system. However, coherent modulation combined with various digital signal processing (DSP) techniques yields even greater capacity. This is because some modulation formats allow for more than one bit per symbol, or state of information, and thus provide better spectral efficiency. For example, in Figure 1, 8 quadrature amplitude modulation (8QAM) has three bits per symbol, at a symbol rate of 22 gigabaud (Gbaud) on 2 polarizations with a Forward Error Correction (FEC) overhead of 20 percent to carry 100 Gb/s in a 25 gigahertz (GHz) channel. The spectral efficiency can further be increased by spacing channels closer together, as opposed to the International Telecommunications Union’s Telecommunication Standardization Sector’s (ITU-T) fixed grid spacing of 100 GHz for 10 Gb/s systems. Even if a fixed channel spacing of 50 GHz is used, the capacity increases 20-fold over an older 10 Gb/s system. However, as seen in Figure 1, coherent modulation allows for a variety of spectral widths and thus a flexible spectral grid, or gridless spectrum, enabling even tighter channel spacing on a cable.

Figure 1: Coherent Modulation OverviewAs in radio and wireline transmission, coherent optical phase modulation is more robust than amplitude modulation. As distances increase, the modulation format capacity must decrease, with a corresponding decrease in spectral efficiency. This is the crux of the subsea cable business. As seen from Figure 2, trans-Atlantic systems can support more capacity than trans-Pacific ones because of the modulation that can be supported over the distance.

The latest subsea capacity-reach performance is 100 Gb/s using 8QAM over 10,500 km in a 22 GHz channel for a spectral density of 4.5 b/s/Hz as showcased recently on Seaborn Networks’ Seabras-1 cable. To achieve this level of performance, innovative advanced coherent techniques are required to overcome the physical limitations of the fiber for optimal capacity-reach performance.

Figure 2: Modulation for Capacity-ReachDispersion Can Be a Good Thing

Coherent optical transmission is truly a disruptive technology for subsea. Not only does it give significantly more capacity on the cable but the cable doesn’t need to be compensated. In fact, contrary to what one might intuitively think, transmission performance is even better if the cable is uncompensated. Since linear dispersion can be calculated for the length of the cable, it can be compensated not by the fiber as used to be the case, but by the DSP of the optical engine. However, the real benefit of an uncompensated cable is that linear chromatic and polarization dispersion mitigates the non-linear effects of cross-phase modulation (XPM) and self-phase modulation (SPM). How is that possible? Consider multiple wavelengths propagating at their various speeds down the length of a fiber. Instead of each modulated wavelength briefly occupying the same point in time on the fiber, allowing for XPM and SPM effects, linear dispersion makes them move past each other quicker and thereby independently, mitigating XPM and SPM.

Sharing Is Always a Good Thing

To achieve the highest capacity over the length of a cable means that one sets the system up, or commissions it, to operate as close as possible to its performance limit. However, the performance margin across the entire spectrum may not be flat, and thus the limit must be set to either accommodate the weakest portion of the spectrum or for a compromised level that optimizes capacity. Using a technique called soft-decision forward error correction (SD-FEC) gain sharing, each individual optical channel’s performance can be monitored and the available energy of the system can be balanced across the spectrum to compensate for channels whose margin of performance is below a desired commissioning level. As seen in Figure 3, two channels out of 20 were compensated to operate above the commissioning level for a 10 percent gain in capacity.

Figure 3: Gain SharingHarry Would Be Pleased

Figure 4: Nyquist SubcarriersHarry Nyquist’s theorems are the foundation of digital signal processing. Infinera utilizes Nyquist in a unique way to further mitigate XPM and SPM for even better capacity-reach performance in much the same way as digital subscriber line (DSL) technology uses discrete multitone to mitigate line impairments and noise effects. Instead of a single carrier bearing 100 percent of the capacity, multiple carriers are spaced at just the right distance and modulated at just the right baud rate to bear a portion of the overall capacity so that the aggregate of each Nyquist subcarrier equals the total capacity of just the single carrier. The effect is an overall increase of 0.75 decibels (dB) of performance margin, which is almost 20 percent.

Figure 5: Optimal Non-linear Effects MitigationSince the Nyquist subcarriers can be spaced six times closer than a single carrier, wavelength stability and locking are essential. Infinera’s fourth-generation Infinite Capacity Engine (ICE4) uniquely assures that the subcarriers will not drift, and because of the super-channel precision from a single ICE4, tighter channel spacing can be achieved for increased spectral density.

ACT Now!

As new uncompensated subsea cables connect the continents, advanced coherent technologies like Nyquist subcarriers and SD-FEC gain sharing, now available with Infinera’s ICE4 Advanced Coherent Toolkit (ACT), can increase the capacity of a cable up to 40 percent by allowing for an 8QAM system (22 GHz spacing) where only a quadrature phase-shift keying (QPSK) system (37.5 GHz spacing) would have been used previously. Also, cables that with can operate with 100 Gb/s 8QAM can realize an improvement in spectral efficiency of up to 12 percent (from 25 to 22 GHz). Such capacity improvements are not just marginal improvements, but real game changers for subsea operators.

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