100 Gig

Gazettabyte asked industry executives what trends and highlights they noted at the recent European Conference on Optical Communication (ECOC) event, held in Valencia. Here are three views.

 

Valery Tolstikhin, head of a design consultancy, Intengent

ECOC was a big show and included a number of satellite events, such as the 6^th European Forum on Photonic Integration, the 3^rd Optical Interconnect in Data Center Symposium and Market Focus, all of which I attended. So, lots of information to digest. 

My focus was mainly on data centre optical interconnects and photonic integration.

 

Data centre interconnects

What became evident at ECOC is that 50 Gig modulation and the PAM-4 modulation format will be the basis of the next generation (after 100 Gig) data centre interconnect. This is in contrast to the current 100 Gig non-return-to-zero (NRZ) modulation using 25 Gig lanes.

This paves the way towards 200 Gig (4 x PAM-4 lanes at 25 Gig) and 400 Gig (4 x PAM-4 lanes at 50 Gig) as a continuation of quads of 4 x NRZ lanes at 25 Gig, the state-of-the-art data centre interconnect still to take off in terms of practical deployment. 

The transition from 100 Gig to 400 Gig seems to be happening much faster than from 40Gig to 100 Gig. And 40 Gig serial finally seems to have gone; who needs 40 Gig when 50 Gig is available?

Another observation is that despite the common agreement that future new deployments should use single-mode fibre rather than multi-mode fibre, given the latter’s severe reach limitation that worsens with modulation speed, the multi-mode fibre camp does not give up easily. 

That is because of the tons of multi-mode fibre interconnects already deployed, and the low cost of gallium arsenide 850 nm VCSELs these links use. However, the spectral efficiency of such interconnects is low, resulting in high multi-mode fibre count and the associated cost. This is a strong argument against such fibre. 

Now, a short-wave WDM (SWDM) initiative is emerging as a partial solution to this problem, led by Finisar. Both OM3 and OM4 multi-mode fibre can be used, extending link spans to 100m at 25 Gig speeds. 

 

Single mode fibre 4 x 25 Gig QSFP28 pluggables with a reach of up to 2 km, which a year ago were announced with some fanfare, seems to have become more of a commodity.

 

The SWDM Alliance was announced just before ECOC 2015, with major players like Finisar and Corning on board, suggesting this is a serious effort not to be ignored by the single mode fibre camp.

Lastly, single mode fibre 4 x 25 Gig QSFP28 pluggables with a reach of up to 2 km, which a year ago were announced with some fanfare, seems to have become more of a commodity.  Two major varieties – PSM and WDM – are claimed and, probably shipping, by a growing number of vendors. 

Since these are pluggables with fixed specs, the only difference from the customer viewpoint is price. That suggests a price war is looming, as happens in all massive markets. Since the current price still are an order of magnitude or more above the target $1/Gig set by Facebook and the like, there is still a long way to go, but the trend is clear. 

This reminds me of that I’ve experienced in the PON market: a massive market addressed by a standardised product that can be assembled, at a certain time, using off-the-shelf components. Such a market creates intense competition where low-cost labour eventually wins over technology innovation.

 

Photonic integration 

Two trends regarding photonic integration for telecom and datacom became clear at ECOC 2015.

One positive development is an emerging fabless ecosystem for photonic integrated circuits (PICs), or at least an understanding of a need for such. These activities are driven by silicon photonics which is based on the fabless model since its major idea is to leverage existing silicon manufacturing infrastructure. For example, Luxtera, the most visible silicon component vendor, is a fabless company. 

There are also signs of the fabless ecosystem building up in the area of III-V photonics, primarily indium-phosphide based. The European JePPIX programme is one example. Here you see companies providing foundry and design house services emerging, while the programme itself supports access to PIC prototyping through multi-project wafer (MPW) runs for a limited fee. That’s how the ASIC business began 30 to 40 years ago.  

A link to OEM customers is still a weak point, but I see this being fixed in the near future. Of course, Intengent, my design house company, does just that: links OEM customers and the foundries for customised photonic chip and PIC development.

 

As soon as PICs give a system advantage, which Infinera’s chips do, they become a system solution enabler, not merely ordinary components made a different way

 

The second, less positive development, is that photonic integration continues to struggle to find applications and markets where it will become a winner. Apart from devices like the 100 Gig coherent receiver, where phase control requirements are difficult to meet using discretes, there are few examples where photonic integration provides an edge. 

Even a 4 x 25 Gig assembly using discrete components for today’s 100 Gig client side and data centre interconnect has been demonstrated by several vendors. It then becomes a matter of economies of scale and cheap labour, leaving little space for photonic integration to play. This is what happened in the PON market despite photonic integrated products being developed by my previous company, OneChip Photonics. 

On a flip side, the example of Infinera shows where the power of photonic integration is: its ability to create more complicated PICs as needed without changing the technology.

One terabit receiver and transmitter chips developed by Infinera are examples of complex photonic circuits, simply undoable by means of an optical sub-assembly. As soon as PICs give a system advantage, which Infinera’s chips do, they become a system solution enabler, not merely ordinary components made a different way.  

However, most of the photonic integration players - silicon photonics and indium phosphide alike - still try to do the same as what an optical sub-assembly can do, but more cheaply. This does not seem to be a winning strategy.

And a comment on silicon photonics. At ECOC 2015, I was pleased to see that, finally, there is a consensus that silicon photonics needs to aim at applications with a certain level of complexity if it is to provide any advantage to the customer. 

 

Silicon photonics must look for more complex things, maybe 400 Gig or beyond, but the market is not there yet

 

For simpler circuits, there is little advantage using photonic integration, least of all silicon photonics-based ones. Where people disagree is what this threshold level of complexity is. Some suggest that 100 Gig optics for data centres is the starting point but I’m unsure. There are discrete optical sub-assemblies already on the market that will become only cheaper and cheaper. Silicon photonics must look for more complex things, maybe 400 Gig or beyond, but the market is not there yet.

One show highlight was the clear roadmap to 400 Gig and beyond, based on a very high modulation speed (50 Gig) and the PAM-4 modulation format, as discussed. These were supported at previous events, but never before have I seen the trend so clearly and universally accepted.

What surprised me, in a positive way, is that people have started to understand that silicon photonics does not automatically solve their problems, just because it has the word silicon in its name. Rather, it creates new challenges, cost efficiency being an important one.  The conditions for cost efficient silicon photonics are yet to be found, but it is refreshing that only a few now believe that the silicon photonics can be superior by virtue of just being ‘silicon’.

I wouldn’t highlight one thing that I learned at the show. Basically, ECOC is an excellent opportunity to check on the course of technology development and people’s thoughts about it.  And it is often better seen and felt on the exhibition floor than attending the conference’s technical sessions.

For the coming year, I will continue to track data centre interconnect optics, in all its flavours, and photonic integration, especially through a prism of the emerging fabless ecosystem.

 

 

Vishnu Shukla, distinguished member technical staff in Verizon’s network planning group.

There were more contributions related to software-defined networking (SDN) and multi-layer transport at ECOC. There were no new technology breakthroughs as much as many incremental evolutions to high-speed optical networking technologies like modulation, digital signal processors and filtering.

I intend to track technologies and test results related to transport layer virtualisation and similar efforts for 400 Gig-and-beyond transport.

 

 

Vladimir Kozlov, CEO and founder of LightCounting

I had not attended ECOC since 2000. It is a good event, a scaled down version of OFC but just as productive. What surprised me is how small this industry is even 15 years after the bubble. Everything is bigger in the US, including cars, homes and tradeshows. Looking at our industry on the European scale helps to grasp how small it really is.

 

What is the next market opportunity for optics? The data centre market is pretty clear now, but what next? 

 

 Listening to the plenary talk of Sir David Paine, it struck me how infinite technology is. It is so easy to get overexcited with the possibilities, but very few of the technological advances lead to commercial success.

The market is very selective and it takes a lot of determination to get things done. How do start-ups handle this risk? Do people get delusional with their ideas and impact on the world? I suspect that some degree of delusion is necessary to deal with the risks.

As for issues to track in the coming year, what is the next market opportunity for optics? The data centre market is pretty clear now, but what next?