Avago’s Interesting Demos at OFC/NFOEC

As always, the top transceiver manufacturers were represented at OFC, but of the top three datacom transceiver providers, Avago Technologies stood out to me. They had two significant demonstrations:

1. Connecting a 40GBASE-SR4 Ethernet port using its QSFP+ to four standard 10GBASE-SR Ethernet ports with its SFP+ modules. On the surface, this seems pretty easy to do, until you realize that the specifications for the transmitters and receivers in these devices have are very different. The 10G devices could easily overpower the 40G receiver if it’s not designed to handle the higher power. Avago has solved this issue with its parts and hopes to be able to be interoperable with anyone’s transceivers in the near future.
2. A VCSEL-based 25G short-wavelength SFP+ working prototype. At first I was puzzled about this because I couldn’t figure out the application. Well, it turns out there really is none for the 25G part, yet, but showing that it could be done makes you realize that 32G Fibre Channel applications using the SFP+ may not be as far-fetched as we think. And, perhaps we can get a 100GBASE-SR4 (4x25G that isn't in the IEEE standard yet) solution soon.

Stay tuned for more on other developments announced or demonstrated at OFC/NFOEC.

Optical Interconnection Players Strengthening Their Businesses

Molex just purchased Luxtera’s AOC business completing the circle that all the other optical interconnect players started. During the telecom bust in the early 2000’s, Amphenol, FCI, Molex and Tyco Electronics all either de-emphasized their optical interconnect businesses or exited them all together. Now, they have all re-entered. Why?

While they are all working on more high-speed copper solutions like the one Tyco showed for 25G and beyond at SC10, I beleive they also see the writing on the wall. While they won’t admit it, I think they know that beyond 100G copper cable interconnects may have FINALLY reached the end of their useful life. At 40G and 100G, for example, there is still no twisted-pair solution and the direct-attach copper can only reach about 7m reliably.

It has been interesting watching the choices these traditional connector companies have made:

• Amphenol: It never exited the optical interconnect business, but left the transceiver products to Avago, Finisar, JDSU and others until recently. It has a stronghold on the short-reach copper direct-attach market so has inroads at customers for its AOCs and modules.
• FCI: Exited the optics business entirely for a few years but then started again from scratch and subsequently purchased MergeOptics in February 2010. MergeOptics is what was left of Infineon Technologies and still has strong technical abilities in short-reach products. It also has the building blocks to provide all-optical interconnects all the way from the chip (see my previous posts on MergeOptics). They can provide both AOCs and transceiver modules so have the ability to cover all high-speed markets in InfiniBand, Ethernet and Fibre Channel.
• Molex: Purchased Luxtera’s AOC business recently. So while FCI and Tyco are stressing short-wavelength technologies, Molex has turned to custom long-wavelength ones. Luxtera’s technology is based on 1490nm devices, which really doesn’t matter if you’re purchasing an AOC, but will matter if you want transceiver modules. According to company representatives, they will eventually get back into supplying transceiver modules, but there has been no evidence of this as of yet. Perhaps the possession of Luxtera AOCs will prompt this.
• Tyco Electronics: Tyco exited the transceiver business in the early 2000’s, but still had a very active fiber-optic interconnect business – especially for premise wiring (AMP NETCONNECT). It acquired Zarlink Semiconductor’s optical products group in May 2010. Zarlink is on the forefront of parallel-optics technology and was one of the first to introduce AOCs. It does not appear that Tyco intends to supply optical transceiver modules again.

I would never bet against copper re-inventing itself in order to meet the demands of future high-speed networks, but with optical 10G dominating the market currently and 40/100G optical products starting to emerge, it will be an uphill battle for copper solutions to gain traction. And beyond 100G, all bets are off. I’m thinking that these companies are reaching the same conclusions and that if they don’t add optical capabilities soon, they may render themselves obsolete within the next ten years or so. That's not to say that there won't be a vibrant businesses in both copper structured cabling and interconnects over the next ten years - there will be. But I think that R&D dollars will be better spent on optical interconnect technologies rather than trying to figure out how to run 25G signals using copper interconnects (including backplanes.) Or how to convince end-user customers in the US that a shielded structured cabling solution for 40G is better than a short-reach optical one because it will be cheaper - but at what cost to power, cooling and space?

What do you think? I'd love to hear your thoughts.

The 10X10 MSA: Niche, Distraction or the Right Answer? (Continued)

While Vipul has a point that this new MSA is probably a distraction, it is difficult to deny that there is a market for cost-effective devices with optical reaches between 100m and 10km. In fact, 100m to 300m is the market that multi-mode fiber has served so well for the last 20 years. And, 300m to 2km has been a niche for lower-cost 1310nm single mode products like 1000BASE-LX. So I have a slightly different opinion about this 10x10 MSA and whether it’s a niche, distraction or the right answer.

In a recent article written on Optical Reflection, Pauline Rigby quotes Google’s senior network architect, Bikash Koley. About 100GBASE-SR10, he says 100m isn’t long enough for Google – that it won’t even cover room-to-room connections and that “ribbon fibres are hard to deploy, hard to manage, hard to terminate and hard to connect. We don’t like them.” There is an answer for this ribbon-fiber problem – don’t use it. There are many optical fiber manufacturers that now provide round multi-fiber cables that are only “ribbonized” at the ends for use with the 12-position MPO connector and are much easier to install – Berk-Tek, A Nexans Company, AFL and even Corning have released products that address this concern. But, the 100m optical reach is another matter.

I have to agree with Google about one other thing – 4x25G QSFP+ solutions are at least four years away from reality (and I would say probably even longer). This solution will eventually have the low-cost, low-power and high-density Google requires, but not quick enough. I think something needs to be done to address Google’s and others requirements between 300m and 2km in the short term, but I also believe that it needs to be standardized. There is no IEEE variant that would currently cover a 10x10G single mode device. However, there is an effort currently going on in the IEEE for 40G over SMF up to 2km. Perhaps the members of the MSA should look to work with this group to expand its work or start a new related project to cover 100G for 2km as well? I know this was thrown out of the IEEE before, but so were 1000BASE-T and 10GBASE-T initially.

So what I'm saying is that the market is more than a niche - hundreds of millions of dollars of LOMF sales at 1G and 10G would attest to that. And it's more than a distraction because there is a need. But I don't think it's entirely the right answer without an IEEE variant to back it up.

Let us know what you think.

25G/40G VCSELs Driving Short-reach Optical Interconnects

Just a few years ago, laser designers were struggling with stability of their 10G VCSELs. But now, at least one, VI Systems GmbH, claims it will have production-ready 40G VCSELs within the next few years. The German start-up has developed two products it believes will take VCSELs beyond 10G applications - a directly-modulated (DM) device and an electro-optic modulated (EOM) DBR VCSEL. Both are short-wavelength (850nm) lasers.

In a recent press release, VI Systems explains that it “developed the VCSEL products at a wavelength of 850 nm along with a range of extremely fast integrated circuits based on the SiGe BiCMOS (silicon-germanium bipolar junction transistors in complementary metal-oxide-semiconductor) technology. The company uses a patent pending micro-assembly platform for the integration of the opto-electrical components and for alignment to a standard high performance multi-mode glass-based fiber.” The start-up has been presenting data supporting its claims of highly stable devices for more than a year now. It gets there by changing the laser active region material and structure to InAs quantum dot (QD).

Not only is VI Systems working on innovative laser structures, it has also developed new electro-optic integration methods to further reduce the cost of these devices.

I’ve noted in previous posts how VCSELs are the key to low-cost optical networks in the data center. These new VCSELs and packaging methods would bring an even more cost-effective “serial” solution for 40/100G. They could also be used for very short-reach optical connections like for chip-to-chip, on-board or board-to-board. Perhaps these inventive products will rival Avago’s MicroPOD and Luxtera’s OptoPHY (also in previous posts). Based on the presentations that VI Systems has released, it sure appears that its management completely understand the needs of both the data center and optical interconnect markets so could very well give incumbents in the industry some competition.

Why Polarity Matters (Part 2)

If you’ve read my previous posts on the subject, you know that polarity can be a tricky matter and it’s even more complicated when you try to choose it for your data center cabling. You really have to choose based on several factors:

1. Patch cords – method A has two different patch cords that you have to stock, but the upside is that it’s pretty simple to follow where the signal is going and if you happen to be out of one type of patch cord, you can really take the one you have and just flip the fibers as a temporary fix until you can get the other patch cords. Of course this isn’t recommended, but if you’re in a bind and need to get up-and-running right away, it will work. With methods B and C you have the same patch cord on each end so no need to worry about this, but if you happen to have the wrong cassettes or backbone, nothing will work and you'll have to wait to get the correct ones.
2. Cassettes and backbone cables – you need to make sure you buy all of one method of polarity or your system won’t work. If you’re concerned about supply, all three polarity methods are available from multiple vendors, but Method A is “preferred” by most.
3. Upgradability – this is where it can get dicey. Typically your pre-terminated assemblies are running Gigabit applications today and a few may be running 10G. Any of the polarities will work at these data rates. But when you move to 40/100G, methods A and B have straight forward paths, while C does not. Also, you’ll want to make sure you use the highest grade of LOMF available, which is OM4 – this will give you the best chance of being able to reuse your backbones up to 125m. If you need something longer, you’ll need to go to SMF.

If you are thinking about installing pre-terminated cassette-based assemblies now for 10G with an upgrade path to 40 and 100G, you need to consider the polarity method you use. Unlike today's 2-fiber configurations, with one send and one receive, the standards for 40G and 100G Ethernet implementations use multiple parallel 10G connections that are multiplexed. While 40/100G equipment vendors will tell you that polarity is not an issue, care must be taken if you want to reuse this installed base.

40G will use four 10G fibers to send and four 10G fibers to receive, while 100G uses either four 25G fibers or ten 10G fibers in each direction. Because 40 and 100G will be using the MPO connector, if the polarity method is carefully chosen, you will be able to reuse your backbone cables. This is enabled by the fact that the IEEE took much care in specifying the system so that you can connect any transmit within a connection on one end of the channel to any receive on the other end.

Those selecting fiber to support 10G now and 40G in the near future need to understand what will be involved in transitioning and repurposing their cable plant. In order to upgrade using method A, you can replace the cassettes with MPO-to-MPO patch panels and MPO-to-MPO patch cords and it will enable flexibility to address moves, adds and changes as well as promoting proper installation best practices. The polarity flip will need to be accomplished in either an A-to-A patch cord or possibly with a key up/key down patch panel.

Method B multimode backbone cables can also readily support 40G applications. For a structured cabling approach, method B will still use a patch panel and patch cords, though as with current method B, both patch cords could be A-to-B configuration. While Method C backbones could be used, they are not recommended for 40G as completing the channel involves complex patch cord configurations.

It appears that 100G will use either the 12-fiber (4x25G) or the 24-fiber (10x10G) MPO connector. With transmits in the top row and receives in the bottom row, the connection will still be best made using a standardized structured cabling approach as described above.

There are many suppliers of pre-terminated optical assemblies including Belden, Berk-Tek, a Nexans Company, CommScope, Corning, Panduit, Siemon, Tyco Electronics NetConnect as well as many smaller shops that give quick-turn assemblies like Cxtec CablExpress and Compulink.

How the 40/100G Ethernet Shift to Parallel Optics Affects Data Center Cabling

Most data centers are cabled with at least Category 5e and some MMF. To upgrade to 10G, data center managers need to either test their entire installed base of Category 5e to make sure it is 10G-worthy or replace it with Category 6A or 7. And their MMF should be of at least the OM3 (2000 MHz.km) variety or the 300m optical-reach is in question. Unless, they want to use 10GBASE-LX4 or LRM modules that are about 10x the price of 10GBASE-SR devices. But what happens when you want to look beyond 10G to the next upgrade?

Last month I talked about how at 40/100G there is a shift to parallel-optics. Unlike today’s two-fiber configurations, with one send and one receive, the standards for 40G and 100G Ethernet specify multiple parallel 10G connections that are aggregated. 40GBASE-SR4 will use four 10G fibers to send and four 10G fibers to receive, while 100GBASE-SR10 will use ten 10G fibers in each direction.

What this means to the data center operator is that they may need to install new cable. Unless they’ve started to install pre-terminated fiber assemblies using the 12-position MPO connectors – these can be re-used if polarity is chosen carefully. Polarity is the term used in the TIA-568 standard to explain how to fiber (wire) to make sure each transmitter is connected to a receiver on the other end of a multi-fiber cable.

There are three polarity methods defined in the TIA standard and each has its advantages and disadvantages, but only two of the three will allow you to easily reuse your installed pre-term assemblies for 40/100G – methods A or B. I’ll explain why in my subsequent posts.