The VCSEL Advantage

There are basically two types of lasers used in fiber optic transmission systems today:  edge-emitters and surface emitters.  The most prevalent high-speed edge-emitters are FP and DFB.  The beam emission for these devices is parallel to the substrate.  In the case of VCSELs, the light is emitted vertical to the substrate.

Short-wavelength VCSELs have been a part of the optical networking world since Honeywell introduced them in the early 1990s.  The devices were adopted quickly to replace unreliable and costly CD lasers in the datacom market.  Due to their inherent low cost, low power and small size, VCSELs became the light source of choice in enterprise networks.  They are also credited with enabling Gigabit transmission in that space and are currently being used in over 90 percent of Fibre Channel and Ethernet transceivers.   By taking what was learned at 850 nm and extending it to 1310 and to 1550-nm wavelengths, companies are now starting to show that they can drastically reduce the cost and size of transmitters.

Historically, longer wavelengths of 1300 to 1700 nm have been more difficult to produce in the VCSEL construction, because of the refractive index of InGaAsP.  This material is generally used for edge-emitters in these wavelengths and does not change very much with composition, which makes it difficult to produce components.  But in the early 2000s, development of different combinations of III-V elements led to long-wavelength VCSELs.  Several manufacturers such as Bandwidth9 with its tunable, 1550-nm VCSEL;  Cielo Communications, E2O and Picolight with their  1310-nm VCSELs had proven that lasers supporting wavelengths higher than 980 nm were possible to produce in volume. In fact, before JDSU acquired Picolight, it had several multi-Gigabit transceivers it produced with 1310-nm VCSELs. JDSU has since discontinued that line and, it seems, its support of 1310-nm VCSELs.

Key advantages of the VCSEL at production-level include the following:

• High Yields. VCSELs can be processed with as many as 20,000 individual lasers on a three-inch wafer.  Even if 20 percent of these are lost due to processing yields (a high number by VCSEL manufacturers standards), this is still a far higher yield than their edge-emitting cousins.
• Testing at the Wafer Level.  VCSELs can be tested before the wafer is diced.  Most edge-emitting lasers (FPs and DFBs) must be cleaved from the wafer and packaged before they can be tested, and are therefore tested individually, which increases processing costs and decreases yields significantly
• Easier Coupling and Packaging.  Another important advantage of the VCSEL structure is that its circular cross-section gives better control over beam size and divergence than for edge-emitters, allowing for much easier coupling of the fiber to the VCSEL output and easier alignment during packaging.

Table I shows a comparison of FP, DFB and VCSEL solutions, an availability status, and a list of some of the component manufacturers.

 

Table I:  Comparison of  VCSEL, FP and DFB Technologies
Attribute	VCSEL	FP	DFB
Cost	Low	High
Optical Output Power
Power Consumption
Size	Small (vertical construction)	Large (planar construction)
Mode Stability	Good	Fair
Testing	On chip	Packaged assembly
Manufacturing	Easy (20, 000 devices on 3 inch wafer)	Difficult
Packaging	Easy
Coupling to Fiber	Efficient	Inefficient
Modulation	Direct up to 12 Gbps	Direct only up to 2.5 Gbps then must be external
Drive circuitry	Simple	Complicated
Monolithic Integration	With receiver and electronic driver components	With other optical components
Suppliers	850 nm:  Agilent, Aerius Photonics, Applied Optoelectronics, Inc., Oclaro, Optowell, Emcore, EpiWorks, FCI/MergeOptics, Finisar, JDSU, Raycan, TE Connectivity, VI Systems 1310 nm:  Alight Technologies, Beam Express, JDSU, Raycan, Vertilas, VI Systems 1550 nm:  Raycan, Princeton Optronics, Vertilas	Agilent, Excelight, Finisar, JDSU, Modulight, Oclaro, OpNext	Agilent, Bookham,  JDSU, Excelight, Finisar, Fujitsu, Oclaro, OpNext

Long-wavelength VCSELs have started to emerge again mainly due to some new process technologies now being leveraged. Two companies stand out to me with their technology developments of long-wavelength VCSELs – Vertilas and VI Systems.

SFP+ - The New Optical RJ45?

For those of you that have been in the industry for what seems to be 100 years, but is really about 25 years, you know that the one “connector” that hasn’t changed much is the RJ45. While there have been improvements by adding compensation for the error that was made way back when AT&T developed the wiring pattern (splitting the pair causing major crosstalk issues), the connector itself has remained intact. Contrastingly, optical connectors for datacom applications have changed several times – ST to SC to MT-RJ to LC. They have finally seemed to settle on the LC and perhaps on a transceiver form factor – the SFP+. The SFP was originally introduced at 1G, was used for 2G and 4G and with slight improvements has become the SFP+ and the dominant form factor now used for 10G. Well, it is in the process of getting some slight improvements again and promises to make it all the way to 32G. That’s six generations of data rates – pretty impressive. But how?

The INCITS T11.2 Committee's Fibre Channel Physical Layer – 5 (FC-PI-5) standard was ratified in September. It specifies 16G Fibre Channel. Meanwhile, the top transceiver manufacturers have been demonstrating pre-standard 16G SFP+ SW devices. But, wait a minute – short-wavelength VCSELs were supposed to be very unstable when trying to modulate them at data rates above 10G right? Well, it seems that at least Avago and Finisar have figured this out. New microcontrollers and adding at least one clock and data recovery (CDR) device in the module to help clean up the signals have proven to be keys. Both vendors believe it is possible to do this and not add too much cost to the modules. In fact, both also think that possibly by adding electronic dispersion compensation (EDC) they can push the SFP+ to 32G as well - which is the next step for Fibre Channel - hoping to stop at 20G and 25G to cover developments in Ethernet and InfiniBand.

And what about long wavelength devices? It has always been a challenge fitting the components needed to drive long distances into such a small package mainly because the lasers need to be cooled. But not anymore – Opnext has figured it out. In fact, it was showing its 10km 16G FC SFP+ devices long before any of the SW ones were out (March 2010). Of course, this isn't surprising considering Opnext has already figured out 100G long haul as well.

These developments are important to datacom optical networking for a few of reasons:  

1. They show that Fibre Channel is not dead.
2. The optical connector and form factor "wars" have seemed to subsided so transceiver manufacturers and optical components vendors can focus on cooperation instead of positioning.
3. They will impact the path other networking technologies are taking – Ethernet and InfiniBand are using parallel optics for speeds above 10G – will they switch back to serial?

Stay tuned for more on these points later.

 

SC10 and Optical Transcievers

It’s a beautiful time of year in New Orleans for the top supercomputing companies to show their wares. While I wouldn’t consider SC10 exactly the place to sell optical components, there were a few new developments there. SCinet – the network that is always built at the top HPC conference – boasted 100G Ethernet as well as OTu4. Alcatel-Lucent, Ciena, Cisco, Force10 and Juniper, among others donated equipment to build this network. Module vendors Avago Technologies, Finisar and Reflex Photonics contributed QSFP and CFP 40G and 100G devices to the cause.

Meanwhile, the Ethernet alliance was showing two demonstrations in its booth – a converged network running FCoE and RoCE over 40GigE and 100GigE. Nineteen different vendors participated in this demo that was run by the University of New Hampshire Interoperability Lab. Both CFPs and QSFPs were used in this demo.

Some of you may wonder why I would attend SC10. I keep my eye on the HPC market because it usually indicates where the broader data center market will be in a few years. And, in fact, even medium-sized businesses’ data centers with higher computational needs are starting to resemble small HPC centers with their server clusters using top-of-rack switching.

Most of the top optical transceiver vendors and even some of the smaller ones see this market as an opportunity as well. While InfiniBand still uses a lot of copper interconnects, for 40G and 120G, this is changing. QSFP was the standout for 40G IB displays and CXP AOCs were shown for 120G as well. Avago Technologies was the first to announce a CXP module at the show.

Some believe that the CXP will be short-lived because there is progress being made on 4x25 technologies – Luxtera announced its 25G receivers to go with its 25G transmitter that it announced earlier this year. But it will still be a few years before all of the components for 25G will be ready for system’s developers to spec in. Tyco Electronics had a demonstration at their booth showing it is possible to run 28G over eight inches of a PCB, but this was still a prototype. And Xilinx has announced a chip for 28G electrical transceivers that can be used with this board design. But, none of these devices are even being tested by equipment manufacturers yet and the CXP has already been adopted by a few. So I think the CXP may have more life in it than some people may think.

AOCs (Part 2)

Summary of a few more AOC Implementations:

Avago Technologies had a late entry into the AOC market with its 10GBASE-CX4 replacement and QSFP+ products. But they have a rich history in parallel optics so have quickly come up to speed their products. While they may have been somewhat late to market, Avago has an existing customer base to peddle its wares to.

Finisar’s products include Quadwire and Cwire AOCs to address early adoption of 40G and 100G. Quadwire is Finisar’s mainstream product, both in terms of its use of the VCSEL arrays the company produces in volume at its Texas fab, and in terms of its use of the popular QSFP form factor.

The high end of the Finisar product line is designed to exploit anticipated interest in 100G Ethernet and 12-channel QDR InfiniBand. Cwire offers an aggregate data rate of 150 Gbps and a CXP interface. Not only does this represent the direction of high-end enterprise cluster design, but it allows Finisar to utilize the most integrated VCSEL arrays it manufactures. The 12-channel array also represents the most cost-effective per-laser manufacturing option, allowing Finisar to take advantage of its expertise in designing large VCSEL-arrays. The benefit in high channel count can also be seen in power dissipation. While the single serial channel of Laserwire dissipates 500mW per end, the 12-channel Cwire dissipates less than 3W per end – half the power dissipation per channel.

MergeOptics (now part of FCI) was born of the old Infineon which was once a powerhouse in the optical transceiver markets—both telecom and datacom. It emerged in 2006 with its SFP and then SFP+ products and is now one of the first entrants for 40G and 100G AOCs. Unlike most of its competitors, it is focused on 10G and above products so can bring them to market rather quickly. Its technology is being leveraged for InfiniBand and Ethernet applications.

Stay tuned for the next post for just a little more on AOCs.

Gigabit Transcievers

In our rush to want to discuss all the new technologies, it seems to me that analysts have forgotten that part of our job is to also point out ongoing trends in existing products. So while talking about Gigabit transceivers might not be as appealing as talking about Terabit Ethernet, it’s also a necessity – especially since, without these devices and the continuing revenue they produce, we wouldn’t have 40/100G or even 10G Ethernet. So what are the important points to make about Gigabit transceivers?

• The market for Gigabit Ethernet transceivers (copper and optical) is expected to be about $2.5-billion in 2010 according to CIR, but it is also supposed to start declining in 2011 when more 10GigE will take its place.
• Pricing for a 1000BASE-SX SFP module is now at about $20 for OEMs. End users still pay Cisco or Brocade or their agents about 8x that much (more about this later).
• Low pricing makes it difficult on profit margins so transceiver vendors hope to make it up in volume.
• While SFP is certainly the preferred form factor, there is still a decent amount of GBIC modules being sold.
• SFP direct-attach copper cable assemblies have become an option for top-of-rack switches to servers instead of using UTP Category patch or fiber cabling, although the majority of implementations today are still UTP patch cords, mainly because the connections within the rack are still 100M with the uplink being Gigabit Ethernet of the 1000BASE-SX variety.
• While 10/100/1000 ports are the norm for desktop and laptop computers, most of these devices are still connected back through standard Category 5e or 6 cabling to 100M switch ports in the telecom room.
• Gigabit Fibre Channel business is pretty much non-existent now. It was quickly replaced by 2G and has progressed through 4G and 8G is expected to become the volume application this year. Look for more on Fibre Channel in future posts.
• Avago Technologies and Finisar top the list of vendors for 1000BASE-SR devices. JDSU has all but disappeared from the scene, mainly because they have de-emphasized this business in favor of their telecom products. In fact, rumor has it that JDSU is shopping its datacom transceiver business and has been for some time.

A note on JDSU: It appears that the optical components giant has taken the technology that was developed at IBM, E2O and Picolight and thrown it away. Picolight was once a leader in parallel optics and, along with E2O, long-wavelength VCSELs. IBM pioneered v-groove technology and the oxide layer that enabled the next leap in speed and improved reliability for 850nm VCSELs. All of these technologies look like they are destined to die a slow, painful death after being acquired by JDSU. The company’s attention is clearly focused on its tunable technology and telecom applications, which is where, of course, it started. JDSU has never had a good reputation for assimilating acquisitions, so none of this should be a surprise. I was optimistic when JDSU bought these companies thinking that now these emerging technologies would be supported by a larger pocketbook. What is the reasoning for JDSU deemphasizing the technologies it acquired? Is it trying to get rid of short-reach competition in hopes that all optical networking would move towards long-wavelength devices? This would have been naïve; the likes of Finisar, Avago, MergeOptics and others would still be supporting 850nm optics and there remains a healthy market for them in enterprise networks and data centers—albeit a very competitive one as stated above.

 

Other 10GigE Transceiver Markets – ER, LX4 and LRM

Some of you may have noticed that in my last post I neglected to talk about three other 10-Gigabit Ethernet variants – LX4, LRM and ER. That’s because the content was already long enough and I wanted to focus on the volume data center applications. Now, I’ll discuss the others.

10GBASE-ER runs over SMF at 1550nm for up to 40km. While there are a few service providers that might choose to do this, the vast majority of them choose WDM through the OTN instead. There may be some private networks that have need for this variant as well which is what prompted the IEEE include it in the standard. These transceivers are priced out of typical budgets for the average enterprise at over $4000.

10GBASE-LX4 was originally introduced to address installed base of FDDI-grade (not laser-optimized) MMF, but can also be used with higher-grades of LOMF as well as SMF. It uses CWDM to send four wavelengths (thus the X4) between 1269.0 to 1355.9nm running at data rates of 2.5 Gbps each. LX4 modules are available in both X2 and XENPAK form factors and from at least a couple of sources such as Emcore and Hitachi Cable. As you can imagine, because these devices have four lasers and four detectors with their associated electronics, they cost appreciably more than either the SR or LR transceivers. The module alone retails for about $2000, which means that the per port cost would probably around $2500. But, you most likely wouldn’t fill your switch with these modules of course; you would only use them as needed where you wanted to re-use existing installed fiber.

In response to the high priced LX4, 10GBASE-LRM variant was developed. It was enabled by chip companies such as Clariphy and Scintera with some new technology, electronic dispersion compensation (EDC), that could push 10G serial to longer distances on MMF. It took a while to develop the standard and the consequence was that LX4 really took much of the market it was intended for. However, once products were released and supported by the top-tier transceiver manufacturers (Avago, Finisar, Opnext), it has really taken much of the business away from LX4. LRM modules are now available in SFP+ packages as well, which clearly indicates the vendors think there will be an ongoing market for them.

One note of caution – if you intend to use either the LX4 or the LRM modules, you need to make sure that both ends of your channel have them, otherwise it won’t work.

VCSELs – The Enabling Factor of Fiber in the Data Center

Optical technology proponents have argued for many years that fiber is about to take over all of networking. But, time and time again we have seen copper technologies reinvent themselves to serve at least the last 100 meters in LANs. But with the complicated digital signal processing that is needed to enable the 100-meter operation of copper comes a cost – power consumption. And in data center operations, power consumption may be the single most important issue still needing to be solved.

Before the EPA performed their study on data center power consumption and before the creation of the Green Grid, data center managers were worried more about running out of space than out of power. Now, with complicated electronics and the better utilization of server processing through virtualization, lowering power consumption has become more imperative.

VCSEL-based short-wavelength fiber optic networks may be the answer. As mentioned in a previous post, on a port-by-port basis, 10GBASE-SR devices consume four times less power than 10GBASE-T ones. And when you have thousands of these ports within your data center, the total power consumption adds up quickly. Stay tuned for further quantitative analyses of copper versus fiber in the data center.

Finisar is one of the leading manufacturers of VCSELs, and they sell the short wavelength transceivers to LAN and SAN equipment providers including Brocade, Cisco, QLogic , HP and EMC. While transceivers generally sell at very low margins, they are an essential part of keeping costs down and power consumption low in data center networks.

Contributing Analyst - David Gross.

Datacom Transceiver Vendors Transitioning into New Businesses

Have you noticed that it seems like all of the top datacom transceiver suppliers are transitioning their businesses? I’ve already talked about Avago’s new venture with its MicroPOD technology. They seemed to have supplanted Finisar as the technology leader in the space. Finisar has expanded its offerings into more telecom markets and JDSU is all but gone from the scene and focusing more on telecom again.

Finisar seems to be enjoying what may well be short-term success with its Laserwire offering. Since it is a non-standards based solution, it is difficult to believe it will become a mainstream one. While Finisar is offering other AOCs—C.wire (CXP-based) and Quadwire (QSFP-based), it does not seem to be participating in what seems to be a chip-to-chip optical interconnection revolution like Avago and Luxtera are (see previous posts for details) . Finisar used to be the technology leader in the optical transceiver space, it has veered off-course from that strength in preference for market diversification instead—now covering telecom and HPC standards-based solutions as an alternative. But perhaps this is the right move for Finisar, since it has not seemed to hurt its revenue position at all.

JDSU seems to be absent from the short-reach module market. It appears that the optical components giant has taken the technology that was developed at IBM, E2O and Picolight and thrown it away. Picolight was once a leader in parallel optics and, along with E2O, long-wavelength VCSELs. IBM pioneered v-groove technology and the oxide layer that enabled the next leap in speed and improved reliability for 850nm VCSELs. All of these technologies look like they are destined to die a slow, painful death after being acquired by JDSU. The company’s attention is clearly focused on its tunable technology and telecom applications, which is where, of course, it started. JDSU has never had a good reputation for assimilating acquisitions, so none of this should be a surprise. I was optimistic when JDSU bought these companies thinking that now these emerging technologies would be supported by a larger pocketbook. What was the reasoning for JDSU deemphasizing the technologies it acquired? Was it trying to get rid of short-reach competition in hopes that all optical networking would move towards long-wavelength devices? This would have been naïve; the likes of Finisar, Avago, MergeOptics and others would still be supporting 850nm optics and there remains a healthy market for them in enterprise networks and data centers—albeit a very competitive one.

According to JDSU, it is focusing on the LH and ULH versions of 40G and 100G first because it does not see the value in the CXP module for short-reach applications. For short-reach, it is focusing on QSFP+ modules, but development of these will take longer. The company claims it is not de-emphasizing its 850nm technology, but just focusing elsewhere first. I’m not so sure. Rumor has it, and I tend to believe that JDSU is looking for buyers for its short-wavelength business.