By Meghan Fuller Hanna
Lightwave last examined the tunable optical dispersion compensation (TODC) market in our April issue (see "TODC Vendors Ready Inline and Integrated Devices," page 15). Though it's been just seven months, a quick survey of TODC vendors reveals the emergence of two key trends during that time: 1) the ramp up of 40 Gbits/sec, and 2) real-not just academic-interest in 100 Gbits/sec. Most TODC vendors already have a roadmap to 100G, but plans are difficult to finalize until the industry figures out exactly what 100G will look like.
The deployment of triple-play networks supporting voice, data, and video traffic has placed additional burdens on backbone networks, necessitating an increase to higher transmission speeds. Carriers like AT&T and Verizon already have begun to implement 40G links, placing the onus on system vendors to finalize their 40G strategies. These strategies must include some way to compensate for chromatic dispersion, which is characterized by a spreading of the light pulses as they travel down an optical fiber. Though 10-Gbit/sec systems sometimes require compensation, it is particularly critical at 40G and higher.
"If you're a system integrator and you offer a 10-gig system, you have to show some 40G in your laboratory," notes Yair Itzhar, vice president of sales and marketing at Civcom (www.civcom.com). "Their customers demand from them continuity in their product." In addition to the company's 10G single- and multichannel Manageable Dispersion Compensation Modules (MDCMs), Civcom also recently unveiled a 40G single-channel device for residual dispersion compensation. All are in the final stages of development and have been sent to Tier 1 and Tier 2 customers for evaluation, says Itzhar.
Martin Guy, vice president of technology and product development at TeraXion (www.teraxion.com), reports that his company has shipped more than 2,000 units this year alone, and he estimates that 80% of those units are used to combat residual dispersion in 40G applications. In fact, he claims that 2007 has been a banner year for TeraXion, which has increased its number of units shipped 200% year-over-year.
Avanex (www.avanex.com) debuted a 40G TODC at the European Conference on Optical Communications (ECOC) back in September, and chief technology officer Giovanni Barbarossa confirms that "there is more activity at 40 gig today than there was just a few months ago."
There are two flavors of TODC: one for residual compensation, in which individual TODCs are used for each channel to provide dynamic adjustment at the receiver, and one for inline compensation, which is essentially a replacement for dispersion-compensating fiber (DCF). While system vendors are still weighing the business case for inline compensation (though at least one vendor, Civcom, has a 10G inline TODC for metro applications), the market for residual compensation is heating up, particularly at 40G.
TODCs used for residual or per-channel compensation must be compact and cost-effective, says Barbarossa. "Cost-effective means the per-channel dispersion compensation has to be comparable to what the per-channel compensation would be if you had to do it inline. So if you take the price of an inline box that can do all channels and divide it by 40, you should have the terminal application. I can tell you right now, no one is close to this number," he says. "It's challenging, but we'll try to get there."
ANDevices (www.andevices.com) believes it has a cost-effective residual device in its planar lightwave circuit (PLC)-based TODC, which recently earned 10G design wins with two major companies, reports Wenhua Lin, vice president of technology and new product development. While the company leverages the same technology for 40G, customer requirements have become more stringent, she says.
"The dispersion number that we were talking to customers about two years ago was around 200 to 300 psec/nm," she recalls. "Now, the specification the customers are asking for has increased to 400 psec/nm and even higher." As a result, ANDevices is now developing a new device specifically for 40G applications: an arrayed-waveguide-grating-based dispersion compensator with both a wider pass band and a wider dispersion window than the company's existing PLC-based device, which Lin says has found its sweet spot at 10G.
Higher capacity, not higher speed
None of the TODC vendors are willing to reveal too much about their 100G plans, in part because no one really knows what the 100G market will look like: Will it be serial architecture? Will it be a parallel architecture? And if parallel, will the industry embrace a 10Ã�10 implementation, a 5Ã�20, a 2Ã�40, etc.? Which advanced modulation scheme, if any, will win the day? The answers to these questions have profound design implications for the TODC vendors.
Barbarossa reports that Avanex does not have anything in development for 100G. That statement may seem odd given the hype surrounding 100G, but, says Barbarossa, it's important to make the distinction between 100G speed and 100G capacity.
"There are some companies, for example, that are working on four channels of 25 gig to come up with a 100-Gigiabit Ethernet solution," he says. "But the speed there is 25 gig; it's not 100 gig. Or, for example, 10 channels at 10G. The speed is not really 100; the speed is 10. Chromatic dispersion is a problem when you increase the speed, not when you increase the capacity," he says.
Barbarossa says the highest-speed project he has heard about is the development of a 2Ã�50-Gbit/sec implementation that uses two DQPSK modulators at 50 Gbits/sec for a combined total of 100G.
All of the vendors interviewed for this story nevertheless confirm that their system vendor customers are interested in and/or currently developing 100G systems, despite the lack of industry consensus in what those systems should look like. Both ANDevices and TeraXion say they have shipped TODC devices for use in prototype 100G systems, likely based on a parallel architecture. ANDevices reports that its customer is using its standard PLC-based 40G TODC for per-channel compensation in a 100G system. "We don't have a very clear picture of what the architecture looks like or what exactly they need on the component side," Lin admits, "but it's something we will pay attention to."
Despite the uncertainty surrounding high-speed transmission, the TODC market should experience a 100% compound annual growth rate over the next five years, to net $245 million by 2012, according to a new report from CIR (www.cir-inc.com).
In an attempt to spur market growth even further, Avanex has taken the lead in trying to establish a multisource agreement (MSA) to standardize the electronics on the TODC devices, namely the interfaces, says Barbarossa. "The same thing happened in transponders with 300-pin," he notes. "That really has been keeping the cost of transponders low, at least from the interface standpoint, and we want to do the same for dispersion compensation."
Barbarossa would not divulge any further details because, at press time, Avanex had not yet presented its ideas to all the players in the TODC space. However, he says Avanex aims to develop as broad an MSA as possible to include all the TODC vendors, which would require an MSA that is technology agnostic. "What people are going to use optically is their differentiation," he says.
Editor's note: Visit www.lightwaveon line.com for a follow-up article detailing new features and products that TODC vendors are currently developing.
Meghan Fuller Hannais senior editor at Lightwave.
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