Dale’s Web Log

Yokogawa Electric Corp. and Fujitsu Ltd today announced the joint development of what they claim are the world’s first practical 40Gbps optical transmission technologies using differential quadrature phase shift keying (DQPSK). The two companies say they are planning to incorporate the technologies in various new products for 40Gbps ultra high-speed optical transmission networks.

The proliferation of optical access networks that directly connect households via optical fibers and the construction of next-generation networks have led to a increasing demand for greater capacity in inter-city optical transmission networks. In order to meet this demand, carriers are considering an increase in maximum transmission speed from the 10Gbps of today’s optical transmission networks to 40Gbps.

Typically, when transmission speed is increased, distortion caused by polarization mode dispersion (PMD) becomes pronounced, limiting transmission reach. For example, transmission reach is limited to a maximum of 100 km when transmitting a 40Gbps signal using a standard binary modulation in an optical fiber that meets the PMD specification (0.2 psec per square-root-kilometer) recommended by the ITU-T. Thus, inter-city transmission, which requires long-distance transmission of more than several hundred kilometers, has not been possible.

Seeking to overcome this obstacle, advances are being made in investigating DQPSK-type transmission, which is tolerant to waveform distortion due to PMD, and its high performance has been confirmed in the laboratory experiments. However, the configuration of a DQPSK format is complex, and thus large size and high power consumption of the optical transceivers have proved to be challenges.

Yokogawa Electric and Fujitsu Limited, in cooperation with Fujitsu Laboratories Ltd, have successfully developed what they claim are the world’s first practical 40Gbps DQPSK optical transmission technologies, including:

DQPSK LN optical modulator
The LN optical modulator for DQPSK modulation, which was developed by Fujitsu and operates with the world’s lowest drive voltage, enables a compact optical transmission component design and lower power consumption.

Dedicated ICs and devices that enable DQPSK
Compact, low power consumption, dedicated ICs and other devices that enable DQPSK, including a driver device optimized for the DQPSK LN optical modulator; optical/electrical conversion devices that operate stably despite PMD waveform distortion; and clock and data recovery devices were developed with Yokogawa Electric’s InP Hetero-Junction Bipolar Transistor (InP HBT) technology.

Compact optical transmission module
Control technology was developed that allows the newly developed key devices to operate in a stable manner. The companies also developed a mounting technology that enables a compact size, making possible a compact 110- x 320- x 40-mm package equipped with all functions necessary for 40-Gbit/sec DQPSK in the transmission equipment and a low-power consumption of 35 W (with case temperature of 72 ° Celsius).

According to the companies, 100 units of 40Gbps DQPSK optical transceivers were manufactured, and transmission performance and stable operation–despite environmental changes such as temperature fluctuations and variations in supply voltages–were confirmed. Furthermore, the transmission reach as limited by PMD was found to be approximately eight times better than that of standard binary modulation, say the companies.

The resulting technology is expected to significantly reduce the time it will take to implement major inter-city high-capacity optical networks.

The new technologies were developed under a strategic partnership, established between Yokogawa and Fujitsu in March of 2006, to jointly develop core system technologies and key components for ultra high-speed optical transmission systems with the cooperation of Fujitsu Laboratories Ltd. Sample products were on display at last week’s OFC/NFOEC Conference in Anaheim, CA.

ANAHEIM, Calif. — OFC/NFOEC — If 100Gbps Ethernet gathers pace quickly enough, it might put a crimp in the lifespan of the 40Gbps generation.

That’s one possibility being discussed here at OFC/NFOEC, as industry executives wonder whether 40Gbps might see a shortened lifespan due to pressure from both 10- and 100Gbps alternatives.

“We see the 40Gbps deployment as more of a stepping stone,” says Saeid Aramideh, vice president of marketing for CoreOptics Inc. “Not that we have stopped our activity there, but certainly we see our future being 100Gbps-based. My personal belief is that with the coming of 100Gbps transmission in the WAN, the 40Gbps life cycle could be short-lived.”

Metro and long-haul 100Gbps deployments are years off — most sources are saying 2012; AT&T Inc. has suggested 2010 — while 40Gbps deployments are underway now. AT&T has lit its OC768 backbone, and here at OFC/NFOEC, Verizon Communications Inc. officials said they also plan to build a 40Gbps core.

But here’s the catch. It’s generally accepted that for 40Gbps sales to take off, enabling 40Gbps to usurp 10Gbps, the cost should be no more than 2 to 2.5 times as much as 10Gbps. So far, 40Gbps prices aren’t there.

“The cost economics of 10Gbps are so strong right now, it’s limiting 40Gbps to only those cases where they have to use it,” says Roy Rubenstein, research director with the transceiver market research firm, LightCounting . A typical, short-reach, 40Gbps transceiver can carry a $20,000 to $25,000 price tag, he notes.

So, if 100Gbps optics manage to catch up by costing, say, about five times as much as 10Gbps, could that cut short the 40Gbps generation? “Depending on where 40Gbps moves, you might see an intercept point with 100Gbps, but it’s too early to tell,” says Mike Ricci, a senior vice president at JDS Uniphase Corp.

What might make that intercept point possible is the amount of attention being lavished on 100Gbps transmission. The 100Gbps name-dropping at OFC/NFOEC includes prominent vendors such as Alcatel-Lucent, Infinera Corp, and CoreOptics customer Siemens Communications Group .

“There’s a window for 40Gbps. If people get the prices right, they can have a chance,” LightCounting’s Rubenstein says.

The optics vendors pushing 40Gbps don’t appear too worried, considering 100Gbps transmission is still pretty far from reality. “If there’s a need for 100Gbps, it’ll happen, but at this point I don’t see a significant threat to the investments made in 40Gbps,” says Ed Cornejo, director of product marketing at Opnext Inc.

That doesn’t mean Opnext is ignoring the next wave, as it’s already engaging in 100Gbps laser research in its lab. On a panel at Monday’s Optical Society of America Executive Forum, Opnext CEO Harry Bosco said the tough part, when it comes to transceivers, will be finding the chips to work at that speed.

And recent M&A activity shows confidence in the upcoming 40Gbps market. Two of this week’s acquisitions — Kailight Photonics Ltd. by Optium Corp., and Kodeos Communications Inc. by Finisar Corp. — “show people are getting serious about their 40Gbps portfolios,” Rubenstein says. Kailight is shipping 40Gbps modules, while Kodeos, more of a 10Gbps vendor, uses long-haul encoding techniques that could be useful at 40Gbps, he says.

— Craig Matsumoto, West Coast Editor, Light Reading