Electronic Design

Happy Days Are Here Again For Fiber-Optical Communications

Jointly held with the National Fiber Optic Engineers Conference March 25-29, this year's Optical Fiber Communications Conference was a happy affair. Attendance was up well over last year, with more than 14,000 on site at the Anaheim Convention Center. The general attitude was upbeat and positive. With over 500 exhibitors, the mood was similar to the time just prior to the big fiber-optical downturn around 2001. But the fiber-optical communications business is booming again and well beyond recovering from past problems.

The conference was sponsored jointly by the IEEE Communications Society, the IEEE Lasers and Electro-Optics Society (LEOS), the Optical Society of America and Telcordia Technologies, and welcomed a host of distinguished keynoters. John Negroponte of MIT's Media Laboratory discussed his One Laptop Per Child program. C.C. Fan, a retired professor at Tsinghua University, gave an overview of the optical fiber networks in mainland China. Mark Wegleitner, senior vice president at Verizon, talked about the growth and technology in Verizon's optical fiber systems.

In the awards ceremony, Emmanuel Desurivire of Alcatel received the 21st John Tyndall Award. Professor David Payne of the University of Southampton, U.K., received the 2007 IEEE Photonics Award. And in between all of these luminaries and exhibits, several key trends were apparent.

First, there was lots of action in passive optical networks (PONs). Many companies exhibited products for the fiber-to-the-home (FTTH) PON boom in Asia, which also is showing some life in the U.S. Asian PONs use EPON (the Ethernet version), while U.S. PONs use GPON (the gigabit version). Verizon is continuing its rollout of its FiOS FTTH PON system with a target of 18 million subscribers by 2011.

Considering the large number of vendors, this segment has to be doing well. For example, Ignis Photonyx of Norway is manufacturing planar lightwave circuit (PLC) devices like splitters/combiners and array waveguides (AWGs). Also, broadband and optical products supplier JDSU is acquiring Picolight, which is one of the pioneers in vertical-cavity surface-emitting lasers (VCSELs). Picolight's VCSEL-based 850- and 1310-nm short- and medium-reach transceivers should have a huge positive influence on JDSU.

Second, this show put any doubts about the status of 10-Gbit/s optical networks to rest, with lots of 10 Gigabit transceivers and other products for Ethernet as well as Sonet/synchronous digital hierarchy (SDH). Avago Technologies showed its SFP+ form factor transceiver. The SFP+ form factor seems to be emerging as the most promising standard for Ethernet, Sonet, and Fibre Channel.

Recent predictions by LightCounting indicate that the market for 10 Gigabit Ethernet optical components used in enterprise network equipment is expected to grow by a 35% compound annual growth rate from 2006 to 2010. 10 Gigabit now appears to be the new “sweet spot” in optical fiber systems.

Another rising trend is renewed work in higher speeds. The big driver for upgrading to faster systems, of course, is the expected forthcoming video on demand (VOD) and Internet Protocol TV (IPTV) glut. Before the fiber-optical crash early this decade, there was a big push to develop 40-Gbit/s products and systems.

The Sonet/SDH OC-768 standard runs at 39.812 Gbits/s, or what most designers call 40 Gbits/s. There also was some discussion about a 40-Gbit/s Ethernet version. But that has been abandoned and replaced with a commitment by the IEEE to produce a 100-Gbit/s Ethernet standard in the near future, which maintains the x10 speed increments traditional with Ethernet.

Verizon recently announced that it is increasing its data rate in some sections of its ultra-long-haul (ULH) optical network to 40 Gbits/s from the current 10 Gbits/s beginning with the link between New York and Washington, D.C. The link uses 80 wavelengths in a dense wavelength-division multiplexing (DWDM) system. The next step is 100 Gbits/s with trials to begin in about 18 months.

Other companies offered ideas, products, and solutions for 100 Gbits/s and beyond. Avago demonstrated how its parallel VCSEL optics currently represent the best solution for 100 Gbits/s based on cost and reliability. Siemens reported new electronic hardware that achieved 107 Gbits/s over a single fiber channel. And, an IBM paper revealed a prototype optical transceiver chip set capable of speeds to 160 Gbits/s.

Next, there's lots of interest in new modulation methods for high-speed optical transmission. Most modulation to date is just amplitude shift keying (ASK) or on-off keying (OOK), where the data just switches the laser beam off and on.

To beat the various dispersion problems, modulation methods like differential phase-shift keying (DPSK) and differential quadrature phase-shift keying (DQPSK) are now being tested and adopted. Even the decades-old duobinary technique is being resurrected. These methods extend the reach of 40-Gbit/s transmissions. We can expect further experimentation with various modulation methods as the push toward 40 Gbits/s and 100 Gbits/s progresses.

Additionally, the conference offered lots of papers, talks and workshops on dispersion. Polarization-mode dispersion (PMD) and chromatic dispersion kill very high-speed optical performance. So, there's a great deal of research, development and experimentation with products and methods to minimize these problems.

New types of fiber and electronic equalization techniques at the receiver lead the pack. There were numerous papers on implementing maximum likelihood sequence estimation (MLSE) equalization techniques that appear to offer the most promising solution to extend range at high data rates.

Finally, there were plenty of other hot products and technologies. Reconfigurable optical add-drop multiplexers (ROADMs) using wavelength switching were prevalent, as were tunable lasers, radio over fiber, and generic multiprotocol label switching (GMPLS).

There also was lots of renewed interest in plastic optical fiber (POF). POF is larger and easier to work with. It uses either very simple connectors or no connector and is inexpensive. By using equalization techniques, POF can be used at higher data rates over distances of less than 300 meters.

Agilent Technologies introduced a unique optical receiver stress test solution. Called the N4917A, this test system accurately characterizes and verifies standard conformance of receiver optical subassemblies and transceiver modules operating up to 12.5 Gbits/s.

All in all, the Optical Fiber Communications Conference was a great show targeting the premier technology that carries the Internet load. It was good to see this industry return to growth. For more, look for my Technology Report on fiber optics in our July 19 issue.

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