Crucial Tech: VCSELs

Tiny lasers are going to make wires the buggy whips of the next millennium.

For the past 20 years, technology has been driven by steady improvements in lasers and silicon chips. Smaller and faster chips brought the power of a Cray supercomputer to videogame consoles; cheaper and more accurate lasers brought the CD player and high-speed, fiber-optic networks.

Now these two dynamos have been grafted together in what is probably the most important innovation of the decade: vertical cavity surface emitting lasers, or VCSELs (pronounced "VIX-els"). These tiny lasers, each less than half the width of a human hair, are fabricated the same way that computer chips are. They bring all the advantages of optics, such as increased bandwidth and reduced power consumption, down to the chip level.

Just as we've seen telephone companies rip out old copper lines and replace them with fiber-optic cables that can carry hundreds of thousands of times more traffic, now we're going to see the copper wires in our computers and electronic devices replaced by VCSEL-equipped fibers.

Instead of dozens of wires connecting a graphics card to the motherboard, for example, a couple of tiny VCSELs will beam the data to equally tiny optical detectors two or three inches away. VCSELs will be able to transmit far more data than metal wires and they'll require much less power.

This is just one of the technology's applications. VCSELs will turn up in everything from printers to network switches. The first rollouts have already begun.

VCSELs were first described by professor Kenichi Iga at the Tokyo Institute of Technology during the late 1970s. But it wasn't until 1989 that Jack Jewell at Bell Labs figured out how to make them practical. Jewell was a long-haired, West Coast type in the staid confines of New Jersey, and his employers saw his VCSEL project as too harebrained to waste equipment time on. So, when a friend at nearby Bellcore offered the use of his company's equipment one weekend, Jewell was finally able to fabricate the tiny lasers. Amazingly enough, they worked.

The lasers Jewell had crafted were incredible not just because they were small, but because they could be manufactured the same way as chips. That meant that many of the same techniques that have powered Moore's Law could now be applied to lasers. And they have been. Since 1991, researchers backed by Darpa and a handful of companies such as Honeywell and Motorola have refined VCSEL technology so that it is cheaper, faster, and more versatile. The results are jaw-dropping.

Even if you don't try that hard, says Anis Husain of Darpa, a VCSEL is capable of transmitting data at 6 Gbps, and far faster rates have been shown in the lab. Unlike conventional lasers, VCSELs can be packed closely together to form two-dimensional arrays. That means a 10-by-10 array of VCSELs could be used for an aggregate transfer rate of 600 Gbps.

VCSELs are about 10-by-10-by-2 microns. That's almost a hundred times smaller than a CD laser, notes Philippe Marchand, a researcher at the University of California at San Diego. And compared with a metal wire, which requires 20 to 40 milliwatts to transfer an equivalent amount of data, they require far less power to operate a few milliwatts. Within a year, says Marchand, VCSELs will require only 1 or 2 milliwatts per gigabit per second. Suddenly, copper wires in a computer will be as obsolete as copper lines in the Internet backbone.

We've already seen this transition with the copper wires that connect nearby computers. The newest generation of local-area networks Gigabit Ethernet relies on VCSELs and fiber-optic cables. Next, VCSELs will replace the ribbons that connect boards inside computers. The first rollouts, in the form of network interface cards, have already begun from companies like Vixel and Hewlett-Packard. Before VCSELs can really take off, manufacturing and assembly processes that allow for precision alignment between VCSELs and detectors on neighboring components will need to be developed. For now, fiber-optic cables are used as interconnects, but development engineers are working on ways to eliminate them.

All of this may sound like science fiction. But just a few years ago, so did the thought of a Cray computer fitting inside a shoebox. VCSELs are now on the same dizzyingly exponential curve.

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