Fast Forward: Electrons vs. Photons

Posted 04/19/2011 at 10:07am | by Tom Halfhill

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I’ve seen the light, and it’s dark. Intel’s new Thunderbolt technology, formerly code-named Light Peak, is making its debut as something more like Copper Peak. Instead of the futuristic fiber-optic cables we were promised, we’re getting plain old copper cables that would be passably familiar to Thomas Edison.

Score another victory for electrons. They may be tiny, but they’re wiry. (Ahem.) Not easily will they be shoved aside by photons (which, after all, are massless). Someday, fiber optics will replace most of our copper, but that day has not yet arrived.

Who snuffed out the light in Light Peak? One culprit is Intel’s intrepid Light Peak engineering team, which managed to wring more throughput from copper than expected. Thunderbolt combines PCI Express with DisplayPort on a single serial cable with two bidirectional channels, providing 10 gigabits per second per channel. That performance matches Intel’s initial goal for an optical cable.

Such speeds are not new for copper—10-gigabit Ethernet has been around for years—but sustaining that performance over long cables without data errors is difficult. Consequently, Thunderbolt’s copper cables are limited to about 3 meters. For longer runs, Intel will introduce extended optical cables later this year.

The other culprit working against photons is cost. Electrical connections are cheaper than optical connections, which matters a lot to the PC industry’s razor-thin profit margins. It’s not that copper wire is cheaper than glass fiber. It’s that photons can’t replace electrons entirely. Microprocessors and memory chips are electrical circuits, which need electrons. Although optical cables can carry data signals as photons, each cable termination requires a special interface chip that converts photons into electrons or vice versa.

It turns out that Intel is the only source for Thunderbolt interface chips, because Thunderbolt is Intel’s proprietary technology. It’s a “standard” only in the sense that anyone can implement Thunderbolt on a computer, display, or peripheral—if they buy the chips from Intel. Lack of competition tends to keep costs higher.

Thunderbolt is more thunder and less lightning than many people expected. Still, it’s an important step toward a photonic future.