Tuesday, May 11, 2010

Fiber Optic Communications Without The Fiber

It’s generally acknowledged that we are eventually going to run out of bandwidth capability using twisted pair copper. We’re in serious danger of running out of wireless bandwidth now. The FCC is already scouring the spectrum, looking for underutilized frequencies that can be assigned to wireless broadband. Will technology soon grind to a halt because we’ve used up all the spectral natural resources? Not if we see the light!

Reading by the light of the LED router?Radio frequencies are truly in limited supply. The lower frequencies don’t have as much value because the lower the frequency, the lower the information carrying capacity. The higher portions of the electromagnetic spectrum are also limited because they can be expensive to deploy and have shorter range propagation characteristics. WiFi is pretty much tapped out for broadband. That trusty WiFi router isn’t up to transporting HDTV. But your reading light might be.

In a development that is somewhere between odd and ingenious, German researchers are looking at piggybacking digital signal transmission on normal household lighting. If it works it could easily be expanded to office and factory environments as well.

So, do you just plug your modem into your desk lamp, or what? As you might expect, the types of lighting we’re using now aren’t worth much for data transmission. The intensity of incandescent light varies so slowly that we don’t get flicker even from 60 Hz light dimmers that chop up the power line voltage. Fluorescent isn’t much more responsive, but LED lighting sure is.

LEDs have been used as cheap substitutes for lasers in short range fiber optic links. They are the ubiquitous transmitter for television and other remote controls. Those use infrared LEDs, so you can’t see the transmission. The amount of data transmitted to change channels or volume is also nearly trivial. But that’s no ding against LEDs. As solid state devices, they are capable of very high modulation rates. What we need now is a combination of high power LEDs with the optimum color for room lighting at low enough prices that people will use them to replace the hot incandescent bulbs or compact fluorescent lights they have now.

This may be a technology of the future, but I’ll bet it’s the near future. Everybody is using CFLs now. You can find them for as little as a dollar each in the big box stores. I remember a few years ago when they went for $10 or $20 and were only being bought by early adopters. LEDs are on a similar learning curve. Those on sale in retail stores are as pricy as the early compact fluorescents. They also seem to be much lower in light output than equivalent size bulbs. But that’s going to change, and fast, as manufacturing scales up and new designs come on the market.

Don’t be surprised if your next wireless router is really a desk or ceiling lamp. The hall lights might act as repeaters to send the signal around corners. Current research has the bandwidth up to 230 Mbps with expectations to double that with upgraded terminal equipment. That’s fast enough for today’s high bandwidth applications. Further research will likely increase bandwidths into Gbps territory, perhaps enabling 1000 Mbps wireless links to computers using LEDs and photodiodes. GigE to the desktop with no wires? It could happen... sooner than you think.

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