MEMS the Word
MEMS devices may be almost too small to see, but they pack a wallop. MEMS, which is short for micro-electro-mechanical systems, are tiny machines -- complete with minuscule mirrors, gears, and wheels -- that are built on chips. In the future the technology may be used to construct microrobots that can move around inside your body to perform such tasks as cleaning up clogged arteries or taking a close-up view of your heart.
Today MEMS are being used to make optical data switches that allow information to be transmitted at the speed of light. One of those new switches, the LambdaRouter, which was developed by Lucent Technologies, contains hundreds of tiny, movable MEMS micromirrors, each only a fraction of an inch in diameter. The mirrors beam high-speed data streams from one optical fiber to the next by quickly tilting in just the right direction.
Brilliant, you might say -- in more ways than one. But wait. Haven't we seen similar devices before?
Interestingly, the first instruments that transmitted data across beams of light were built and used more than a century ago, though of course they weren't quite as sophisticated as the current batch are. Most popular in the early 19th century was the heliograph, which was invented in 1810 by the German mathematician Carl Friedrich Gauss. The heliograph sported two mirrors that could be tilted by an operator to point in just the right direction. The first mirror reflected the light of the sun (or the moon) onto the second mirror, which was set up to beam the light to a remote observer. The operator interrupted the beam with a shutter to send a simple binary signal (zeros and ones) over a long distance, much as a modern data stream travels over an optical fiber.
Charles Babbage, an Englishman who designed an early precursor of the computer, entered the optical-communications arena in 1851 with a plan for a light-flashing machine that he named the "occulting telegraph." This is how Babbage described his device: "I then, by means of a small piece of clock-work and a lamp, made a numerical system of occultation, by which any number might be transmitted to all those within sight of the source of light."
Upon receiving a description of Babbage's contraption, the U.S. Congress appropriated $5,000 -- a considerable sum at the time -- for occulting-telegraph experiments. It's not clear what the outcome of the experiments was, but a couple of decades later the American army started using machines to transmit data across beams of light, most notably heliographs. In 1886, for instance, Nelson Miles, the general perhaps best known for his capture of Geronimo, the leader of the Chiricahua Apaches, used a network of heliographs to transmit messages to his troops while fighting various Native American tribes. His network comprised 27 signaling stations in Arizona, placed 25 to 30 miles apart.
Records from that time indicate that between May 1, 1886, and September 30, 1886, a total of 2,276 messages containing 80,012 words were transmitted over the network. The average speed of the system was reportedly 16 words per minute, or roughly 10 bits per second. Clearly, the technology rewarded those who could express themselves succinctly. The Native Americans, of course, had their own optical-transmission system, which dated back further still. Most likely, the data rates achieved with smoke signaling could have rivaled those of Miles's network.
If you have a 56K modem on your PC, your messages travel more than a thousand times faster than those that were sent on the early optical systems, on both sunny and rainy days. The new micromirrored LambdaRouter MEMS data switch, operating at one terabit (1012 bits) per second, vastly outdoes even that: it could easily have transmitted Miles's 80,012 words in one second -- a million times over, that is.
Gerard J. Holzmann is a researcher at Lucent Technologies' Bell Laboratories in Murray Hill, N.J.
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