Wireless communication forces us to bridge the "goldilocks gap": the expensive territory that lies between two inexpensive but unattractive extremes.
With this months reported successful tests, in Italy, of the first microscopic, solid-state, terahertz laser, we can hope that we may soon be offered a wireless menu that includes the choice "just right."
At one extreme, radio has long used wavelengths of tens or hundreds of meters, including the bands below 30MHz (longer than about 10 meters), ironically called short waves and once thought to be above the frequency range of value for practical communications.
After all, at wavelengths of 200 meters or more, stations could count on ground-wave propagation to follow the curve of the earth; short-wave experimenters, in contrast, exposed themselves to the vagaries of "skip" propagation that relied on the ionosphere to bounce transmitted waves back to the surface.
Unfortunately, these debates took place when a symphony orchestra concert represented high-bandwidth content. Even FM-quality audio demands only the equivalent of about 100,000 bits per second, which we can easily squeeze even into a channel width of only tens of kilohertz. The problem is that there are only several dozen such channels in the wavelength range from 200 meters to infinity—even one Ethernet channel is out of the question.
Microwaves, with much more bandwidth to spare at their centimeter wavelengths, might seem to be at the other extreme, but theyre still on the near side of the gap—and all the wavelengths from short wave up through microwave are hotly contested territories, even if microwaves do perform better for cooking than for bad-weather communication. Think about energy absorption by water molecules.
The far side of the Goldilocks gap lies in the infrared and visible-light wavelengths, a few hundred nanometers or shorter. Infrared and light waves are really cheap to produce, but theyre readily blocked by even a sheet of paper.
Wouldnt it be nice to have something thats just right?
Thats why people are so excited about terahertz waves (T-waves for short), which readily penetrate even concrete. Expect to hear more about this next generation of wireless technologies.
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