Still waiting to download full-length movies over the Internet or chat on a video phone? To meet such data-transmitting needs, companies have recently been pursuing a strategy called free-space optics, in which an infrared laser beams data to a receiver on your rooftop. A new laser reported online this week by Science may be able to make that connection.
Free-space optics might avoid the hassle of running fiber-optic cables directly to homes and offices, but the only cheap semiconductor lasers available aren't up to the job. They work at a relatively short wavelength of about 1.5 micrometers, and the beams typically travel only a few hundred meters before being absorbed by water vapor in the air.
To solve this problem, a research team led by Jérôme Faist and Mattias Beck of the University of Neuchâtel, Switzerland, made a new semiconductor infrared laser with a wavelength of about 9 micrometers. Because water vapor absorbs only a tiny amount of light at that wavelength, free-space optical systems built with the new laser should work at distances of 2 kilometers.
The team designed a novel structure for a "quantum cascade laser." In this type of laser, the wavelength of the light is determined by the thickness of the active materials used. Each device consists of numerous semiconductor layers. When an electric current flows through them, electrons cascade down an electronic waterfall, an energetic staircase with numerous steps; when an electron hits a step, it emits a laser photon. The team made their laser shorter and narrower than others. "That allows electrons to tunnel more efficiently through the whole structure" and generate less heat, Beck says. The new lasers not only work at room temperature but can produce a continuous beam of light without burning out.
"We're very excited about it," says Jim Plante, president of Maxima Corp., a San Diego, California, company that is working to develop free-space optics technology. "With this technology we can conquer the weather." And he says the lasers could also open a wealth of new research opportunities in atmospheric chemistry and medical diagnostics.