In an optically denser medium such as a semiconductor, this limit is reduced by a factor of the index of refraction (expressed mathematically as ~3.0) of a semiconductor in this case to about 250 nanometers.
The limit is sometimes called the diffraction limit, a property associated with any wave, such as a beam of light. Current theory says you can't make a laser smaller than this diffraction limit or smaller than 250 nanometers for a semiconductor laser for communications devices.
The research teams at ASU and Eindhoven are showing there are ways around this supposed limit, Ning says.
One way is by the use of a combination of semiconductors and metals such as gold and silver.
"It turns out that the electrons excited in metals can help you confine a light in a laser to sizes smaller than that required by the diffraction limit," Ning explains. "Eventually, we were able to make a laser as thin as about one quarter of the wavelength or smaller, as opposed to one half."
Ning and Hill have achieved something like that by using a "metal-semiconductor-metal sandwich structure," in which the semiconductor is as thin as 80 nanometers and is sandwiched between 20-nanometer dielectric layers before putting metal layers on each side.
They have demonstrated that such a semiconductor/dielectric layer, thinner than the diffraction limit, and squeezed between metal layers, can actually emit laser light a laser with the smallest thickness of any ever produced. The structure, however, has worked only in a low-temperature operating environment. The next step is to achieve the same laser light emission at room temperature.
Researchers worldwide are interested in integrating such metallic structures with semiconductors to produce smaller nanolasers because of the promise of applications for smaller lasers in a wide range of technologies.
"This is the first time that anyone has sho
|Contact: Joe Kullman|
Arizona State University