London - Electrical engineers have built the smallest room-temperature nanolaser to date, as well as a highly efficient “thresholdless” laser that funnels all its photons into lasing, without any waste.
The two new lasers, developed by a team of researchers from the University of California, San Diego, require very low power to operate, which is an important breakthrough since lasers usually require greater and greater “pump power” to begin lasing as they shrink to nano sizes.
The small size and extremely low power of these nanolasers could make them very useful components for future optical circuits packed on to tiny computer chips.
Mercedeh Khajavikhan and her UC San Diego Jacobs School of Engineering colleagues suggest that the thresholdless laser may also help researchers as they develop new metamaterials, artificially structured materials that are already being studied for applications from super-lenses that can be used to see individual viruses or DNA molecules to “cloaking” devices that bend light around an object to make it appear invisible.
Yeshaiahu (Shaya) Fainman, co-author of the study said that all lasers require a certain amount of “pump power” from an outside source to begin emitting a coherent beam of light or “lasing”. A laser’s threshold is the point where this coherent output is greater than any spontaneous emission produced.
The smaller a laser is, the greater the pump power needed to reach the point of lasing. To overcome this problem, the UC San Diego researchers developed a design for the new lasers that uses quantum electrodynamic effects in coaxial nanocavities to alleviate the threshold constraint.
Like a coaxial cable hooked up to a television, only at a much smaller scale, the laser cavity consists of a metal rod enclosed by a ring of metal-coated, quantum wells of semiconductor material.
Khajavikhan and the rest of the team built the thresholdless laser by modifying the geometry of this cavity.
The new design also allowed them to build the smallest room-temperature, continuous wave laser to date. The new room-temperature nanoscale coaxial laser is more than an order of magnitude smaller than their previous record smallest nanolaser published in Nature Photonics less than two years ago.
The whole device is almost half a micron in diameter, by comparison, the period at the end of this sentence is nearly 600 microns wide.
Fainman said that these highly efficient lasers would be useful in augmenting future computing chips with optical communications, where the lasers are used to establish communication links between distant points on the chip. Only a small amount of pump power would be required to reach lasing, reducing the number of photons needed to transmit information.
The nanolaser designs appear to be scalable, meaning that they could be shrunk to even smaller sizes, an extremely important feature that makes it possible to harvest laser light from even smaller nanoscale structures, the researchers note.
This feature eventually could make them useful for creating and analysing metamaterials with structures smaller than the wavelength of light currently emitted by the lasers.
The study has been recently published in Nature.
Today : Sunday - May 27, 2012, 10:35am (GMT+5.5)
