US researchers claim world`s smallest laser
Physicists at The University of Texas at Austin, US, claim to have developed the world’s smallest semiconductor laser, in collaboration with colleagues in Taiwan and China. Constructed from GaN, the researchers believe the laser marks a breakthrough for emerging photonic technology with applications from computing to medicine. Miniaturisation of semiconductor lasers is key for the development of faster, smaller, more precise, and lower energy photon-based technologies, such as ultrafast computer chips, highly sensitive biosensors for detecting, treating and studying disease and next-generation communication technologies. Such photonic devices could use nanolasers to generate optical signals but the size and performance of photonic devices have been restricted by what’s known as the three-dimensional optical diffraction limit. "We have developed a nano-laser device that operates well below the 3-D diffraction limit,” says Chih-Kang “Ken” Shih, professor of physics at The University of Texas at Austin. “We believe our research could have a large impact on nano-scale technologies.” Writing in the journal Science, Shih, graduate student Charlotte Sanders and colleagues report the first operation of a continuous-wave, low-threshold laser below the 3-D diffraction limit, which emits a green light. The device is constructed of a gallium nitride nano-rod that is partially filled with indium gallium nitride. The nano-rod is placed on top of a thin insulating layer of silicon that in turn covers a layer of silver film that is smooth at the atomic level. According to Shih, his lab has been developing these materials for more than 15 years, and has built a molecular beam epitaxy (MBE) system to create the smooth silver thin film critical to the function of laser. The atomic-level smoothness is key to building photonic devices that don't scatter and lose plasmons, waves of electrons that can be used to move large amounts of data. "Size mismatches between electronics and photonics have been a huge barrier to realise on-chip optical communications and computing systems,” said Shangjr Gwo, professor at National Tsing Hua University in Taiwan.
llustration of the nanoscale semiconductor structure used for demonstrating the ultralow-threshold nanolaser. A single nanorod is placed on a thin silver film (28 nm thick). The resonant electromagnetic field is concentrated at the 5-nm-thick silicon dioxide gap layer sandwiched by the semiconductor nanorod and the atomically smooth silver film.