27 July 2012

World Smallest Semiconductor Laser - Breakthrough in Photonic Technology

Semiconductor lasers are eyed to be the next generation in laser technology. These lasters are compact, can be mass produced, easily integrated into applications, their properties are being improved constantly, they are becoming more and more powerful and efficient and they have found a widespread use as pumps for solid–state lasers.

The active medium of the laser is a semiconductor. This is similar to the ones found in an LED. The most common of this is formed from a p-n junction and powered by injected electric current. The former devices are sometimes referred to as injection laser diodes to distinguish them from optically pumped laser diodes.

The majority of the materials used by the semiconductor are based on a combination of elements in the third group of the Periodic Table (Aluminum (Al), Gallium (Ga), Indium (In)) and the fifth group (Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb)). This group of elements are referred to as the III-V compounds. Examples include GaAs, AlGaAs, InGaAs and InGaAsP alloys. The cw laser emission wavelengths are normally within 630~1600 nm, but recently InGaN semiconductor lasers were found to generate cw 410 nm blue light at room temperature. The semiconductor lasers that can generate blue-green light uses materials which are the combination of elements of the second group (Cadmium (Cd) and Zinc (Zn)) and the sixth group (Sulfur (S), Selenium (SE)).

This is an illustration of the nanoscale semiconductor structure used for demonstrating the ultra-low-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.
Credit: (c)Science

World's smallest semiconductor laser created by University of Texas scientists

Physicists at The University of Texas at Austin, in collaboration with colleagues in Taiwan, have developed the world's smallest semiconductor laser, a breakthrough for emerging photonic technology with applications from computing to medicine.

The scientists report their efforts in this week's Science.

Miniaturization of semiconductor lasers is key for the development of faster, smaller 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 and transmit information, and have the potential to replace electronic circuits. But the size and performance of photonic devices have been restricted by what's known as the three-dimensional optical diffraction limit.

Video: New Class of Semiconductor Lasers - Quantum Cascade Lasers

"We have developed a nanolaser device that operates well below the 3-D diffraction limit," said Chih-Kang "Ken" Shih, professor of physics at The University of Texas at Austin. "We believe our research could have a large impact on nanoscale technologies."

In the current paper, Shih and his colleagues report the first operation of a continuous-wave, low-threshold laser below the 3-D diffraction limit. When fired, the nanolaser emits a green light. The laser is too small to be visible to the naked eye.

The device is constructed of a gallium nitride nanorod that is partially filled with indium gallium nitride. Both alloys are semiconductors used commonly in LEDs. The nanorod is placed on top of a thin layer of silicon that in turn covers a layer of silver film that is smooth at the atomic level.

It's a material that the Shih lab has been perfecting for more than 15 years. That "atomic smoothness" is key to building photonic devices that don't scatter and lose plasmons, which are waves of electrons that can be used to move large amounts of data.

"Atomically smooth plasmonic structures are highly desirable building blocks for applications with low loss of data," said Shih.

Nanolasers such as this could provide for the development of chips where all processes are contained on the chip, so-called "on-chip" communication systems. This would prevent heat gains and information loss typically associated with electronic devices that pass data between multiple chips.

"Size mismatches between electronics and photonics have been a huge barrier to realize on-chip optical communications and computing systems," said Shanjr Gwo, professor at National Tsing Hua University and a former doctoral student of Shih's.


University of Texas at Austin
National Tsing Hua University
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