Evanescent lasers to speed up data transmission
It is refreshing to note that some scientists also have a solid literary culture. Researchers at UC Santa Barbara (UCSB) have built the world's first mode-locked silicon evanescent laser. But what is an 'evanescent' laser? It is a step toward 'combining lasers and other key optical components with the existing electronic capabilities in silicon.' In other words, this research work will provide a way to integrate optical and electronic functions on a single chip. As these evanescent lasers can produce stable short pulses of laser light, they will be useful for many optical applications, such as high-speed data transmission or highly accurate optical clocks.
Above is a diagram of this mode-locked silicon evanescent laser (Credit: UCSB). This research work has been led by John Bowers, professor of electrical and computer engineering, and his Optoelectronics Research Group at UCSB.
Bowers and his team "have used [the above] platform to demonstrate electrically-pumped lasers emitting 40 billion pulses of light per second. This is the first ever achievement of such a rate in silicon and one that matches the rates produced by other mediums in standard use today. These short pulses are composed of many evenly spaced colors of laser light, which could be separated and each used to transmit different high-speed information, replacing the need for hundreds of lasers with just one."
The results of this research work have also been announced by the Optical Society of America in this news release, which doesn't add much to the UCSB one. Here is a short excerpt. "Creating optical components in silicon will lead to optoelectronic devices that can increase the amount and speed of data transmission in computer chips while using existing silicon technology. Employing existing silicon technology is a desirable goal because it would represent a potentially less expensive and easier-to-implement way of mass-producing future-generation devices that use both electrons and photons to process information, rather than just electrons as has been the case in the past."
This research work will be published by Optics Express in its September issue under the name "Mode-locked silicon evanescent lasers" (Volume 15, Issue 18, Pages 11225-11233, September 2007). But it is already available online. Here is the abstract. "We demonstrate electrically pumped lasers on silicon that produce pulses at repetition rates up to 40 GHz. The mode locked lasers generate 4 ps pulses with low jitter and extinction ratios above 18 dB, making them suitable for data and telecommunication transmitters and for clock generation and distribution. Results of both passive and hybrid mode locking are discussed. This type of device could enable new silicon based integrated technologies, such as optical time division multiplexing (OTDM), wavelength division multiplexing (WDM), and optical code division multiple access (OCDMA)."
Here is a link to the full article (PDF format, 9 pages, 966 KB), from which the above diagram has been extracted.
For more information, this research effort is based on a previous work done by UCSB and Intel last year. In 2006, the team led by John Bowers created laser light from electrical current on silicon by placing a layer of indium phosphide (InP) above the silicon.
This also was reported by Optics Express under the name "Electrically pumped hybrid AlGaInAs-silicon evanescent laser" (Volume 14, Issue 20, Pages 9203-9210, October 2006). Here is the beginning of the abstract. "An electrically pumped light source on silicon is a key element needed for photonic integrated circuits on silicon. Here we report an electrically pumped AlGaInAs-silicon evanescent laser architecture where the laser cavity is defined solely by the silicon waveguide and needs no critical alignment to the III-V active material during fabrication via wafer bonding." Finally, here is a link to the full article (PDF format, 8 pages).
Sources: University of California - Santa Barbara news release, August 21, 2007; Optical Society of America news release, via EurekAlert!, August 21, 2007; and various websites
You'll find related stories by following the links below.