Researchers generate high-speed pulses of laser light on silicon, speeding data transmission

August 21, 2007

WASHINGTON, Aug. 21 - In the Sept. 3 issue of Optical Society of America's Optics Express, published online today, researchers announce that they have built the world's first "mode-locked silicon evanescent laser." Mode-locked evanescent lasers can deliver stable short pulses of laser light that are useful for many optical applications, including high-speed data transmission, multiple wavelength generation, remote sensing (LIDAR) and highly accurate optical clocks. This new work is a significant step toward the goal of combining lasers and other key optical components on silicon, providing a way to integrate optical and electronic functions on a single chip and enabling new types of integrated circuits. It introduces a more practical technology with lower cost, lower power consumption and more compact devices.

Summary
Present-day computer technology depends on weak electrical currents for data communication within the silicon-based microprocessor. By causing silicon to emit light and exhibit other potentially useful optical properties, integration of photonic devices on silicon becomes possible. The problem in the past - it is extremely difficult, nearly impossible, to create a laser in silicon.

Less than one year ago, a research team led by John Bowers at the University of California, Santa Barbara and Intel successfully created laser light from electrical current on silicon by placing a layer of indium phosphide (InP), an important technology in high-speed communication, above the silicon. In this new study, electrically-pumped lasers emitting 40 billion pulses of light per second were demonstrated, built on the hybrid silicon platform developed the year prior. This is the first-ever achievement of such a rate in silicon and one that matches the rates produced by other media 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.

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 advance was made possible by funds from the Microsystems Technology Office of the Defense Advanced Research Projects Agency (DARPA) at the United States Department of Defense.

Paper
"Mode-Locked Silicon Evanescent Lasers," Optics Express, Vol. 15, Issue 18.

Abstract
We demonstrate electrically pumped lasers on silicon that produce pulses at repetition rates up to 40 GHz, even without RF drive. 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).
-end-
For a copy of the paper, please contact OSA's
Colleen Morrison, 202.416.1437, cmorri@osa.org.

The Optical Society

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