July 13, 1999 HAIFA, Israel, and NEW YORK, N.Y. July 6, 1999 -- Two reseachers at the Technion-Israel Institute of Technology in Haifa, Israel, have discovered that small lasers can produce complex patterns of tiny optical vortices, whirlpools of light less than ten thousandth of an inch across. The finding, which will be published in the July 9 Science, could be used as the basis of new methods of high speed data transmission and processing.
The Technion team, Drs. Meir Orenstein and Jacob Scheuer, used lasers called VCSELs (vertical cavity surface-emitting lasers), which produce laser light over a surface some 20 microns on a side (about a thousand of an inch). These lasers are used routinely for such applications as optical communication over glass fibers and are normally designed to produce a single smooth beam of light. The Technion team, however, modified the lasers by doubling their size and increasing the current fed into them by three to six-fold, which causes the laser beam to break up and organize itself into the complex patterns observed.
Like any laser, the VCSEL operates by bouncing light back and forth between mirrors in a material that amplifies the light. But in the conditions used in the experiment, the amount of light produced changed how much the light is amplified, in turn changing the amount of light at any point. In this way the material itself builds up patterns of light and dark.
"What we observed were regular arrays of optical vortices" Dr. Orenstein explains.
An optical vortex is like a tornado in air or the whirlpool formed around a bathroom drain, except that it is made of light. Light is an electro-magnetic wave and in an optical vortex, the direction of the wave motion rotates around a central axis, like water around a drain; the closer to the axis, that faster the rotation. In an optical vortex, unlike a fluid vortex, this velocity rises without limit as the center is approached. The Technion experiments showed that the vortices spontaneously formed patterns of figure-eights and arrays of three, five and seven vortices as the researchers increased the current to the tiny laser.
Previous experiments by other researchers had produced such optical vortices, but they had always required much larger and more complicated devices for their production, and had not produced such complicated patterns.
"These are by far the most complex and tiniest vortices that have been produced spontaneously -- with any input pattern on our part," Orenstein explains.
The vortices are extremely interesting theoretically because vortex structure appears so widely in nature -- in gases, fluids, the magnetized gas called plasmas and even in living things, as in the helix of DNA. While Orenstein and Scheuer believe they understand how the vortices arise in the laser, it is still not clear why this particular pattern occurs rather than others.
The miniature vortices may have practical uses as well. When the optical vortices leave the laser and are transmitted through space or an optical fiber, they always retain their vortex structure and the direction in which they are spinning. Such vortices can therefore be used to transmit information at high speed over long distances, thus improving optical fiber communications. Other more exotic applications include using the vortices to trap individual atoms at their center and immobilize them, cooling them to very low temperatures. The Technion work has shown that producing and controlling such light whirlpools may be far easier than anyone else had thought.
The Technion-Israel Institute of Technology is the country's premier scientific and technological center for applied research and education. It commands a worldwide reputation for its pioneering work in communications, electronics, computer science, biotechnology, water-resource management, materials engineering, aerospace and medicine, among others. The majority of Israel's engineers are Technion graduates, as are most of the founders and managers of its high-tech industries. The Technion's 13,000 students and 700 faculty study and work in its 19 faculties and 30 research centers and institutes in Haifa.
The American Technion Society (ATS) supports the Technion. Based in New York City, it is the leading American organization supporting higher education in Israel. The ATS has raised $720 million since its inception in 1940, half of that during the last seven years. Technion societies are located in 24 countries around the world.
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