• PDF / 7,539,640 Bytes
• 8 Pages / 576 x 777.6 pts Page_size
• 73 Downloads / 185 Views

DOWNLOAD

REPORT

---

Researchers Develop Semiconductor Laser that Produces Low-Divergence Beam Scientists at the University of Rochester, in collaboration with scientists from IBM and the National Nanofabrication Facility (NNF) at Cornell University, have designed and built a semiconductor laser that produces a low-divergence circular beam of light. Previously, a semiconductor laser produced only oblong-shaped beams. The Rochester beam diverges less than one-half of one degree, compared to 30 degrees for the typical commercial semiconductor laser. The typical beam of light from the semiconductor lasers used for sending telecommunications signals is egg-shaped and broadens very quickly; when it is squeezed into a circular optical fiber, sometimes only 30 percent of the light successfully transmits into the fiber. The rest is shunted away or filtered out as engineers use layers of optics to focus the oval into a circle, with some light lost at each layer. 'The shape of the typical laser beam limits how much light you can get into the fiber," said Dennis Hall, professor at the University's Institute of Optics and principal investigator. The 150-micron-wide device designed at Rochester is a surface-emitting laser made of gallium arsenide. The novel part is a concentric circle grating made up of 600 grooves etched into the semiconductor surface. As the laser light fans out from the center of the grating toward the grooves, the waves are deflected by the grating's ridges and interfere with each other, producing a coherent laser beam which is emitted from its surface. A small portion of the light escapes out the sides of the grating, a feature which may be useful in developing arrays of such lasers, Hall noted. "People have wanted to obtain a circular beam from a semiconductor laser for a long time, but they didn't think it could be done," says Hall. Such a laser could be used in a variety of settings, in particular, for applications such as telecommunications and optical recording. The laser was designed at Rochester and several have been built using electron beam lithography facilities at IBM and at the NNF at Cornell. Other researchers, most notably at Northern Telecom in Canada, are also working on lasers utilizing concentric circle gratings, but have not yet demonstrated a circular beam. Hall and his colleagues have written about their work in Applied Physics Letters and the Journal of Vacuum Science and Tech-

nology and have presented it at several op-

tics conferences. Hall's colleagues include former graduate student Turan Erdogan (now with Bell Labs), engineer Oliver King, and associate professor Gary Wicks; Erik Anderson of the IBM T.J. Watson Research Center in Yorktown Heights; and M.J. Rooks of the National Nanofabrication Facility at Cornell.

W. Lincoln Hawkins Undergraduate Research Fellowship Established George Campbell Jr., president of the National Action Council for Minorities in Engineering (NACME), announced in February the establishment of the W. Lincoln Hawkins Undergraduate Research Fellowship. The award honors Hawk