Switching with a light touch.

Nowadays, a great deal of information travels as pulses of infrared light  along optical fibers. Routing and processing this information requires linking optical signals with electronic circuits. Similar capabilities are needed for sending and receiving optical signals via fiber or air between chips or electronic devices, if optical links replace the copper wires conventionally used for making such connections.

As one step toward developing high-capacity optical switches for information processing, David A. B. Miller and his coworkers at AT&T Bell Laboratories in Holmdel, N.J., have demonstrated a practical method for integrating high-performance gallium arsenide-based optoelectronics with high-density silicon-based circuitry on a single chip.

"You start with silicon integrated circuits, and you can put a large number of these so-called quantum well diodes on top of them," Miller says. Moreover, this fabrication method can readily keep pace with improvements in silicon technology.

Each optical diode, about 15 by 45 micrometers in size, can absorb light to generate electric signals on the chip. At the same time, changing the voltage applied to a diode controls how much light it transmits, allowing the diode to emit a modulated light beam. "I can write information into these structures, and I can read it out, using hundreds or thousands of light beams at a time," Miller says.