Sound signals surf on waves of light.

As a means of carrying signals from one place to another, nothing beats light.

Fast and frictionless, photons trounce electrons as the ideal carriers of information.

As computers get ever speedier, scientists are finding that microprocessors are pushing the physical limits of electric conduction. So researchers have been looking for ways to use pulses of light to ferry digital information within a computer.

Now, Jurgen Michel and Lionel C. Kimerling, materials scientists at the Massachusetts Institute of Technology, have used light to transmit messages-specifically, the sound of a voice. They've fabricated an integrated circuit, a single chip made entirely of silicon, that combines conventional semiconducting logic with optical data transfer.

Their circuit consists of three components-an erbium-silicon light-emitting diode, a device to guide the light waves, and a detector to pick up the processed signal at the other end. Although others have used light to carry signals, he adds, this is the first success with a single silicon chip, which would fit inside a computer.

Although the long-term goal isn't to transmit chatter, says Michel, the circuit proves that one can use light to move information 'from one place to another on a chip or between chips.' The technique could obviate the need for metallic interconnections, which limit signal-processing speed on chips.

Computers would still use conventional semiconductors and microelectronics to perform calculations.

'With the metal interconnects in use today, it's hard to push microprocessors faster than 1 gigahertz,' Michel says. This speed represents 1 billion operations per second. Using silicon-based optical electronics, it's possible to double or even quadruple that rate, he believes.