Colored glass lights future optics route.

Thousands of years ago, craftsmen made glasses in vibrant gold, red, and blue hues by mixing metal dusts into fire-melted sand. The ancients followed "magic" recipes to produce these decorative materials.

Now, with better formulas and more modern tools at hand, scientists are rediscovering colored glasses -- as promising materials for use in optical computers and light-based electronics. Using a technique called ion implantation to embed metal ions in glassy and crystalline substrates, a group of scientists led by Richard E Haglund Jr. of Vanderbilt University in Nashville can precisely engineer colored glasses to control the transmission of light.

"These composite materials could function as the nonlinear element in an all-optical circuit," Hagfund told SCIENCE NEWS.

To build ultra-fast electronics that use photons instead of electrons, two types of light-conducting materials must be developed: those that focus and speed traveling light beams and others that act as switches, allowing only certain kinds of light to pass (SN: 6/22/91, p.389).

Colored glasses could potentially perform the latter, "logical" function, says Haglund. They gain their "intelligence" by combining the optical properties of transparent glass and opaque metals. "Some light goes all the way through the glass," he explains, "but light absorbed by metal clusters is captured temporarily and then reradiated."

With ion implantation- commonly used in the semiconductor industry to etch silicon chips -the group can manipulate the size, density, and geometry of the nanometer-size metal clusters that form in the glass. This control could not have been achieved using the old chemical methods for making glasses because of the limitations of chemical thermodynamics, he says.

Using an ion implantation device, the researchers shoot an accelerated stream of metal ions back and forth across a surface. So far, the team has tried embedding gold, copper, silver, lead, erbium, bismuth, and platinum into silica and silicate glasses, lithium niobate, and sapphire crystals. Hagfund and his co-workers at Oak Ridge (Tenn.) National Laboratory and the City College of New York report their findings on the optical properties of silica implanted with gold in the April 12 APPLIED PHYSICS LETTERS.

"It's possible these metal-nanocluster composite materials could be effectively integrated into a future fiber-optic system," comments Peter W..E. Smith, executive director of the Ontario Laser and Lightwave Research Center at the University of Toronto. If these glasses show few of the detrimental thermal effects that plague some optical materials, they could be used in fast optical switching devices that route signals in a communications network, Smith says.

The next challenge for Haglund's group will be to design a composite that can split a light beam for use in a wave-guide device.