Light chips find a place to take root

Light-based microcircuits could process more information and do it more quickly than electronic ones, theorists predict. They also would run much cooler and free of electromagnetic interference. However, there’s no material suitable for chips using photons that’s equivalent to semiconductors using electrons.

Crystals of silicon shells may help usher in all-optical telecommunications circuits. Blanco et al./Nature

By taking cues from a natural material—the opal—researchers in Canada and Spain have come up with a possible feedstock for light chips (SN: 8/7/99, p. 87). While cheap and easy to mass-produce, this new crystal refuses to pass or absorb light in the 1.5-micrometer wavelength range favored for fiber-optic communications.

That gap in permitted wavelengths enables designers to create optical components such as laser cavities, waveguides, and optical transistors in the material, says Sajeev John of the University of Toronto. Carving holes, lines, or other features into the crystal would selectively let light in and control its behavior.

In the May 25 Nature, the researchers report growing glass balls—870 nanometers in diameter—in solution and then carefully sedimenting them to stack with military precision. After sintering the balls together, the team filled the interstices with silicon. Acid then etched away the glass-ball template, which has a structure resembling an opal’s, leaving a crystal of silicon shells. Such material has been the “holy grail” of photonic crystal research, John says.

It is “a very important development,” agrees Eli Yablonovitch of the University of California, Los Angeles. For lasers and other active components, he suggests, photonic crystals of other substances, such as gallium arsenide, may prove better.

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