Hybrid-plastic light source may yield optical chip

June 19, 2003
Researchers at the University of Toronto developed a hybrid plastic that produces light at wavelengths useful for fiber-optic communication.

The development may lead to an optical computer chip.

The material is a plastic embedded with quantum dots that convert electrons into photons. "While others have worked in quantum dots before, we have shown how quantum dots can be tuned and incorporated into the right materials to address the whole set of communication wavelengths," says Ted Sargent, U of T Electrical and Computer Engineering professor. The team created nanocrystals of lead sulfide using a technique that let them work at room pressure and at temperatures less than 150°C. Usually, creating these crystals means working in a vacuum at temperatures approaching 600 to 800°C. Despite the precise way in which quantum-dot crystals are created, the crystal surfaces are unstable. For stability, researchers coated them with a special layer of molecules. The resulting crystals were then combined with a semiconducting polymer material to create a thin, smooth film of the hybrid polymer.

Sargent explains that when the electrons cross the conductive polymer, they encounter "canyons" with a quantum dot sitting at the bottom. Electrons must fall over the edge of the canyon and reach the bottom before producing light. Researchers tailored the stabilizing molecules to ensure a flow of electrons into the light-producing canyons.

The colors of light generated, ranging in wavelength from 1.3 to 1.6 µm, spanned the full range of colors used to communicate information using light. "We've shown that our hybrid plastic can convert electric current into light, with promising efficiency and with a defined path towards further improvement," says Sargent. "This light source combined with fast electronic transistors, light modulators, light guides, and detectors, puts the optical chip in view," adds Sargent.

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