New optical components could speed nets

A research breakthrough at Northwestern University may lead to new fiber-optic network components, boosting the speed of existing networks by a factor of four to 16 without increasing costs or requiring more lines to be laid.

The US patent office granted Bruce W. Wessels, professor of materials science and engineering and electrical and computer engineering, two patents for a device and material for integrated optical circuits. The first is a thin-film electro-optical modulator that provides a faster and better way to add information to the light stream, while the second is for a specialized thin-film material for optical amplifiers.

Right now, there are two known ways to increase the amount of information flowing down a single fiber-optic line, Wessels said. The number of wavelengths of laser light can be increased, the technique used in dense wave division multiplexing, or DWDM. Or, the frequency with which the light is turned on and off can be increased.

Wessels, in collaboration with Seng-Tiong Ho, associate professor of electrical and computer engineering, and Ho's graduate students, developed a device to read faster frequency modulation. Current optical networks are limited to 2.5GHz transmission speeds, Wessels said. "At higher speeds, you need something called an electro-optical modulator."

The researchers, supported by the Defense Advanced Research Projects Agency (DARPA) and Northwestern's Materials Research Science and Engineering Center, developed thin film electro-optical modulators, waveguides and optical amplifiers using ferroelectric material.

Because the new device uses less material than the lithium-niobate crystals currently employed to modulate and amplify light, Wessels anticipates the cost for the components will remain the same or possibly be reduced. And because the thin-film can be used to coat materials with better optical properties, transmission speeds can be improved to 10 GHz in the near term, and 40 GHz after, he said. The researchers have demonstrated thin film modulators working at 20 GHz. The optical components also could improve data transmission in local area networks and speed up optical connections in computers.

They have already produced workable prototype devices on substrates other than silicon, but Wessels said they want integrated optical circuits on silicon, a combination that promises low cost and high volume. They hope to have an integrated modulator device on silicon working in the near future.

Wessels compared the device to the creation of the integrated circuit. "Optical networks use hybrid devices," he said, describing lasers, amplifiers and photodetector -- separate devices employed together to read data coming out of one end of a fiber. The one-micron thick film used in Wessels' device could lead to an integrated optical circuit, which can be miniaturized like microchip circuits and applied in similar ways.

Northwestern University, in Evanston, Illinois, can be reached at +1-847-491-3741 or at

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