New devices could hold key to practical integrated optics

EVANSTON, Ill. — Northwestern University researchers have developed new optical components that could help bring high-speed, wideband networks to the home, enabling bigger and more complex packages of information, such as movies, to be sent and received with personal computers. The optical components also could improve data transmission in local area networks and speed up optical connections in computers.

Bruce W. Wessels, professor of materials science and engineering and electrical and computer engineering, has received two U.S. patents for a device and material for integrated optical circuits: a thin film electro-optical modulator that provides a faster and better way to add information to the light stream (U.S. patent 6,118,571) and a specialized thin film material for optical amplifiers (U.S. patent 6,122,429). Wessels collaborated with Seng-Tiong Ho, associate professor of electrical and computer engineering, on the device work. Wessels’ and Ho’s graduate students also contributed to the patented work.

Wessels will report on recent developments of this novel technology at a special symposium, "Optoelectronic Materials and Technology in the Information Age," to be held by the American Ceramic Society April 22-25.

The explosive growth of the Internet has produced demand for greater network capacity. While integrated optical circuits hold promise for providing increased bandwidth to everyone from individuals to telecommunications companies, the optical components currently available are based on hybrid technology. Large, expensive and inefficient, these components limit the bandwidth available, causing a major bottleneck in the network.

To address this problem, large-scale integration of optical components is needed, similar to the approach taken by the microelectronics industry. However, integration of optical components has proven to be extremely difficult because the material must be optically transparent while also maintaining its optical activity.

Wessels and Ho believe they have a solution. They developed thin film electro-optical modulators, waveguides and optical amplifiers using ferroelectric material that has superior properties to the bulk crystals currently used in optical circuits. (A thin film is a material one micron or less in thickness.) Once integrated with lasers and photodetectors, the devices could enable widespread applications of integrated optical circuits.

"In order to take telecommunications and optical networks to the next level, we need inexpensive electro-optic modulators that operate at high speeds and with low voltage that can be integrated," said Wessels. "Our thin film modulator has these properties and is key to producing a truly integrated optical circuit. With the bulk crystals, integration is limited."

Wessels recently teamed up with SVT Associates, a small company serving the telecommunications and optoelectronic industries, to develop and commercialize this technology for thin film integrated optics. Wessels and his colleagues have already produced workable prototype devices on substrates other than silicon, but their ultimate goal is to develop 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.

The researchers have demonstrated thin film modulators that work at frequencies as high as 20 gigahertz. "These results are 10 times better than previously tested thin film ferroelectric devices and demonstrate the feasibility of the technology," said Wessels.

The thin film integrated optics research is supported by the Defense Advanced Research Projects Agency (DARPA) and Northwestern’s Materials Research Science & Engineering Center, which is supported by the National Science Foundation.