Device Offers Promise For Faster Optical Communications

"This is the first time that anybody has realized this technology could be modified for a different function," said Andrew Weiner, a professor of electrical and computer engineering who specializes in "ultra-fast optics" and high-speed fiber optics.

The finding has potentially significant implications because researchers and industry are trying to increase the speed and capacity of optical fibers, which are replacing wires for transmitting Internet data over high-speed lines between cities.

Optical communication systems transmit signals over hair-thin glass fibers, each capable of carrying huge amounts of data over as many as 100 channels.

The numerous channels, however, are mixed together when they are transmitted and must be untangled, or "de-multiplexed," at the receiving end so the data can be recovered. The process could be likened to tuning a radio receiver to select one channel out of the numerous frequencies being transmitted.

A device used to separate the channels, or wavelengths, in optical fibers is called an arrayed waveguide grating, which is actually a complex optical circuit contained on a glass-silicon wafer about one or two inches in diameter.

Weiner and research engineer Daniel Leaird have demonstrated that the same device might help to dramatically increase the transmission speed and the amount of data that can be sent over a single channel. They will present their findings Tuesday (5/8), during the Conference on Lasers and Electro-Optics in Baltimore. The conference is sponsored by the Optical Society of America and the Lasers and Electro-optics Society of the Institute of Electrical and Electronics Engineers.

The device can turn a single pulse of laser light into a rapid-fire burst of 21 pulses, each separated by only two trillionths of a second. That's at least 10 times faster than the transmission speed of each channel in state-of-the-art commercial optical communication systems.

Weiner's research group earlier pioneered optical systems that "shape" and manipulate pulses of laser light, technology now being used in laboratories around the world, especially in physics and chemistry research to study and control ultra-fast processes inside molecules.

Recently, Leaird and Weiner developed a new type of "pulse shaper" for generating ultra-fast packets of data sent over optical fibers. In their new research, they have shown that commercially available arrayed waveguide gratings can be modified to perform a function similar to their laboratory pulse-shaping system. The commercial waveguide gratings are much smaller and more sturdy than the bulky laboratory equipment, making them ideal for practical applications.

"We realized that, rather than just being used to separate wavelengths, these arrayed waveguide gratings might have another application that nobody seemed to recognize," Weiner said. "If you send a pulse of light into one of these devices you can get a burst of pulses coming out."

In the research findings to be presented Tuesday, Weiner and Leaird worked with S. Shen, a former Purdue doctoral student who is now an engineer at Lucent Technologies in Holmdel, N.J.; and A. Sugita, S. Kamei, H. Yamada, M. Ishii, and K. Okamoto, from NTT Photonics Laboratories, in Japan.