Switch offers cheap local-long distance link

By Kimberly Patch, Technology Research News

University of Rochester researchers have found a way to switch laser light pulses using a different wavelength of light as a control, opening up the possibility of a cheaper switch for bridging local and long distance telecommunications networks.

The switch consists of a tiny indium phosphide semiconductor and a laser, which are relatively inexpensive off-the-shelf components.

"The device is what we call a flip-flop switch," said Govind Agrawal, a professor of optics at the University of Rochester. "The output of this device can be switched between the on and off state using ... optical signals at different wavelengths," he said.

The device works as a switch because the control wavelength is shorter than the wavelength used to carry information. Because it is shorter, the control wavelength is absorbed by the semiconductor, where it is converted to electrons. "That means I can change the gain of the device," said Agrawal. The gain represents an on signal. A different control wavelength turns the switch off.

For example, if the device is operating at a red wavelength, and the control signal that turns the device on is green and the control signal that turns it off is blue, "what is turning on and off is only the red light, said Agrawal.

Because it can be switched as quickly as 10 billion times a second it is fast enough to keep up with multigigabyte data streams as a wavelength converter.

The work "is an extension of the basic ideas of using laser diodes for some kind of network switching," said David A. B. Miller, professor of electrical engineering and applied physics at Stanford University.

"It looks like it could be a relatively simple and practical way of performing [the] kind of wavelength conversion switching... useful for interfacing local networks to long distance networks," Miller said. In addition, "it has the advantage of using only relatively standard, inexpensive components," he said.

While the device can convert between 1.3- and 1.5-micron wavelengths, it does not claim to solve the difficult and important problem of switching signals between wavelengths within the 1.5 micron band, Miller added. The wavelengths within this band are generated by Wavelength Division Multiplexing (WDM), a technique used to cram multiple telecommunications signals on a single fiber-optic cable.

The researchers have demonstrated the switching action in the lab in a device the size of a grain of sand. However, the equipment attached to the device is bulky. The next step is making a true prototype, said Agrawal.

The optical switch could be technically ready for practical use in three years, said Agrawal.

Agrawal's research colleagues were Drew Maywar and Yoshiaki Nakano. The research was funded by the National Science Foundation.

The researchers published their findings in a pair of technical papers: "1.31-to-1.55 micron Wavelength Conversion by Optically Pumping a Distributed Feedback Amplifier," in the July, 2000 issue of IEEE Photonics Technology Letters, and "Robust Optical Control of an Optical-Amplifier-Based Flip-Flop," in the January 31, 2000 issue of Optics Express.

Timeline:   3 years
Funding:   Government
TRN Categories:   Optical Computing; Optoelectronics and Photonics
Story Type:   News
Related Elements:   Technical paper, "1.31-to-1.55 micron Wavelength Conversion by Optically Pumping a Distributed Feedback Amplifier," IEEE Photonics Technology Letters, July 2000; Technical paper, "Robust Optical Control of an Optical-Amplifier-Based Flip-Flop," Optics Express, January 31, 2000


November 8, 2000

Page One

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Chip promises faster light-to-circuit link

Coffee effect could benefit circuit connections

Tiny silicon crystals loom large

Switch offers cheap local-long distance link


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