University of Rochester

New Optical Switch Removes Barrier to Light-Speed Communications

October 24, 2000

A device that has the potential to remove a major bottleneck between optical networks has been built by researchers from the University of Rochester. The device, developed in conjunction with the University of Tokyo, is so flexible that it can reformat the information that is shuttled around the information superhighway in ways and at speeds that no other device today can match. Engineers hope the device-smaller than a grain of sand-will allow fast optical data conversion that could spur the development of extensive local fiber-optic communications networks.

Researchers created the device, which has no moving parts, from off-the-shelf components, making it much less expensive to produce than competing devices that need complicated, custom-designed parts. The universities have recently applied for a joint patent on the device, called an optical flip-flop switch.

"What makes this switch special is its speed and flexibility," says Govind Agrawal, professor of optics and co-inventor of the device. "This kind of device is something the communications industries have been looking for for a long time."

The tiny switch acts like a shade on a window, opening and closing in a billionth of a second, allowing only an exact amount of light through-and only at the right wavelength.

The switch consists of a laser and a microscopic piece of semiconductor material called indium phosphide that acts like a sentry on the lookout for pulses of light in a wide range of wavelengths important to telecommunications or other applications. When a pulse of light (say at "wavelength A") comes down an optical fiber and strikes the semiconductor, the material becomes transparent to the device's laser-in essence, the shade opens. The laser, shining at "wavelength B," shines through for a split second before the shade closes again, re-creating the original pulse of light in the new wavelength. In less than a billionth of a second, the pulse has been converted from wavelength A to B, a crucial event in bridging different optical networks.

Converting a pulse's wavelength so quickly is especially important where two fiber optic networks intersect, such as at the junction of local and long-distance telephone networks. While a long-distance company may move voices in one wavelength, a local phone company may use a different wavelength, necessitating a fast conversion. Today, this is usually done by converting the light pulses to electronics so computers can convert the wavelengths, but this exchange between light and electronics slows the conversion and is expensive. Engineers have been working for years to develop light-to-light wavelength-converting switches that never need electronics. Several light-to-light routing switches exist today, but these do not convert wavelengths.

The new switch is also exceptionally good at removing another hurdle that slows the junction of optical networks. Different networks use different lengths of pulses; the new switch operates so quickly that it can customize the length of the pulses by simply varying the time before "shutting the shade." Leaving the shade open a little longer results in a longer pulse; shutting it sooner makes a shorter pulse, allowing any network to receive the exact pulse length it needs.

One of the surprising aspects of this device is that all of its parts have been commercially available for years. "Everything we needed to build this was there all along," says Drew Maywar, an optics doctoral candidate at the University of Rochester's Institute of Optics and co-inventor of the switch. "It's just that no one ever thought of doing it this way before."

One of the breakthroughs in the design of the switch came to Maywar while he was visiting the University of Tokyo as part of his graduate research. He was trying to explain the workings of conventional switches to another student when it dawned on him that if he could find a way to reverse the "opening of the shade," he could develop an ultra-fast switching device. Nine months later he had a working prototype.

"A lot of people told me I was foolish to pursue my idea," he says. "They thought there was no way the weak light in an optical fiber would be enough to reverse the process."

Maywar used his experience in basic optical science from the University of Rochester with the available technology at the University of Tokyo to build the prototype just before returning to Rochester.

Agrawal's group has published two papers on the device in the last year, the first outlining the optical switching capabilities and the other detailing wavelength conversion. Photonics Spectra magazine estimates that because of the demands of the Internet, the optical switching market in North America and Europe will reach $15 billion by 2004.




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