March 2001

A Better Optical Switch

Fiber Optics: Holography takes optical switching to nanosecond speeds.

By Eric S. Brown

The dream of a speedy all-optical Internet has so far been thwarted by a vexing bottleneck: optical switches must convert data to an electrical signal to switch data from one optical fiber to the next, then convert the data back to optical to speed it on its way. This conversion requires costly and bulky equipment, and when you scale up to the high-bandwidth data streams demanded by the latest optical networks, these switches are no longer cost-effective. A better solution is an all-optical device that can affordably switch gigabytes of data without skipping a beat.

Researchers have tried optical switching devices such as arrays of tiny mirrors, liquid crystals and ink-jet bubbles, but an Israeli startup called Trellis Photonics may have a better idea: holograms. The company claims its new "electroholographic" device is as scalable as mirrors while offering faster switching and better reliability. Developed by Aharon J. Agranat at the California Institute of Technology and the Hebrew University of Jerusalem, Trellis's technology creates ribbonlike holograms within crystals that are arranged in rows and columns like a trellis. When electrically charged, the holograms can selectively deflect specific colors onto new paths, while the rest of the light wavelengths pass through unaffected.

The device can switch data in as little as 10 nanoseconds (billionths of a second), which is comparable to the speed of optical-electrical switches, and future versions will switch even faster. Yet in today's market, an optical switch is judged by the number of wavelengths it can process, not the speed of its switching. "At this point, nanosecond switching doesn't really matter," says Jay Patel, an analyst at the Yankee Group. But Sterling Perrin, an analyst at IDC, suggests the switch's quickness may eventually bear fruit when intelligent optical routers are developed that can analyze and optimize the path of individual data packets. Says Perrin, "That's when you'll need a switch with nanosecond speeds."

Trellis Photonics recently received a secondary $25 million round of venture funding. Carriers will beta-test the Trellis device this spring, with general availability planned for the fall. If it lives up to its billing, the dream of an all-optical network could be closer than expected.