Lee Center for Advanced Networking

Kerry Vahala studies the physics of new photonic devices that could one day be used in communications networks. Lee Center member, Jenkins Professor of Information Science and Technology, and Professor of Applied Physics at Caltech, Vahala says that in less than two decades, copper wire, which once crisscrossed the world, has largely been replaced by optical fiber.

Optical fiber, which carries guided light waves instead of an electronic signal, can carry much more information than copper wire. A single strand of optical fiber can carry a terabit of data every second. In high bandwidth optical cables, information travels in parallel wavelength channels (like colors, if the light were visible). In “wavelength-division multiplexing” (WDM), each channel has a data rate that is comparable to the rates for electronic switches and signal conditioners. But together, the wavelengths carry much more. Huge aggregate bandwidths result from running many different wavelength channels together down a single fiber.

But even while photonic transmission lines were replacing electronic ones, says Vahala, electronic circuits reached an unprecedented level of sophistication in terms of processing power and signal conditioning. Today, signal conditioning and switching functions are the domain of electronics, and information transport-over-distance is the domain of photonics.

In the future, says Vahala, lightwave technology will have to shoulder more of the functions. This is because each time a signal is switched or processed in some way, the wavelength channels must be de-multiplexed, converted to electrical form for processing, then converted back to light waves for the optical fiber, a costly and messy process. Keeping data in the form of lightwaves and processing it as lightwaves would be more efficient, says Vahala. This does not mean that photonics will replace electronics, he says, only that photonics will play a greater role in the future.

Vahala’s research group studies photonic components designed to solve future optical filtering, switching, and generation problems. Their “Raman laser,” which is 1,000 times more efficient than previous devices, efficiently stores light inside a small spherical glass bead (or resonator). A stretched optical fiber permits efficient coupling of light into the sphere. Vahala’s group has also made a similar resonator on a silicon chip and are looking for ways to use arrays of these devices as monolithic sources and wavelength selective switches.

Vahala is also cofounder of Xponent Photonics Inc., based in Monrovia, California. Xponent is devoted to developing solutions for the manufacture of a wide range of less expensive optical components.