Campus Team Creates a First: An Integrated Light Circuit

A UCSB research team has for the first time incorporated on a single chip both a widely tunable laser and an all-optical wavelength converter. This creates an integrated photonic circuit for transcribing data from one color of light to another, a key to realizing an all-optical network.

Consider data transmission over the Internet as if it were a telephone call between Los Angeles and New York. What enables two people to talk is the dedicated line between them. On the Internet the long-distance transport of information is via optical fibers, or light pipes, that move nu­merous colors over a single fiber at the same time. Each color represents a dedicated line for the transmission of data.

Data moves between coasts through nodes of the Internet, where the capability is needed to switch information, for example, arriving on one fiber as orange photons to continue the next leg of its journey on another fiber as red photons because orange already is in use at the relay. Curently, switching from one color to another has to be done by converting photons to electrons, switching electronically, and converting electrons back to photons.

The tunable laser—a laser capable of rapidly dialing up different colors—supplies a new color for the wavelength converter to copy information conveyed from another signal riding on a different color. The new, postage-stamp-sized indium phosphide platform is a tunable "photon copier." This all-optical switch would eliminate electronics as the middleman and represents a key technological step towards an all-optical network.

Past attempts to engineer photonic circuits have located the two components on separate chips. Fabricating them on the same platform represents a technological breakthrough. Among integration's many benefits is maintaining the quality of the signal by not moving light on and off the chip many times.

Daniel Blumenthal, leader of the research group and a professor of electrical and computer engineering, figures his successful demonstration of an integrated photonic chip means more to come. "People are now accustomed," he said, "to think of a silicon substrate with a seemingly innumerable number of transistors on it. But that sophisticated electronic technology of today began back in the 1960s with a couple of transistors; photonics is just beginning to enter that stage."

UCSB graduate student Milan Masanovic presented the findings at a materials conference earlier this year. That presentation earned him the conference's Best Student Paper Award.

Masanovic is a student of Blumenthal and research team co-leader Larry Coldren, professor of electrical and computer engineering, who is the inventor of the tunable laser used in the experiment. The other three authors on the paper are Blumenthal's graduate student Vikrant Lal and Coldren's students Erik Skogen and Jonathon Barton.

The research is being conducted under the auspices of a four-year, $3.5 million DARPA grant for which Blumenthal is principal investigator.