Metamaterial aims to speed up GaN-based LEDs' modulation rate for underwater communications

Jan. 24, 2014

San Diego, CA--University of California, San Diego (UCSD) researcher Zhaowei Liu and colleagues have taken the first steps in developing high-modulation-rate blue and green LEDs for underwater optical communications.

John Wallace

UCSD graduate student Dylan Lu is working with electrical engineering professor Zhaowei Liu on a project to develop high-modulation-rate LED systems for underwater optical communication.

San Diego, CA--University of California, San Diego (UCSD) researcher Zhaowei Liu and colleagues have taken the first steps in developing high-modulation-rate blue and green LEDs for underwater optical communications. They have created a nanostructured metamaterial with silver (Ag) and silicon (Si) that boosts the spontaneous emission rate rate of a fluorescent light-emitting dye molecule (rhodamine) by a factor of 76, as well as increasing the emission intensity of the dye by a factor of 80.¹

Aiming at underwater-transmission wavelengths

“The major purpose of this program is to develop a better light source for communication purposes,” says Liu. “But this is just a first step in the whole story. We have proved that this artificial, manmade material can be designed to enhance light emission and intensity, but the next step will be to apply this on conventional LEDs.”

Extremely high modulation rates in gallium nitride (GaN)-based blue- and green-emitting LEDs is a missing link that is necessary for increasing the rate at which information can be sent via optical channels underwater, such as between ships and submarines, submarines and divers, underwater environmental sensors and unmanned underwater vehicles, or other combinations (water transmits best in blue and green).

Currently, the modulation rate for GaN-based LEDs is less than one gigahertz, a rate slower than the speed of most WiFi signals, says Liu.

The rhodamine molecule used in the UCSD experiment gives off a yellow-green hue. The next step for the researchers will be to pair the nanostructured metamaterial with GaN-based LEDs.

“The design of the materials may not be the hardest thing,” said UCSD graduate student Dylan Lu, who noted that the metamaterial will work with LEDs that have been manufactured to a specific industry standard. “I think the major challenge, to apply it to LEDs, will be an integration issue.”

Liu recently won a grant from the Office of Naval Research (ONR) to develop the high-modulation-rate blue and green LED systems; the grant totals a little more than $500,000 over three years.

Source: http://www.jacobsschool.ucsd.edu/news/news_releases/release.sfe?id=1471

REFERENCE:

1. Dylan Lu et al., Nature Nanotechnology (2014) doi:10.1038/nnano.2013.276

About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.