A team from Lawrence Berkeley National Laboratory led by Chinese-American professor Zhang Xiang has developed a broadband technology so fast it would enable the download of an entire 3D movie in only a few seconds.

The breakthrough, which could be available to consumers in three to five years, was made possible by the team's invention of a graphene-based optical modulator.

With one-atom-thick sheets of carbon densely packed in a honeycomb crystal lattice, the modulator is 100 times faster than conventional optical devices in use today.

'Extremeband'

"Instead of broadband, we will have 'extremeband'," said Zhang. "What we see here and going forward with graphene-based modulators are tremendous improvements, not only in consumer electronics, but in any field that is now limited by data transmission speeds."

Traditional Internet communication is widely based on copper cables carrying electrical signals, but today's demands for speed are greater than wires can carry. Optical cable provides a vastly faster solution using light instead of electronic sound to transmit binary signals.

The researchers from Berkeley built a tiny optical device that uses graphene as a switch to turn light on and off because the material responds strongly to light.

They put a single graphene layer on top of a silicon waveguide that converts electrical signals into modulated light.

10,000 times faster

If better quality graphene is used the rate could theoretically reach 500 gigahertz, which could lead to speeds 10,000 times faster than copper cable.

"This will be a huge impact on future data communication ranging from the Internet and cloud computing to video and entertainment," he told China Daily.

Their work was published in the journal Nature on June 2.

"The invention is a combination of physics and electronics engineering," said Liu Ming, a post-doctoral researcher in Zhang's lab and lead author of the study. "We did something that those who study graphene have never tried."

Optical modulators made from lithium niobate are already available for commercial use. Zhang said his prototype graphene modulator is "comparable to current products, but due to its unique design, it has a potential to be 100 times faster".

Temperature

Current designs also pose challenges due to their large size, cost and high sensitivity to temperature.

The lithium niobate device is too big to be put in a computer chipset, but a graphene optical modulator could be tiny enough - just 25 square microns, some 400 times smaller than the thickness of a human hair.

Zhang believed that they made "the world's smallest optical modulator".

Liu said it is so small it can be easily be placed anywhere in a computer.

As well, lithium niobate modulators cost $4,000 to $5,000, but the graphene device "could be made for less than a dollar", said Liu.

"The graphite in a pencil can provide enough graphene to fabricate 1 billion optical modulators," he added.

The conductivity of graphene also remains constant down to very low temperatures.

The team has applied for an invention patent and is in the process to considering the many possibilities for commercialization.

Liu said the final target is "to integrate the modulator in every CPU", but the first step is to promote installation of optical fiber in every household.

China Daily

(China Daily 06/08/2011 page17)