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Graphene promises 'extremeband' networking

A team of researchers operating out of the University of California at Berkeley have discovered a new use for wonder-material graphene: optical modulators that could lead to a dramatic boost in broadband speeds.

The research team, led by engineering professor Ziang Zhang, have succeeded in creating an optical modulator featuring graphene - a one-atom-thick layer of crystallised carbon which has long been touted as the next wonder material in computing and a possible replacement for traditional transitors in the next generation of chips.

Optical modulators, which feature the ability to switch a beam of light on or off, are the basis of modern optical communication systems - and are used in the switches that form the backbone of the Internet. While overall speed of communications is limited by several factors, one of the biggest is the speed at which the modulator can switch - and the team's graphene-based modulator promises to be very fast indeed.

"Graphene enables us to make modulators that are incredibly compact and that potentially perform at speeds up to ten times faster than current technology allows," explained Zhang of his team's creation. "This new technology will significantly enhance our capabilities in ultrafast optical communication and computing."

Published in the Nature journal this week, the team's research led them to create a modulator from electrically-tuned graphene capable of absorbing the wavelengths of light commonly used in digital communications systems. With an increase in performance of up to ten times over existing optical modulators coupled with a significant decrease in size and power demand, Zhang's modulator could be the breakthrough for which the increasingly-straining networks have been waiting.

Using one of the more curious properties of graphene - its ability to turn transparent at certain positive voltages - the team was able to develop an optical modulator which uses varying voltages to alter the graphene's Fermi level. At a certain Fermi level, the light is absorbed - and the signal 'switched off.' Increasing the voltage slightly increases the Fermi level and turns the graphene transparent - meaning the signal is 'switched on.'

In the lab, the team has been able to create optical modulators operating at a speed of one gigahertz - but claim that the technology could scale to around 500GHz in a single modulator.

It's not just the ability of the graphene-based optical modulator to quickly switch on and off that makes it a breakthrough, however - but the size shrink that comes as a result of a switch in materials. With the prototype device just 25 square microns in size - around 400 times smaller than a human hair - the team's creation is significantly smaller than anything else on the market.

"Scaling down the optical device also makes it faster," claimed Zhang, "because the single atomic layer of graphene can significantly reduce the capacitance - the ability to hold an electric charge - which often hinders device speed."

A final property of the graphene-based optical modulator offers the promise of a new category of network connectivity: 'extremeband.' The ability for graphene to absorb or transmit light across a far broader spectrum than current modulators - thousands of nanometres, rather than the tens of nanometres currently possible - means that more data can be encoded into each signal.

"Graphene-based modulators not only offer an increase in modulation speed, they can enable greater amounts of data packed into each pulse," Zhang claimed. "Instead of 'broadband,' we will have ‘extremeband.’ 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, including bioinformatics and weather forecasting."

Feng Wang, head of UC Berkeley's Ultrafast Nano-Optics Group, worked with Zhang on the project - and is confident of its success. "The impact of this technology will be far-reaching," he claimed. "In addition to high-speed operations, graphene-based modulators could lead to unconventional applications due to graphene’s flexibility and ease in integration with different kinds of materials."

Despite graphene's many impressive properties - it's the thinnest and strongest crystalline material yet discovered, and can be stretched like rubber while retaining its excellent conductivity of both electricity and heat - engineers have struggled to take graphene-based technologies out of the lab and into commercial products.

Sadly, Zhang's work is no exception: while prototype devices have been created, the professor admits that the technology is a few years away from production lines. "We hope to see industrial applications of this new device in the next few years," he concluded.