Ming Liu / UC Berkeley

Schematic illustration of the graphene-based optical modulator. A layer of graphene (black fishnet) is placed on top of a silicon waveguide (blue), which is used as an optical fiber to guide light. Electric signals sent in from the side of the graphene through gold (Au) and platinum (Pt) electrodes alter the amount of photons the graphene absorbs

Researchers have used graphene, a one-atom thick layer of crystallized carbon, to create a device that could potentially stream high-definition 3-D movies onto a smartphone in a matter of seconds.

The device, a tiny optical modulator, currently switches light on and off. This switching is the fundamental characteristic of a network modulator, which controls how fast data packets are transmitted. The faster the data pulses are sent out, the greater the volume of information that can be sent.

"This is the world's smallest optical modulator, and the modulator in data communications is the heart of speed control," Xiang Zhang, an engineering professor at the University of California at Berkeley who led the research, said in a press release.

"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. The new technology will significantly enhance our capabilities in ultrafast optical communication and computing." 

Prize-worthy material
The device is based on graphene, which was first extracted from graphite — the same material as pencil lead — in 2004 with Scotch tape. This achievement earned Konstantin Novoselov and Andre Geim at the University of Manchester a Nobel Prize in Physics last year.

Graphene is already being eyed for a range of technologies such as lighter and cheaper body armor, touchscreen displays and chemical sensors. It is the thinnest, strongest crystalline material yet known, can be stretched like rubber and is an excellent conductor of heat and electricity.

Zhang and his colleagues took advantage of the conducting ability, tuning graphene electrically to absorb light in wavelengths used in data communications.

They found that the energy of the electrons, referred to as Fermi level, can be easily altered depending upon the voltage applied to the material. The graphene's Fermi level in turn determines if the light is absorbed or not.

When a sufficient negative voltage is applied, electrons are drawn out of the graphene and are no longer available to absorb photons. The light is switched on because the graphene becomes totally transparent as the photons pass through, UC Berkeley explains.

Graphene is also transparent at certain positive voltages because, in that situation, the electrons become packed so tightly that they cannot absorb the photons. Zhang's team found a sweet spot in the middle where there is just enough voltage applied so the electrons can prevent the photons from passing, effectively switching the light off.

The breakthrough is described online May 8 in Nature.  Xiaobo Yin, co-lead author of the paper and a research scientist in Zhang's lab, described it this way in the press release:

"If graphene were a hallway, and electrons were people, you could say that, when the hall is empty there's no one around to stop the photons. In the other extreme, when the hall is too crowded, people can't move and are ineffective in blocking the photons. It's in between these two scenarios that the electrons are allowed to interact with and absorb the photons and the graphene becomes opaque."

Optical modulator
To create the optical modulator, the team layered graphene on top of a silicon wafer. They were able to achieve a modulation speed of 1 gigahertz, but noted the speed could theoretically reach as high as 500 gigahertz for a single modulator.

Using graphene in this way allows the researchers to scale down technologies that rely on photonics, such as fiber optic lines. The team has already shrunk a graphene-based modulator down to 25 square microns, which is roughly 400 times smaller than a human hair.

Even at this size, graphene can absorb a broad spectrum of light, ranging over thousands of nanometers from ultraviolet to infrared wavelengths. This allows graphene to carry more data than current state-of-the-art modulators, which operate at bandwidths of up to 10 nanometers.

"Instead of broadband, we will have extremeband," Zhang said.

So, yes, that really does mean a high-definition 3-D movie streamed to your smartphone in a matter of seconds.

—Via University of California at Berkeley

More articles on graphene:

• Graphene: Thin stuff is a big fat deal
• For wonder material graphene, Nobel Prize is just the start
• Physicists win Nobel for carbon breakthrough
• Scientists make nanosheets with high-tech potential