Graphene optical modulators hold promise for ultra fast communications

The team of researchers, led by UC Berkeley engineering professor Xiang Zhang, built a tiny optical device that uses graphene to switch light on and off. Measuring just 25 square microns, roughly 400 times smaller than a human hair, they believe it could soon allow consumers to stream full length, hd, 3d movies onto a smartphone in a matter of seconds. "This is the world's smallest optical modulator, and the modulator in data communications is the heart of speed control," said Zhang. "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. This new technology will significantly enhance our capabilities in ultra fast optical communication and computing." According to Zhang, the researchers were able to tune the graphene electrically to absorb light in wavelengths used in data communication. They found that that the energy of the electrons, referred to as its Fermi level, could be easily altered depending upon the voltage applied to the material. The graphene's Fermi level in turn determined if the light was absorbed or not. When a sufficient negative voltage was applied, the electrons were drawn out of the graphene and were no longer available to absorb photons. "The light was 'switched on' because the graphene became completely transparent as the photons passed through," explained Zhang. "The graphene was also transparent at certain positive voltages because, in that situation, the electrons became packed so tightly that they could not absorb the photons." The researchers found what they described as a 'sweet spot' in the middle where the electrons could prevent the photons from passing, effectively switching the light 'off'. "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," said Xiaobo Yin, a research scientist at Zhang's lab. "In the other extreme, when the hall is too crowded, people can't move and are ineffective in blocking the photons. It's inbetween these two scenarios that the electrons are allowed to interact with and absorb the photons, and the graphene becomes opaque." Yin said the team was able to achieve a modulation speed of 1 gigahertz, but noted that the speed could theoretically reach as high as 500 gigahertz for a single modulator. "We believe graphene based modulators could overcome the space barrier of optical devices," he said. "They not only offer an increase in modulation speed, they can enable greater amounts of data packed into each pulse. 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. We hope to see industrial applications of this new device in the next few years."