Graphene Modulators Could Break Network Speed Limits

The layer of graphene (black fishnet) placed on top of a silicon optical fiber (blue), is charged by electrical signals to alter the light flow into pulses .[Photo: UC Berkeley]
Fiber optic networks are at the forefront of record-setting Internet speeds. Now the scientists at the University of California, Berkeley have developed a graphene modulator that could push the curve forward by a ten-fold leap.

The team electrically tuned the atom-thick layers of carbon to absorb light at wavelengths used in data communication. The graphene medium was then fashioned into modulators and placed into tiny optical network cables to switch the light transmitting the data on and off.

"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 UC Berkeley engineering professor Xiang Zhang, who led the research group. “This new technology will significantly enhance our capabilities in ultrafast optical communication and computing."

The data transfer speed is dependent on how quickly the modulator can pulse the light. Inside of the optical cables, a modulator switches from transparent and opaque as its electrons are charged. The researchers found that graphene modulator achieved a modulation speed of 1 gigahertz and could theoretically reach as high as 500 gigahertz (500 billion cycles a second).

Scanning electron microscope image magnifying of the sheet of graphene (blue) charged to block the the light passing though the silicon waveguide (red). [Photo: UC Berkeley]

Thanks to the tiny 25-square-micron size of these graphene modulators, optical cables could do away with the modulators measuring in millimeters used now. In effect, the optic cables could be shrunk which could potentially reduce their capacitance--the ability to hold an electric charge--and lead to faster data transmission.

Zhang’s colleague Feng Wang, assistant professor of physics and head of the Ultrafast Nano-Optics Group at UC Berkeley, added that the graphene could be tuned to other frequencies. “Graphene can also be used to modulate new frequency ranges, such as mid-infrared light, that are widely used in molecular sensing."

Discovered in 2004, graphene soon became a highly regarded substance in electronics because it is flexible, the thinnest and strongest crystalline material, pliable like rubber, compatible with silicon, and an excellent conductor of heat and electricity. In addition, researchers say that the graphene material is cheap and easy to produce.

Ming Liu, a post-doctoral researcher in Zhang's lab and co-lead author of the study, elaborated that “the graphite in a pencil can provide enough graphene to fabricate 1 billion optical modulators."

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