Researchers from the Universities of Bath and Exeter have shown that a few layers of graphene stacked on top of each other could act as a formidable material for optical switches, delivering speeds up to 100 times faster than current telecommunications technology.

Optical switches are a crucial part of our telecommunications infrastructure and although their performance is already quite impressive, researchers have long suspected that a class of materials named semimetals (which includes graphene) could be used to make them even better.

Graphene and next-gen telecommunications

When light hits a doped semiconductor, the resulting energy makes electrons jump from a lower-energy state (the valence band) through a small gap (the energy gap) and into a higher-energy state (the conduction band) in which electrons can move more freely, conducting electricity. Eventually, when the initial energy has been exhausted, the electrons go back to their original state, through the band gap and back to the valence band.

To establish whether a material can be used to process information quickly, researchers need to look closely at how electrons flow up and down the energy gap in that material. The critical factor is the recombination time – the time it takes for an electron to make the trip back from the conduction to the valence band.

In recent years researchers have advanced the hypothesis that graphene could be an excellent material for optoelectronics, but they couldn't test their hypothesis because graphene is a semimetal, or a "zero-gap semiconductor." In other words, in graphene there is no energy gap between the valence and the conduction band, and this means that scientists aren't able to effectively analyze its potential with current techniques.

The Bath researchers found a way to measure recombination time in semimetals such as graphene. They did so by measuring how the electrons moved in the infrared part of the spectrum, transitioning between different quantum states. What this adds up to is that the researchers' suspicions proved to be right: while ordinary optical switches respond at rate of a few picoseconds (around a trillionth of a second), the physicists observed that the recombination time of an optical switch using a few stacked layers of graphene was of the order of only one hundred femtoseconds – nearly one hundred times quicker.

This could open the door to significantly faster telecommunication, but it is also an important step toward the development of graphene-based quantum cascade lasers, which could be used for anything from remote sensing of environmental gases and pollutants, breathalizers, medical diagnostics, lasers, collision avoidance, and even cruise control for your car.

The research is published in the journal Physical Review Letters.

Source: University of Bath