Graphene has shown itself, once again, to be capable of great wonders, as IBM demonstrates a notch filter that operates in the terahertz – or infrared - range. The company also showed off a linear polariser using the same stacked material.
Terahertz radiation (sub-millimetre electro-magnetic type radiation, not the nuclear type) is of interest because it can pass through many things, such as fog, clouds, clothing, paper and card – but is stopped by metal or water. This makes it potentially useful for security devices, for example, but also means it is very short range and notoriously hard to detect or manipulate.
IBM Fellow and paper co-author Phaedon Avouris told EETimes: "Unfortunately, today there are very few ways of manipulating terahertz waves such as polarizing and filtering it, but because graphene operates well at terahertz frequencies we have concentrating on creating these types of devices."
Despite its thinness, the researchers explain in their paper: "Graphene interacts strongly with light over a wide wavelength range… It has particularly strong potential in far-infrared and terahertz optoelectronics due to its high carrier mobility and conductivity."
The IBM team began by testing how the radiation interacted with a single layer of graphene, but found it wasn’t sensitive enough. So the idea of stacking graphene sheets was born.
Writing in the current edition (April 22) of Nature Nanotechnology, the IBM researchers describe using stacks of graphene sheets interleaved with an insulator, to build the photonics devices. The fabrication involved three deposition steps and a single lithographic step to pattern the stacks into an array of microdisks.
Varying the size of the disks, the number of layers in the stacks, the type of doping that the graphene underwent, allowed the scientists to tune the filter to a particular frequency.
The next step, the team says, is tuning the stacks to the frequencies in use in current optical communications.