While new breakthroughs continue to come in using graphene (or cousins of graphene) for electronics applications, research in the area of using graphene for photonics applications is growing.
The latest use of graphene for photonics comes from IBM where researchers have created a graphene/insulator superlattice capable of serving as a terahertz frequency notch filter and linear polarizer, according to an article in EE Times.
IBM has certainly been a trailblazer in using graphene for electronics applications over the years, such as their graphene transistor work and then later an integrated circuit. But IBM—along with other researchers outside of Big Blue—has also been hard at work looking at how graphene could be used in optoelectronics.
IBM Fellow Phaedon Avouris told EE Times that "In addition to its good electrical properties, graphene also has exceptional optical properties. In particular, it absorbs light from the far-infrared to the ultra-violet."
It is in the terahertz frequency that graphene’s optical properties were of particular interest to the IBM team. Tunable notch filters have become fairly ubiquitous in optoelectronics, but they didn’t really operate at the terahertz frequency. The new application seemed that a good way to take advantage of graphene's terahertz frequency capabilities.
“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," said Avouris.
As good as graphene is at operating at terahertz frequencies, when single-layer graphene is used carrier concentration and resonant frequency are too weak for it to be used in photonics applications. This is where the IBM researchers' work began and they developed a multi-layer graphene/insulator superlattice that improved the carrier density and the resonant frequency.
“We have found that graphene interaction with electromagnetic radiation is particularly strong in the terahertz range, however with a single layer of graphene the interaction was still not strong enough," Hugen Yan, a member of the Nanoscale Science and Technology Group at IBM's T. J. Watson Research Lab (Yorktown Heights, N.Y.) was quoted as saying. "But by using a multi-layer stack structure in microdisk arrays we achieved frequency selectivity in the terahertz range, allowing us to tune the desired resonant frequency."
The devices that IBM have developed could find their way into future mid- and far-infrared photonic devices, such as detectors and modulators. The next step for the researchers will be to tune the devices for infrared frequencies typically used in optical communications equipment.