Researchers Reaping Benefits From Exploiting Graphene’s Optical Properties
The optical properties of graphene come to it naturally and researchers don’t need a band gap to exploit them
Early research focus with graphene was aimed at applying it to electronics. This is easy to understand given the threat of silicon running out of steam in keeping up with Moore's Law. However, many experts believe that the real opportunity for graphene may be in the area of photonics and optoelectronics. One of the main reasons for this optimism is that these applications play to graphene’s strengths rather than its weaknesses.
Graphene's high carrier mobility enables ultrafast extraction of photo-generated carriers, which leads to high-bandwidth operation. Graphene also has a wide spectral range from the ultraviolet to the infrared.
Some of the success graphene has shown in optoelectronic applications include: an ultrafast "mode-locked" graphene laser, graphene-based photodetectors, and optical switches just to name a few.
This past quarter we have witnessed some significant research developments in the application of graphene to optoelectronics.
In June, Spanish researchers at CIC nanoGUNE outside of San Sebastian, the Institute of Photonic Sciences (ICFO) near Barcelona, and the company Graphenea located at the CIC nanoGUNE research center have demonstrated that an optical antenna made from graphene can capture infrared light and transform it into graphene plasmons.
To understand what graphene plasmons are, it is good to understand that surface plasmons are the oscillations that occur on the structure of a metal surface when photons strike its surface exciting its electrons. Recently, research revealed that graphene and other two-dimensional materials produce plasmons as well. These graphene plasmons as they’ve come to be know have an advantage over the surface plasmons that metal surfaces produce because they can be tuned and controlled by a voltage gate.
The Spanish researchers demonstrated that a metal rod placed on graphene can serve as an antenna for infrared light and transform it into graphene plasmons in much the same way a radio antenna converts radio waves into electromagnetic waves in a metal cable.
“We introduce a versatile platform technology based on resonant optical antennas for launching and controlling of propagating graphene plasmons, which represents an essential step for the development of graphene plasmonic circuits”, said team leader Rainer Hillenbrand in a press release.
Researchers at Swinburne University of Technology in Melbourne, Australia have discovered that graphene oxide (GO) possesses a record-breaking optical nonlinearity. Optical nonlinearity is the ability of a medium to have its optical properties (transmission, refraction, etc.) manipulated by changing the intensity of the light traveling through it. Optical nonlinearity makes it possible to use light to control light so we can operate fiber optic networks.
Now that GO’s high optical nonlinearity has been established it should open up its use in high-performance integrated photonic devices for all-optical communications, biomedicine, and photonic computing, according to the Australian researchers.
In research that sounds more like it came from the lab of “Q” from the James Bond movies, researchers at the University of Michigan believe that graphene could enable an infrared-capable contact lens.
In research published in Nature Nanotechnology, the Michigan researchers devised a new method to exploit graphene’s natural ability to detect the entire infrared spectrum. Prior to this work, you couldn’t really take advantage of this capability of graphene because it can only absorb about 2.3 percent of the light that hits it. This is not enough to generate an electrical signal, and without a signal it can’t operate as an infrared sensor.
The Michigan researchers devised a new method for generating the electrical signal. Instead of trying to measure the electrons that are released when the light strikes the material, they amplified an electrical current that is near the electrical signals generated by the incoming light.
The result is a device that has very nearly the same sensitivity as cooled mid-infrared detectors, but achieves it at room temperature. Even in the early prototypes produced by the researchers they have been able to make the infrared sensors the size of a standard contact lens.