Photonics - Page 10

Nobel Prize-winner (together with Andre Geim) Professor and Kostya Novoselov Professor Volodya Falko from Lancaster University have released a graphene roadmap. The roadmap discusses the different possible applications for graphene and also the different ways to produce the material.

The authors says that the first key application is conductors for touch-screen displays (replacing ITO), where they expect can be commercialized within 3-5 years. They also see rollable e-paper displays soon - prototypes could appear in 2015. Come 2020, we can expect graphene-based devices such as photo-detectors, wireless communications and THz generators. Replacing silicon and delivering anti-cancer drugs are interesting applications too - but these will only be possible at around 2030.

Trying to investigate several doping methods for graphene, researchers have found a way to dope graphene with light. This kind of doping is selective and reversibly - meaning that you can change the material attributes using different light colors, angles or polarization. To achieve that doping method, the researchers attached a plasmonic nano antenna to the graphene. The graphene was doped by hot electrons generated from the antenna.

The doping can be controlled by changing the antenna size or the laser's wavelength and power density. n-type graphene provided a larger doping efficiency than p-type graphene.

Researchers from the Technical University of Denmark (DTU) and the University of Wuppertal (BUW) say that graphene can be used to develop hyperlens able to work in the terahertz range. Fabricating hyperlens able to capture teraherz waves is very challenging, because the lens must behave as a metal in one direction and an insulator in the other direction. Metals can be used (this has been experimentally shown) but then the device cannot be tunable.

Graphene, however, can easily change its properties using electrostatic fields, magnetic fields or chemical doping. The researchers suggest using narrow (starting from 40 nm) tapered graphene wires embedded into polymer. This achieves the very properties needed for hyperbolic dispersion - the wave "feels" it as metal along the wires and as dielectric perpendicular to the wires. The hyperlens can be tuned by applying voltage to the various graphene layers, and can be used not only to image, but also to concentrate terahertz radiation in small volumes.

Researchers from the Texas Technical University demonstrated that uniform dispersion of TiO(2) on graphene is critical for the photocatalytic effect of the composite. The researchers used a hydrothermal method to synthesize TiO(2) nanowires (NW) and then fabricate graphene-TiO(2) nanowire nanocomposite (GNW).

The researchers found that by the composite graphene, GNP and TNW has a higher performance than each individual material. Nanowires were found to have more uniform dispersion on graphene with less agglomeration, resulting in more direct contact between the TiO(2) and graphene. This shows that the relative photocatalytic activity of GNW is much higher than GNP and pure NWs or Graphene-TiO(2) nanoparticle.

Nokia filed a new patent for a graphene-based photo detector. The new detector uses graphene as a photo-collecting layer, and also uses a graphene nanoribbon that acts as a field effect transistor to amplify the current and transfer it to the control electronics. Stacking several such detectors on top of each other with color filters can be done to detect colors.

The big advantage of this graphene-based photo detector is graphene's transparency. The graphene sheet itself absorbs only 2.3% of the light (and does it very evenly across the whole light spectrum) and so should perform much better than CMOS in low light conditions. The graphene sensor will also be vastly thinner than current technologies, and potentially cheaper to produce (once graphene itself is available on the cheap).

Researchers from Columbia and Singapore discovered that graphene has a remarkable optical nonlinear behavior - which could lead to ultra low power photonic integrated circuits. The researchers managed to use a single sheet of graphene and silicon to generate microwave photonic signals and perform parametric wavelength conversion at telecommunication wavelengths.

The researchers say that by optically driving the electronic and thermal response in the hybrid silicon-graphene chip they could generate a RF carrier on top of the transmitted laser beam and control its modulation with the laser intensity and color. The resonant quality of this cheap is 50 times lower than the best pure-silicon chip.

Graphene has been used to develop photodetectors for quite some time (quantum dots have been found to enhance the sensitivity just last month), and now researchers from the University of Maryland (UMD) discovered that using bilayer graphene can be used to make ultra fast, broad-range photodetectors.

The team made a prototype device, which unfortunately has a high electrical resistance and so needs a lot of light to be useful. They are working to lower this now.

Researchers from the Institute of Photonic Sciences (ICFO) in Barcelona, Spain have developed a highly sensitive photodetector that uses graphene and quantum dots. They say that the new device is a billion times more sensitive to light than previous graphene-based photodetectors because of the quantum dots. A photo-detector such as this can be used in light sensors, solar cells, infrared cameras and biomedical imaging.

Graphene's external quantum efficiency (EQE) is low as it absorbs less than 3% of the light that falls on it. It is also quite difficult to actually extract the electrical current from the graphene. Adding the quantum dots on the graphene sheet helps both of these issues.

Researchers from the Iowa State University discovered that Graphene behaves like a laser when excited with very short femtosecond light pulses. Graphene has been shown to have two technologically important properties population inversion of electrons and optical gain. This means that Graphene can be used to make a variety of optoelectronics devices, including broadband optical amplifiers, high-speed modulators, and absorbers for telecommunications and ultra fast lasers.

We already heard of some infra-red graphene related research: Infrared detection using graphene nanoribbons and a graphene-based technology for use in low-cost infrared imaging applications for the US military.

IBM researchers managed to develop a graphene insulator superlattice that achieves a Teraherz frequency notch filter and a linear polarizer. These kinds of devices can be used in mid- and far-infrared photonic devices, including detectors, modulators and three-dimensional metamaterials. Terhertz is interesting because this kind of frequencies can penetrate paper, wood and other solid objects.

IBM managed to create these devices by using a multi-layer graphene/instulator superlattice and a multi-layer stack structure in microdisk arrays.