Photonics - Page 12

According to researchers from the University of Texas at Austin, a single layer of graphene may be used to create a thin metamaterial cover to suppress the scattering from a passive object. Graphene's unique features of ultra-high mobility and largely tunable Fermi level may naturally provide the required reactive properties in a single atomic layer. Graphene's effective surface impedance can be tuned (in real time) which makes dynamically tunable and switchable cloaking operation possible.

A graphene invisibility cloak will be the thinnest possible - a 2D sheet of atoms. It will operate in the THz spectrum.

Researchers from the National University of Singapore (NUS) and A*STAR developed a new method to create Quantum Dots from Graphene. The idea is to start with a C60 fullerene (a soccer ball like spherical carbon structure that costs of 60 carbon atoms) and 'open' them up (or decompose them) at high temperature using ruthenium as a catalyst.

The researcher performed the decomposition using a sparser coverage of fullerenes on the catalytic ruthenium surface than previously tried - which gave the fullerenes room to prevent carbon atoms from diffusing from one fullerene to the next.

Researchers from the National University of Singapore (NUS) invented a graphene-based an ultra-slim broadband polarizer. They say that such a polarizer can broaden the bandwidth of fiber optic networks. A graphene polarizer covers the telecommunication bands from visible to mid-infrared which means that it can be a complete solution for multiple-channel communications.

The team says that unlike regular polarizers (made from thin metal film or semiconductor dielectric) a graphene polarizer has the unique ability to filter out transverse-magnetic-mode and supports transverse-electric-mode surface wave propagation.

Researchers from the University of California, Berkeley built an optical modulator (switches light on and off) using Graphene. This is the basis of network modulators (which use light to transmit data). The graphene based modulator is the world's smallest and fastest - which could help create faster communication devices. In fact Graphene can be used to create modulators that are up to ten times faster than any current technology based modulators.

The researchers found out that tuning graphene electrically (applying voltage) causes it to absorb light in wavelength that are used for data communications (it alters the Graphene's Fermi level). At certain voltages Graphene becomes transparent, and lets light through. If you change the voltage around that level you can change whether the material is transparent or not - and basically it becomes a light switch.

Researchers from the National Physical Laboratory (NPL) together with an international team of scientists have published a research into how light can be used to control the electrical properties of graphene. This research opens the door to highly sensitive graphene based electronic devices.

The researchers have revealed that when graphene is coated with light sensitive polymers, its unique electrical properties can be precisely controlled and therefore exploited. The polymers also protect the graphene from contamination. Light modified graphene chips have already been used at NPL in ultra precision experiments to measure the quantum of the electrical resistance.

An international team of physicists discovered that the polarization of light can be rotated by almost 6° as it passes through a single sheet of graphene in a magnetic field. The team believes that graphene could be exploited in new devices that switch light using electric and magnetic fields.

Graphene was not expected to generate a large rotation because the angle is proportional to the thickness of the material in magnetic fields, and Graphene is just one atomic layer thick.

Korean researchers from the Seoul National University say that they've developed a technology to produce LEDs by using Graphene sheets. They have cultured nitride thin-films on a sheet on Graphene. The nitride thin films show excellent characteristics at room temperature, such as stimulated emission.

IBM Research demoed a 10 Gbit/sec optical link that has a Graphene photodetector (fabricated on a silicon-on-insulator substrate).

The vertical-incidence metal-graphene-metal photodetector achieved 6.1 milliamps per watt at the communications wavelength of 1.55 microns, but was shown to be useful over a very wide bandwidth of 300 nanometers to 6 microns, making the graphene optical link a promising candidate not only for communications, but for remote sensing, environmental monitoring and surveillance.

Researchers from Cambridge (UK) and CNRS (France) have developed an ultra-fast mode-locked laser using Graphene. Graphene based lasers can be easier and cheaper to make than semiconductor saturable absorber mirrors (SESAMs) based lasers, and will be less limited in their bandwidth.

Graphene ultra-fast laser

The team studied how light is absorbed in graphene and how photo-excited charge carriers behave in the material. In particular, they highlighted the key role of "Pauli blocking" in saturating the light absorption. Because of the Pauli exclusion principle, when pumping of electrons in the excited state is quicker than the rate at which they relax, the absorption saturates. This is because no more electrons can be excited until there is "space" available for them in the excited state.

Researchers from Sweden and the US have produced a new transparent lighting component that is made from Graphene. They say it is cheap to make and fully recyclable, and might be an alternative to OLED Lighting. The new device is called an Organic Light-emitting Electrochemical Cell, or LEC. The Graphene is used for an electrode. 

LECs can be made using a roll-to-roll process, because all of its parts can be made from liquid solutions.