Photonics - Page 13

A group of researchers from Singapore, led by Dingyuan Tang are using a Graphene-Polymer composite as a laser locker. A laser locker is used to oscillate laser modes in phase, giving rise to short and very intense light pulses. Graphene can be used as a mode locker because it is a ‘saturable absorber’, that is, its light absorbance decreases rapidly with increasing light intensity — an essential property for passive mode lockers.

The team approached this application by introducing a graphenepolymer composite film into an erbium-doped fiber laser. Encapsulating graphene in the polymer host passivate the graphene from ambient oxygen, which prevents photooxidation and optical bleaching by high-powered lasers, says Tang.

A team of researchers from the UK and Germany have succeeded to make single layers of Graphene luminescent by exposing them to oxygen plasma.

The photoluminescence observed is uniform and extends across large areas in the layers. It is also possible to make thin hybrid structures by etching just the top layers in a sample using the plasma, while leaving underlying layers intact. "This combination of photoluminescent and conductive layers could be used in optoelectronics and sandwich light-emitting diodes," said Andrea Ferrari of Cambridge University.

IBM researchers are using graphene sheets to make photo(light) detectors. Graphene transports electrons very quickly, tens of times faster than current photo detectors (made by materials called III-V semiconductors), and can also absorb more light frequencies (visible and infrared).

It is already known that when metal contacts are deposited on graphene, electric fields are generated at the interface between the two materials. So the researchers took advantage of this field. Their device is a piece of multilayered graphene with metal contacts on top. When they shine light near the contact, the field separates the electrons and holes, and a current is generated.

Scientists of the Physikalisch-Technische Bundesanstalt (PTB) have succeeded in making graphene visible on gallium arsenide. Previously it has only been possible on silicon oxide. Now that they are able to view with a light optical microscope the graphene layer, which is thinner than one thousandth of a light wavelength, the researchers want to measure the electrical properties of their new material combination.