Graphene, an ultra-flat monolayer of carbon atoms in a hexagonal crystal lattice, has attracted a strong wave of research interest due to its unique electrical and photonic properties. For its discovery as the first two dimensional material in the world, two UK Scientists were awarded the 2010 Nobel Prize in physics.
Now, Dr. Han Zhang at the Service OPERA-photonique – Applied Science Faculty, ULB, and Dr. Qiaoliang Bao (first author) and Professor Kian Ping Loh (corresponding author) at the National University of Singapore, demonstrate the world's thinnest polarizer, which relies on the coupling, guiding and polarizing of electromagnetic waves by graphene. They claim that this breakthrough will someday allow the integration on all-photonic circuits for high-speed optical communications.
Optical polarizers are elementary components of coherent and quantum optical communications by splitting the polarization state of an optical signal. Nowadays, there are rising demands for high-speed optical communications based on mobiles, calling for the miniaturization of optoelectronic devices. However, conventional optical polarizers (sheet, prism and Brewster-angle polarizer) are expensive, bulky, and discrete and may require additional alignment. Thanks to graphene’s ultra-broadband optical property induced by its exceptional energy band structure, as-demonstrated graphene polarizer shows very broad operation bandwidth, at least from visible to mid-infrared. By fabricating graphene polarizer, with combined advantages of low cost (down to several euros), compact footprint, ultra-fast relaxation time and broad operation range, they anticipate that this device will enable new architectures for on-chip high-speed optical communications.
In addition to the industrial potentials, the research -- published in Nature Photonics, on May 30 -- is of fundamental importance. It tackles how light propagates along an ultra-thin two dimensional surface. By the virtue of fiber based optical channel, now we can readily uncover how graphene guides and interacts with electromagnetic waves, with polarizing effect attributed to the differential attenuation of two polarization modes. This new conceptual finding will definitely lead to new physics, for example, localized waves or surface plasmon in graphene lattice. In the following years, researchers from the photonics, plasmonics and nano-science research communities may find in this graphene polarizer structure as a new testing ground for the ideas and methods they have been researching on their own fields, paving the way for all-carbon photonic-plasmonics devices.
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