Researchers at the National University of Singapore have invented a graphene-based polarizer that can broaden the bandwidth of prevailing optical fibre-based telecommunication systems.

The graphene research team, led by Professor Kian Ping Loh at the National University of Singapore, invented an ultra-slim broadband polarizer that uses graphene, a single-atomic-layer crystallized carbon, to convert light beam into polarized light.

This is the first experimental demonstration of using graphene as an ultrathin waveguide to couple and modulate light. Light modulation by means of polarization management is vital to avoid signal fading and error in coherent optical communications as well as optical gyroscopes and interferometric sensors.

In principle, the polarizing ability of graphene covers the telecommunication bands from visible to mid-infrared. This means that graphene polarizer can provide all-in-one solution for multiple-channel high-speed optical communications, the researchers said.

The researchers skilfully transferred graphene grown by chemical vapour deposition on the side-polished optical fibre to fabricate the graphene polarizer and measured light polarization at different wavelengths.

Unlike 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.

"The results reported in this paper can have a strong impact in the development of graphene-based optical devices for photonic applications ... the science behind it is excellent ..." says professor Antonio Castro Neto of National University of Singapore.

The Singapore team has earlier pioneered graphene mode-locked lasers in 2009. This work was another breakthrough in bringing graphene photonics a step closer to real applications.

"In the near future, we can envision ultrathin graphene-based photonic circuits with multiple functions of light creation, routing, modulation or detection," said Dr. Qiaoliang Bao, who is the project leader of the pioneering work.

The broadband graphene polarizer work was published in the journal Nature Photonics and appeared online on 29 May 2011.

The other Singapore-based partners of this research included teams from Singapore's Nanyang Technological University and Institute of Materials Research and Engineering. One Belgium group from Universite Libre de Bruxelles participated in the project and verified the work of the Singapore group.

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