Singapore researchers invent broadband graphene polarizer

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

"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.

More information: Broadband graphene polarizer, Nature Photonics (2011) doi:10.1038/nphoton.2011.102

Conventional polarizers can be classified into three main modes of operation: sheet polarizer using anisotropic absorption media, prism polarizer by refraction and Brewster-angle polarizer by reflection. These polarizing components are not easily integrated with photonic circuits. The in-line fibre polarizer, which relies on polarization-selective coupling between the evanescent field and birefringent crystal or metal is a promising alternative because of its compatibility with most fibre-optic systems. Here, we demonstrate the operation of a broadband fibre polarizer based on graphene, an ultrathin two-dimensional carbon material. The out-coupled light in the telecommunication band shows a strong s-polarization effect with an extinction ratio of 27 dB. Unlike polarizers made from thin metal film, a graphene polarizer can support transverse-electric-mode surface wave propagation due to its linear dispersion of Dirac electrons.

Provided by National University of Singapore