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Fibre has its limits too

- Wits University

Wits researchers in optical communications explore ways to drastically increase the optical fibre bandwidth.

Over the past five years, there has been a fivefold increase in internet traffic and this trend is expected to continue steadily, globally. Thus far, the demand for high bandwidth has been met by implementing optical fibre communication.

But soon the limit in the amount of data that can be communicated through fibres with current technologies will be reached. Research in the Structured Light group (School of Physics) at Wits, headed by Distinguished Professor Andrew Forbes, aims to explore ways to drastically increase the optical fibre bandwidth by utilising patterns of light.

Patterns have the ability to carry an infinite amount of information and presently represent a resource not used in optical communication

Bienvenu Ndagano is a Masters student trying to find novel ways to encode and transmit information through free space and optical fibres using patterns of light.

“I am looking at a property of light called orbital angular momentum, which causes light to twist.  The number of twists present in a beam of light can be counted and used to encode information in the same way a computer would count zeros and ones and translate them into bits of information,” explains Ndagano.

Together with his colleagues, he generates light with a twist by shaping a laser beam to give it a finite number of twists.

“We can either give it a single number of twists or multiple numbers of twists simultaneously. We send the shaped laser beam through an optical fibre and we analyse the output by counting the number of measured twists and comparing it to the number of twists generated at the input.”

Thus far Ndagano can measure the number of twists at the output with high fidelity when compared to the input.

“We applied our technique to send pictures through an optical fibre. By associating the colour of each pixel on a picture to a twist number, we were able to transform a picture into sequences of twisted light beams that were sent through the fibre and transformed back to pixels to recreate the picture.

Recently the group have demonstrated a free space, fibre, free space link using this twisted light.  The work, done in the Wits laboratory in collaboration with researchers from the University of Jena (Germany), was selected as a highlighted paper by the Journal of Optics (UK).  The work also won numerous student awards for Ndagano, most recently at the international conference of SPIE, Photonics West, in San Francisco (USA).