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School of Physical and Chemical Sciences

Developing optical amplifiers

We live in a connected world. We make use of broadband, mobile telephone networks, cable and satellite TV, and all the other sophisticated communication systems that modern cutting-edge technology has provided us with.

Impressive though all this technology is, there is always room for improvement, particularly when it comes to reducing costs by finding cheaper ways to make the systems work. Scientists in the School of Physics and Astronomy (SPA), working with colleagues in Chemistry and Materials, have developed new technology that may do just that.

Modern telecommunications systems are based around optical fibres, sending signals around the world in the form of light that travels along the fibres. These fibres can be extremely long; for example there are fibres across all of the world’s oceans. Over such large distances, the light signal becomes weaker as some of it is absorbed by the fibre.

After about 100km the signal is so weak that it cannot be interpreted by a receiver. To overcome this problem, amplifiers are placed along the optical fibre to boost the signal so that the receiver at the end sees a good strong signal.

Making an amplifier that boosts a light signal, rather than an electrical signal in a piece if wire, is quite a challenge. The technology to do this has only been available at a reasonable cost for about 20 years. But even still, it represents quite a significant financial outlay when putting together a communications system. So a cheaper amplifier would be a big step forward.

Most optical amplifiers work by "pumping" energy into a substance through which the light signal passes, in such a way that the light can pick up some of that energy as it passes through, thereby amplifying the signal. The materials currently used to achieve this require a lot of energy to be pumped in so that enough of it can be transferred to the light signal. Powerful lasers (~100kW/cm2) are needed to provide the amount of energy needed — and they can be quite expensive.

A group led by Prof. William Gillin in SPA has developed a new material that is able to transfer the pumping energy to the light signal more efficiently, meaning that a much less powerful — and therefore cheaper — laser can be used to provide the energy boost.

By reducing the cost of the amplifiers needed to maintain a signal along large lengths of optical fibre, this new technology has the potential to make communications systems cheaper and more efficient.