Mixing Light and Electricity for Innovative Electronics
SOURCE: The European Commission Research and Innovation Information Centre

The integrated circuits that have been driving the information technology revolution are reaching their physical limit. EU-funded scientists are now looking at light as a replacement for electric signals. In their search for smaller, faster, low-energy alternatives, they are reporting promising work on light particles called 'polaritons', paving the way for next-generation circuits for use in devices such as computers and smartphones.

The hunt is on to find ever-more compact, powerful and flexible electronics as the information technology revolution gathers speed. At the same time, future information storage, transfer and processing components used in devices such as computers and smartphones must cost less, be more energy efficient and generate less heat.

There is however trouble ahead because today's integrated circuits (microchips) – using just electrical components and signals – are reaching their physical limit in terms of speed, size and energy efficiency.

Scientists need to find completely new ways to process data. Optics and photonics, which use light, are promising alternatives. A very new branch of these fields – polaritonics – uses light particles (photons) strongly coupled to electronic excitations ('excitons') to produce hybrid quasi-particles called exciton-polaritons (polaritons for short).

The EU-funded POLALAS project has reported good progress in developing tiny photonic nanostructures for polaritonic applications. Progress in this field would give a further boost to technological progress on a global scale, says project coordinator Professor Richard Abram of the UK's Durham University Physics Department.

Reducing the cost of communication systems would also make them more affordable for people in the developing world, allowing them to participate in the global communications revolution, he adds.
POLALAS concentrated on theoretical and experimental research into polaritons and their applications in photonic nanostructures. This work has prepared the ground for the commercial launch of faster, more energy-efficient lasers that are able to operate at room temperature. This is an advance that has not been achieved to date for similar electrically-driven laser devices.

The technical breakthrough is also expected to be useful for the modelling of organic solar cells and for the design of new ICT devices – such as low-power lasers for use in future fibre-optic communications networks.

"Polaritons are one of the most topical and exciting areas of physics, and the ability to confine and control them spatially opens up new opportunities in fundamental research and device applications," says Prof. Abram.

Enlightening work
POLALAS supported scientific exchanges between St Petersburg and laboratories in the UK, Lithuania and Italy. The exchange involving Rome resulted in important new work on the fundamental properties of 'polariton condensates'.

Such condensation is generally only seen in physical systems when they are cooled to near absolute zero, but for polaritons it is actually possible at near room temperature, according to Prof. Abram.
Polaritons can be used as the basis of a radically new type of laser and the Italian team has been able to adapt its versatile device simulator, TiberCad, to predict the behaviour of proposed device designs.

That work also benefited from the practical input of the world-leading polariton laser group at the École Polytechnique Fédérale de Lausanne in Switzerland.

POLALAS had access to another state-of-the-art facility in Russia which was able to 'grow' new semiconductor nanostructures for experimental studies. The project's use of a novel catalytic technique for growing nanowires has since been widely cited in research literature.

Several members of the project team, in collaboration with international colleagues, have also proposed a new kind of compact and efficient terahertz (THz) emitter based on a modified polariton laser.

The consortium was also responsible for reporting the first experimental observation of 'Tamm plasmon-polaritons', an optical excitation predicted to exist between a metal film and a multi-layered dielectric mirror. Dielectric is a term that can be used to indicate the energy storing capacity of a material (by means of polarisation).

POLALAS scientists think the phenomenon could be used to produce polariton-based, all-optical integrated circuits. Modelling has demonstrated that the signals generated in this way can be suitably controlled and that the structures have the potential to provide fast, low-power circuits.

Valuable Exchange
POLALAS, which ran from 1 January 2009 until 30 April 2012, provided "valuable opportunities" for researchers to work closely with colleagues and gain access to specialist facilities in other European laboratories for substantial periods, notes Prof. Abram.

"It was particularly attractive to young researchers looking to gain experience and establish their scientific careers," he says.

POLALAS' groundbreaking work on exciton-polaritons should be of interest to a wide academic and industrial audience while, at the same time, help to maintain Europe's world leading position in the field, says Prof. Abram.