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EU project targets photonic integration

05 Dec 2007

The chemistry of paint is the unlikely starting point of a EU project to develop new materials for building all-optical integrated circuits for telecommunications processing and routing.

The goal of the three-year project, codenamed "NewTon" (not an acronym), is to develop a new fabrication process for three-dimensional photonic crystals – nanostructured materials with unusual optical properties including strong wavelength- and angle-dependent reflections. Using these structures it is possible to make waveguides that channel light around 90 degree bends with no losses, which would allow optical circuits to be miniaturized.

The project has received €2.87 million in funding, of which €1.98 million comes from the EU under its sixth framework programme. Led by the Laser Zentrum Hannover (LZH) in Germany, the project participants also include the chemical company BASF in Germany, Thales Aerospace division and the École Nationale Supérieure des Télécommunications in France, the Technical University of Denmark, and Photon Design in the UK.

In the first stage of the project, the researchers at BASF have developed a monodispersed solution of polymer particles – similar to the dispersions used in emulsion paints – that can self-organize into a regular crystal structure. The spaces between spherical particles are then filled with silicon, and the polymer burned away using a laser, resulting in a hard structure that is the inverse of the original crystal. This structure is the photonic crystal.

In the next stage, researchers at LZH will use laser processing to introduce localized changes into the crystal structure to form waveguides. By the end of the project in December 2008, the project participants hope to have demonstrated basic optical functions like waveguides, splitters, and filters using this approach.

One of the key challenges is how to make uniform particles of the appropriate size and chemistry. Paint emulsions typically have particle sizes of 100-200 nm, but to see effects in the infrared part of the spectrum used for telecoms requires larger particles of around 1 μm in diameter. "We are now designing the particle in such a way that they don't form a film, they form a crystal arrangement after evaporation of water," explains Reinhold Leyrer, who is project leader at the polymer research division of BASF.

The project goal to miniaturize optical circuits is quite futuristic, but already significant progress has been made, says Leyrer. "In our lab we are already able to produce 1 μm polymer particles, and have done the first experiments to form single crystals," he says. "We are writing a paper, but we will only publish when we are sure it is a real result that can be reproduced." The team has already published results for crystal structures that show strong angle-dependent reflections at visible wavelengths.

The scientists envisage that all-optical circuits could have the same importance for telecoms that electronic circuits do for computers.

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