Trade.Information

Topic Name: Researchers Say Three-dimensional photonic crystals will revolutionize telecommunications

Category: Chemical

Research persons: BASF Research Team

Location: BASF, Germany

Details

Smaller, faster, more efficient: BASF research scientists are helping to revolutionize the future world of telecommunications – with the aid of three-dimensional photonic crystals. In a three-year project, BASF is researching into the development of these crystals together with partners such as Hanover Laser Center, Thales Aerospace Division, Photon Design Ltd., the Technical University of Denmark and the Ecole Nationale Supérieure des Télécommunications de Bretagne. By the end of 2008, the partners in the "NewTon" project expect to have developed the first functional components of this new technology. The long-term goal is to use three-dimensional photonic crystals as construction elements in telecommunication. Half of the project is being funded by the European Union.

Many times more information can be transmitted by light in the same time as has so far been possible with electricity. This is why telephone conversations, websites, photographs or music, for example, are now increasingly being transmitted in optical fibers. At present, however, this technology still has one drawback at the "network nodes". Indeed, at these nodes the routing of the information to the end-user is still done electrically, because no competitive, compact all-optical routing processor is yet available. This costs time and energy.

This is where the research activities of BASF and its partners come into the picture. They are developing a photonic crystal capable of reflecting only single colors of the white light depending on the observation angle. This phenomenon is known from nature: the splendid, shimmering colors on butterfly wings derive from the properties of photonic crystals.

"A structured three-dimensional photonic crystal could be the key component for a compact optical semiconductor or even for an all-optical routing processor", is the opinion of Dr. Reinhold J. Leyrer who is BASF’s project leader in Polymer Research division. "Converting optical signals into electrical signals would then be superfluous". But the scientists first have to develop a stable, structured three-dimensional photonic crystal. And exactly this is the goal of the EU project "NewTon". This kind of basic research projects are especially suited to activate the European scientific competence, in order to strengthen the competitiveness of the whole region and of all involved industrial branches.

The production of these crystals is based on aqueous dispersions, a key competence of BASF. These dispersions contain polymer spherical particles measuring about 200 nanometers which, when the fluid evaporates, are forming a homogeneous protective film as it is expected with the paints. Depending from the chemical structure of the polymer particles they can also arrange themselves into a regular lattice structure, forming a crystal. The challenge facing the Ludwigshafen scientists is to enlarge the polymer particles contained in the dispersions to 1000 nanometers in such a way, that they all have exactly the same diameter. Using emulsion polymerization, they also apply an additional structure measuring less than 20 nanometers onto the polystyrene particles. The intention is to develop the most stable possible, large volume, three-dimensional crystal into which one of the project partners will then introduce the desired structure, the so called "defects".

Light at certain wavelengths then travels along these defects and even around sharp corners: the photonic crystal then acts as a photoconductor and takes the control over the propagation of light. The resulting structured crystal lattice is used in the further manufacturing process as a template, as the scientists call it. The spaces between the polymer spherical particles in the crystal lattice are filled with silicon. The researchers then "burn" the polymer particles out of the lattice. The result: a stable structure that is a mirror image of the original crystal. Crystals of this type could be used as components for an all-optical routing processor in telecommunications.

Manufacturers of components for telecommunication systems would benefit most from the use of photonic crystals. Since the crystals are smaller than electronic components, equipment would also become increasingly smaller and cheaper – while simultaneously offering improved performance. Components and equipment based on photonic crystals would also be more resistant and less vulnerable to electromagnetic radiation. End users will gain from these advances. In the long term, transmitting information through electrical signals will restrict speed and transmission capacity in telecommunications. The long-term goal is therefore to develop a communications technology based entirely on transmitting information by light waves. The research activities of the "NewTon" project are laying the foundations for this scenario.

Note for Photonic crystals

Photonic crystals are periodic optical (nano)structures that are designed to affect the motion of photons in a similar way that periodicity of a semiconductor crystal affects the motion of electrons. Photonic crystals occur in nature and in various forms have been studied by science for the last 100 years.
Photonic crystals are composed of periodic dielectric or metallo-dielectric (nano)structures that affect the propagation of electromagnetic waves (EM) in the same way as the periodic potential in a semiconductor crystal affects the electron motion by defining allowed and forbidden electronic energy bands. Essentially, photonic crystals contain regularly repeating internal regions of high and low dielectric constant. Photons (behaving as waves) propagate through this structure - or not - depending on their wavelength. Wavelengths of light (stream of photons) that are allowed to travel are known as "modes". Disallowed bands of wavelengths are called photonic band gaps. This gives rise to distinct optical phenomena such as inhibition of spontaneous emission, high-reflecting omni-directional mirrors and low-loss-waveguiding, amongst others.

Note for Emulsion polymerization

Emulsion polymerization is a type of radical polymerization that usually starts with an emulsion incorporating water, monomer, and surfactant. The most common type of emulsion polymerization is an oil-in-water emulsion, in which droplets of monomer (the oil) are emulsified (with surfactants) in a continuous phase of water. Water-soluble polymers, such as certain polyvinyl alcohols or hydroxyethyl celluloses, can also be used to act as emulsifiers/stabilizers. The name "emulsion polymerization" is a misnomer that arises from a historical misconception. Rather than occurring in emulsion droplets, polymerization takes place in the latex particles that form spontaneously in the first few minutes of the process. These latex particles are typically 100 nm in size, and comprise many individual polymer chains. The particles are stopped from coagulating with each other because each particle is surrounded by the surfactant ('soap'); the charge on the surfactant repels other particles electrostatically. When water-soluble polymers are used as stabilizers instead of soap, the repulsion between particles arises because these water-soluble polymers form a 'hairy layer' around a particle that repels other particles, because pushing particles together would involve compressing these chains.

Note for Electromagnetic radiation

Electromagnetic (EM) radiation is a self-propagating wave in space with electric and magnetic components. These components oscillate at right angles to each other and to the direction of propagation, and are in phase with each other. Electromagnetic radiation is classified into types according to the frequency of the wave: these types include, in order of increasing frequency, radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.
EM radiation carries energy and momentum, which may be imparted when it interacts with matter.
Electromagnetic waves were first predicted by James Clerk Maxwell and subsequently confirmed by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, revealing the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave.
According to Maxwell's equations, a time-varying electric field generates a magnetic field and vice versa. Therefore, as an oscillating electric field generates an oscillating magnetic field, the magnetic field in turn generates an oscillating electric field, and so on. These oscillating fields together form an electromagnetic wave.