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Controlling the Direction of Light --New Milestone in Physics

 

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Researchers at King's College London, Anatoly Zayats and his team, working with collaborators from Universitat Politècnica de València in Spain, show how their use of circularly polarised light - light containing spinning photons (fundamental particles) - and metallic nanostructures achieve a 'water wheel' effect to send light waves in a single direction along a metal surface. Their findings are surprising because such unidirectional waves have not been controlled in this way before. The research has profound implications for optical communications and information processing technologies.

Nanophotonics involves the study of light and how it interacts with structures at distances smaller than the wavelength of light. At this scale, interactions of tiny electric fields created by charged particles can have intriguing effects on light's movements. These effects often occur through interference, a phenomenon seen when two or more waves interact.

Elliptically polarized dipole, pictured as two rotating opposite charges, designed to excite surface plasmons unidirectionally in a nearby metal surface. The height of the metal surface represents the simulated surface charge density. Credit: Francisco J. Rodríguez-Fortuño

The scientists have improved on previous cumbersome attempts to use light to control the travelling direction of electromagnetic waves in materials. Many of these attempts have been inefficient. Until now, attempts to produce unidirectional light have only worked using single wavelengths and have not allowed for the resultant wave's direction to be easily switched.

'Wave interference is a basic physics phenomenon, known for many centuries, with myriad applications," said 
Zayats, from the Department of Physics at King's. "When we observed that it can lead to unidirectional guiding when spin carrying photons are used, we could not at first believe that such a fundamental effect had been overlooked all this time. We now work on developing its applications in nanophotonicsand quantum optics.'

The team used circularly polarised light to illuminate a small metal structure. The spinning photons in the polarised light caused the electrons in this nanostructure to move in circles, clockwise or anticlockwise depending on the direction of the photons' spin. If this structure is then brought close to an optical waveguide or a metal surface, waves in these materials moved in one selected direction only. This type of control, using circular polarisation, has not been achieved before.

Circularly polarized dipole over a metal surface, exciting surface plasmons unidirectionally. The height of the metal surface represents the surface charge density. Credit: Francisco J. Rodríguez-Fortuño

If the polarisation direction of the light is changed, the ultimate direction of the excited wave can be reversed. Researchers have compared the effect to a 'water wheel' operating in a river, with the wheel being the small metallic structure and the water being the stream of light.

The unidirectional waves arise through interference in the 'near field'. This electromagnetic interference is similar to that seen when two or more waves meet on the surface of a pond. The 'near field' refers to the proximity of the waveguide to the nanostructure illuminated with the polarised light.

For more information: "Near-Field Interference for the Unidirectional Excitation of Electromagnetic Guided Modes," by F.J. Rodríguez-Fortuño et al. Science, 2013.www.sciencemag.org/content/340/6130/328.abstract

Journal reference: Science

The Daily Galaxy via King's College London

Comments

hello. amazing illustration of cause and effect without placing an axis of direction for the light. perhaps a nano crystal would give direction.

The information of life shows evidence of being streamed through out the cosmos within its radiation. I'm thinking of Left handed amino acids and how they can be produced in sterile water with the exposure to polarized light.

A Unique property that light undergoes while interacting with nano-structured material surfaces. It can be used for future communications involving quantum computers!

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