Guiding terahertz radiation

University of Utah engineers have designed stainless steel foil sheets with patterns of perforations that successfully served as wire-like waveguides to transmit, bend, split and combine terahertz radiation.

This February, British researchers reported that they used computer simulations and some experiments to show that indentations punched across an entire sheet of copper-clad polymer could hold terahertz radiation close to the sheet's surface. That led them to conclude the far-infrared light could be guided along such a material's surface.

But the London researchers did not actually manipulate the direction the terahertz radiation moved, such as by bending or splitting it.

'We have demonstrated the ability to do this, which is a necessary requirement for making terahertz guided-wave circuits,' said Ajay Nahata, an associate professor of electrical and computer engineering at Utah.

To do so, the researchers used pieces of stainless steel foil about 4 inches long, 1 inch wide and 625 microns thick. They perforated the metal with rectangular holes, each measuring 500 microns by 50 microns. The rectangular holes were arranged side by side in three different patterns to conduct the terahertz radiation.

One line of rectangles served as a 'wire' and carried terahertz radiation. A Y shaped line was used to split the far-infrared light, similar to a splitter used to route a home cable TV signal to separate television sets. And two lines that curved close to each other in the middle - like an X where the two lines come close but don't touch - was used to couple the teraherz radiation.

The straight pattern successfully carried terahertz radiation in a straight line. The other two patterns changed the direction the terahertz radiation was moving by splitting it or coupling it, Nahata said. The study showed the terahertz radiation was closely confined both vertically (within 1.69mm of the foil's surface) and horizontally (within 2mm of the pattern of rectangles as it moved over them).

The design of the waveguide means that it carries terahertz radiation in the form of surface plasma waves - also known as plasmons or plasmon polaritons - which are analogous to electrons in electrical devices or photons of light in optical devices. The surface plasma waves are waves of electromagnetic radiation at a terahertz frequency that are bound to the surface of the steel foil because they are interacting with moving electrons in the metal.