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Nano-Lightpipes

Everybody knows that it is impossible to propagate light through structures smaller than the wavelength of light... but Seed Project 1 has belied this conventional wisdom, showing propagation of light along waveguides whose lateral dimensions are a few nanometers, or a few percent of the wavelength of light. The key is to exploit the tendency for electromagnetic excitations to "hop" between electric dipoles (such as fluorescent dye molecules or metal nanoparticles).

Researchers in Seed 1 demonstrated propagation of light through two types of subwavelength-scale waveguides. The first is a DNA waveguide in which a fluorescence excitation hops from an optical donor molecule bound to one end of the DNA backbone to an acceptor molecule at the other end through dye molecules tethered at intervals in between. These fluorescence resonant energy transfer waveguides have so far shown that light can take several hops between molecules bound to DNA, and this can be extended to many hops along a longer waveguide.

The second nanoscale waveguide structure is called a "plasmon wire," which is a chain of metal nanoparticles along which light hops from one particle to another. Light can even propagate around sharp corners and through nanoscale networks -- all of which are impossible in conventional optical waveguides. This work was covered in Nature Materials in 2003. So much for conventional optical wisdom!

For further information, please contact Professor Harry Atwater, team leader of Seed Progect 1: (626) 395-2197 or haa@daedalus.caltech.edu.

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