PerspectiveApplied Physics

Antenna-Guided Light

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Science  21 Oct 2011:
Vol. 334, Issue 6054, pp. 317-318
DOI: 10.1126/science.1213278

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The bent appearance of a stick half-submerged in water is caused by the difference in refractive indices of air and water—light travels more slowly in water than in air (see the figure, panel A) and refracts and reflects off the air-water interface. Snell's law (1) lets us calculate the bending angle if we know the geometry and the refractive indices. In complex optical instruments, where several lenses, mirrors, and other components may be present, designers control the bending by keeping track of the phase shifts imposed along the wavefront of the light; for example, a light beam can be focused by different phase shifts that occur along a curved lens. These optical components are much larger than the wavelength of light, which limits the minimum size of devices. On page 333 of this issue, Yu et al. (2) show how arrays of structures smaller than the wavelength of light, V-shaped nanoantennas made of gold, bend light by creating abrupt phase shifts through the excitation of resonances. The authors show that these compact “metasurfaces” follow a more general version of Snell's law that accounts for the bending of a light beam in unconventional but potentially useful ways.