August 13, 2011
For most materials, the light that enters is the same light that exits. It may reflect, refract, or attenuate, but it's still the same light. For highly intense light, however, certain 'nonlinear' materials violate this rule of thumb, converting the incoming energy into a brand new beam of light at twice the original frequency, called the second-harmonic. Normally, this frequency doubling process occurs over a distance of many wavelengths, and the direction in which the second-harmonic travels is strictly determined by the nonlinear material. Using a negative-index metamaterial at microwave frequencies, we demonstrate a novel sub-wavelength nonlinear device capable of 'steering' the second-harmonic. This device can even act as a nonlinear mirror, simultaneously doubling and reflecting an incoming wave. This magnitude of control over light is unique to nonlinear metamaterials, and can have important consequences in all-optical communications, where the ability to manipulate light is everything.