Negative refraction in semiconductor metamaterials

We report on a new class of semiconductor metamaterials that exhibits negative refraction for all incident angles in the long-wave infrared region of the spectrum. This optically thick material consists of alternating layers of highly doped InGaAs and intrinsic AlInAs and displays a strongly anisotropic dielectric function that obviates the need for simultaneously negative electric and magnetic responses usually associated with negative refraction. Using reflection and transmission measurements and a comprehensive model of the material, we demonstrate that our material exhibits negative refraction. This is furthermore confirmed through a straight-forward beam optics experiment. The spectral region of negative refraction, has a bandwidth = 27%, and its starting wavelength is controlled by the electron density in the doped layers; for our choice of semiconductor heterostuctures it can be located anywhere above ~8.8 µm. This material has great potential for waveguiding and imaging applications in the long-wave infrared.