CST – Computer Simulation Technology

Three-dimensional optical metamaterial with a negative refractive index
Jason Valentine, Shuang Zhang, Thomas Zentgraf, Erick Ulin-Avila, Dentcho A. Genov, Guy Bartal, Xiang Zhang
Volume: 455, 18 September 2008
Metamaterials are artificially engineered structures that have properties, such as a negative refractive index1–4, not attainable with naturally occurring materials. Negative-index metamaterials (NIMs) were first demonstrated for microwave frequencies5,6, but it has been challenging to design NIMs for optical frequencies and they have so far been limited to optically thin samples because of significant fabrication challenges and strong energy dissipation in metals7,8. Such thin structures are analogous to a monolayer of atoms,making it difficult to assign bulk properties such as the index of refraction. Negative refraction of surface plasmons was recently demonstrated but was confined to a two-dimensional waveguide9. Three-dimensional (3D) opticalmetamaterials have comeinto focus recently, including the realization of negative refraction by using layered semiconductor metamaterials and a 3D magnetic metamaterial in the infrared frequencies; however, neither of these had a negative index of refraction10,11. Here we report a 3D opticalmetamaterial having negative refractive index with a very high figure of merit of 3.5 (that is, lowloss).Thismetamaterial ismade of cascaded ‘fishnet’ structures,with a negative index existing over a broad spectral range.Moreover, it can readily be probed fromfree space, making it functional for optical devices. We construct a prism made of this optical NIMto demonstrate negative refractive index at optical frequencies, resulting unambiguously from the negative phase evolution of the wave propagating inside the metamaterial. Bulk optical metamaterials open up prospects for studies of 3D optical effects and applications associated with NIMs and zero-indexmaterials such as reversed Doppler effect, superlenses, optical tunnelling devices12,13, compact resonators and highly directional sources14.

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