Three-dimensional optical metamaterial with a negative refractive index
Three-dimensional optical metamaterial with a negative refractive index
复制标题
DOI：
10.1038/nature07247
复制
发表时间：
2008-09-18
期刊：
影响因子：
64.8
通讯作者：
Zhang, Xiang
中科院分区：
文献类型：
--
作者：
Valentine, Jason;Zhang, Shuang;Zhang, Xiang
超材料是人工设计的结构，具有自然存在的材料无法达到的特性，例如负折射率（1-4）。负折射率超材料（NIM）首先被证明用于微波频率（5，6），但是设计用于光学频率的NIM具有挑战性，并且由于金属中显著的制造挑战和强能量耗散，迄今为止它们仅限于光学薄样品（7，8）。这种薄的结构类似于单层原子，使得很难分配诸如折射率之类的整体性质。表面等离子体激元的负折射最近被证明，但仅限于二维波导（9）。三维（3D）光学超材料最近已经成为焦点，包括通过使用层状半导体超材料和3D磁性超材料在红外频率中实现负折射;然而，这些都不具有负折射率（10，11）。在这里，我们报告了一种具有负折射率的3D光学超材料，其品质因数非常高，为3.5（即，低损耗）。这种超材料由级联的“渔网”结构制成，在宽光谱范围内存在负折射率。此外，它可以很容易地从自由空间探测，使其功能的光学设备。我们构建了一个棱镜，这种光学NIM证明在光学频率的负折射率，明确地从负相位演化的超材料内传播的波。块体光学超材料开辟了与NIM和零折射率材料相关的3D光学效应和应用的研究前景，例如反向多普勒效应，超透镜，光学隧道器件（12，13），紧凑型谐振器和高度定向源（14）。
Metamaterials are artificially engineered structures that have properties, such as a negative refractive index(1-4), not attainable with naturally occurring materials. Negative- index metamaterials (NIMs) were first demonstrated for microwave frequencies(5,6), 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 metals(7,8). 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 waveguide(9). Three- dimensional ( 3D) optical metamaterials have come into 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 refraction(10,11). Here we report a 3D optical metamaterial having negative refractive index with a very high figure of merit of 3.5 ( that is, low loss). This metamaterial is made of cascaded 'fishnet' structures, with a negative index existing over a broad spectral range. Moreover, it can readily be probed from free space, making it functional for optical devices. We construct a prism made of this optical NIM to 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-index materials such as reversed Doppler effect, superlenses, optical tunnelling devices(12,13), compact resonators and highly directional sources(14).