Three-dimensional optical metamaterial with a negative refractive index

Abstract

Metamaterials are artificially engineered structures that have properties, such as a negative refractive index, not attainable with naturally occurring materials. Negative-index metamaterials (NIMs) were first demonstrated for microwave frequencies, 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. 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. 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. 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, compact resonators and highly directional sources.

Negative Refraction in Weyl Semimetals

“…[9][10][11][12] These structures usually contain an array of split ring resonators [6,[13][14][15] or dielectric photonic crystals with periodically modulated ε and µ, [2,6,16] which are often complicated to fabricate. To overcome the difficulties, in this paper we predict that negative refraction can take place in a bulk Weyl semimetal (WSM) even without having negative µ and without constructing complicated structure.…”

Symmetry breaking and optical negative index of closed nanorings

“…Significant efforts have been devoted to scale NIMs down to the optical domain. The fishnet of metaldielectric multilayers is one of the most successful optical NIM structures [12][13][14][15][16] . The magnetic responses of such structures result from the excitation of gap surface plasmons, and the electrical responses are governed by the cut-off frequency of the waveguide mode of the air holes, resulting in negative-phase index 15,16 .…”

Realization of Variable Three‐Dimensional Terahertz Metamaterial Tubes for Passive Resonance Tunability

“…[1][2][3][4] A split ring resonator (SRR) is one of the typical metamaterials structures. In order to extend its resonance bandwidth, terahertz metamaterials with resonance tunability were developed recently.…”