Experimental Demonstration of Near-Infrared Negative-Index Metamaterials

Abstract

Metal-based negative refractive index materials have been extensively studied in the microwave region. However, negative-index metamaterials have not been realized at near-IR or visible frequencies due to difficulties of fabrication and to the generally poorer optical properties of metals at these wavelengths. In this paper, we report the first fabrication and experimental verification of a transversely structured metal-dielectric-metal multilayer exhibiting a negative refractive index around 2 µm. Both the amplitude and the phase of the transmission and reflection were measured experimentally, and are in good agreement with a rigorous coupled wave analysis. PACS: 78.20.Ci; 42.25.Bs; 42.79.Dj Negative refractive-index materials are of great interest for a variety of potential applications. 1 Because natural negative refractive index materials do not exist, artificial structures have been proposed and fabricated that exhibit an effective negative index over limited frequency ranges. 2 The two principal approaches to the realization of negative refraction are metamaterials and photonic crystals. Metamaterials typically use metallic structures to provide a negative permittivity and use resonant structures (inductor-capacitor tank circuits) with a scale much smaller than the wavelength to provide a negative permeability leading to negative refraction, while § Email: brueck@chtm.unm.edu photonic crystals exhibit negative refraction as a consequence of band-folding effects. In the microwave region, negative index materials have been demonstrated using both approaches, while in the visible spectral region, negative refraction has been recently predicted. 3 In recent work, magnetically resonant structures exhibiting negative permeability have been demonstrated in the mid-infrared. 4,5 Despite theoretical studies and numerical modeling, 6,7 demonstration of negative refraction at near-infrared (near-IR) and visible wavelengths is as yet missing and, therefore, the experimental demonstration of a negative refractive index around 2 µm presented here represents an important milestone.Extension of metamaterials based on split ring resonators 8 to near-IR and visible wavelengths necessarily involves complicated and often difficult fabrication for the nanoscale metallic structures used to generate the requisite resonances. On the other hand, much of the photonic crystal literature has focused on all-dielectric structures because of their low-loss characteristics.Recent related work has used periodic metallic structures to couple incident radiation to surface plasma waves giving enhanced optical transmission through arrays of sub-wavelength holes in a metal film. 9,10 In this work, a hybrid approach is introduced which uses a pair of metal layers separated by a dielectric to provide resonant interactions (e. g. distributed inductance/capacitance) along with a periodic array of holes through the film stack to facilitate interaction with the surface plasma waves of the composite structure.The structure consists of a glass subs...

Metamaterials: a new frontier of science and technology

“…19 These challenges impelled researchers to seek alternative designs other than the combination of metallic wires and SRRs. The most successful optical NIMs so far are the fishnet structure, [20][21][22] which consists of two layers of metal meshes separated by a dielectric spacer layer ( Fig. 4(b)).…”

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 .…”

Hybridization effect in coupled metamaterials

“…Shalaev and colleagues found that such nanorod pairs could also be used to produce MP resonance and negative refraction at the optical communication wavelength of 1.5 μm [18,19]. Almost at the same time, S. Zhang et al proposed a double-fishnet structure to obtain negative refraction at about 2 μm [20]. Although Shalaev and S. Zhang verified that their structures possessed a negative refraction index by measuring the phase difference of the transmitted waves, they could not directly observe the negative refraction in their monolayer metamaterial structures.…”

“…In the optical frequency range, fishnet structures are well-known magnetic metamaterials [20], constructed by a metal/insulator/metal (MIM) sandwich with perforated periodic nanohole arrays, schematically shown in Figure 9. This structure can somewhat be regarded as an extension of the metal film perforated with nanoholes that exhibits well-known extraordinary optical transmission (EOT) discovered by T. W. Ebessen in 1998 [78].…”