Realization of broadband negative refraction in visible range using vertically stacked hyperbolic metamaterials

Bang, Sanghun; So, Sunae; Rho, Junsuk

doi:10.1038/s41598-019-50434-3

Cited by 48 publications

(41 citation statements)

References 45 publications

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“…Previous works have discussed the dependence of the effective properties on the metamaterial thickness, this is, on the number of MIM cavities composing the structure. [ 29,32–34 ] It has been shown that by reaching a minimum number of stacked layers, the multilayered fishnet metamaterials converge to the so‐known bulk metamaterial regime. [ 28,35 ] At this limit, metamaterials present unambiguous effective properties independently of the number of unit cells or the angle of incidence, exhibiting weak angular dispersion.…”

Section: Resultsmentioning

confidence: 99%

Electrodeposited Negative Index Metamaterials with Visible and Near Infrared Response

Gómez‐Castaño

Garcia‐Pomar

Pérez

et al. 2020

Advanced Optical Materials

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by the geometry rather than the constituent materials, which led to the field of metamaterials. Over the last decades, metamaterials research has grown exponentially due to the exceptional possibilities that they offer to manipulate light. Examples of extraordinary properties include artificial chirality, [1] super absorption, [2] extraordinary optical transmission, [3] optical magnetism, [4] or negative refraction. [5] From the several reported structures for achieving negative index metamaterials (NIMs) at optical frequencies, the multilayer fishnet design stands out as the most promising architecture in terms of tunability, figure of merit (FOM), and strong negative values. [6] Its design lies on metal-insulator-metal (MIM) stacks drilled with a 2D periodic array of holes. When the metallic layers are close enough, the propagating surface plasmon polaritons (SPPs) at the internal interfaces overlap, leading to the excitation of so-called gap surface plasmons (GSPs). [7] In this situation, out-of-phase currents are generated in the metallic strips, inducing a magnetic dipole in the insulator layer. This artificial magnetism along with the electric response arising from the metallic layers are the source of the negative refractive index (RI). [8] In the recent years, there has been an increasing interest in the commercial applications of metamaterials. However, the implementation of these architectures in an actual device is not an easy task. Recent advances in nanofabrication have enabled the high-throughput and up scalable production of NIMs using patterning methods such as self-assembly [9-11] or nanoimprint lithography (NIL), [12,13] where the proper arrangement gave rise to negative index at optical frequencies. In particular, the inspiring works by Gao et al. [13] demonstrated large area metamaterials operating at visible and telecommunication frequencies using a subtractive lift-off process combined with metal evaporation and reactive ion etching. Despite the scalability of the patterning techniques used in these works, most of them involve several steps, make use of top-down expensive methods such as electron beam evaporation or implies transferring steps that can damage the structures. In terms of the absolute values achieved, there is still room for improvement for large area NIMs. A record value of −0.73 at 710 nm being the lowest negative refractive index achieved in the visible range with an scalable technique so far. [13] It is also worth noting that obtaining NIMs with a negligible angular Negative index metamaterials have revolutionized the field of photonics because of their unconventional electromagnetic properties absent in naturally occurring materials. It remains a challenge however, to achieve strong negative refractive index at optical frequencies over large areas in a device compatible fashion. In this work, a scalable method for the straightforward production of fishnet-like negative index metamaterials combining soft nanoimprinting and electrodeposition is reported. In four simple steps...

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Section: Resultsmentioning

confidence: 99%

Electrodeposited Negative Index Metamaterials with Visible and Near Infrared Response

Gómez‐Castaño

Garcia‐Pomar

Pérez

et al. 2020

Advanced Optical Materials

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“…BPPs with large wave vectors propagate into pre-designed bulk hyperbolic metamaterials (HMMs) [ 111 ]. HMMs composed of alternatively deposited metal/dielectric multilayers exhibit a hyperbolic dispersion instead of elliptical dispersion, allowing for a larger-area and uniform deep subwavelength pattern to be generated inside a photoresist [ 34 , 112 ]. So far, 45 nm and 25 nm resolutions of half-pitch (

and

) have been fabricated and simulated with different interference patterns, respectively [ 113 ].…”

Section: Optical Methodsmentioning

confidence: 99%

Scalable and High-Throughput Top-Down Manufacturing of Optical Metasurfaces

Lee

et al. 2020

Sensors

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Metasurfaces have shown promising potential to miniaturize existing bulk optical components thanks to their extraordinary optical properties and ultra-thin, small, and lightweight footprints. However, the absence of proper manufacturing methods has been one of the main obstacles preventing the practical application of metasurfaces and commercialization. Although a variety of fabrication techniques have been used to produce optical metasurfaces, there are still no universal scalable and high-throughput manufacturing methods that meet the criteria for large-scale metasurfaces for device/product-level applications. The fundamentals and recent progress of the large area and high-throughput manufacturing methods are discussed with practical device applications. We systematically classify various top-down scalable patterning techniques for optical metasurfaces: firstly, optical and printing methods are categorized and then their conventional and unconventional (emerging/new) techniques are discussed in detail, respectively. In the end of each section, we also introduce the recent developments of metasurfaces realized by the corresponding fabrication methods.

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“…If each layer is sufficiently small compared to the working wavelength, a vertical HMM can be considered an anisotropic homogenous medium. The permittivities can be calculated using EMT expressed as [ 36,38,39 ]

ε_{false∥} = f ε_{normald} + false(1 - f false) ε_{normalm}

ε_{⊥} = \frac{ε_{normald} ε_{normalm}}{f ε_{normalm} + false(1 - f false) ε_{normald}}

where ɛ ∥ is the effective permittivity along the parallel direction of the layer, ɛ ⊥ is the effective permittivity along the perpendicular direction of the layer, ɛ d is the permittivity of the dielectric material, ɛ m is the permittivity of the metallic material, and f is the filling ratio of the dielectric to metal. However, if each layer is not sufficiently thin, complex optical phenomena appear at the interfaces such as reflection and diffraction.…”

Section: Numerical Analysismentioning

confidence: 99%

“…The dispersion relation of the vertical HMM for transverse‐magnetic (TM)‐polarized light is described as [ 36 ]

\frac{k_{x}^{2} + k_{y}^{2}}{ε_{⊥}} + \frac{k_{z}^{2}}{ε_{∥}} = k_{0}^{2} = {((), \frac{ω}{c})}^{2}

where k x , k y , k z are directional wave vectors in the HMM, k 0 is a wave vector in vacuum, ω is an angular frequency, and c is the speed of light in vacuum. The direction of ɛ ⊥ is parallel to the z ‐direction.…”

Section: Numerical Analysismentioning

confidence: 99%

“…The resonance limits the bandwidth of the working wavelength and induces high resistive losses. [ 36 ] Recently, vertical HMMs (vertical HMMs) have been proposed to overcome these limits. [ 36,37 ] Because the negative refraction in the vertical HMMs does not rely on resonance, the working wavelength range can be much wider with low resistive losses.…”

Section: Introductionmentioning

confidence: 99%

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Critical Layer Thickness Analysis of Vertically Stacked Hyperbolic Metamaterials for Effective Negative Refraction Generation

Cho

Badloe

et al. 2020

Advcd Theory and Sims

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Vertically stacked narrow metal‐dielectric multilayered structures known as vertical hyperbolic metamaterials (vertical HMMs) are proposed for broadband negative refraction. The thickness of each layer is required to be subwavelength for effective medium theory (EMT) to be applicable. Therefore, each layer should be thin, forcing the aspect ratio to become extremely high. This requirement makes the fabrication of vertical HMMs difficult. Thus, it is important to determine the limit of the layer thickness for the realization of vertical HMM. In this study, the critical layer thicknesses of vertical HMMs are investigated numerically at the wavelengths of 400, 500, 600, and 700 nm. It is concluded that the critical layer thicknesses for both vertical and horizontal HMMs depend on the permittivity along the perpendicular direction of the layers. The maximum critical layer thickness of vertical HMMs, with a value of 0.22, is produced by a structure composed of gold and silicon dioxide at the wavelength of 500 nm, while the critical layer thickness tends to be smaller if silver is employed. It is believed that this study can provide a useful database as quantitative indicators which can be exploited in designing nanostructures using EMT.

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Realization of broadband negative refraction in visible range using vertically stacked hyperbolic metamaterials

Cited by 48 publications

References 45 publications

Electrodeposited Negative Index Metamaterials with Visible and Near Infrared Response

Electrodeposited Negative Index Metamaterials with Visible and Near Infrared Response

Scalable and High-Throughput Top-Down Manufacturing of Optical Metasurfaces

Critical Layer Thickness Analysis of Vertically Stacked Hyperbolic Metamaterials for Effective Negative Refraction Generation

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