A Helical Metamaterial for Broadband Circular Polarization Conversion

Kaschke, Johannes; Blume, Leonard; Wu, Lin; Thiel, Michael; Bade, K.; Yang, Zhenyu; Wegener, Martin

doi:10.1002/adom.201500194

Cited by 158 publications

(110 citation statements)

References 49 publications

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“…Recently, a novel design based on helical metamaterials has been introduced [65]. The design consists of two gold helices with opposing handedness connected by a small arc as depicted in Figure 9(a).…”

Section: Circular Polarization Convertermentioning

confidence: 99%

Optical and Infrared Helical Metamaterials

Kaschke

Wegener

2016

Nanophotonics

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By tailoring metamaterials with chiral unit cells, giant optical activity and strong circular dichroism have been achieved successfully over the past decade. Metamaterials based on arrays of metal helices have revolutionized the field of chiral metamaterials, because of their capability of exhibiting these pronounced chiro-optical effects over previously unmatched bandwidths. More recently, a large number of new metamaterial designs based on metal helices have been introduced with either optimized optical performance or other chiro-optical properties for novel applications. The fabrication of helical metamaterials is, however, challenging and even more so with growing complexity of the metamaterial designs. As conventional two-dimensional nanofabrication methods, for example, electron-beam lithography, are not well suited for helical metamaterials, the development of novel three-dimensional fabrication approaches has been triggered. Here, we will discuss the theory for helical metamaterials and the principle of operation. We also review advancements in helical metamaterial design and their limitations and influence on optical performance. Furthermore, we will compare novel nano-and microfabrication techniques that have successfully yielded metallic helical metamaterials. Finally, we also discuss recently presented applications of helical metamaterials extending beyond the use of far-field circular polarizers.

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Section: Circular Polarization Convertermentioning

confidence: 99%

Optical and Infrared Helical Metamaterials

Kaschke

Wegener

2016

Nanophotonics

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“…This makes them attractive for applications involving CPL. [6,8,[37][38][39] Thus, the nonlinear optical response of helical metamaterials is of particular interest as they already demonstrate strong linear chiroptical effects. However, until recently it has been very difficult to fabricate high quality helical metamaterials for use at optical frequencies.…”

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confidence: 99%

Strong Rotational Anisotropies Affect Nonlinear Chiral Metamaterials

et al. 2017

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complications as the technique can become too sensitive, making it difficult to separate the desirable and undesirable contributions to the SHG signal. An example of an undesirable complication is extrinsic chirality, [15,16] which affects the nonlinear susceptibility tensor components in SHG. [17,18] Any anisotropy present in the sample can have a similar effect and our work here focuses on highlighting the effects of rotational anisotropy. We begin by selecting the sample geometry.Chirality is intrinsically a 3D property; however, a great number of works have focused on so-called "planar" nanostructures. A few recent examples include S-shaped nanostructures, [19,20] three-and fourfold symmetric propellers, [21] and heptamers. [22] These planar chiral nanostructures are very attractive because of their ease of fabrication with electron beam lithography. The necessary 3D symmetry-breaking arises from a dissymmetry along the axis perpendicular to the sample plane, [23] for instance, due to the presence of a substrate on one side of the sample and air on the other. Although planar meta/nanomaterials are thus 3D, it is clear that their threedimensionality is not very pronounced. At optical frequencies, various 3D structured meta/nanomaterials have been proposed, such as rosettes, [24,25] twisted arcs, [26] 3D shuriken, [27] stacked split rings, [28,29] oligomers, [30,31] gyroids, [32] and helices. [33][34][35][36] Of all these examples, the latter (i.e., the helix) is the archetypical chiral structure. The strong interaction of nanohelices with circularly polarized light (CPL) gives rise to large chiroptical effects, such as circular dichroism. This makes them attractive for applications involving CPL. [6,8,[37][38][39] Thus, the nonlinear optical response of helical metamaterials is of particular interest as they already demonstrate strong linear chiroptical effects. However, until recently it has been very difficult to fabricate high quality helical metamaterials for use at optical frequencies. Herein, we have investigated a chiral metamaterial made of nanohelices, with substantially subwavelength dimensions (<λ/10). As the archetypical chiral geometry, the helical design is particularly suitable because it is pronouncedly 3D, it gives rise directly to superchiral field configurations along the center of the helix, and its structural chirality parameter is straightforward to estimate as a function of varying dimensions. [33,40] Within this metamaterial, we clearly identify three different rotational anisotropies and demonstrate how they can mask the true chiral effect, rendering the SHG-CD signals unreliable. Our experimental results highlight the need for a general method to extract the true chiral contributions to the SHG signal. Here, we use a method for approximating these contributions. Although not fully rigorous, this method yields three measures of the chirality: averaged SHG-CD, direct inspection of the chiral component of the effective susceptibility tensor, and evaluation of the chiral coefficients tha...

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“…Metamaterials with the chirality, referred to as * ueda@kit.ac.jp chiral metamaterials, determine the macroscopic constitutive relations of the effective media including not only permittivity and permeability but also chirality for bi-anisotropic media, by appropriately designing meta-atoms [26][27][28][29][30][31][32][33][34]. So far, various applications of the chiral metamaterials have been proposed and demonstrated [35][36][37][38][39]. However, little is known about the edgelike mode propagation in the chiral metamaterials at the operation frequencies far below the photonic band gaps due to the Bragg scattering.…”

Section: Introductionmentioning

confidence: 99%

Observation of asymmetric electromagnetic field profiles in chiral metamaterials

et al. 2018

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We experimentally observe asymmetric electromagnetic field profiles along two-dimensional chiral metamaterials. The asymmetric field profiles depending on the chirality and the operation frequency have been reproduced well by the numerical simulation. Around a chiral meta-atom, distribution of a Poynting vector is found to be shifted asymmetrically. These results are explained in terms of an analogy with the side-jump mechanism in the electronic anomalous Hall systems.

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A Helical Metamaterial for Broadband Circular Polarization Conversion

Cited by 158 publications

References 49 publications

Optical and Infrared Helical Metamaterials

Optical and Infrared Helical Metamaterials

Strong Rotational Anisotropies Affect Nonlinear Chiral Metamaterials

Observation of asymmetric electromagnetic field profiles in chiral metamaterials

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