Experimental demonstration of spectrally broadband Huygens sources using low-index spheres

We show that the anti-reflection performance of nano-particle arrays on top of solar cell stacks is related to two conditions: a high enough degree of discrete rotational symmetry of the array and the ability of the system to suppress cross-talk between the two handednesses (helicities) of the electromagnetic field upon light-matter interaction.For particle-lattice systems with high enough degree of discrete rotational symmetry 2π/n for n ≥ 3), our numerical studies link the suppression of backscattering to the ability of the system to avoid the mixing between the two helicity components of the incident field. In an exemplary design, we optimize an array of TiO 2 disks placed on top of a flat heterojunction solar cell stack and obtain a three-fold reduction of the current 1 arXiv:1902.07546v3 [physics.optics] 5 Jun 2019 loss due to reflection with respect to an optimized flat reference. We numerically analyze the helicity preservation properties of the system, and also show that a hexagonal array lattice, featuring a higher degree of discrete rotational symmetry, can improve over the anti-reflection performance of a square lattice. Importantly, the disks are introduced in an electrically decoupled manner such that the passivation and electric properties of the device are not disturbed. IntroductionMinimal reflection is an obvious design goal in solar cell technology which attracts much research attention. Different approaches to anti-reflection (AR) range from chemical texturing of the silicon waver 1,2 to sophisticated AR coatings 3-7 and plasmonic structures 8-10 .Recently, the use of arrays of dielectric nano-structures is being investigated as a possible avenue to improve AR properties of solar cells [11][12][13][14][15][16] . Due to the low profiles of the patterning nanostructures, this approach is suitable for ultra thin film solar cells. Clearly, understanding the underlying physical principles behind backscattering minimization is relevant for the AR aspect of solar cell design.Much of the nanophotonics research on backscattering minimization stems from the 1983 article of Kerker et al. 17 . This early work showed that a sphere whose relative electric permittivity and magnetic permeability are equal exhibits zero backscattering under plane wave illumination, i.e., there is no energy in the specular back reflection direction, independently of the polarization of the illuminating plane wave. Since then, the theoretical and experimental works on zero backscattering have been numerous, see e.g. Refs. 18-26. On the theoretical side, the relationship between electromagnetic duality symmetry and zero backscattering 18,20,27 has provided a new point of view on Kerker's result by connecting the backscattering suppression to a fundamental symmetry in electromagnetism. A system is symmetric under duality transformations 29 if and only if its electric and magnetic responses to incident radiation are equivalent. This equivalence connects directly to Kerker's = µ

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“…39 The alignment of different resonances can then increase the helicity preserving bandwidth. 26,40 4 Methods…”

Section: Discussionmentioning

confidence: 99%

Insights into Backscattering Suppression in Solar Cells from the Helicity-Preservation Point of View

et al. 2019

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“…40 Thus far, the Huygens source has attracted extensive attention for production of unidirectional far-field antennas. 41,42 Based on this far-field property, efficient Huygens metasurfaces with arbitrary EM wave fronts have recently been proposed for all-dielectric [43][44][45][46] and actively controlled systems. 47 Specifically, Picardi et al 48 theoretically revealed the near-field directionality of a Huygens dipole.…”

Section: Introductionmentioning

confidence: 99%

Anomalous unidirectional excitation of high-k hyperbolic modes using all-electric metasources

et al. 2021

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The unidirectional excitation of near-field optical modes is a fundamental prerequisite for many photonic applications, such as wireless power transfer and information communications. We experimentally construct all-electric Huygens and spin metasources and demonstrate anomalous unidirectional excitation of high-k hyperbolic modes in two types of hyperbolic metasurfaces. We use a Huygens metasource to study the unidirectional excitation of hyperbolic bulk modes in a planar hyperbolic metamaterial (HMM). Specifically, unidirectional excitation is the same as that in free space in the vertical direction, but opposite to that in free space in the horizontal direction. This anomalous unidirectional excitation is determined by the anisotropic HMM dispersion. In addition, we use a spin metasource to observe the anomalous photonic spin Hall effect in a planar hyperbolic waveguide. For a near-field source with a specific spin, the guide mode with a fixed directional wave vector is excited due to spin-momentum locking. Because the directions of momentum and energy flows in the HMM waveguide are opposite, the unidirectional excitation of hyperbolic guided modes is reversed. Our results not only uncover the sophisticated electromagnetic functionalities of metasources in the near-field but may also provide novel opportunities for the development of integrated optical devices.

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“…This approach has already been proven successful in predicting some different effects that the two properties can have in light–matter interactions. [ 36–38 ]…”

Section: Introductionmentioning

confidence: 99%

Directional Coupling of Emitters into Waveguides: A Symmetry Perspective

Lamprianidis

Zambrana‐Puyalto

Rockstuhl

et al. 2021

Laser & Photonics Reviews

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Recent experiments demonstrate strongly directional coupling of light into waveguide modes. Here, the symmetry mechanisms behind this effect are studied, and it is shown that the analysis of the symmetries and symmetry‐breakings of the emitter‐waveguide system allows to qualitatively understand directional coupling in several situations. The authors consider emitters either centered in a median plane of the waveguide, or displaced from it, and whose emissions have a well‐defined angular momentum in either one of the two different axis typically chosen experimentally, which are called transverse and vertical. These insights are matched by simulations, and previous experimental measurements. It is shown that handedness plays a secondary role in directional coupling. The spin‐momentum locking concept is generalized to an exponentially strong locking between the transverse angular momentum and the preferential coupling direction. A new selection rule is obtained that controls the coupling of electric(magnetic) multipolar emissions into waveguide modes. An experiment is proposed featuring a transverse magnetic bias that aggregates the directional emissions from many quantum dots on top of waveguides, in contrast to the typically used vertical bias, which effectively restricts experiments to using a single quantum dot. Finally, the Huygens' dipole is analyzed and the symmetries that enable its directional behavior revealed.

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Experimental demonstration of spectrally broadband Huygens sources using low-index spheres

Cited by 20 publications

References 44 publications

Insights into Backscattering Suppression in Solar Cells from the Helicity-Preservation Point of View

Insights into Backscattering Suppression in Solar Cells from the Helicity-Preservation Point of View

Anomalous unidirectional excitation of high-k hyperbolic modes using all-electric metasources

Directional Coupling of Emitters into Waveguides: A Symmetry Perspective

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