@article{26747,
  abstract     = {{Metasurfaces provide applications for a variety of flat elements and devices due to the ability to modulate light with subwavelength structures. The working principle meanwhile gives rise to the crucial problem and challenge to protect the metasurface from dust or clean the unavoidable contaminants during daily usage. Here, taking advantage of the intelligent bioinspired surfaces which exhibit self-cleaning properties, a versatile dielectric metasurface benefiting from the obtained superhydrophilic or quasi-superhydrophobic states is shown. The design is realized by embedding the metasurface inside a large area of wettability supporting structures, which is highly efficient in fabrication, and achieves both optical and wettability functionality at the same time. The superhydrophilic state enables an enhanced optical response with water, while the quasi-superhydrophobic state imparts the fragile antennas an ability to self-clean dust contamination. Furthermore, the metasurface can be easily switched and repeated between these two wettability or functional states by appropriate treatments in a repeatable way, without degrading the optical performance. The proposed design strategy will bring new opportunities to smart metasurfaces with improved optical performance, versatility, and physical stability.}},
  author       = {{Lu, Jinlong and Sain, Basudeb and Georgi, Philip and Protte, Maximilian and Bartley, Tim and Zentgraf, Thomas}},
  issn         = {{2195-1071}},
  journal      = {{Advanced Optical Materials}},
  number       = {{1}},
  publisher    = {{Wiley}},
  title        = {{{A Versatile Metasurface Enabling Superwettability for Self‐Cleaning and Dynamic Color Response}}},
  doi          = {{10.1002/adom.202101781}},
  volume       = {{10}},
  year         = {{2022}},
}

@article{30195,
  abstract     = {{While plasmonic particles can provide optical resonances in a wide spectral range from the lower visible up to the near-infrared, often, symmetry effects are utilized to obtain particular optical responses. By breaking certain spatial symmetries, chiral structures arise and provide robust chiroptical responses to these plasmonic resonances. Here, we observe strong chiroptical responses in the linear and nonlinear optical regime for chiral L-handed helicoid-III nanoparticles and quantify them by means of an asymmetric factor, the so-called g-factor. We calculate the linear optical g-factors for two distinct chiroptical resonances to −0.12 and –0.43 and the nonlinear optical g-factors to −1.45 and −1.63. The results demonstrate that the chirality of the helicoid-III nanoparticles is strongly enhanced in the nonlinear regime.}},
  author       = {{Spreyer, Florian and Mun, Jungho and Kim, Hyeohn and Kim, Ryeong Myeong and Nam, Ki Tae and Rho, Junsuk and Zentgraf, Thomas}},
  issn         = {{2330-4022}},
  journal      = {{ACS Photonics}},
  keywords     = {{Electrical and Electronic Engineering, Atomic and Molecular Physics, and Optics, Biotechnology, Electronic, Optical and Magnetic Materials}},
  number       = {{3}},
  pages        = {{784–792}},
  publisher    = {{American Chemical Society (ACS)}},
  title        = {{{Second Harmonic Optical Circular Dichroism of Plasmonic Chiral Helicoid-III Nanoparticles}}},
  doi          = {{10.1021/acsphotonics.1c00882}},
  volume       = {{9}},
  year         = {{2022}},
}

@article{29902,
  author       = {{Reineke Matsudo, Bernhard and Sain, Basudeb and Carletti, Luca and Zhang, Xue and Gao, Wenlong and Angelis, Costantino and Huang, Lingling and Zentgraf, Thomas}},
  issn         = {{2198-3844}},
  journal      = {{Advanced Science}},
  keywords     = {{General Physics and Astronomy, General Engineering, Biochemistry, Genetics and Molecular Biology (miscellaneous), General Materials Science, General Chemical Engineering, Medicine (miscellaneous)}},
  number       = {{12}},
  publisher    = {{Wiley}},
  title        = {{{Efficient Frequency Conversion with Geometric Phase Control in Optical Metasurfaces}}},
  doi          = {{10.1002/advs.202104508}},
  volume       = {{9}},
  year         = {{2022}},
}

@article{30964,
  author       = {{Gao, Wenlong and Sain, Basudeb and Zentgraf, Thomas}},
  issn         = {{2331-7019}},
  journal      = {{Physical Review Applied}},
  keywords     = {{General Physics and Astronomy}},
  number       = {{4}},
  publisher    = {{American Physical Society (APS)}},
  title        = {{{Spin-Orbit Interaction of Light Enabled by Negative Coupling in High-Quality-Factor Optical Metasurfaces}}},
  doi          = {{10.1103/physrevapplied.17.044022}},
  volume       = {{17}},
  year         = {{2022}},
}

@inproceedings{34465,
  author       = {{laeim, Huddad and Schlickriede, Christian and Chaisakul, Papichaya and Chattham, Nattaporn and Panitchakan, Hathai and Siangchaew, Krisda and Zentgraf, Thomas and Pattanaporhratana, Apichart}},
  booktitle    = {{Metamaterials, Metadevices, and Metasystems 2022}},
  editor       = {{Engheta, Nader and Noginov, Mikhail A. and Zheludev, Nikolay I.}},
  publisher    = {{SPIE}},
  title        = {{{Design and investigation of a metalens for efficiency enhancement of laser-waveguide coupling in a limited space system}}},
  doi          = {{10.1117/12.2629789}},
  year         = {{2022}},
}

@article{31480,
  abstract     = {{Optical geometric phase encoded by in-plane spatial orientation of microstructures has promoted the rapid development of numerous functional meta-devices. However, pushing the concept of the geometric phase toward the acoustic community still faces challenges. In this work, we utilize two acoustic nonlocal metagratings that could support a direct conversion between an acoustic plane wave and a designated vortex mode to obtain the acoustic geometric phase, in which an orbital angular momentum conversion process plays a vital role. In addition, we realize the acoustic geometric phases of different orders by merely varying the orientation angle of the acoustic nonlocal metagratings. Intriguingly, according to our developed theory, we reveal that the reflective acoustic geometric phase, which is twice the transmissive one, can be readily realized by transferring the transmitted configuration to a reflected one. Both the theoretical study and experimental measurements verify the announced transmissive and reflective acoustic geometric phases. Moreover, the reconfigurability and continuous phase modulation that covers the 2π range shown by the acoustic geometric phases provide us with the alternatives in advanced acoustic wavefront control.}},
  author       = {{Liu, Bingyi and Zhou, Zhiling and Wang, Yongtian and Zentgraf, Thomas and Li, Yong and Huang, Lingling}},
  issn         = {{0003-6951}},
  journal      = {{Applied Physics Letters}},
  keywords     = {{Physics and Astronomy (miscellaneous)}},
  number       = {{21}},
  publisher    = {{AIP Publishing}},
  title        = {{{Experimental verification of the acoustic geometric phase}}},
  doi          = {{10.1063/5.0091474}},
  volume       = {{120}},
  year         = {{2022}},
}

@article{28254,
  abstract     = {{With the rapid advances of functional dielectric metasurfaces and their integration on on-chip nanophotonic devices, the necessity of metasurfaces working in different environments, especially in biological applications, arose. However, the metasurfaces’ performance is tied to the unit cell’s efficiency and ultimately the surrounding environment it was designed for, thus reducing its applicability if exposed to altering refractive index media. Here, we report a method to increase a metasurface’s versatility by covering the high-index metasurface with a low index porous SiO2 film, protecting the metasurface from environmental changes while keeping the working efficiency unchanged. We show, that a covered metasurface retains its functionality even when exposed to fluidic environments.}},
  author       = {{Geromel, René and Weinberger, Christian and Brormann, Katja and Tiemann, Michael and Zentgraf, Thomas}},
  issn         = {{2159-3930}},
  journal      = {{Optical Materials Express}},
  number       = {{1}},
  pages        = {{13--21}},
  publisher    = {{Optica}},
  title        = {{{Porous SiO2 coated dielectric metasurface with consistent performance independent of environmental conditions}}},
  doi          = {{10.1364/ome.444264}},
  volume       = {{12}},
  year         = {{2022}},
}

@article{32068,
  abstract     = {{Inspired by plant grafting, grafted vortex beams can be formed through grafting two or more helical phase profiles of optical vortex beams. Recently, grafted perfect vortex beams (GPVBs) have attracted much attention due to their unique optical properties and potential applications. However, the current method to generate and manipulate GPVBs requires a complex and bulky optical system, hindering further investigation and limiting its practical applications. Here, a compact metasurface approach for generating and manipulating GPVBs in multiple channels is proposed and demonstrated, which eliminates the need for such a complex optical setup. A single metasurface is utilized to realize various superpositions of GPVBs with different combinations of topological charges in four channels, leading to asymmetric singularity distributions. The positions of singularities in the superimposed beam can be further modulated by introducing an initial phase difference in the metasurface design. The work demonstrates a compact metasurface platform that performs a sophisticated optical task that is very challenging with conventional optics, opening opportunities for the investigation and applications of GPVBs in a wide range of emerging application areas, such as singular optics and quantum science.}},
  author       = {{Ahmed, Hammad and Intaravanne, Yuttana and Ming, Yang and Ansari, Muhammad Afnan and Buller, Gerald S. and Zentgraf, Thomas and Chen, Xianzhong}},
  issn         = {{0935-9648}},
  journal      = {{Advanced Materials}},
  keywords     = {{Mechanical Engineering, Mechanics of Materials, General Materials Science}},
  number       = {{30}},
  publisher    = {{Wiley}},
  title        = {{{Multichannel Superposition of Grafted Perfect Vortex Beams}}},
  doi          = {{10.1002/adma.202203044}},
  volume       = {{34}},
  year         = {{2022}},
}

@inproceedings{46484,
  abstract     = {{Efficient third-harmonic generation control is theoretically studied. Dielectric nanostructures placed on the metallic substrate could offer effective geometric-phase modulation on third-harmonic signals by selecting proper structure rotational symmetry.}},
  author       = {{Liu, Bingyi and Huang, Lingling and Zentgraf, Thomas}},
  booktitle    = {{Conference on Lasers and Electro-Optics}},
  location     = {{San Jose, USA}},
  publisher    = {{Optica Publishing Group}},
  title        = {{{Efficient Third-harmonic Generation Control with Ultrathin Dielectric Geometric-phase Metasurface}}},
  doi          = {{10.1364/cleo_qels.2022.fth1a.7}},
  year         = {{2022}},
}

@article{32088,
  abstract     = {{Subwavelength dielectric resonators assembled into metasurfaces have become a versatile tool for miniaturizing optical components approaching the nanoscale. An important class of metasurface functionalities is associated with asymmetry in both the generation and transmission of light with respect to reversals of the positions of emitters and receivers. The nonlinear light–matter interaction in metasurfaces offers a promising pathway towards miniaturization of the asymmetric control of light. Here we demonstrate asymmetric parametric generation of light in nonlinear metasurfaces. We assemble dissimilar nonlinear dielectric resonators into translucent metasurfaces that produce images in the visible spectral range on being illuminated by infrared radiation. By design, the metasurfaces produce different and completely independent images for the reversed direction of illumination, that is, when the positions of the infrared emitter and the visible light receiver are exchanged. Nonlinearity-enabled asymmetric control of light by subwavelength resonators paves the way towards novel nanophotonic components via dense integration of large quantities of nonlinear resonators into compact metasurface designs.}},
  author       = {{Kruk, Sergey S. and Wang, Lei and Sain, Basudeb and Dong, Zhaogang and Yang, Joel and Zentgraf, Thomas and Kivshar, Yuri}},
  issn         = {{1749-4885}},
  journal      = {{Nature Photonics}},
  keywords     = {{Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials}},
  pages        = {{561–565}},
  publisher    = {{Springer Science and Business Media LLC}},
  title        = {{{Asymmetric parametric generation of images with nonlinear dielectric metasurfaces}}},
  doi          = {{10.1038/s41566-022-01018-7}},
  volume       = {{16}},
  year         = {{2022}},
}

@article{25605,
  abstract     = {{The nonlinear process of second harmonic generation (SHG) in monolayer (1L) transition metal dichalcogenides (TMD), like WS2, strongly depends on the polarization state of the excitation light. By combination of plasmonic nanostructures with 1L-WS2 by transferring it onto a plasmonic nanoantenna array, a hybrid metasurface is realized impacting the polarization dependency of its SHG. Here, we investigate how plasmonic dipole resonances affect the process of SHG in plasmonic–TMD hybrid metasurfaces by nonlinear spectroscopy. We show that the polarization dependency is affected by the lattice structure of plasmonic nanoantenna arrays as well as by the relative orientation between the 1L-WS2 and the individual plasmonic nanoantennas. In addition, such hybrid metasurfaces show SHG in polarization states, where SHG is usually forbidden for either 1L-WS2 or plasmonic nanoantennas. By comparing the SHG in these channels with the SHG generated by the hybrid metasurface components, we detect an enhancement of the SHG signal by a factor of more than 40. Meanwhile, an attenuation of the SHG signal in usually allowed polarization states is observed. Our study provides valuable insight into hybrid systems where symmetries strongly affect the SHG and enable tailored SHG in 1L-WS2 for future applications.}},
  author       = {{Spreyer, Florian and Ruppert, Claudia and Georgi, Philip and Zentgraf, Thomas}},
  issn         = {{1936-0851}},
  journal      = {{ACS Nano}},
  number       = {{10}},
  pages        = {{16719--16728}},
  title        = {{{Influence of Plasmon Resonances and Symmetry Effects on Second Harmonic Generation in WS2–Plasmonic Hybrid Metasurfaces}}},
  doi          = {{10.1021/acsnano.1c06693}},
  volume       = {{15}},
  year         = {{2021}},
}

@article{21631,
  abstract     = {{<jats:p>Secret sharing is a well-established cryptographic primitive for storing highly sensitive information like encryption keys for encoded data. It describes the problem of splitting a secret into different shares, without revealing any information to its shareholders. Here, we demonstrate an all-optical solution for secret sharing based on metasurface holography. In our concept, metasurface holograms are used as spatially separable shares that carry encrypted messages in the form of holographic images. Two of these shares can be recombined by bringing them close together. Light passing through this stack of metasurfaces accumulates the phase shift of both holograms and optically reconstructs the secret with high fidelity. In addition, the hologram generated by each single metasurface can uniquely identify its shareholder. Furthermore, we demonstrate that the inherent translational alignment sensitivity between two stacked metasurface holograms can be used for spatial multiplexing, which can be further extended to realize optical rulers.</jats:p>}},
  author       = {{Georgi, Philip and Wei, Qunshuo and Sain, Basudeb and Schlickriede, Christian and Wang, Yongtian and Huang, Lingling and Zentgraf, Thomas}},
  issn         = {{2375-2548}},
  journal      = {{Science Advances}},
  number       = {{16}},
  title        = {{{Optical secret sharing with cascaded metasurface holography}}},
  doi          = {{10.1126/sciadv.abf9718}},
  volume       = {{7}},
  year         = {{2021}},
}

@article{22215,
  abstract     = {{Topological states of light represent counterintuitive optical modes localized at boundaries of finite-size optical structures that originate from the properties of the bulk. Being defined by bulk properties, such boundary states are insensitive to certain types of perturbations, thus naturally enhancing robustness of photonic circuitries. Conventionally, the N-dimensional bulk modes correspond to (N – 1)-dimensional boundary states. The higher-order bulk-boundary correspondence relates N-dimensional bulk to boundary states with dimensionality reduced by more than 1. A special interest lies in miniaturization of such higher-order topological states to the nanoscale. Here, we realize nanoscale topological corner states in metasurfaces with C6-symmetric honeycomb lattices. We directly observe nanoscale topology-empowered edge and corner localizations of light and enhancement of light–matter interactions via a nonlinear imaging technique. Control of light at the nanoscale empowered by topology may facilitate miniaturization and on-chip integration of classical and quantum photonic devices.}},
  author       = {{Kruk, Sergey S. and Gao, Wenlong and Choi, Duk-Yong and Zentgraf, Thomas and Zhang, Shuang and Kivshar, Yuri}},
  issn         = {{1530-6984}},
  journal      = {{Nano Letters}},
  number       = {{11}},
  pages        = {{4592–4597}},
  publisher    = {{ACS}},
  title        = {{{Nonlinear Imaging of Nanoscale Topological Corner States}}},
  doi          = {{10.1021/acs.nanolett.1c00449}},
  volume       = {{21}},
  year         = {{2021}},
}

@article{22450,
  abstract     = {{We realize and investigate a nonlinear metasurface taking advantage of intersubband transitions in ultranarrow GaN/AlN multi-quantum well heterostructures. Owing to huge band offsets, the structures offer resonant transitions in the telecom window around 1.55 µm. These heterostructures are functionalized with an array of plasmonic antennas featuring cross-polarized resonances at these near-infrared wavelengths and their second harmonic. This kind of nonlinear metasurface allows for substantial second-harmonic generation at normal incidence which is completely absent for an antenna array without the multi-quantum well structure underneath. While the second harmonic is originally radiated only into the plane of the quantum wells, a proper geometrical arrangement of the plasmonic elements permits the redirection of the second-harmonic light to free-space radiation, which is emitted perpendicular to the surface.}},
  author       = {{Mundry, Jan and Spreyer, Florian and Jmerik, Valentin and Ivanov, Sergey and Zentgraf, Thomas and Betz, Markus}},
  issn         = {{2159-3930}},
  journal      = {{Optical Materials Express}},
  number       = {{7}},
  publisher    = {{OSA}},
  title        = {{{Nonlinear metasurface combining telecom-range intersubband transitions in GaN/AlN quantum wells with resonant plasmonic antenna arrays}}},
  doi          = {{10.1364/ome.426236}},
  volume       = {{11}},
  year         = {{2021}},
}

@article{22723,
  author       = {{Yoon, Gwanho and Tanaka, Takuo and Zentgraf, Thomas and Rho, Junsuk}},
  issn         = {{0022-3727}},
  journal      = {{Journal of Physics D: Applied Physics}},
  title        = {{{Recent progress on metasurfaces: applications and fabrication}}},
  doi          = {{10.1088/1361-6463/ac0faa}},
  volume       = {{54}},
  year         = {{2021}},
}

@article{28255,
  abstract     = {{Topological photonic crystals (TPhCs) provide robust manipulation of light with built-in immunity to fabrication tolerances and disorder. Recently, it was shown that TPhCs based on weak topology with a dislocation inherit this robustness and further host topologically protected lower-dimensional localized modes. However, TPhCs with weak topology at optical frequencies have not been demonstrated so far. Here, we use scattering-type scanning near-field optical microscopy to verify mid-bandgap zero-dimensional light localization close to 100 THz in a TPhC with nontrivial Zak phase and an edge dislocation. We show that because of the weak topology, differently extended dislocation centers induce similarly strong light localization. The experimental results are supported by full-field simulations. Along with the underlying fundamental physics, our results lay a foundation for the application of TPhCs based on weak topology in active topological nanophotonics, and nonlinear and quantum optic integrated devices because of their strong and robust light localization.}},
  author       = {{Lu, Jinlong and Wirth, Konstantin G. and Gao, Wenlong and Heßler, Andreas and Sain, Basudeb and Taubner, Thomas and Zentgraf, Thomas}},
  issn         = {{2375-2548}},
  journal      = {{Science Advances}},
  number       = {{49}},
  title        = {{{Observing 0D subwavelength-localized modes at ~100 THz protected by weak topology}}},
  doi          = {{10.1126/sciadv.abl3903}},
  volume       = {{7}},
  year         = {{2021}},
}

@article{26987,
  abstract     = {{Optical metasurfaces are perfect candidates for the phase and amplitude modulation of light, featuring an excellent basis for holographic applications. In this work, we present a dual amplitude holographic scheme based on the photon sieve principle, which is then combined with a phase hologram by utilizing the Pancharatnam–Berry phase. We demonstrate that two types of apertures, rectangular and square shapes in a gold film filled with silicon nanoantennas are sufficient to create two amplitude holograms at two different wavelengths in the visible, multiplexed with an additional phase-only hologram. The nanoantennas are tailored to adjust the spectral transmittance of the apertures, enabling the wavelength sensitivity. The phase-only hologram is implemented by utilizing the anisotropic rectangular structure. Interestingly, such three holograms have quantitative mathematical correlations with each other. Thus, the flexibility of polarization and wavelength channels can be utilized with custom-tailored features to achieve such amplitude and phase holography simultaneously without sacrificing any space-bandwidth product. The present scheme has the potential to store different pieces of information which can be displayed separately by switching the wavelength or the polarization state of the reading light beam.}},
  author       = {{Frese, Daniel and Sain, Basudeb and Zhou, Hongqiang and Wang, Yongtian and Huang, Lingling and Zentgraf, Thomas}},
  issn         = {{2192-8614}},
  journal      = {{Nanophotonics}},
  number       = {{18}},
  pages        = {{4543--4550}},
  publisher    = {{De Gruyter}},
  title        = {{{A wavelength and polarization selective photon sieve for holographic applications}}},
  doi          = {{10.1515/nanoph-2021-0440}},
  volume       = {{10}},
  year         = {{2021}},
}

@article{25227,
  abstract     = {{<jats:title>Abstract</jats:title><jats:p>Quantum well (QW) heterostructures have been extensively used for the realization of a wide range of optical and electronic devices. Exploiting their potential for further improvement and development requires a fundamental understanding of their electronic structure. So far, the most commonly used experimental techniques for this purpose have been all-optical spectroscopy methods that, however, are generally averaging in momentum space. Additional information can be gained by angle-resolved photoelectron spectroscopy (ARPES), which measures the electronic structure with momentum resolution. Here we report on the use of extremely low-energy ARPES (photon energy ~ 7 eV) to increase depth sensitivity and access buried QW states, located at 3 nm and 6 nm below the surface of cubic-GaN/AlN and GaAs/AlGaAs heterostructures, respectively. We find that the QW states in cubic-GaN/AlN can indeed be observed, but not their energy dispersion, because of the high surface roughness. The GaAs/AlGaAs QW states, on the other hand, are buried too deep to be detected by extremely low-energy ARPES. Since the sample surface is much flatter, the ARPES spectra of the GaAs/AlGaAs show distinct features in momentum space, which can be reconducted to the band structure of the topmost surface layer of the QW structure. Our results provide important information about the samples’ properties required to perform extremely low-energy ARPES experiments on electronic states buried in semiconductor heterostructures.</jats:p>}},
  author       = {{Hajlaoui, Mahdi and Ponzoni, Stefano and Deppe, Michael and Henksmeier, Tobias and As, Donat Josef and Reuter, Dirk and Zentgraf, Thomas and Springholz, Gunther and Schneider, Claus Michael and Cramm, Stefan and Cinchetti, Mirko}},
  issn         = {{2045-2322}},
  journal      = {{Scientific Reports}},
  title        = {{{Extremely low-energy ARPES of quantum well states in cubic-GaN/AlN and GaAs/AlGaAs heterostructures}}},
  doi          = {{10.1038/s41598-021-98569-6}},
  volume       = {{11}},
  year         = {{2021}},
}

@article{21821,
  abstract     = {{We present a combined experimental and numerical study of the far-field emission properties of optical travelling wave antennas made from low-loss dielectric materials. The antennas considered here are composed of two simple building blocks, a director and a reflector, deposited on a glass substrate. Colloidal quantum dots placed in the feed gap between the two elements serve as internal light source. The emission profile of the antenna is mainly formed by the director while the reflector suppresses backward emission. Systematic studies of the director dimensions as well as variation of antenna material show that the effective refractive index of the director primarily governs the far-field emission pattern. Below cut off, i.e., if the director’s effective refractive index is smaller than the refractive index of the substrate, the main lobe results from leaky wave emission along the director. In contrast, if the director supports a guided mode, the emission predominately originates from the end facet of the director.}},
  author       = {{Leuteritz, T. and Farheen, Henna and Qiao, S. and Spreyer, F. and Schlickriede, Christian and Zentgraf, Thomas and Myroshnychenko, Viktor and Förstner, Jens and Linden, S.}},
  issn         = {{1094-4087}},
  journal      = {{Optics Express}},
  keywords     = {{tet_topic_opticalantenna}},
  number       = {{10}},
  title        = {{{Dielectric travelling wave antennas for directional light emission}}},
  doi          = {{10.1364/oe.422984}},
  volume       = {{29}},
  year         = {{2021}},
}

@article{21475,
  author       = {{Frese, Daniel and Wei, Qunshuo and Wang, Yongtian and Cinchetti, Mirko and Huang, Lingling and Zentgraf, Thomas}},
  issn         = {{2330-4022}},
  journal      = {{ACS Photonics}},
  number       = {{4}},
  pages        = {{1013--1019}},
  title        = {{{Nonlinear Bicolor Holography Using Plasmonic Metasurfaces}}},
  doi          = {{10.1021/acsphotonics.1c00028}},
  volume       = {{8}},
  year         = {{2021}},
}