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Prof. Dr. Thomas Zentgraf

Prof. Dr. Thomas Zentgraf

Ultrafast Nanophotonics

Head - Professor

Center for Optoelectronics and Photonics (CeOPP)

Chairman - Professor

Institute for photonic quantum systems (PhoQS)

Member - Professor

Transregional Collaborative Research Centre 142

Member - Professor - Projektleiter

+49 5251 60-5865
+49 5251 60-5886
Pohlweg 47-49
33098 Paderborn
Prof. Dr. Thomas Zentgraf
10/2020 - today

Chairman of the Center for Optolectronics & Photonics Paderborn

04/2011 - today

Professor for Applied Physics, Head of the Ultrafast Nanophotonics Group

Department of Physics, Paderborn University, Germany

08/2015 - 01/2016

Guest Professor

Department of Physics, Kasetsart University, Bangkok, Thailand

09/2007 - 03/2011

Research Associate

Department for Mechanical Engineering, University of California at Berkeley, USA

07/2006 - 08/2007


4th Physics Institute, University of Stuttgart, Germany

01/2003 - 06/2006

PhD student

Max Planck Institute for Solid State Research, Stuttgart, Germany

09/2005 - 11/2005

Visiting Researcher

Lawrence Berkeley National Laboratory, Berkeley (USA)

03/2000 - 01/2001

Master Student

Fraunhofer Institute for Applied Optics and Precision Mechanics, Jena, Germany

Open list in Research Information System


Geometric-phase metalens to be used for tunable optical tweezers in microfluidics

R. Geromel, R. Rennerich, T. Zentgraf, H. Kitzerow, Liquid Crystals (2023), pp. 1-11


Tailoring the directive nature of optical waveguide antennas

H. Farheen, L. Yan, T. Leuteritz, S. Qiao, F. Spreyer, C. Schlickriede, V. Quiring, C. Eigner, C. Silberhorn, T. Zentgraf, S. Linden, V. Myroshnychenko, J. Förstner, in: Integrated Optics: Devices, Materials, and Technologies XXVII, SPIE, 2023, pp. 124241E

We demonstrate the numerical and experimental realization of optimized optical traveling-wave antennas made of low-loss dielectric materials. These antennas exhibit highly directive radiation patterns and our studies reveal that this nature comes from two dominant guided TE modes excited in the waveguide-like director of the antenna, in addition to the leaky modes. The optimized antennas possess a broadband nature and have a nearunity radiation efficiency at an operational wavelength of 780 nm. Compared to the previously studied plasmonic antennas for photon emission, our all-dielectric approach demonstrates a new class of highly directional, low-loss, and broadband optical antennas.


A Versatile Metasurface Enabling Superwettability for Self‐Cleaning and Dynamic Color Response

J. Lu, B. Sain, P. Georgi, M. Protte, T. Bartley, T. Zentgraf, Advanced Optical Materials (2022), 10(1), 2101781

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.

Second Harmonic Optical Circular Dichroism of Plasmonic Chiral Helicoid-III Nanoparticles

F. Spreyer, J. Mun, H. Kim, R.M. Kim, K.T. Nam, J. Rho, T. Zentgraf, ACS Photonics (2022), 9(3), pp. 784–792

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.

Efficient Frequency Conversion with Geometric Phase Control in Optical Metasurfaces

B. Reineke Matsudo, B. Sain, L. Carletti, X. Zhang, W. Gao, C. Angelis, L. Huang, T. Zentgraf, Advanced Science (2022), 9(12), 2104508

Spin-Orbit Interaction of Light Enabled by Negative Coupling in High-Quality-Factor Optical Metasurfaces

W. Gao, B. Sain, T. Zentgraf, Physical Review Applied (2022), 17(4), 044022

Multichannel Superposition of Grafted Perfect Vortex Beams

H. Ahmed, Y. Intaravanne, Y. Ming, M.A. Ansari, G.S. Buller, T. Zentgraf, X. Chen, Advanced Materials (2022), 2203044

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.

Asymmetric parametric generation of images with nonlinear dielectric metasurfaces

S.S. Kruk, L. Wang, B. Sain, Z. Dong, J. Yang, T. Zentgraf, Y. Kivshar, Nature Photonics (2022), 16, pp. 561–565

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.

Design and investigation of a metalens for efficiency enhancement of laser-waveguide coupling in a limited space system

H. laeim, C. Schlickriede, P. Chaisakul, N. Chattham, H. Panitchakan, K. Siangchaew, T. Zentgraf, A. Pattanaporhratana, in: Metamaterials, Metadevices, and Metasystems 2022, SPIE, 2022


Broadband optical Ta2O5 antennas for directional emission of light

H. Farheen, L. Yan, V. Quiring, C. Eigner, T. Zentgraf, S. Linden, J. Förstner, V. Myroshnychenko, Optics Express (2022), 30(11), pp. 19288

Highly directive antennas with the ability of shaping radiation patterns in desired directions are essential for efficient on-chip optical communication with reduced cross talk. In this paper, we design and optimize three distinct broadband traveling-wave tantalum pentoxide antennas exhibiting highly directional characteristics. Our antennas contain a director and reflector deposited on a glass substrate, which are excited by a dipole emitter placed in the feed gap between the two elements. Full-wave simulations in conjunction with global optimization provide structures with an enhanced linear directivity as high as 119 radiating in the substrate. The high directivity is a result of the interplay between two dominant TE modes and the leaky modes present in the antenna director. Furthermore, these low-loss dielectric antennas exhibit a near-unity radiation efficiency at the operational wavelength of 780 nm and maintain a broad bandwidth. Our numerical results are in good agreement with experimental measurements from the optimized antennas fabricated using a two-step electron-beam lithography, revealing the highly directive nature of our structures. We envision that our antenna designs can be conveniently adapted to other dielectric materials and prove instrumental for inter-chip optical communications and other on-chip applications.

Experimental verification of the acoustic geometric phase

B. Liu, Z. Zhou, Y. Wang, T. Zentgraf, Y. Li, L. Huang, Applied Physics Letters (2022), 120(21), 211702

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.

Porous SiO2 coated dielectric metasurface with consistent performance independent of environmental conditions

R. Geromel, C. Weinberger, K. Brormann, M. Tiemann, T. Zentgraf, Optical Materials Express (2022), 12(1), pp. 13-21

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.


Extremely low-energy ARPES of quantum well states in cubic-GaN/AlN and GaAs/AlGaAs heterostructures

M. Hajlaoui, S. Ponzoni, M. Deppe, T. Henksmeier, D.J. As, D. Reuter, T. Zentgraf, G. Springholz, C.M. Schneider, S. Cramm, M. Cinchetti, Scientific Reports (2021), 11, 19081

<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>

Influence of Plasmon Resonances and Symmetry Effects on Second Harmonic Generation in WS2–Plasmonic Hybrid Metasurfaces

F. Spreyer, C. Ruppert, P. Georgi, T. Zentgraf, ACS Nano (2021), 15(10), pp. 16719-16728

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.

Nonlinear Bicolor Holography Using Plasmonic Metasurfaces

D. Frese, Q. Wei, Y. Wang, M. Cinchetti, L. Huang, T. Zentgraf, ACS Photonics (2021), 8(4), pp. 1013-1019


Optical secret sharing with cascaded metasurface holography

P. Georgi, Q. Wei, B. Sain, C. Schlickriede, Y. Wang, L. Huang, T. Zentgraf, Science Advances (2021), 7(16), eabf9718

<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>

Selective Etching of (111)B-Oriented AlxGa1−xAs-Layers for Epitaxial Lift-Off

T. Henksmeier, M. Eppinger, B. Reineke, T. Zentgraf, C. Meier, D. Reuter, physica status solidi (a) (2021), 218(3), pp. 2000408

GaAs-(111)-nanostructures exhibiting second harmonic generation are new building blocks in nonlinear optics. Such structures can be fabricated through epitaxial lift-off using selective etching of Al-containing layers and subsequent transfer to glass substrates. Herein, the selective etching of (111)B-oriented AlxGa1−xAs sacrificial layers (10–50 nm thick) with different aluminum concentrations (x = 0.5–1.0) in 10\% hydrofluoric acid is investigated and compared with standard (100)-oriented structures. The thinner the sacrificial layer and the lower the aluminum content, the lower the lateral etch rate. For both orientations, the lateral etch rates are in the same order of magnitude, but some quantitative differences exist. Furthermore, the epitaxial lift-off, the transfer, and the nanopatterning of thin (111)B-oriented GaAs membranes are demonstrated. Atomic force microscopy and high-resolution X-ray diffraction measurements reveal the high structural quality of the transferred GaAs-(111) films.

Nonlinear Imaging of Nanoscale Topological Corner States

S.S. Kruk, W. Gao, D. Choi, T. Zentgraf, S. Zhang, Y. Kivshar, Nano Letters (2021), 21(11), pp. 4592–4597

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.

Nonlinear metasurface combining telecom-range intersubband transitions in GaN/AlN quantum wells with resonant plasmonic antenna arrays

J. Mundry, F. Spreyer, V. Jmerik, S. Ivanov, T. Zentgraf, M. Betz, Optical Materials Express (2021), 11(7), 2134

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.

Recent progress on metasurfaces: applications and fabrication

G. Yoon, T. Tanaka, T. Zentgraf, J. Rho, Journal of Physics D: Applied Physics (2021), 54, 383002


Dielectric travelling wave antennas for directional light emission

T. Leuteritz, H. Farheen, S. Qiao, F. Spreyer, C. Schlickriede, T. Zentgraf, V. Myroshnychenko, J. Förstner, S. Linden, Optics Express (2021), 29(10), 14694

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.

Observing 0D subwavelength-localized modes at ~100 THz protected by weak topology

J. Lu, K.G. Wirth, W. Gao, A. Heßler, B. Sain, T. Taubner, T. Zentgraf, Science Advances (2021), 7(49), eabl3903

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.

A wavelength and polarization selective photon sieve for holographic applications

D. Frese, B. Sain, H. Zhou, Y. Wang, L. Huang, T. Zentgraf, Nanophotonics (2021), 10(18), pp. 4543-4550

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.


All-dielectric silicon metalens for two-dimensional particle manipulation in optical tweezers

T. Chantakit, C. Schlickriede, B. Sain, F. Meyer, T. Weiss, N. Chattham, T. Zentgraf, Photonics Research (2020), 8(9), pp. 1435-1440


A dielectric metasurface optical chip for the generation of cold atoms

L. Zhu, X. Liu, B. Sain, M. Wang, C. Schlickriede, Y. Tang, J. Deng, K. Li, J. Yang, M. Holynski, S. Zhang, T. Zentgraf, K. Bongs, Y. Lien, G. Li, Science Advances (2020), 6(31), eabb6667

<jats:p>Compact and robust cold atom sources are increasingly important for quantum research, especially for transferring cutting-edge quantum science into practical applications. In this study, we report on a novel scheme that uses a metasurface optical chip to replace the conventional bulky optical elements used to produce a cold atomic ensemble with a single incident laser beam, which is split by the metasurface into multiple beams of the desired polarization states. Atom numbers ~10<jats:sup>7</jats:sup> and temperatures (about 35 μK) of relevance to quantum sensing are achieved in a compact and robust fashion. Our work highlights the substantial progress toward fully integrated cold atom quantum devices by exploiting metasurface optical chips, which may have great potential in quantum sensing, quantum computing, and other areas.</jats:p>

Plasmonic metasurfaces for controlling harmonic generations

T. Zentgraf, S. Chen, G. Li, S. Zhang, in: Nanoantennas and Plasmonics: Modelling, design and fabrication, The Institution of Engineering and Technology, 2020


Metasurfaces help lasers to mode-lock

B. Sain, T. Zentgraf, Light: Science & Applications (2020), 9, pp. 67

Polarization-Encrypted Orbital Angular Momentum Multiplexed Metasurface Holography

H. Zhou, B. Sain, Y. Wang, C. Schlickriede, R. Zhao, X. Zhang, Q. Wei, X. Li, L. Huang, T. Zentgraf, ACS Nano (2020), 14(5), pp. 5553–5559


Nonlinear imaging with all-dielectric metasurfaces

C. Schlickriede, S.S. Kruk, L. Wang, B. Sain, Y. Kivshar, T. Zentgraf, Nano Letters (2020), 20(6), pp. 4370–4376


Second harmonic imaging of plasmonic Pancharatnam-Berry phase metasurfaces coupled to monolayers of WS2

F. Spreyer, R. Zhao, L. Huang, T. Zentgraf, Nanophotonics (2020), 9(2), pp. 351–360

<jats:p>The nonlinear processes of frequency conversion such as second harmonic generation (SHG) usually obey certain selection rules, resulting from the preservation of different kinds of physical quantities, e.g. the angular momentum. For the SHG created by a monolayer of transition-metal dichalcogenides (TMDCs) such as WS<jats:sub>2</jats:sub>, the valley-exciton locked selection rule predicts an SHG signal in the cross-polarization state. By combining plasmonic nanostructures with a monolayer of TMDC, a hybrid metasurface is realized, which affects this nonlinear process because of an additional polarization conversion process. Here, we observe that the plasmonic metasurface modifies the light-matter interaction with the TMDC, resulting in an SHG signal that is co-polarized with respect to the incident field, which is usually forbidden for the monolayers of TMDC. We fabricate such hybrid metasurfaces by placing plasmonic nanorods on top of a monolayer WS<jats:sub>2</jats:sub> and study the valley-exciton locked SHG emission from such system for different parameters, such as wavelength and polarization. Furthermore, we show the potential of the hybrid metasurface for tailoring nonlinear processes by adding additional phase information to the SHG signal using the Pancharatnam-Berry phase effect. This allows direct tailoring of the SHG emission to the far-field.</jats:p>

Nonlinear Wavefront Control by Geometric-Phase Dielectric Metasurfaces: Influence of Mode Field and Rotational Symmetry

B. Liu, B. Sain, B. Reineke, R. Zhao, C. Meier, L. Huang, Y. Jiang, T. Zentgraf, Advanced Optical Materials (2020), 8(9), 1902050

Nonlinear Pancharatnam–Berry phase metasurfaces facilitate the nontrivial phase modulation for frequency conversion processes by leveraging photon‐spin dependent nonlinear geometric‐phases. However, plasmonic metasurfaces show some severe limitation for nonlinear frequency conversion due to the intrinsic high ohmic loss and low damage threshold of plasmonic nanostructures. Here, the nonlinear geometric‐phases associated with the third‐harmonic generation process occurring in all‐dielectric metasurfaces is studied systematically, which are composed of silicon nanofins with different in‐plane rotational symmetries. It is found that the wave coupling among different field components of the resonant fundamental field gives rise to the appearance of different nonlinear geometric‐phases of the generated third‐harmonic signals. The experimental observations of the nonlinear beam steering and nonlinear holography realized in this work by all‐dielectric geometric‐phase metasurfaces are well explained with the developed theory. This work offers a new physical picture to understand the nonlinear optical process occurring at nanoscale dielectric resonators and will help in the design of nonlinear metasurfaces with tailored phase properties.

All-optical switching of a dye-doped liquid crystal plasmonic metasurface

B. Atorf, H. Mühlenbernd, T. Zentgraf, H. Kitzerow, Optics Express (2020), 28(6), pp. 8898-8908



Nonlinear optics in all-dielectric nanoantennas and metasurfaces: a review

B. Sain, C. Meier, T. Zentgraf, Advanced Photonics (2019), 1(2), pp. 024002

Free from phase-matching constraints, plasmonic metasurfaces have contributed significantly to the control of optical nonlinearity and enhancement of nonlinear generation efficiency by engineering subwavelength meta-atoms. However, high dissipative losses and inevitable thermal heating limit their applicability in nonlinear nanophotonics. All-dielectric metasurfaces, supporting both electric and magnetic Mie-type resonances in their nanostructures, have appeared as a promising alternative to nonlinear plasmonics. High-index dielectric nanostructures, allowing additional magnetic resonances, can induce magnetic nonlinear effects, which, along with electric nonlinearities, increase the nonlinear conversion efficiency. In addition, low dissipative losses and high damage thresholds provide an extra degree of freedom for operating at high pump intensities, resulting in a considerable enhancement of the nonlinear processes. We discuss the current state of the art in the intensely developing area of all-dielectric nonlinear nanostructures and metasurfaces, including the role of Mie modes, Fano resonances, and anapole moments for harmonic generation, wave mixing, and ultrafast optical switching. Furthermore, we review the recent progress in the nonlinear phase and wavefront control using all-dielectric metasurfaces. We discuss techniques to realize all-dielectric metasurfaces for multifunctional applications and generation of second-order nonlinear processes from complementary metal–oxide–semiconductor-compatible materials.

Strong nonlinear optical response from ZnO by coupled and lattice-matched nanoantennas

M. Protte, N. Weber, C. Golla, T. Zentgraf, C. Meier, Journal of Applied Physics (2019), 125, 193104


Nonreciprocal Asymmetric Polarization Encryption by Layered Plasmonic Metasurfaces

D. Frese, Q. Wei, Y. Wang, L. Huang, T. Zentgraf, Nano Letters (2019), 19(6), pp. 3976-3980

As flexible optical devices that can manipulate the phase and amplitude of light, metasurfaces would clearly benefit from directional optical properties. However, single layer metasurface systems consisting of two-dimensional nanoparticle arrays exhibit only a weak spatial asymmetry perpendicular to the surface and therefore have mostly symmetric transmission features. Here, we present a metasurface design principle for nonreciprocal polarization encryption of holographic images. Our approach is based on a two-layer plasmonic metasurface design that introduces a local asymmetry and generates a bidirectional functionality with full phase and amplitude control of the transmitted light. The encoded hologram is designed to appear in a particular linear cross-polarization channel, while it is disappearing in the reverse propagation direction. Hence, layered metasurface systems can feature asymmetric transmission with full phase and amplitude control and therefore expand the design freedom in nanoscale optical devices toward asymmetric information processing and security features for anticounterfeiting applications.

Reconfigurable metasurface hologram by utilizing addressable dynamic pixels

T. Li, Q. Wei, B. Reineke, F. Walter, Y. Wang, T. Zentgraf, L. Huang, Optics Express (2019), 27(15), pp. 21153-21162


Silicon metasurfaces for third harmonic geometric phase manipulation and multiplexed holography

B. Reineke, B. Sain, R. Zhao, L. Carletti, B. Liu, L. Huang, C. de Angelis, T. Zentgraf, Nano Letters (2019), 19(9), pp. 6585–6591


Metasurface interferometry toward quantum sensors

P. Georgi, M. Massaro, K.H. Luo, B. Sain, N. Montaut, H. Herrmann, T. Weiss, G. Li, C. Silberhorn, T. Zentgraf, Light: Science & Applications (2019), 8, pp. 70


Simultaneous Spectral and Spatial Modulation for Color Printing and Holography Using All-dielectric Metasurfaces

Q. Wei, B. Sain, Y. Wang, B. Reineke, X. Li, L. Huang, T. Zentgraf, Nano Letters (2019), 19(12), pp. 8964–8971


Four‐Wave Mixing Holographic Multiplexing Based on Nonlinear Metasurfaces

Z. Lin, L. Huang, Z.T. Xu, X. Li, T. Zentgraf, Y. Wang, Advanced Optical Materials (2019), 7(21), pp. 1900782


Dynamic control of mode modulation and spatial multiplexing using hybrid metasurfaces

Z. Lin, L. Huang, R. Zhao, Q. Wei, T. Zentgraf, Y. Wang, X. Li, Optics Express (2019), 27(13), pp. 18740-18750

Miniaturized Metalens Based Optical Tweezers on Liquid Crystal Droplets for Lab-on-a-Chip Optical Motors

S. Suwannasopon, F. Meyer, C. Schlickriede, P. Chaisakul, J. T-Thienprasert, J. Limtrakul, T. Zentgraf, N. Chattham, Crystals (2019), 9(10), pp. 515

<jats:p>Surfaces covered with layers of ultrathin nanoantenna structures—so called metasurfaces have recently been proven capable of completely controlling phase of light. Metalenses have emerged from the advance in the development of metasurfaces providing a new basis for recasting traditional lenses into thin, planar optical components capable of focusing light. The lens made of arrays of plasmonic gold nanorods were fabricated on a glass substrate by using electron beam lithography. A 1064 nm laser was used to create a high intensity circularly polarized light focal spot through metalens of focal length 800 µm, N.A. = 0.6 fabricated based on Pancharatnam-Berry phase principle. We demonstrated that optical rotation of birefringent nematic liquid crystal droplets trapped in the laser beam was possible through this metalens. The rotation of birefringent droplets convinced that the optical trap possesses strong enough angular momentum of light from radiation of each nanostructure acting like a local half waveplate and introducing an orientation-dependent phase to light. Here, we show the success in creating a miniaturized and robust metalens based optical tweezers system capable of rotating liquid crystals droplets to imitate an optical motor for future lab-on-a-chip applications.</jats:p>

Strong Nonlinear Optical Activity Induced by Lattice Surface Modes on Plasmonic Metasurface

S. Chen, B. Reineke, G. Li, T. Zentgraf, S. Zhang, Nano Letters (2019), 19(9), pp. 6278-6283



Metasurface holography: from fundamentals to applications

L. Huang, S. Zhang, T. Zentgraf, Nanophotonics (2018), 7(6), pp. 1169-1190

Multichannel vectorial holographic display and encryption

R. Zhao, B. Sain, Q. Wei, C. Tang, X. Li, T. Weiss, L. Huang, Y. Wang, T. Zentgraf, Light: Science & Applications (2018), 7(1)


Nonlinear Quasi-Phase Matching with metasurfaces

S. Heron, B. Reineke, S. Vezian, T. Zentgraf, B. Damilano, P. Genevet, in: 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials), IEEE, 2018


Near-field plasmonic beam engineering by complex amplitude modulation based on metasurface (Conference Presentation)

L. Sun, X. Zhang, R. Zhao, X. Li, J. Wang, B. Bai, Y. Wang, T. Zentgraf, L. Huang, X. Song, in: Nanophotonics VII, SPIE, 2018


Third Harmonic Generation Enhanced by Multipolar Interference in Complementary Silicon Metasurfaces

S. Chen, M. Rahmani, K.F. Li, A. Miroshnichenko, T. Zentgraf, G. Li, D. Neshev, S. Zhang, ACS Photonics (2018), 5(5), pp. 1671-1675


Spin and Geometric Phase Control Four-Wave Mixing from Metasurfaces

G. Li, G. Sartorello, S. Chen, L.H. Nicholls, K.F. Li, T. Zentgraf, S. Zhang, A.V. Zayats, Laser & Photonics Reviews (2018), 12(6), 1800034


Editorial for the theories and applications of metasurfaces

Z. Guo, X. Chen, T. Zentgraf, Journal of Physics D: Applied Physics (2018), 51(15), 150201


Controlling the phase of optical nonlinearity with plasmonic metasurfaces

S. Chen, G. Li, K.W. Cheah, T. Zentgraf, S. Zhang, Nanophotonics (2018), 7(6), pp. 1013-1024


Nanoscale Polarization Manipulation and Encryption Based on Dielectric Metasurfaces

R. Zhao, L. Huang, C. Tang, J. Li, X. Li, Y. Wang, T. Zentgraf, Advanced Optical Materials (2018), 1800490


Imaging the rainbow

T. Zentgraf, Nature Nanotechnology (2018), 13(3), pp. 179-180


Imaging through Nonlinear Metalens Using Second Harmonic Generation

C. Schlickriede, N. Waterman, B. Reineke, P. Georgi, G. Li, S. Zhang, T. Zentgraf, Advanced Materials (2018), 30(8), 1703843


Selective Diffraction with Complex Amplitude Modulation by Dielectric Metasurfaces

X. Song, L. Huang, C. Tang, J. Li, X. Li, J. Liu, Y. Wang, T. Zentgraf, Advanced Optical Materials (2018), 6(4), 1701181


Tailored UV Emission by Nonlinear IR Excitation from ZnO Photonic Crystal Nanocavities

S.P. Hoffmann, M. Albert, N. Weber, D. Sievers, J. Förstner, T. Zentgraf, C. Meier, ACS Photonics (2018), 5, pp. 1933-1942

Efficient frequency conversion by combined photonic–plasmonic mode coupling

N. Weber, S.P. Hoffmann, M. Albert, T. Zentgraf, C. Meier, Journal of Applied Physics (2018), 123(10), 103101


Switchable Plasmonic Metasurface Utilizing the Electro-Optic Kerr Effect of a Blue Phase Liquid Crystal

B. Atorf, S. Friesen, R. Rennerich, H. Mühlenbernd, T. Zentgraf, H. Kitzerow, Polymer Science, Series C (2018), 60, pp. 55-62


Switchable Plasmonic Holograms Utilizing the Electro-Optic Effect of a Liquid-Crystal Circular Polarizer

B. Atorf, H. Rasouli, H. Mühlenbernd, B.J. Reineke, T. Zentgraf, H. Kitzerow, The Journal of Physical Chemistry C (2018), 122(8), pp. 4600-4606


Switchable Plasmonic Metasurface Utilizing the Electro-Optic Kerr Effect of a Blue Phase Liquid Crystal

B. Atorf, S. Friesen, R. Rennerich, H. Mühlenbernd, T. Zentgraf, H. Kitzerow, Polymer Science, Series C (2018), pp. 55-62



Volumetric Generation of Optical Vortices with Metasurfaces

L. Huang, X. Song, B. Reineke, T. Li, X. Li, J. Liu, S. Zhang, Y. Wang, T. Zentgraf, ACS Photonics (2017), pp. 338-346


Optimisation of stability and charge transferability of ferrocene-encapsulated carbon nanotubes

P. Prajongtat, S. Sriyab, T. Zentgraf, S. Hannongbua, Molecular Physics (2017), 116(1), pp. 9-18


Single-pixel computational ghost imaging with helicity-dependent metasurface hologram

H. Liu, B. Yang, Q. Guo, J. Shi, C. Guan, G. Zheng, H. Mühlenbernd, G. Li, T. Zentgraf, S. Zhang, Science Advances (2017), 3(9), e1701477


Rotational Doppler shift induced by spin-orbit coupling of light at spinning metasurfaces

P. Georgi, C. Schlickriede, G. Li, S. Zhang, T. Zentgraf, Optica (2017), 4(8), 1000


Beam switching and bifocal zoom lensing using active plasmonic metasurfaces

X. Yin, T. Steinle, L. Huang, T. Taubner, M. Wuttig, T. Zentgraf, H. Giessen, Light: Science & Applications (2017), 6(7), e17016


Directional Emission from Dielectric Leaky-Wave Nanoantennas

M. Peter, A. Hildebrandt, C. Schlickriede, K. Gharib, T. Zentgraf, J. Förstner, S. Linden, Nano Letters (2017), 17(7), pp. 4178-4183

Manipulation of vector beam polarization with geometric metasurfaces

Q. Guo, C. Schlickriede, D. Wang, H. Liu, Y. Xiang, T. Zentgraf, S. Zhang, Optics Express (2017), 25(13), 14300


Double resonant plasmonic nanoantennas for efficient second harmonic generation in zinc oxide

N. Weber, M. Protte, F. Walter, P. Georgi, T. Zentgraf, C. Meier, Physical Review B (2017), 95(20)


Nonlinear photonic metasurfaces

G. Li, S. Zhang, T. Zentgraf, Nature Reviews Materials (2017), 2(5), 17010


Ultrathin Nonlinear Metasurface for Optical Image Encoding

F. Walter, G. Li, C. Meier, S. Zhang, T. Zentgraf, Nano Letters (2017), 17(5), pp. 3171-3175


Nonlinear Metasurface for Simultaneous Control of Spin and Orbital Angular Momentum in Second Harmonic Generation

G. Li, L. Wu, K.F. Li, S. Chen, C. Schlickriede, Z. Xu, S. Huang, W. Li, Y. Liu, E.Y.B. Pun, T. Zentgraf, K.W. Cheah, Y. Luo, S. Zhang, Nano Letters (2017), 17(12), pp. 7974-7979


Liquid crystals and precious metal: from nanoparticle dispersions to functional plasmonic nanostructures

B. Atorf, T. Funck, T. Hegmann, S. Kempter, T. Liedl, K. Martens, H. Mühlenbernd, T. Zentgraf, B. Zhang, H. Kitzerow, M. Urbanski, Liquid Crystals (2017), pp. 1-19



Spin and wavelength multiplexed nonlinear metasurface holography

W. Ye, F. Zeuner, X. Li, B. Reineke, S. He, C. Qiu, J. Liu, Y. Wang, S. Zhang, T. Zentgraf, Nature Communications (2016), 7, 11930


Rotational Doppler effect in nonlinear optics

G. Li, T. Zentgraf, S. Zhang, Nature Physics (2016), 12(8), pp. 736-740


Designermaterialien für nichtlineare Optik

H. Probst, T. Zentgraf, Physik in unserer Zeit (2016), 47(2), pp. 84-89


Giant Nonlinear Optical Activity of Achiral Origin in Planar Metasurfaces with Quadratic and Cubic Nonlinearities

S. Chen, F. Zeuner, M. Weismann, B. Reineke, G. Li, V.K. Valev, K.W. Cheah, N.C. Panoiu, T. Zentgraf, S. Zhang, Advanced Materials (2016), 28(15), pp. 2992-2999


Helicity-Preserving Omnidirectional Plasmonic Mirror

S. Xiao, H. Mühlenbernd, G. Li, M. Kenney, F. Liu, T. Zentgraf, S. Zhang, J. Li, Advanced Optical Materials (2016), 4(5), pp. 654-658


Doppler-Effekt für rotierende Objekte

T. Zentgraf, Physik in unserer Zeit (2016), 47(4), pp. 163-164


Simulations of high harmonic generation from plasmonic nanoparticles in the terahertz region

Y. Grynko, T. Zentgraf, T. Meier, J. Förstner, Applied Physics B (2016), 122(9), pp. 242



Nonlinear optical sub-bandgap excitation of ZnO-based photonic resonators

C.A. Bader, F. Zeuner, M.H.W. Bader, T. Zentgraf, C. Meier, Journal of Applied Physics (2015), 118(21), 213105


Coupling Mediated Coherent Control of Localized Surface Plasmon Polaritons

F. Zeuner, M. Muldarisnur, A. Hildebrandt, J. Förstner, T. Zentgraf, Nano Letters (2015), 15(6), pp. 4189-4193

Broadband Hybrid Holographic Multiplexing with Geometric Metasurfaces

L. Huang, H. Mühlenbernd, X. Li, X. Song, B. Bai, Y. Wang, T. Zentgraf, Advanced Materials (2015), 27(41), pp. 6444-6449


Continuous control of the nonlinearity phase for harmonic generations

G. Li, S. Chen, N. Pholchai, B. Reineke, P.W.H. Wong, E.B. Pun, K.W. Cheah, T. Zentgraf, S. Zhang, Nature Materials (2015), 14(6), pp. 607-612


Metasurface holograms reaching 80% efficiency

G. Zheng, H. Mühlenbernd, M. Kenney, G. Li, T. Zentgraf, S. Zhang, Nature Nanotechnology (2015), 10(4), pp. 308-312


Amplitude- and Phase-Controlled Surface Plasmon Polariton Excitation with Metasurfaces

H. Mühlenbernd, P. Georgi, N. Pholchai, L. Huang, G. Li, S. Zhang, T. Zentgraf, ACS Photonics (2015), 3(1), pp. 124-129



Manipulating wave propagation with geometric metasurfaces: fundamentals and applications

L. Huang, X. Chen, B. Bai, Q. Tan, G. Jin, T. Zentgraf, S. Zhang, in: Plasmonics, SPIE, 2014


Ag‐nanoparticles in PA-templates

A. Ezhova, J. Lindner, M. Muldarisnur, T. Zentgraf, K. Huber, 2014

Symmetry-Selective Third-Harmonic Generation from Plasmonic Metacrystals

S. Chen, G. Li, F. Zeuner, W.H. Wong, E.Y.B. Pun, T. Zentgraf, K.W. Cheah, S. Zhang, Physical Review Letters (2014), 113(3)


Hochauflösende Holografie

T. Zentgraf, Physik in unserer Zeit (2014), 45(2), pp. 58-59


Electro-optic tuning of split ring resonators embedded in a liquid crystal

B. Atorf, H. Mühlenbernd, M. Muldarisnur, T. Zentgraf, H. Kitzerow, Optics Letters (2014), 39(5), 1129


Effect of Alignment on a Liquid Crystal/Split-Ring Resonator Metasurface

B. Atorf, H. Mühlenbernd, M. Muldarisnur, T. Zentgraf, H. Kitzerow, ChemPhysChem (2014), 15(7), pp. 1470-1476


Tunable infrared resonance spectra of split ring resonators embedded in a liquid crystal

B. Atorf, H. Muhlenbernd, T. Zentgraf, H. Kitzerow, in: 2013 7th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics, IEEE, 2014



Blue-green emitting microdisks using low-temperature-grown ZnO on patterned silicon substrates

M. Ruth, T. Zentgraf, C. Meier, Optics Express (2013), 21(21), 25517


Interference-induced asymmetric transmission through a monolayer of anisotropic chiral metamolecules

S. Zhang, F. Liu, T. Zentgraf, J. Li, Physical Review A (2013), 88(2)


Three-dimensional optical holography using a plasmonic metasurface

L. Huang, X. Chen, H. Mühlenbernd, H. Zhang, S. Chen, B. Bai, Q. Tan, G. Jin, K. Cheah, C. Qiu, J. Li, T. Zentgraf, S. Zhang, Nature Communications (2013), 4


Reversible Three-Dimensional Focusing of Visible Light with Ultrathin Plasmonic Flat Lens

X. Chen, L. Huang, H. Mühlenbernd, G. Li, B. Bai, Q. Tan, G. Jin, C. Qiu, T. Zentgraf, S. Zhang, Advanced Optical Materials (2013), 1(7), pp. 517-521


Metalens with convex and concave functionality

S. Zhang, X. Chen, L. Huang, B. Bai, Q. Tan, G. Jin, H. Mühlenbernd, T. Zentgraf, G. Li, C. Qiu, SPIE Newsroom (2013)


Helicity dependent directional surface plasmon polariton excitation using a metasurface with interfacial phase discontinuity

L. Huang, X. Chen, B. Bai, Q. Tan, G. Jin, T. Zentgraf, S. Zhang, Light: Science & Applications (2013), 2(3), pp. e70-e70



Dual-polarity plasmonic metalens for visible light

X. Chen, L. Huang, H. Mühlenbernd, G. Li, B. Bai, Q. Tan, G. Jin, C. Qiu, S. Zhang, T. Zentgraf, Nature Communications (2012), 3, 1198

Dispersionless Phase Discontinuities for Controlling Light Propagation

L. Huang, X. Chen, H. Mühlenbernd, G. Li, B. Bai, Q. Tan, G. Jin, T. Zentgraf, S. Zhang, Nano Letters (2012), 12(11), pp. 5750-5755


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