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Subject: search.filters.subject.530Institute: search.filters.UBSInstitut.Stuttgart Research Centre of Photonic Engineering (SCoPE)Institute: search.filters.UBSInstitut.4. Physikalisches InstitutPublication Type: search.filters.UBSTyp.ZeitschriftenartikelStart date: 2018Author: search.filters.author.Weiss, Thomas

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    Inverse design of all-dielectric metasurfaces with accidental bound states in the continuum
    (2023) Gladyshev, Sergei; Karamanos, Theodosios D.; Kuhn, Lina; Beutel, Dominik; Weiss, Thomas; Rockstuhl, Carsten; Bogdanov, Andrey
    Metasurfaces with bound states in the continuum (BICs) have proven to be a powerful platform for drastically enhancing light–matter interactions, improving biosensing, and precisely manipulating near- and far-fields. However, engineering metasurfaces to provide an on-demand spectral and angular position for a BIC remains a prime challenge. A conventional solution involves a fine adjustment of geometrical parameters, requiring multiple time-consuming calculations. In this work, to circumvent such tedious processes, we develop a physics-inspired, inverse design method on all-dielectric metasurfaces for an on-demand spectral and angular position of a BIC. Our suggested method predicts the core–shell particles that constitute the unit cell of the metasurface, while considering practical limitations on geometry and available materials. Our method is based on a smart combination of a semi-analytical solution, for predicting the required dipolar Mie coefficients of the meta-atom, and a machine learning algorithm, for finding a practical design of the meta-atom that provides these Mie coefficients. Although our approach is exemplified in designing a metasurface sustaining a BIC, it can, also, be applied to many more objective functions. With that, we pave the way toward a general framework for the inverse design of metasurfaces in specific and nanophotonic structures in general.
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    Dielectric Mie voids : confining light in air
    (2023) Hentschel, Mario; Koshelev, Kirill; Sterl, Florian; Both, Steffen; Karst, Julian; Shamsafar, Lida; Weiss, Thomas; Kivshar, Yuri; Giessen, Harald
    Manipulating light on the nanoscale has become a central challenge in metadevices, resonant surfaces, nanoscale optical sensors, and many more, and it is largely based on resonant light confinement in dispersive and lossy metals and dielectrics. Here, we experimentally implement a novel strategy for dielectric nanophotonics: Resonant subwavelength localized confinement of light in air. We demonstrate that voids created in high-index dielectric host materials support localized resonant modes with exceptional optical properties. Due to the confinement in air, the modes do not suffer from the loss and dispersion of the dielectric host medium. We experimentally realize these resonant Mie voids by focused ion beam milling into bulk silicon wafers and experimentally demonstrate resonant light confinement down to the UV spectral range at 265 nm (4.68 eV). Furthermore, we utilize the bright, intense, and naturalistic colours for nanoscale colour printing. Mie voids will thus push the operation of functional high-index metasurfaces into the blue and UV spectral range. The combination of resonant dielectric Mie voids with dielectric nanoparticles will more than double the parameter space for the future design of metasurfaces and other micro- and nanoscale optical elements. In particular, this extension will enable novel antenna and structure designs which benefit from the full access to the modal field inside the void as well as the nearly free choice of the high-index material for novel sensing and active manipulation strategies.
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    Modeling of second-harmonic generation in periodic nanostructures by the Fourier modal method with matched coordinates
    (2018) Defrance, Josselin; Schäferling, Martin; Weiss, Thomas
    We present an advanced formulation of the Fourier modal method for analyzing the second-harmonic generation in multilayers of periodic arrays of nanostructures. In our method, we solve Maxwell’s equations in a curvilinear coordinate system, in which the interfaces are defined by surfaces of constant coordinates. Thus, we can apply the correct Fourier factorization rules as well as adaptive spatial resolution to nanostructures with complex cross sections. We extend here the factorization rules to the second-harmonic susceptibility tensor expressed in the curvilinear coordinates. The combination of adaptive curvilinear coordinates and factorization rules allows for efficient calculation of the second-harmonic intensity, as demonstrated for one- and two-dimensional periodic nanostructures.