arXiv subjects

Isabelle Staude

Publications and source records attributed to Isabelle Staude.

At least 19 recordsLinked to original sources

arXiv2026

Scalable Cyclic Olefin Copolymer Encapsulation for High Optical Quality of TMD Monolayers

Monolayer transition metal dichalcogenides (TMDs) combine a direct bandgap, strongly bound excitons, and pronounced second-order optical nonlinearity, which makes them promising materials for ultrathin optoelectronic and nanophotonic devices. However, their optical performance is often degraded by environmental exposure and substrate-induced charge trapping, motivating the development of scalable encapsulation strategies. Here, we investigate spin-coated cyclic olefin copolymer (COC) as a scalable encapsulant for TMDs. Room-temperature and cryogenic optical spectroscopy reveal enhanced photoluminescence and second-harmonic generation, accompanied by excitonic linewidth narrowing and an increased exciton-to-trion ratio. In addition, COC encapsulation induces an excitonic peak splitting and an overall spectral blueshift. First-principles calculations attribute these spectral modifications to local symmetry breaking at the chalcogen interface and macroscopic compressive strain, respectively. These findings establish spin-coated COC as an effective, scalable encapsulation strategy and a potential platform for post-growth excitonic and band-structure engineering.

cond-mat.mtrl-sci↗

arXiv2026

Direct Wafer Bonding of Crystal-Ion-Sliced GaP Thin Films for Photonic Applications

Gallium phosphide (GaP) is a promising material platform for integrated photonics because of its high refractive index, broad optical transparency, and strong second-order nonlinear response. Here, we demonstrate GaP-on-insulator thin films fabricated by crystal ion slicing and direct wafer bonding, using fused silica and SiO$_2$/Si/Si thermally oxidized silicon substrates as representative platforms. Unlike GaP thin-film platforms that rely on heteroepitaxial growth or sacrificial-layer release, the presented approach enables the flexible integration of crystalline GaP thin films, independent of both donor and target substrates. Following post-transfer annealing, the films exhibit near-bulk crystalline quality with low residual strain, smooth surfaces suitable for nanophotonic fabrication, and homogeneous bonding interfaces. Furthermore, annealing restores the linear optical dispersion (n and k) approaching that of epitaxially grown GaP with estimated plane wave absorption loss of 0.9 dB/cm at 1550 nm in the telecom C-band. The demonstrated approach establishes a scalable pathway toward high-quality GaP thin-film photonics compatible with versatile heterogeneous integration and back-end-of-line CMOS processing.

physics.optics↗

arXiv2026

Gallium phosphide on insulator for nanophotonics and quantum technologies

Gallium phosphide is a promising material platform for visible and near-infrared photonics and quantum technologies owing to its high refractive index, low optical absorption, and strong second-order nonlinearity. Here, we demonstrate the fabrication of GaP-on-insulator substrates by ion slicing. The splitting depth and exfoliation behavior of bulk GaP are tailored by controlling the He$^{+}$ ion implantation energy and fluence, enabling thin-film transfer onto amorphous substrates by anodic bonding and plasma-enhanced direct wafer bonding. Channeling Rutherford backscattering spectrometry and X-ray diffraction confirm that the transferred layers retain their single-crystalline structure, while implantation-induced disorder and optical absorption are substantially reduced by annealing at 500 {\deg}C and subsequent polishing. The annealed films exhibit linear optical properties approaching those of bulk GaP. In addition, a (110)-oriented GaP thin film shows the characteristic polarization dependence expected from the zinc-blende second-order nonlinear susceptibility tensor, demonstrating a near-pristine second-order nonlinear response. This flexible fabrication approach enables the integration of high-quality single-crystalline GaP with variable orientation for free-space and integrated nanophotonics as well as nonlinear and quantum optical devices.

physics.optics↗

arXiv2026

Spatiotemporal Metasurface for Ultrafast All-Optical Wavefront Shaping

Optical metasurfaces have established themselves as exceptional nanophotonic platforms to control the properties of light at subwavelength scales. By properly designing the geometry and spatial arrangement of their constituent meta-atoms, engineered phase gradients can be imparted to an incoming field, thereby tailoring its wavefront with a virtually unlimited number of control knobs. However, once fabricated, a metasurface has a permanently fixed optical response. Here, we introduce a strategy for dynamic control, by theoretically predicting and experimentally demonstrating all-optical, reversible, and ultrafast wavefront shaping in a periodic semiconductor nanowire metasurface. A strongly astigmatic femtosecond optical pump pulse is used to photoexcite the resonant metasurface non-uniformly, inducing a transient, spatially inhomogeneous permittivity modulation that reshapes the wavefront of a delayed probe pulse. Ultrafast imaging measurements reveal transient defocusing of the transmitted field at selected probe wavelengths, with a switching time below one picosecond. Quantitative numerical modelling elucidates the defocusing mechanism as arising from the interplay between the unperturbed optical response of the resonant metasurface and the pump-induced spatial permittivity gradient. Our work establishes a fully all-optical and ultrafast route to the dynamic analogue of passive wavefront shaping in gradient metasurfaces, paving the way to all-optically reconfigurable metalenses.

physics.optics↗

arXiv2026

Sensitive biodetection in flow using metasurface hosting quasi-bound state in the continuum resonances

We have designed optical metasurfaces hosting high-quality factor quasi-bound state in the continuum (q-BIC) resonances for optical biosensing in flow. The unit cell of the metasurface contains two rectangular bars. An asymmetry factor is introduced by varying the gap width between the bars, to enable optical coupling to a q-BIC resonance confined to the air gap between neighboring nanoresonators. The location of the resonances makes them highly sensitive to changes in the local refractive index, leading to experimental bulk refractive index sensitivities exceeding 315 +/- 22 nm/RIU and a figure-of-merit of 66 +/- 5 RIU-1. Successful streptavidin-biotin binding was observed by measuring the metasurface transmission in real-time by exposing the metasurface to various concentrations of analytes via a commercial microfluidic flow cell apparatus. The experimental limit of detection, defined as 3{\sigma} above noise, was found to be 1.8x10-8 M. This platform represents a compact optical approach for point-of-care diagnostics with fast read-out.

physics.optics↗

arXiv2026

Insights into the Nature of Quantum Emitters in Electron-Irradiated hexagonal Boron Nitride

Quantum emitters in hexagonal boron nitride (hBN) have emerged as a promising solid-state platform for quantum technology applications. However, a persistent challenge in the field is the unclear origin of many observed emission lines, particularly in the visible range, which can be difficult to distinguish from signals arising from organic or process-induced contamination during sample preparations and handling. This ambiguity limits both the reproducibility of emitter generation and the reliable identification of truly intrinsic quantum defects. This work provides a step-by-step framework to assess whether quantum emitters in electron-irradiated hBN are associated with organic contaminants introduced during sample preparation. We employ hyperspectral imaging, thermal annealing, and oxygen plasma etching to investigate the origin of the green-yellow emitters in electron-irradiated hBN. The combined results not only rule out organic contamination as the source of emission but also provide insight into the spectral variability, thermal stability, and vertical localization of the emitters generated in electron-irradiated hBN that was created without any pre- or post-processing. In addition, our experiments demonstrate the feasibility of creating stable emitters in hBN with thicknesses below 10 nm. These findings provide practical guidance for the identification and controlled implementation of hBN-based single-photon emitters in quantum photonic devices.

physics.optics↗

arXiv2026

All-optical control of nonlinear emission from resonant metasurfaces

Nonlinear optics underpins a broad range of photonic technologies, from classical and quantum light sources to emerging nonlinear photonic neural networks. Yet, conventional nonlinear optical devices exhibit static functionality: their transfer characteristics and emission profiles are dictated by the intrinsic nonlinear process and locked by fabrication, limiting adaptability. Here, we introduce an ultra-thin metasurface platform that enables dynamic reconfiguration of nonlinear functionality in a contact-less fashion. By leveraging all-optical control of the optical torque exerted on liquid crystal molecules infiltrating a resonant metasurface, we achieve tunable polynomial nonlinear transfer functions based on third-harmonic generation process. This mechanism further allows real-time modulation of nonlinear weighting across different diffraction orders, revealing a previously unexplored interplay between mode structure and nonlinear emission. Our approach opens up a pathway toward field-programmable nonlinear photonic systems, offering unprecedented flexibility for reconfigurable nonlinear signal processing and adaptive photonic computing.

physics.optics↗

arXiv2026

Enhancement of Circular Dichroism in Chiral Dielectric Metasurfaces by Ion Beam Irradiation

Resonant chiral dielectric metasurfaces can support circular dichroism exceeding that of natural materials, but their small dissipative losses simultaneously limit the maximization of circular dichroism, which inherently relies on absorption. Importantly, while the condition for optimal circular dichroism in resonant structures can be rigorously formulated based on the concept of critical coupling, controlling the amount of absorption experimentally, and ideally tuning it to the optimal value post-fabrication, remains elusive. Here, we experimentally tailor the dissipative losses of chiral bilayer dielectric metasurfaces post-fabrication using energetic ion beam irradiation. Specifically, we study the transmission characteristics of C4-symmetric chiral metasurface consisting of silicon nanocuboid arrays embedded in silica glass using polarization-resolved spectroscopy. We enhance the circular dichroism from 0.70 in the pristine, unirradiated metasurface to 0.85 after irradiation. Our experimental results are complemented by numerical simulations allowing us to retrieve the refractive index changes induced by the ion beam irradiation in the constituent materials of the metasurface. Our work offers a new approach to globally maximize optical chirality in engineered nanostructures, paving the way towards chiral emission and advanced polarization control applications

physics.optics↗

arXiv2026

Valleytronics in 2D Materials Roadmap

Valleytronics exploits non-equivalent energy extrema in the electronic band structure of crystalline solids -- the valley degree of freedom -- to encode, manipulate, and read out information. The advent of 2D materials, first graphene and then transition-metal dichalcogenides, made valley control practical through optical, electrical, and magnetic routes. This foundation has enabled remarkable progress in recent years spanning established frontiers, such as valley exciton physics and valley Hall effects, as well as emerging directions including lightwave valleytronics, nanophotonic integration, flat-band valleytronics, and spin-valley qubits. In parallel, there are sustained efforts to scale up valleytronic materials and to predict new valleytronic platforms. This Roadmap brings together perspectives from leading experts to chart the key opportunities and challenges at the forefront of 2D material valleytronics. Each section captures a snapshot of progress in a key research area, identifies critical open challenges, and outlines pathways toward future valleytronics breakthroughs.

cond-mat.mes-hall↗

arXiv2026

Towards Polarization Routing of Magnetic and Electric Dipolar Emission with Dielectric Metasurfaces

We investigate the polarization properties of emission associated with the magnetic dipole and electric dipole transitions of europium(III) coupled to an anisotropic dielectric metasurface with polarization-engineered electric and magnetic photonic local density of states. The metasurface consists of a square array of Mie-resonant elliptical a-Si:H dimers situated on an SiO$_2$ substrate and embedded in a PMMA film containing Eu(TTA)$_3$. Based on reciprocity principle, it was designed to achieve maximum electric (magnetic) field enhancement in the dimer gap at 610 nm (590 nm) for $x$-polarized ($y$-polarized) normally incident light in order to selectively enhance the electric dipole (magnetic dipole) emission into the $x$-polarized ($y$-polarized) emission channel, respectively. Momentum-resolved spectroscopy and back-focal plane imaging of emission of the fabricated light-emitting metasurface clearly reveal the intended polarization-dependent emission behaviour, with the $x$-polarized ($y$-polarized) emission showing a reduced (enhanced) ratio of the magnetic-/electric dipole emission intensity, correspondingly where the magnetic dipole emission is enhanced with a magnetic field enhancement from the nanostructures. The demonstrated polarization-dependent interaction of a designed nanostructure with the electric- and magnetic dipolar transitions of trivalent lanthanide ions opens an avenue towards routing of emission of different multipolar orders into different polarization channels.

physics.optics↗

arXiv2026

Spatio-spectrally tailored multimode metasurface lasers in the visible range

Spectrally engineered multifrequency nanolasers are highly desirable for on-chip photonics, multiplexed biosensing, and display technologies; yet, achieving them within a single compact platform remains challenging. Here, we demonstrate multimode lasing from symmetry-broken TiO2 metasurfaces integrated with an SU8 slab waveguide containing Rhodamine 6G. By co-engineering guided-mode resonances, surface lattice resonances near Rayleigh anomalies, and quasi-bound states in the continuum, we realize complementary high-Q feedback pathways that overlap with the gain spectrum. The direction of the lasing emission is tailored through outcoupling via second-order Bragg diffraction and Rayleigh anomaly conditions, supporting both normal and oblique emission. Experiments reveal discrete lasing outputs across ~100 nm bandwidth (548-648 nm), spanning nearly the full Rhodamine 6G emission band, with thresholds as low as ~7 nJ per pulse (35.7 uJ/cm^2) and up to four concurrent lasing peaks from a single device. These results establish a metasurface-dye platform for multifrequency and angle-selective lasing, opening new opportunities for compact, multifunctional nanophotonic sources.

physics.optics↗

arXiv2025

Inverse-Designed Superchiral Hot Spot in Dielectric Meta-Cavity for Ultra-Compact Enantioselective Detection

Chiral nanophotonic structures have garnered considerable interest in recent years due to their potential to enhance the efficacy of chirality-sensitive biomolecular detection. Designing metaplatforms to enhance chiroptical signals under linearly polarized excitation is particularly appealing due to the minimal chiral background and the ease of controlling excitation polarization. Here, a novel two-step inverse design scheme for dielectric lossless metasurfaces with superchiral hot spots is proposed. The method extends the local density of field enhancements for non-chiral fields into the chiral regime and significantly surpasses previous enhancements in super-chiral field generation. It has been demonstrated that by leveraging the excitation of high quality factor modes with small mode volumes, it is theoretically possible to convert linearly polarized plane waves into a superchiral hot spot with record-high enhancement in the near-field optical chirality up to 104. A prototype is successfully implemented using advanced nanofabrication technologies. The optical characterization of the prototype demonstrates a 102-fold enhancement in optical chirality. The findings of this study unveil novel prospects for chiral spectroscopy with ultra-compact devices, underscoring the role of machine learning and physics-based inverse design in the development of cutting-edge, functional photonic structures.

physics.optics↗

arXiv2025

Linear and Nonlinear Optical Properties of SiO$_2$/TiO$_2$ Heterostructures Grown by Plasma Enhanced Atomic Layer Deposition

Second harmonic (SH) radiation can only be generated in non-centrosymmetric bulk crystals under the electric-dipole approximation. Nonlinear thin films made from bulk crystals are technologically challenging because of complex and high temperature fabrication processes. In this work, heterostructures made of amorphous materials SiO$_2$ and TiO$_2$ were prepared by a CMOS-compatible technique named plasma enhanced atomic layer deposition (PEALD) with deposition temperature at 100 {\deg}C. By using the uniaxial dispersion model, we characterized the form-birefringence properties, which can enable the phase matching condition in waveguides or other nonlinear optical applications. By applying a fringe-based technique, we determined the largest diagonal component of the effective second-order bulk susceptibility $\chi_{zzz}^{(2)}$ = 1.30$\pm$0.13 pm/V at a wavelength of 1032 nm. Noteworthy, we observed strong SH signals from two-component nanolaminates, which are several orders of magnitude larger than from single layers. The SH signals from our samples only require the broken inversion symmetry at the interface. Here optical properties of nanocomposites can be precisely tuned by the promising PEALD technology.

cond-mat.mtrl-sci↗

arXiv2025

Polarization Dependent Enhancement of Magnetic Dipolar Emission with Silicon Nanodimers

Eu(TTA)3 complexes are used as an emission source in the presence of high refractive index dielectric nanostructures. These nanostructures support Mie-type resonances that modify the local density of optical states. Specifically, the silicon dimer provides polarization-dependent electric and magnetic field enhancement in the dimer gap to modify the electric dipolar and magnetic dipolar emissions of the Eu3+ at 610 nm and 590 nm, respectively. Finite element method simulations are used to determine the optimal parameters for the sample and to demonstrate the polarization-dependent emission enhancement of dipolar emitters in the gap. A two-step electron beam lithography process is used to fabricate the hybrid nanoscopic structures, with a Eu3+ doped electron beam resist located only in the center of the dimer. The results demonstrate the potential of these nanostructures to selectively tailor the emission of the two distinct dipolar transitions by engineering the resonant nanostructures. Our work highlights the potential of magnetic light-matter interactions as a novel degree of freedom.

physics.optics↗

arXiv2025

Directional and contra-directional coupling in Huygens' metawaveguide microring resonators

Huygens' metawaveguides represent a transformative concept in photonic device engineering, enabling unprecedented control over light propagation. This study presents, for the first time, integrated Huygens'-based microring resonators and directional and contra-directional couplers, specifically designed for operation at the S- and C-band telecommunication wavelengths. By leveraging the unique properties of resonant Huygens' waveguides, we demonstrate efficient evanescent directional coupling with high-Q resonators, characterized by negative group index and near-zero dispersion, which are critical for enhancing performance in compact, high-performance add-drop filters. The research further explores the implications of these novel structures on group index and group velocity dispersion, providing insights into their potential applications in nonlinear optics and quantum information technologies. Notably, the introduction of a hybrid subwavelength grating-Huygens' contra-directional coupler facilitates backward coupling between resonant and non-resonant metawaveguides, achieving a broad spectral rejection bandwidth. Our findings advance the integration of resonant metamaterials into scalable photonic platforms, laying the groundwork for innovative applications in optical communications, quantum photonics and sensing systems.

physics.optics↗

arXiv2025

Tunable Resonant Metasurfaces Empowered by Atomically Thin Semiconductors

Nanophotonics has recently gained new momentum with the emergence of a novel class of nanophotonic systems consisting of resonant dielectric nanostructures integrated with single or few layers of transition metal dichalcogenides (2D-TMDs). Thinned to the single layer phase, 2D-TMDs are unique solid-state systems with excitonic states able to persist at room temperature and demonstrate notable tunability of their energies in the optical range. Based on these properties, they offer important opportunities for hybrid nanophotonic systems where a nanophotonic structure serves to enhance the light-matter interaction in the 2D-TMDs, while the 2D-TMDs can provide various active functionalities, thereby dramatically enhancing the scope of nanophotonic structures. In this work, we combine 2D-TMD materials with resonant photonic nanostructures, namely, metasurfaces composed of high-index dielectric nanoparticles. The dependence of the excitonic states on charge carrier density in 2D-TMDs leads to an amplitude modulation of the corresponding optical transitions upon changes of the Fermi level, and thereby to changes of the coupling strength between the 2D-TMDs and resonant modes of the photonic nanostructure. We experimentally implement such a hybrid nanophotonic system and demonstrate voltage tuning of its reflectance as well as its different polarization-dependent behavior. Our results show that hybridization with 2D-TMDs can serve to render resonant photonic nanostructures tunable and time-variant $-$ important properties for practical applications in optical analog computers and neuromorphic circuits.

physics.optics↗

arXiv2025

Systematic Study of Amorphous ABC Heterostructures at the Atomic Scale as a Second-Order Nonlinear Optical Metamaterial

Systematic exploration of amorphous ABC heterostructures revealed that nanoscale morphological modifications markedly improved their artificial bulk second-order susceptibility. These amorphous birefringent heterostructures were fabricated through plasma-enhanced atomic layer deposition of three oxides, effectively breaking the centrosymmetry on the nanoscale. We observe a dependence of the optical nonlinearity on the thickness variation of three constituent materials, SiO$_2$, TiO$_2$, and Al$_2$O$_3$, ranging from tens of nanometers to the atomic scale, and these thin films exhibit second-order susceptibility at their interfaces. Our findings reveal that the enhancement of nonlinear optical properties is strongly correlated with a high density of layers and superior interface quality, where the interface second-order nonlinearity transitions to bulk-like second-harmonic generation. An effective bulk second-order susceptibility of $\chi_{zzz} = 2.0 \pm 0.2$~pm/V at the wavelength of 1032~nm is achieved, comparable to typical values for conventional monocrystalline nonlinear materials.

physics.app-ph↗

arXiv2025

Valley-dependent emission patterns enabled by plasmonic nanoantennas

Selective control over the emission pattern of valley-polarized excitons in monolayer transition metal dichalcogenides is crucial for developing novel valleytronic, quantum information, and optoelectronic devices. While significant progress has been made in directionally routing photoluminescence from these materials, key challenges remain: notably, how to link routing effects to the degree of valley polarization, and how to distinguish genuine valley-dependent routing from spin-momentum coupling - an optical phenomenon related to electromagnetic scattering but not the light source itself. In this study, we address these challenges by experimentally and numerically establishing a direct relationship between the intrinsic valley polarization of the emitters and the farfield emission pattern, enabling an accurate assessment of valley-selective emission routing. We report valley-selective manipulation of the angular emission pattern of monolayer tungsten diselenide mediated by gold nanobar dimer antennas at cryogenic temperature. Experimentally, we study changes in the system's emission pattern for different circular polarization states of the excitation, demonstrating a valley-selective circular dichroism in photoluminescence of 6%. These experimental findings are supported by a novel numerical approach based on the principle of reciprocity, which allows modeling valley-selective emission in periodic systems. We further show numerically, that these valley-selective directional effects are a symmetry-protected property of the nanoantenna array owing to its extrinsic chirality for oblique emission angles, and can significantly be enhanced when tailoring the distribution of emitters. This renders our nanoantenna-based system a robust platform for valleytronic processing.

physics.optics↗