arXiv subjects

Sven Burger

Publications and source records attributed to Sven Burger.

At least 73 records · Page 4Linked to original sources

arXiv2019

Efficient determination of bespoke optically active nanoparticle distributions

We provide a computational method for quickly determining the correct distribution of optically active nanoparticles for a desired response. This is achieved by simulating the optical response of single nanoparticles and performing a statistical averaging over different sizes. We find good agreement between experiment and theory for the transmission, reflectance and absorption of both an ordered and disordered array. By repeating the simulation for different particle distributions, we show that the method is capable of accurately predicting the correct nanoparticle distribution for a desired optical response. We provide a referential graph for predicting the optical response of different Ag nanoparticle distributions on a glass substrate, which can be extended to other substrate and particle materials, and particle shapes and sizes.

physics.optics↗

arXiv2018

Using effective medium theories to design tailored nanocomposite materials for optical systems

Modern optical systems are subject to very restrictive performance, size and cost requirements. Especially in portable systems size often is the most important factor, which necessitates elaborate designs to achieve the desired specifications. However, current designs already operate very close to the physical limits and further progress is difficult to achieve by changing only the complexity of the design. Another way of improving the performance is to tailor the optical properties of materials specifically to the application at hand. A class of novel, customizable materials that enables the tailoring of the optical properties, and promises to overcome many of the intrinsic disadvantages of polymers, are nanocomposites. However, despite considerable past research efforts, these types of materials are largely underutilized in optical systems. To shed light into this issue we, in this paper, discuss how nanocomposites can be modeled using effective medium theories. In the second part, we then investigate the fundamental requirements that have to be fulfilled to make nanocomposites suitable for optical applications, and show that it is indeed possible to fabricate such a material using existing methods. Furthermore, we show how nanocomposites can be used to tailor the refractive index and dispersion properties towards specific applications.

physics.optics↗

arXiv2018

Design rules for customizable optical materials based on nanocomposites

Nanocomposites with tailored optical properties can provide a new degree of freedom for optical design. However, despite their potential these materials remain unused in bulk applications. Here we investigate the conditions under which they can be used for optical applications using Mie theory, effective medium theories, and numerical simulations based on the finite element method. We show that due to scattering different effective medium regimes have to be distinguished, and that bulk materials can only be realized in a specific parameter range. Our analysis also enables us to quantify the range of validity of different effective medium theories, and identify design rules on how the free material parameters should be adjusted for specific applications.

physics.optics↗

arXiv2018

Riesz-projection-based theory of light-matter interaction in dispersive nanoresonators

We introduce a theory to analyze the behavior of light emitters in nanostructured environments rigorously. Based on spectral theory, the approach opens the possibility to quantify precisely how an emitter decays to resonant states of the structure and how it couples to a background, also in the presence of general dispersive media. Quantification on this level is essential for designing and analyzing topical nanophotonic setups, e.g., in quantum technology applications. We use a numerical implementation of the theory for computing modal and background decay rates of a single-photon emitter in a diamond nanoresonator.

physics.optics↗

arXiv2018

Role of Geometric Shape in Chiral Optics

The distinction of chiral and mirror symmetric objects is straightforward from a geometrical point of view. Since the biological as well as the optical activity of molecules strongly depend on their handedness, chirality has recently attracted high interest in the field of nano-optics. Various aspects of associated phenomena including the influences of internal and external degrees of freedom on the optical response have been discussed. Here, we propose a constructive method to evaluate the possibility of observing any chiral response from an optical scatterer. Based on solely the T-matrix of one enantiomer, planes of minimal chiral response are located and compared to geometric mirror planes. This provides insights into the relation of geometric and optical properties and enables identifying the potential of chiral scatterers for nano-optical experiments.

physics.optics↗

arXiv2018

Nanophotonic enhanced two-photon excited photoluminescence of perovskite quantum dots

All-inorganic CsPbBr3 perovskite colloidal quantum dots have recently emerged as promising material for a variety of optoelectronic applications, among others for multi-photon-pumped lasing. Nevertheless, high irradiance levels are generally required for such multi-photon processes. One strategy to enhance the multi-photon absorption is taking advantage of high local light intensities using photonic nanostructures. Here, we investigate two-photon-excited photoluminescence of CsPbBr3 perovskite quantum dots on a silicon photonic crystal slab. By systematic excitation of optical resonances using a pulsed near-infrared laser beam, we observe an enhancement of two-photon-pumped photoluminescence by more than one order of magnitude when comparing to using a bulk silicon film. Experimental and numerical analyses allow relating these findings to near-field enhancement effects on the nanostructured silicon surface. The results reveal a promising approach for significant decreasing the required irradiance levels for multi-photon processes being of advantage in applications like low-threshold lasing, biomedical imaging, lighting and solar energy.

physics.optics↗

arXiv2018

Modelling of standard and specialty fibre-based systems using finite element methods

We report on the investigation of an approach for modelling light transmission through systems consisting of several jointed optical fibres, in which the analytical modelling of the waveguides was replaced by Finite Element Modelling (FEM) simulations. To validate this approach we first performed FEM analysis of standard fibres and used this to evaluate the coupling efficiency between two singlemode fibres under different conditions. The results of these simulations were successfully compared with those obtained using classical analytical approaches, by demonstrating a maximum loss deviation of about 0.4 %. Further, we performed other more complex simulations that we compared again to the analytical models. FEM simulations allow addressing any type of guiding structure, without limitations on the complexity of the geometrical waveguide cross section and involved materials. We propose as example of application the modelling of the light transmitted through a system made of a hollow core photonic crystal fibre spliced between two singlemode standard optical fibres, and qualitatively compare the results of the simulation with experimental results.

physics.app-ph↗

arXiv2018

Online measurement of optical fibre geometry during manufacturing

Online measurement of diameters and concentricities of optical fibre layers, and the coating layer in particular, is one of the challenges in fibre manufacturing. Currently available instruments can measure concentricity and diameter of layers offline, and are not suitable for precise monitoring or control of the manufacturing process in real time. In this work, we use two laser beams, positioned orthogonally to illuminate the fibre from two sides, and calculate deviations from the expected geometry by analysing the scattering pattern. To measure the diffraction pattern we use two 8K linear array detectors, with the scattered light incident directly on the sensors. Each detector is capturing approximately 90 degree angular range directly behind the fibre. The two measurement channels are positioned at different heights. The scattered pattern is modelled mathematically with finite-element and Fourier-modal methods, with various diameter and concentricity deviations. The sensitivities of the changes in the scattering pattern are identified in respect to these deviations. Since calculations are computationally intensive, the sensitivities are pre-calculated in advance, and the real-time measurement is based on pattern recognition. The symmetry of the pattern is used to differentiate between diameter and concentricity variations. We performed online measurements with the prototype instrument in production conditions, and show that this method is sensitive enough to measure deviations of under 1 μm in diameter and concentricity of the coating layer.

physics.optics↗

arXiv2018

Antireflective nanotextures for monolithic perovskite-silicon tandem solar cells

Recently, we studied the effect of hexagonal sinusoidal textures on the reflective properties of perovskite-silicon tandem solar cells using the finite element method (FEM). We saw that such nanotextures, applied to the perovskite top cell, can strongly increase the current density utilization from 91% for the optimized planar reference to 98% for the best nanotextured device (period 500 nm and peak-to-valley height 500~nm), where 100% refers to the Tiedje-Yablonovitch limit. In this manuscript we elaborate on some numerical details of that work: we validate an assumption based on the Tiedje-Yablonovitch limit, we present a convergence study for simulations with the finite-element method, and we compare different configurations for sinusoidal nanotextures.

physics.app-ph↗

arXiv2018

Enhanced photon-extraction efficiency from InGaAs/GaAs quantum dots in deterministic photonic structures at 1.3 μm fabricated by in-situ electron-beam lithography

The main challenge in the development of non-classical light sources remains their brightness that limits the data transmission and processing rates as well as the realization of practical devices operating in the telecommunication range. To overcome this issue, we propose to utilize universal and flexible in-situ electron-beam lithography and hereby, we demonstrate a successful technology transfer to telecom wavelengths. As an example, we fabricate and characterize especially designed photonic structures with strain-engineered single InGaAs/GaAs quantum dots that are deterministically integrated into disc-shaped mesas. Utilizing this approach, an extraction efficiency into free-space (within a numerical aperture of 0.4) of (10${\pm}$2) % has been experimentally obtained in the 1.3 μm wavelength range in agreement with finite-element method calculations.

cond-mat.mes-hall↗

arXiv2018

Benchmarking five numerical simulation techniques for computing resonance wavelengths and quality factors in photonic crystal membrane line defect cavities

We present numerical studies of two photonic crystal membrane microcavities, a short line-defect cavity with relatively low quality ($Q$) factor and a longer cavity with high $Q$. We use five state-of-the-art numerical simulation techniques to compute the cavity $Q$ factor and the resonance wavelength $λ$ for the fundamental cavity mode in both structures. For each method, the relevant computational parameters are systematically varied to estimate the computational uncertainty. We show that some methods are more suitable than others for treating these challenging geometries.

physics.comp-ph↗

arXiv2018

Numerical optimization of the extraction efficiency of a quantum-dot based single-photon emitter into a single-mode fiber

We present a numerical method for the accurate and efficient simulation of strongly localized light sources, such as quantum dots, embedded in dielectric micro-optical structures. We apply the method in order to optimize the photon extraction efficiency of a single-photon emitter consisting of a quantum dot embedded into a multi-layer stack with further lateral structures. Furthermore, we present methods to study the robustness of the extraction efficiency with respect to fabrication errors and defects.

physics.comp-ph↗

arXiv2018

Chiral scatterers designed by Bayesian optimization

The helicity or chirality of scattered light is strongly linked to the dual symmetry of the scatterer. The latter depends on chiral materials or on scatterers which are not superimposable with their mirror image. This inherently yields asymmetric structures of various shapes with many degrees of freedom. In order to explore these high dimensional parameter spaces, numerical simulations and especially optimization strategies are a valueable tool. Here, we optimize the emission of chiral line sources in two-dimensional dimer setups using Bayesian optimization. We deduce relevant objective functions from recent theoretical findings for chiral electromagnetic fields and employ rigorous simulations of Maxwell's equations.

physics.optics↗

arXiv2017

Deterministic integration of quantum dots into on-chip multi-mode interference beamsplitters using in-situ electron beam lithography

The development of multi-node quantum optical circuits has attracted great attention in recent years. In particular, interfacing quantum-light sources, gates and detectors on a single chip is highly desirable for the realization of large networks. In this context, fabrication techniques that enable the deterministic integration of pre-selected quantum-light emitters into nanophotonic elements play a key role when moving forward to circuits containing multiple emitters. Here, we present the deterministic integration of an InAs quantum dot into a 50/50 multi-mode interference beamsplitter via in-situ electron beam lithography. We demonstrate the combined emitter-gate interface functionality by measuring triggered single-photon emission on-chip with $g^{(2)}(0) = 0.13\pm 0.02$. Due to its high patterning resolution as well as spectral and spatial control, in-situ electron beam lithography allows for integration of pre-selected quantum emitters into complex photonic systems. Being a scalable single-step approach, it paves the way towards multi-node, fully integrated quantum photonic chips.

physics.app-ph↗

arXiv2016

Locally Enhanced and Tunable Optical Chirality in Helical Metamaterials

We report on a numerical study of optical chirality. Intertwined gold helices illuminated with plane waves concentrate right and left circularly polarized electromagnetic field energy to sub-wavelength regions. These spots of enhanced chirality can be smoothly shifted in position and magnitude by varying illumination parameters, allowing for the control of light-matter interactions on a nanometer scale.

physics.optics↗

arXiv2016

Correlated Diffuse X-ray Scattering from Periodically Nano-Structured Surfaces

Laterally periodic nanostructures were investigated with grazing incidence small angle X-ray scattering. To support an improved reconstruction of nanostructured surface geometries, we investigated the origin of the contributions to the diffuse scattering pattern which is correlated to the surface roughness. Resonant diffuse scattering leads to a palm-like structure of intensity sheets. Dynamic scattering generates the so-called Yoneda band caused by a resonant scatter enhancement at the critical angle of total reflection and higher-order Yoneda bands originating from a subsequent diffraction of the Yoneda enhanced scattering at the grating. Our explanations are supported by modelling using a solver for the time-harmonic Maxwell's equations based on the finite-element method.

cond-mat.mes-hall↗

arXiv2016

Time-Harmonic Optical Chirality in Inhomogeneous Space

Optical chirality has been recently suggested to complement the physically relevant conserved quantities of the well-known Maxwell's equations. This time-even pseudoscalar is expected to provide further insight in polarization phenomena of electrodynamics such as spectroscopy of chiral molecules. Previously, the corresponding continuity equation was stated for homogeneous lossless media only. We extend the underlying theory to arbitrary setups and analyse piecewise-constant material distributions in particular. Our implementation in a Finite Element Method framework is applied to illustrative examples in order to introduce this novel tool for the analysis of time-harmonic simulations of nano-optical devices.

physics.optics↗

arXiv2016

The Optical Chirality Flux as a Useful Far-Field Probe of Chiral Near Fields

To optimize the interaction between chiral matter and highly twisted light, quantities that can help characterize chiral electromagnetic fields near nanostructures are needed. Here, by analogy with Poynting's theorem, we formulate the time-averaged conservation law of optical chirality in lossy dispersive media and identify the optical chirality flux as an ideal far-field observable for characterizing chiral optical near fields. Bounded by the conservation law, we show that it provides precise information, unavailable from circular dichroism spectroscopy, on the magnitude and handedness of highly twisted fields near nanostructures.

physics.optics↗