Lars Thorben Neustock

Optical waveguides with compound multiperiodic grating nanostructures for refractive index sensing

The spectral characteristics and refractive index sensitivity of compound multiperiodic grating waveguides are investigated in theory and experiment. Compound gratings are formed by superposition of two or more monoperiodic gratings. Compared to monoperiodic photonic crystal waveguides, compound grating waveguides offer more degrees of design freedom by choice of component grating periods and duty cycles. Refractive index sensing is achieved by evaluating the wavelength or intensity of guided mode resonances in the reflection spectrum. We designed, fabricated, and characterized 24 different compound multiperiodic nanostructured waveguides for refractive index sensing. Simulations are carried out with the Rigorous Coupled Wave Algorithm (RCWA). The resulting spectra, resonance sensitivities, and quality factors are compared to monoperiodic as well as to three selected aperiodic nanostructures (Rudin-Shapiro, Fibonacci, and Thue-Morse). The refractive index sensitivity of the TE resonances is similar for all types of investigated nanostructures. For the TM resonances the compound multiperiodic nanostructures exhibit higher sensitivity values compared to the monoperiodic nanostructure and similar values as the aperiodic nanostructures. No significant influence of the compound grating duty cycles on the sensitivity is observed.

Simulation methods for multiperiodic and aperiodic nanostructured dielectric waveguides

Nanostructured dielectric waveguides are of high interest for biosensing applications, light emitting devices as well as solar cells. Multiperiodic and aperiodic nanostructures allow for custom-designed spectral properties as well as near-field characteristics with localized modes. Here, a comparison of experimental results and simulation results obtained with three different simulation methods is presented. We fabricated and characterized multiperiodic nanostructured dielectric waveguides with two and three compound periods as well as deterministic aperiodic nanostructured waveguides based on Rudin–Shapiro, Fibonacci, and Thue–Morse binary sequences. The near-field and far-field properties are computed employing the finite-element method (FEM), the finite-difference time-domain (FDTD) method as well as a rigorous coupled wave algorithm (RCWA). The results show that all three methods are suitable for the simulation of the above mentioned structures. Only small computational differences are obtained in the near fields and transmission characteristics. For the compound multiperiodic structures the simulations correctly predict the general shape of the experimental transmission spectra with number and magnitude of transmission dips. For the aperiodic nanostructures the agreement between simulations and measurements decreases, which we attribute to imperfect fabrication at smaller feature sizes.

Adjoint method for estimating Jiles-Atherton hysteresis model parameters

A computationally efficient method for identifying the parameters of the Jiles-Atherton hysteresis model is presented. Adjoint analysis is used in conjecture with an accelerated gradient descent optimization algorithm. The proposed method is used to estimate the Jiles-Atherton model parameters of two different materials. The obtained results are found to be in good agreement with the reported values. By comparing with existing methods of model parameter estimation, the proposed method is found to be computationally efficient and fast converging.

Remote Experimentation with Massively Scalable Online Laboratories

In this paper we present a solution for highly scalable online laboratories at low cost. The Massively Scalable Online Laboratories (MSOL) is an online platform that enables the virtualization of real experiments in a fashion that very closely mimics a physical experiment. Moreover, it includes social features to enable peer-to-peer learning and facilitates the creation of an online community. To add an experiment to the MSOL platform, an existing setup is automatically turned into a data set, accessible through data base queries. In this way, MSOL provides an effective and scalable solution to add an important element to current online education systems at low costs. The MSOL platform might also accompany scientific and engineering papers to add another domain to disseminate qualitative and quantitative data.

Plattformtechnologie für die mobile, markerfreie Proteindetektion

Zusammenfassung Wir präsentieren eine Plattformtechnologie zur gleichzeitigen, mobilen, markerfreien Detektion von mehreren Proteinen. Ein photonischer Kristall, der mit Liganden lokal funktionalisiert ist, dient hier als Sensor. Über ein kompaktes, Kamera-basiertes Messsystem wird die Proteinanbindung an die Sensoroberfläche in ein Intensitätssignal umgewandelt, über dessen Amplitude die Proteinkonzentration bestimmt werden kann. Um das Detektionslimit dieser Technologie weiter zu verbessern, werden hier photonische Kristalle mit einer multiperiodischen und aperiodischen Gitterstruktur simulativ und experimentell untersucht. Dafür werden die Gesamtempfindlichkeit und die Resonanzgüte jeder Struktur bestimmt und mit der bisher verwendeten monoperiodischen Struktur verglichen. Es konnte festgestellt werde, dass sich die Resonanzgüte von mono- über multi- bis aperiodisch deutlich verbessert. Eine Steigerung der Gesamtempfindlichkeit konnte nicht festgestellt werden. Jedoch konnte anhand von Analysen der elektrischen Feldverteilung innerhalb der verschiedenen Strukturen beobachtet werden, dass die Modenausbreitungen in den aperiodischen Strukturen stark lokalisiert wird und die elektrische Feldintensität in diesen „Hot-Spots“ deutlich über der mittleren Feldintensität, die eine flächige Funktionalisierung repräsentiert, liegt. Diese lokale Resonanzausbildung konnte zudem bereits in ersten experimentellen Untersuchungen bestätigt werden.

Simulation of photonic waveguides with deterministic aperiodic nanostructures for biosensing

Photonic waveguides with deterministic aperiodic corrugations offer rich spectral characteristics under surface-normal illumination. The finite-element method (FEM), the finite-difference time-domain (FDTD) method and a rigorous coupled wave algorithm (RCWA) are compared for computing the near-field and far-field properties of structures based on a Rudin-Shapiro binary sequence. All simulation methods predict multiple resonances with sensitivities in the range of 30 nm/RIU to 60 nm/RIU for bulk refractive index measurements. Local functionalization is estimated to improve the sensitivity for biomolecular binding by a factor of 2.97.