Optical properties of black silicon structures ALD-coated with Al 2 O 3

Atomic layer deposited (ALD) Al 2 O 3 coatings were applied on black silicon (b-Si) structures. The coated nanostructures were investigated regarding their reflective and transmissive behaviour. For a systematic study of the influence of the Al 2 O 3 coating, ALD coatings with a varying layer thickness were deposited on three b-Si structures with different morphologies. With a scanning electron microscope the morphological evolution of the coating process on the structures was examined. The optical characteristics of the different structures were investigated by spectral transmission and reflection measurements. The usability of the structures for highly efficient absorbers and antireflection (AR) functionalities in the different spectral regions is discussed

Modeling electro-optical characteristics of broad area semiconductor lasers based on a quasi-stationary multimode analysis

To increase the brightness of broad area laser diodes, it is necessary to tailor the optical properties of their waveguide region. For this purpose, there is the need for simulation tools which can predict the optical properties of the complete device and thus of the outcoupled light. In the present publication, we show a numerical method to calculate typical intensity distributions of the multimode beam inside a high-power semiconductor laser. The model considers effects of mode competition and the influence of the gain medium on the optical field. Simulation results show a good agreement with near and far field measurements of the analyzed broad area laser diodes

Switchable optics based on guided mode resonance in lithographically patterned vanadium dioxide with integrated heating layer

Vanadium dioxide (VO2) has promising applications in smart windows and active micro-optical devices due to its thermochromic properties. However, the successful fabrication and patterning of VO2 thin films with the correct stoichiometry and phase are challenging. In this study, we investigated lithographically patterned and non-patterned VO2 thin films fabricated by reactive ion beam deposition, using variable angle spectroscopic ellipsometry, Raman spectroscopy, and transmission and reflection measurements. The results show that the refractive index and extinction coefficient exhibit significant changes for near-infrared wavelengths when heated above 68 °C, confirming its thermochromic properties. The Raman spectroscopy results indicate the formation of the monoclinic phase VO2(M) after annealing, which was not changed by reactive ion etching. Lithographically structured VO2-layers were successfully realized demonstrating the potential of VO2 as a material for active micro-optical devices, such as guided mode resonance filters with switchable reflectance. The results suggest that VO2 has great potential as a promising material for actively switched optical elements and micro-optical devices

Fabrication influences on a miniaturised stokes polarimeter consisting of stacked nano-optical wire grid polarizer and retarders

The polarization properties of light can be fully controlled with nano-optical wire grid polarizers and artificial birefringent grating structures. We demonstrate an integrated polarimeter based on stacked layers of such elements. However, the optical performance of such elements is fundamentally limited and may be further altered by deviations arising from the fabrication processes. In this contribution we investigate the influences on the polarimetry performance for such a device

Switchable optics based on guided mode resonance in lithographically patterned vanadium dioxide

Vanadium dioxide as a phase change material is usually known for its consideration in smart window applications. However, the attention shifts to using it in actively switched optical elements. The main challenges are the deposition of vanadium dioxide with the correct stoichiometry and phase and the patterning of the material. We propose a design with a corresponding manufacturing process for an actively switchable reflector at 1550 nm wavelength with a contrast near 105 by using the thermochromic effect of vanadium dioxide. The reflectance of the proposed optical element can be controlled between an ultra-low and a high reflecting state. We elaborate on the proposed optical design, the manufacturing process including deposition, annealing and patterning processes, and discuss already achieved results

Modeling and optimization of single-pass laser amplifiers for high-repetition-rate laser pulses

We propose a model for a continuously pumped single-pass amplifier for continuous and pulsed laser beams. The model takes into account Gaussian shape and focusing geometry of pump and seed beam. As the full-wave simulation is complex we have developed a largely simplified numerical method that can be applied to rotationally symmetric geometries. With the tapered-shell model we treat (focused) propagation and amplification of an initially Gaussian beam in a gain crystal. The implementation can be done with a few lines of code that are given in this paper. With this code, a numerical parameter optimization is straightforward and example results are shown. We compare the results of our simple model with those of a full-wave simulation and show that they agree well. A comparison of model and experimental data also shows good agreement. We investigate in detail different regimes of amplification, namely the unsaturated, the fully saturated, and the intermediate regime. Because the amplification process is affected by spatially varying saturation and exhibits a nonlinear response against pump and seed power, no analytical expression for the expected output is available. For modeling of the amplification we employ a four-level system and show that if the fluorescence lifetime of the gain medium is larger than the inverse repetition rate of the seed beam, continuous-wave amplification can be employed to describe the amplification process of ultrashort pulse trains. We limit ourselves to this regime, which implies that if titanium:sapphire is chosen as gain medium the laser repetition rate has to be larger than a few megahertz. We show detailed simulation results for titanium:sapphire for a large parameter set

Fully integrated stokes snapshot imaging polarimeter

We present a new concept for a fully integrated nano-optical snapshot imaging polarimeter. It consists of a nano-optical retarder and polarizer array with various orientations combined with a microlens array and crosstalk module. That facilitates a fast, robust, and compact stokes imaging polarimeter without moving parts for applications at 450 nm wavelength

Fully integrated stokes snapshot imaging polarimeter

We present a new concept for a fully integrated nano-optical snapshot imaging polarimeter. It consists of a nano-optical retarder and polarizer array with various orientations combined with a microlens array and crosstalk module. That facilitates a fast, robust, and compact stokes imaging polarimeter without moving parts for applications at 450 nm wavelength