High voltage fragmentation of composites from secondary raw materials - Potential and limitations.

The comminution of composites for liberation of valuable components is a costly and energy-intensive process within the recycling of spent products. It therefore is continuously studied and optimized. In addition to conventional mechanical comminution innovative new principles for size reduction have been developed. One is the use of high voltage (HV) pulses, which is known to be a technology selectively liberating along phase boundaries. This technology offers the advantage of targeted liberation, preventing overgrinding of the material and thus improving the overall processing as well as product quality. In this study, the high voltage fragmentation of three different non-brittle composites (galvanized plastics, carbon fibre composites, electrode foils from Li-ion batteries) was investigated. The influence of pulse rate, number of pulses and filling level on the liberation and efficiency of comminution is discussed. Using the guideline VDI 2225 HV, fragmentation is compared to conventional mechanical comminution with respect to numerous criteria such as cost, throughput, energy consumption, availability and scalability. It was found that at current state of development, HV fragmentation cannot compete with mechanical comminution beyond laboratory scale.

Relevance of the light line in planar photonic crystal waveguides with weak vertical confinement.

The concept of the so-called light line is a useful tool to distinguish between guided and non-guided modes in dielectric slab waveguides. Also for more complicated structures with 2D mode confinement, the light lines can often be used to divide a dispersion diagram into a region of a non-guided continuum of modes, a region of discrete guided modes and a forbidden region, where no propagating modes can exist. However, whether or not the light line is a concept of practical relevance depends on the geometry of the structure. This fact is sometimes ignored. For instance, in the literature on photonic crystal waveguides, it is often argued that substrate-type photonic crystal waveguides with a weak vertical confinement are inherently lossy, since the entire bandgap including the line defect modes is typically located above the light line of the substrate. The purpose of this article is to illustrate that this argument is inaccurate and to provide guidelines on how an improved light line concept can be constructed.

Mode-locked laser diode with an ultrafast integrated uni-traveling carrier saturable absorber.

A novel two-section integrated mode-locked laser diode (MLLD) with a separate ultrafast uni-traveling carrier (UTC) saturable absorber section and semiconductor optical amplifier gain section is demonstrated. The UTC absorber is composed of a thin p-InGaAsP absorbing layer and an intrinsic InGaAsP collecting layer. By confining the photoexcitation process to the thin highly doped absorbing layer, the diffusion-limited hole extraction process is greatly enhanced. The investigated MLLD produces 600 fs uncompressed optical pulses at a 42 GHz repetition rate.