Abstract-We report taper designs with high transmission efficiencies and with lengths shorter than those needed for adiabatic operation. The tapering occurs between rectangular optical waveguides with the same vertical silicon-on-insulator layer structure, but with different horizontal widths, namely 0.5 and 2.0 µm, and for taper lengths between 0.5 and 3.0 µm. After a comparison between two different optimization methods in a two-dimensional calculation scheme, one of these is repeated using three-dimensional calculations. The results show that, also in the length region where conventional linear and parabolic tapers are not yet adiabatic, tapers with a high efficiency can be designed by applying complex taper structures with more degrees of freedom.

Abstract-We present a compact planar coupler connecting two optical waveguides with highly different widths. The coupler consists of various nonperiodic waveguide sections, whose dimensions are determined using a genetic optimization algorithm. Efficiencies that exceed those of the more conventional designs with similar lengths, like gradual linear tapers, were obtained in silicon-on-insulator using 248-nm-deep ultraviolet lithography.Index Terms-Compact coupler, high index contrast, nonadiabatic taper, optical coupler.

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We present simulation and experimental results to achieve increased light extraction of a substrate emitting OLED. We present a comparison between a grating surface on the OLED and an array of microlenses at the interface between substrate and air. This experimentally gives -in both cases-a relative improvement of approx. 30 %. We also demonstrate the concept of a RC 2 LED, applied to an OLED. The RC 2 LED is composed by adding a high, low and high index layers between ITO and glass, i.e. the interface between organic layers and glass. These extra layers create a cavity which numerically gives a relative improvement of over 60% at the resonance wavelength of the cavity over a wavelength range of 50-100 nm. The influence of an array of micro lenses in addition to the RC 2 layers is also investigated in this paper.

We present a three-dimensional model based on rigorous coupled wave analysis (RCWA) which allows us to study the influence of periodic structures on light extraction in light-emitting diodes. The gratings can be placed both at the interface between the emitting layers and the substrate, where they coherently interact with the dipole field, or at the interface between the substrate and air, where multiple incoherent reflections in the thick substrate contribute to the overall extraction. Even in the case of a grating at the interface between the substrate and air, these multiple incoherent reflections in the substrate still contribute to the overall extraction for large devices, an effect which has been mostly ignored in literature FDTD simulations