Peter Vandersteegen

Efficient nonadiabatic planar waveguide tapers

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 /spl mu/m, and for taper lengths between 0.5 and 3.0 /spl mu/m. 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.

Employing a 2D surface grating to improve light out coupling of a substrate emitting organic LED

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 RC2LED, applied to an OLED. The RC2LED 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 RC2 layers is also investigated in this paper.

Python in Nanophotonics Research

The authors describe how they use Python for nanophotonics research-specifically, they describe using it for electromagnetic modeling, mask design, and process simulation

Light extraction for a doubly resonant cavity organic LED: the RC2LED

The RC2LED is a substrate emitting OLED which has three additional interference layers between the ITO electrode and the glass substrate. This creates two resonant optical cavities. The RC2LED has 2 resonant optical cavities. The first cavity is also present in regular devices and is formed by metal/organic layers/ITO. The second cavity is formed by 3 additional layers: a high refractive index layer (Nb2O5), a low refractive index layer (SiO2) and a high refractive index layer (Nb2O5). The additional layers introduce a strong wavelength dependent improvement of the extraction efficiency compared to the OLED without the additional layers. Our simulations show an improvement of the extraction efficiency of over 70% over a wavelength range of 75 nm compared to an OLED without the 3 layers. Light extraction is worse compared to the reference OLED for wavelengths outside this wavelength range. the when compared to the OLED. This improvement has been experimentally verified for a green OLED with an emission between 500nm and 650 nm. A numerical study shows a relative improvement of 10% for the luminous power efficiency of a 3 color white OLED with the additional layers. The emitted white corresponds with the light emitted by illuminant A. The WOLED has been composed of a fluorescent blue emitter, green and red phosphorescent emitters.

Numerical Investigation of a 2D-Grating for Light Extraction of a Bottom Emitting OLED

An important limiting factor for efficient white light emitting organic LEDs is the total internal reflection occurring at each interface. In a bottom emitting OLED light is trapped by reflection at the interface between the organic layers and glass substrate and at the interface between the glass substrate and air. We investigate the use of a grating at the glass substrate-air interface. In this paper we will discuss the developed 3D-simulation method and several important simulation results. Our simulation method shows that the grating extracts approximately 50% more power in comparison with a planar device. These results are comparable with the use of micro lenses

Luminous power efficiency optimization of a white organic light-emitting diode by tuning its spectrum and its extraction efficiency

We show an increase of the luminous power efficiency of a white organic light-emitting diode (LED) with three emitters by optimizing its spectrum and its extraction efficiency. To calculate this efficiency we use a model with four parameters: the spectra, extraction efficiencies, internal quantum efficiencies of three emitters, and the driving voltage. This luminous power efficiency increases by 30% by use of a spectrum close to the spectrum of the MacAdam limit. This limit gives the highest luminous efficacy for a given chromaticity. We also show that a white organic LED with an inefficient deep blue emitter can give the same luminous power efficiency as a white organic LED with a more efficient light blue emitter, because of their different fractions in the radiant flux. Tuning the extraction efficiency with a microcavity to the spectrum also increases the luminous power efficiency by 10%.

Increasing light extraction of a substrate emitting OLED using a 2D surface grating

We present simulation and experimental results to achieve increased light extraction of a substrate emitting OLED. A 2D grating located at the glass-air interface experimentally gives a relative improvement of approx. 30 %

Simulations of Kerr based non linear optical components with the Complex Jacobi iteration

Summary form only given. We present several non-linear structures simulated with the non-linear complex Jacobi iteration. This method numerically integrates the fields of the Helmholtz equation for points located on a grid. Because the fields are calculated on each grid point this results in a very flexible method. This iterative method refines each iteration step the calculated fields until a desired error has been achieved. The first structure under discussion is a one dimensional study of a cavity surrounded by two Bragg gratings. These two Bragg gratings create a photonic band gap. The introduced cavity creates a resonance wavelength in the middle of this band gap. All light with this resonance wavelength will be transmitted by this structure. Introducing a non-linear material in the cavity will shift the resonance peak to higher wavelengths. A comparison with non-linear eigenmode expansion confirms the accuracy of our simulation tool. We have also shown that the numerical dispersion introduced by a discrete mesh can be controlled if the discretization step Deltax < lambda/20. We will also present preliminary simulation results from a 2 dimensional vertical coupler. Light coupled vertically in the coupler is symmetrically injected in a left and right waveguide. Injection efficiency in one waveguide reaches a maximum for a certain wavelength. Adding non-linearity in the grating material will hopefully result in a shift of this maximum. Parts of this work has been performed in the context of the Belgian IAP photon network

Modeling methods for high-index contrast linear and non-linear nanophotonics

We present several modeling methods for the study of nanophotonic devices: a non-linear eigenmode expansion method and a non-linear complex Jacobi method to model Kerr devices, and an RCWA-based model to study extraction of light from OLEDs using periodic structures

Ultrafast, all-optical regeneration functionalities inside a Kerr-nonlinear platform

We theoretically investigate the potential of a Kerr-nonlinear resonator for all-optical regeneration. In combination with an optical amplifier, this ultra-compact structure allows for an extremely flexible approach in terms of bandwidth and regenerative strength, which can readily be integrated into future nonlinear platforms