Michael Paulus

Light propagation and scattering in stratified media: a Green’s tensor approach

We present a new technique for computing the electromagnetic field that propagates and is scattered in three-dimensional structures formed by bodies embedded in a stratified background. This fully vectorial technique is based on the Green’s tensor associated with the stratified background. Its advantage lies in the fact that only the scatterers must be discretized, the stratified background being accounted for in the Green’s tensor. Further, the boundary conditions at the different material interfaces as well as at the edges of the computation window are perfectly and automatically fulfilled. Several examples illustrate the utilization of the technique for the modeling of photonic circuits (integrated optical waveguides), the study of the optics of metal (surface plasmons), and the development of new optical lithography techniques.

Influence of metal roughness on the near-field generated by an aperture/apertureless probe.

We study the influence of metal roughness on the near‐field distribution generated by an aperture or an apertureless (scattering) probe. Different experimental parameters are investigated: roughness magnitude, aperture form, distribution of the roughness. Our results show that aluminium roughness has a dramatic impact on the emission characteristics of a near‐field probe and in particular on its polarization sensitivity. Apertureless or scattering probes appear to be less sensitive to roughness and to provide a well confined field even with a somewhat rough probe.

Contrast mechanisms in high-resolution contact lithography: A comparative study

We compare three different approaches to high-resolution contact lithography with special emphasis on contrast mechanisms for subwavelength structures. Masks with protruding metal absorbers, masks with absorbers embedded in the transparent background, and masks with air gaps and recessed absorbers are studied. Using the Greens tensor technique we compute the light intensity distribution in the photoresist. The intensity and contrast functions are investigated for different mask geometries (absorber thickness, height of protruding elements), and the difference between chrome and gold as absorber material is discussed. Our results show that embedding the absorbers in a transparent mask material enhances the transmitted intensity and the contrast compared with a mask having protruding metal absorbers. A further improvement is achieved by a topographically patterned mask with air gaps and recessed absorbers. Optimized mask dimensions can be found for which the contrast and the depth of focus are increased

A fully vectorial technique for scattering and propagation in three-dimensional stratified photonic structures

We present a three-dimensional (3D) technique for computing light scattering and propagation in complex structures formed by scatterers embedded in a stratified background. This approach relies on the Greens tensor associated with the background and requires only the discretization of the scatterers, the entire stratified background being accounted for in the Greens tensor. Further, the boundary conditions at the edges of the computation window and at the different material interfaces in the stratified background are automatically fulfilled. Different examples illustrate the application of the technique to the modeling of photonic integrated circuits: waveguides with protrusions (single element ‘grating’) and notches. Subtle effects, like polarization crosstalks in an integrated optics device are also investigated.

How to tap an innocent waveguide

We study the interaction of a mode propagating in a planar waveguide with a three--dimensional rectangular defect (protrusion or notch) in the structure. The scattering by the defect disturbes the propagation of the mode and light is coupled out of the waveguide. To investigate these phenomena we compute electric field distributions with the Greens tensor technique and show movies with varying defect geometries and different mode polarizations. These calculations should be useful for optimizing specific elements in complex photonic circuits.

Near-field distribution in light-coupling masks for contact lithography

We discuss the potential and limitations of light-coupling masks for high-resolution subwavelength optical lithography. Using a three-dimensional fully vectorial numerical approach based on Green’s tensor technique, the near-field distribution of the electric field in the photoresist is calculated. We study the dependence of the illuminating light and the angle of incidence on polarization. Furthermore, we investigate the replication of structures of various sizes and separations. It is predicted that the formation of features in the 60 nm range is possible using light with a 248 nm wavelength. However, with decreasing separation among the features, crosstalk limits the ultimate resolution.

Scattering experiments with a diving cylinder

We present numerical experiments of light scattering by a circular dielectric cylinder embedded in a stratified background, using the Greens tensor technique. The stratified background consists of two or three dielectric layers, the latter forming an anti-reflection system. We show movies of the scattered field as a function of different parameters: polarization, angle of incidence, and relative position of the cylinder with respect to the background interfaces.