Investigate the effect of surface roughness on a nm-scale on the performance of macroscopic optical components.

Surface roughness due to fabrication processes can significantly influence the performance of optical components. For a quantitative investigation of such effects, rigorous simulations of Maxwell's equations on the microscopic level have to be performed. Due to the outstanding convergence properties of higher-order finite elements and due to the nearly arbitrary resolution properties of unstructured spatial FEM meshes, such multi-scale simulations can be approached ideally using JCMsuite.

Fig. 1: Toy example of a microoptical component (size of the computational domain: 120 microns by 320 microns). A Gaussian beam is incident from the top and reflected by TIR.

Fig. 2: Detail of the triangular mesh with a surface roughness of 10nm. (Automatic mesh generation using JCMgeo.)

Figure 1 shows a sample problem: an optical element with a radius of curvature in the mm-range is illuminated by a gaussian beam from the top. We simulate the setup with a smooth surface and with a rough surface. Figure 2 shows a detail of the mesh including roughness (rms-value of few nm). Figure 3 and 4 show resulting near field intensity distributions with (Fig. 3) and without (Fig. 4) roughness. Clearly, the roughness has great impact on the field distribution. Through build-in post-processes, JCMsuite computes the relevant observable quantities (e.g. the angular spectrum of scattered light, or the energy flux to specified regions).

Field with surface roughness

Fig. 4: Intensity distribution without surface roughness.