VirtualLab Fusion Applications

Gratings are some of the most fundamental tools in the arsenal of any optical engineer. To design and analyze this kind of component, the fast physical optics modeling and design software VirtualLab Fusion provides its users with many helpful tools. These include the Parametric Optimization, to easily optimize your systems, and the Parameter Run, which allows you to perform parameter sweeps in order to study the influence of those parameters on the overall behavior of the setup. Furthermore, this enables the use to investigate effects introduced by deviations due to specific fabrication processes in detail. Different solvers are also put at your disposal for the simulation of the interaction of the field with the grating, with different assumptions and the corresponding levels of approximation. These range from the rigorous Fourier Modal method (FMM) to the Thin Element Approximation (TEA), which works well for larger structures with a shallow relief.

The main functionality of an imaging system is to gather as much of the light emanating from each of the object points as possible, and to make those cones of light converge again at the image plane, so that each object point is mapped univocally to its counterpart in the image plane. The performance of such systems is generally judged on the basis of how well this correspondence between object and image points is maintained, with the well-known theoretical limit imposed by the phenomenon of diffraction: even in an optical system that, according to the laws of geometrical optics, will map all the rays coming from one object point exactly to a single, mathematical, image point, diffraction will cause that image point to smear into a small, but finite-sized, spot. This diffraction-limited situation is what the design of an imaging system typically aims for, with the diffraction-limited field having a spherical wavefront. Geometrical deviations from this spherical wavefront are known as “aberrations”, and are characterized using different polynomial bases that help quantify their strength and shape. The presence of aberrations will increase the smearing of the image spot and consequently decrease the quality of the imaging system.

With the fast physical optics software VirtualLab Fusion aberration effects can be studied well. For this week’s newsletter, we have selected two examples related to aberrations: the first, of how the typical wavefront aberrations affect the pattern in focus of a spherical wave, and the second, of how the astigmatism of a high-power laser diode influences performance in the focal region. Using the free space propagation field solver and the Local Plane Interface Approximation (LPIA), diffraction, polarization and vectorial effects that can potentially degrade an image can all be included in the investigation.

Most common designs of augmented and mixed reality (AR & MR) systems incorporate lightguide designs with surfaces that contain micro- and nanostructured regions (gratings) for coupling and pupil expansion purposes. Many of the complex effects which influence the final quality of the device (for example, crucial aspects like how good the uniformity is in the eyebox for the different field-of-view modes that describe the digital image) have their roots in physical optics: polarization (initially of the source, as well as how the polarization changes as the light propagates through the device), coherence, diffraction, etc.

With its Light Guide Toolbox, the fast physical optics software VirtualLab Fusion provides the optical engineer with all the necessary tools to tackle the modeling and design of this type of device. To demonstrate its capabilities we showcase here two examples of simulations of different AR & MR setups.