What’s new?

Many optical systems are, in practice, affected by the presence of stray light.
For example, reflections at the surfaces of each component of the optical system and other scattering processes are causing additional light that interferes with the actually desired signal of the system.
The potential interference patterns which can result - also known as ghost images - may negatively affect the overall performance of the setup and are thus worth investigating in detail.

VirtualLab Fusion’s nonsequential fast physical optics simulation engine allows the optical engineer to include or disregard multiple interactions between surfaces in a flexible, convenient, easy-to-use way. This is achieved by VirtualLab Fusion’s so-called “Channel Concept”, where for each individual surface the corresponding “input-output pair” of channels (transmission and reflection both from left and right, four channels in total) can be opened or closed at will. The software can then automatically determine which paths the light will follow through the system, and trace the electromagnetic field accordingly.

As an example, we showcase an investigation of ghost images in a collimation system, accompanied by another document that provides an in-depth look at the mentioned channel concept:

The methodical observation of astronomic phenomena is one of the oldest forms of optics. Over time, ever more advanced telescopes and other related optics have been developed to give scientists an ever deeper look into our galaxy and the universe.

To analyze the performance of such systems, the fast physical optics modeling and design software VirtualLab Fusion offers the optical engineer multiple tools, ranging from quick system visualization based on ray tracing, to a fully electromagnetic physical-optics propagation of light, including diffractive phenomena.

To showcase the potential of VirtualLab Fusion in the field of astronomy, we highlight the following two use cases this week: The first one presents a full model of the famous Schmidt-Cassegrain telescope, including a discussion of the effects of the Schmidt-Plate. In the second use case we simulate different afocal systems for laser guide stars, based on the work from L. Clermont, et al., "Design of a laser guide star for applications to adaptive optics".

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.

Gratings are some of the fundamental optical components used in many different modern applications and technologies. These components can sometimes be modeled with sufficient accuracy by functional approaches. However, for a thorough study of the effects that a grating introduces into an optical system, a modeling strategy that takes into account the actual structure is required.

VirtualLab Fusion offers a broad range of different specialized solvers for this task, ranging from approximate but fast methods like the Thin Element Approximation (TEA), to rigorous approaches like the Fourier Modal Method (FMM)/Rigorous Coupled-Wave Analysis (RCWA).

In this week's newsletter we showcase two examples that illustrate these solvers in action, playing their role in examples taken from various fields of application.

Hybrid lenses combine the advantages of classic refractive components and diffractive structures, and hence have become a promising approach in different optical applications. In particular, the opposite signs of the dispersion for refractive and diffractive surfaces enable the correction of chromatic aberrations.

In order to model and design such a hybrid element accurately, the in-depth analysis of diffraction effects through the system is a necessity. VirtualLab Fusion’s fast physical optics propagation techniques allow for the accurate modeling of classic lenses and calculation of the diffraction efficiencies of the different orders of a diffractive lens.

To illustrate the capabilities of the software in this regard, we compare the models of a refractive and hybrid eyepiece. In this example, the propagation of light and the corresponding chromatic effects are investigated for on-axis as well as off-axis beams at different wavelengths.