Design decisions for today’s complex systems require insights that are traditionally obtained from make and break testing when critical design decisions need to be made. With ever-increasing complexity, a more streamlined workflow that involves multiphysics simulation is essential. This transition is exemplified in polarization-dependent optical systems that are becoming prevalent in AR/VR where stress birefringence can negatively affect the performance of the optical design. To quantify this effect, we have developed a method that utilizes non-uniform stress data from finite element analysis in conjunction with non-uniform gradient index ray tracing to calculate the polarization and wavefront error as part of a wholistic multiphysics simulation analysis. Practical examples will be used to demonstrate the workflow and to analysis the impact of stress birefringence.
Stress birefringence may lead to appreciable wavefront and polarization errors, especially in polarization sensitive systems. The effect is becoming increasingly important, as complex polarization-dependent and polymer-based optical systems become more prevalent, impacting imaging quality in systems such as Augmented and Virtual Reality. Advancements in multiphysics simulation, including the combination of Finite Element Analysis and optical simulation, enable optical designers to simulate and assess the effect of stress birefringence in the final performance of the optical system. We have developed a simulation method that combines 3D fitting of FEA non-uniform stress data with non-uniform gradient index ray tracing, calculating the polarization and wavefront error from the propagation of the wavefront through the system. We demonstrate the model with practical examples, in which we analyze the impact of stress birefringence on the polarization and image quality. The robustness of the technology is demonstrated with different types of stress data and optical systems.
Performance and reliability requirements for modern optical systems dictate that they can no longer be simulated in isolation without reference to external and environmental factors which can adversely impact image quality. Simultaneously, advances in multi-physics simulation techniques have made it possible to couple the impacts of, for example, thermal changes and structural stresses to optical analysis to better predict performance in operational conditions. Applications where light propagates through a fluid surrounding or within an optical system present a particular simulation challenge in this regard, and one that requires new simulation techniques. In the near-field, variations in pressure, temperature, and density of the fluid give rise to corresponding variations in refractive index that will, in turn, induce optical aberrations in a transmitted wavefront. These aberrations can lead to degraded image quality and line-of-sight errors. Accurate and robust analysis of such effects necessitates the coupling of computational fluid dynamics (CFD), for simulation of turbulent flow, shock waves, etc. with ray tracing to compute key optical metrics. Furthermore, this analysis can be combined with far-field atmospheric effects, including emissivity, absorption, scattering, refraction, to build a comprehensive picture of system performance. The ability to perform multi-physics simulations early in the design process provides the opportunity to develop strategies to identify and mitigate negative performance drivers. We present a solution to model the effects of light propagation through optical fluids accurately and combine this with analysis of structural and thermal effects. This solution will be demonstrated in use cases including electro-optic infrared airborne systems.
This paper provides an accurate and simple simulation workflow for Structural, Thermal and Optical Performance (STOP) analysis on complex optical systems. Applying this workflow to a high-power laser system, we use Ansys Zemax OpticStudio for both optical design and wavefront analysis. Then Ansys Speos is used for optical heat load calculation on each component of the system. Finally, Ansys Mechanical is used to perform thermal and structural analysis, providing this information back to OpticStudio for wavefront error analysis and optical tolerancing. The workflow is fully automated thanks to Ansys System Coupling interface. Besides the ease of use, this workflow captures the impact of structural deformations and refractive index changes on the key performances of any optical system, accounting for opto-mechanical component contributions. The approach can be steady-state or transient.
Our new Contrast Optimization technique allows for robust and efficient optimization on the system MTF at a given spatial frequency. The method minimizes the wavefront differences between pairs of rays separated by a pupil shift corresponding to the targeted spatial frequency, which maximizes the MTF. Further computational efficiency is achieved by using Gaussian Quadrature to determine the pattern of rays sampled. Examples are given to demonstrate the advantages of the technique.
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