Optimization and tolerance for an exit pupil expander with 2D grating as out-coupler

In this report, a simulation method with an example of optimization and tolerance analysis for an exit pupil expander (EPE) system using 2D grating as out-coupler has been proposed and demonstrated. In this design process, the first step is to establish a simulation workflow to dynamically link a raytracing engine and a rigorous coupled wave analysis (RCWA) solver. The RCWA solver, provided by Ansys Lumerical, can accurately calculate optical response of grating in the EPE system by solving Maxwell’s equations. The raytracing engine, provided by Ansys Zemax OpticStudio, is used to evaluate the whole system’s performance, such as efficiency and uniformity. In this step, the strategy of caching and interpolating the data when linking the RCWA solver and the ray-tracing engine is the key to make the simulation process streamlined and efficient. The second step is to prepare the system for optimization and tolerance analysis. A parametric model of the grating is first constructed. The parameters of this grating model are further considered as a function of position on the waveguide, which means the grating shape varies at different positions. The coefficients of this function are then used as variables during optimization and tolerance analysis by Ansys optiSLang. In this step, the spatial uniformity and the efficiency on the eye box are optimized, and the effect of the imperfect grating geometry and material are investigated.