Sequential and non-sequential simulation of volume holographic gratings

Abstract

Background: In the development process of holographic displays like holographic Head-Mounted Displays (hHMD) the simulation of the complete optical system is strongly required. This especially includes the correct behaviour of the volume holographic grating (VHG) in terms of its optical function and its diffraction efficiency. The latter is not supported by the current version of Zemax®; OpticStudio 17, one of the most popular optic simulation tools. Methods: To solve this problem we implemented a C++ code for each raytracing mode of Zemax®;, namely the sequential and non-sequential. The C++ code calculates the grating vector for every single ray traced. Based on the k-sphere formalism the propagation direction of the diffracted light is determined. Furthermore, its diffraction efficiency is defined according to Kogelnik’s coupled-wave theory. The C++ code is compiled and linked into Zemax®; using the Windows Dynamic Link Library (DLL). Results and discussion: The aforementioned DLL enables the simulation of planar and arbitrarily spherical curved VHG and their diffraction efficiency within Zemax®; OpticStudio. This allows the fast, easy and reliable simulation of optical systems which include holograms or holographic optical elements, e.g. hHMD. Especially the simulation of VHG in non-sequential mode can be helpful in order to identify possible stray light paths. Conclusion: The implemented C++ code enables the user to simulate VHG and its diffraction efficiency within Zemax®; Optic Studio.