Full polarimetric evaluation of the anamorphic transfer function for pixelated liquid crystal microdisplays

Abstract

Spatial Light Modulators (SLMs) employing phase-only modulation typically rely on parallel-aligned liquid crystal on silicon (PA-LCoS) microdisplays, known for their high resolution and small pixel size. However, the performance of high-definition pixelated SLM devices is affected by various interpixel cross-talk degradation effects, that manifest differently depending on the orientation and the spatial frequency profile displayed on the microdisplay. This study explores, both experimentally and numerically, the anamorphic spatial frequency transfer function for pixelated PA-LCoS devices. In particular, we focus on the impact of high-frequency binary phase grating profiles with the grating vector parallel and perpendicular to the alignment direction defined by the alignment layer. Experiments are performed with a commercial PA-LCoS microdisplay with eight-micron size pixels. Novel full Stokes light analysis (polarimetric study) of the diffraction orders and diffraction efficiency measurements (radiometric study) provides a deep insight into the anisotropic phenomena involved, showing not only anamorphic degradation in the radiometric but also in the polarimetric performance and dependent on the applied voltage. Computed rigorous electromagnetic numerical results show a very good agreement with the experimental ones. The numerical computation is an essential tool since it enables the connection of the far-field evaluation with the microscopic level: the 3D distribution of the LC director and the near-field values of the illuminating electromagnetic field are known for each applied voltage onto the PA-LCoS microdisplay and show evidence for the anamorphic results in the far-field. Through this rigorous combined radiometric-polarimetric computing approach, we provide evidence of the impact of smaller pixel sizes in this SLM technology and for different fill-factors.