Digital backplane liquid crystal on silicon devices (LCoS) are widely used in wavefront engineering applications due the maturity of the technology, thus the reliability of their performance. A thorough study of the relation between the different control parameters and their effect on the retardance modulation is lacking though. These control parameters, which are the low and high levels of the voltage signal together with the grey level addressed, in relation with the retardance modulation produced are explored across the whole visible spectrum. From a more practical point of view, this enables to decide which voltage parameters across the whole range of possibilities are the most appropriate for a certain wavefront engineering problem without the need to measure them in advance. Additionally, we are interested in the comparison of two different approaches developed in our research group to obtain the retardance modulation to see their possible pros and cons. The results presented are backed by the experimental measurements provided.
Spatial Light Modulators (SLMs) typically use PA-LCoS microdisplays, known for high resolution and small pixel size, for phase-only modulation. However, different phenomena related to the cross-talk, fringing fields between pixels, and out-of-plane reorientation of the liquid crystal director degrade the performance of pixelated SLM devices. The technology faces the challenge of overcoming these phenomena as novel applications require higher pixel size resolutions and smaller pixel sizes. This work applies a numerical workflow that permits the analysis of the different parameters that set up a PA-LCoS microdisplay, e.g., fill factor, pixel size, external voltage and the influence of the LC director and the interaction of light through the structure. Specifically, we focus our analysis on the impact of high-frequency binary phase gratings on the radiometric and polarimetric response with orthogonal grating vectors. The heterogenous LC distribution as a function of the grey level along the 3D structure and the inhomogeneous distribution of the Stokes parameters are analysed, setting up a framework to analyse the nonlinear behaviour of the system and its impact on diffraction and polarimetric performance in future microdisplays with higher resolutions and smaller pixel sizes.
It is well known that Spatial Light Modulators (SLM) are of great interest and used in many different areas because of their continuous capability of light modulation and their potential as a linear variable retarder. However, high-definition SLM devices face the challenge of providing high performance under the influence of different phenomena, such as crosstalk between adjacent pixels, fringing fields, and diffraction effects arising from the finite pixel grid pattern. In this work, a numerical analysis that computes the director orientation as a function of the retardance across specific voltages (gray level) is compared to experimental results. More specifically, this work is focused on analysing how previously mentioned phenomena affect the interpretation of the residual twist angle in parallel-aligned (PA) on SLM. This twist angle is computed from the Stokes parameter and compared to the actual orientation of the director distribution.
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