Comparison of Analogue and Digital Driving Methods for the LC Cell of a Spatial Light Modulator

In this work, we compared the analogue and digital driving methods for setting the phase change of the reflected electromagnetic wave in a spatial light modulator (SLM) cell fabricated using liquid crystal on silicon (LCOS) technology. The spatial light modulator is an optical device that enables precise variation of the phase of reflected light from 0 to $2 \pi$ at different points on a surface with an accuracy better than 1°. The analogue method applies different voltage values to the cell to set a specific phase shift, while the digital method uses two fixed voltage values in pulse width modulation mode. The digital method has certain advantages such as noise immunity and higher accuracy of voltage setting, but has the disadvantage of flicker. An LC cell with a matrix of reflective pixels was assembled and the features of the analogue and digital phase shift driving scheme in it were measured using ellipsometry. It was found that digital control achieves the same phase range as analogue control with a comparable phase flicker of 0.1°. The results obtained will be useful for the design of digital phase shift control circuits in spatial phase modulators.