Phase modulation characteristics analysis of liquid crystal spatial light modulator under oblique incidence

A correction method for obtaining the phase modulation curves of liquid crystal spatial light modulator (LCSLM) systems under oblique incidence is proposed. Considering the reflection and refraction of the interface, the influence of oblique incidence on the LCSLM phase modulation was simulated and analyzed by solving the extended Jones matrix. The polarization interference principle was applied to construct a phase modulation system, the phase modulation was measured at different incident angles, and the measured data were subjected to Fourier fitting. The phase modulation curve was corrected to a straight line using the inverse interpolation method, and the lookup table (LUT) for the gray level and phase was then generated through the line coordinates. The measured results revealed that a larger angle of oblique incidence led to a smaller range of phase modulation. For LCSLM to function over a range from 0 to 2π, the oblique incidence angle should be less than 45°. Experimental results using 25° as an example confirmed the validity of the LUT. The correlation coefficient R between the phase modulation curve and the ideal linear curve was 0.9893, and the root-mean-square error was 0.1888. At incident angles from 0° to 45°, the linearity of the corrected LUT was as good as that of the LUT for vertical incidence, thereby laying the foundation for high-precision beam pointing control.