Liquid Crystal Displays with Variable Viewing Angle Using Diffusers of Electric-Field-Driven Liquid Crystal Lenses

초록

We propose a method for controlling the distance of the image plane in Fourier holograms by using varifocal electric-field-driven liquid crystal (ELC) lenses. In order to reduce the thickness and response time of the ELC lenses, phase Fresnel lenses are employed. The voltages applied to the electrodes of the ELC Fresnel lens are adjusted such that the lens has the same phase retardation distribution as the ideal lens. The focal length can be controlled by changing the phase retardation distribution with the applied voltages. We performed simulations for the image reconstruction of the Fourier holograms with various focal lengths of the ELC Fresnel lens. The interference pattern of the hologram is reconstructed by both a liquid-crystal spatial light modulator (LC-SLM) with the resolution of 1920×1080 and the varifocal Fresnel ELC lens located on the front of the SLM. A plane wave with wavelength of 632.8nm is used as reference beam. The quality of the reconstructed image is evaluated quantitively by comparing the relationship between the RMS value and PSNR of the image according to the focal length of the varifocal ELC Fresnel lens. The results show that the distance of the image plane can be controlled with the varifocal ELC Fresnel lens. However, the results reveal noise in the reconstructed images caused by the aberration of the ELC lens due to phase retardation discrepancy between the ideal lens and the ELC lens. The discrepancy, caused by the quantized phase retardation distribution due to the finite-size electrodes, increases as the focal length of the ELC lens decreases. In order to reduce the aberration of the ELC lens, miniaturization of the electrodes is required for achieving more accurate phase retardation distribution.