[Paper] Evaluation and Analysis of Light Diffraction from One-dimensional Liquid Crystal Devices Using Pixel Pitches more than 1 μm

Abstract

Holography has attracted attention because of its potential for ultimate three-dimensional (3D) display capability. It can physically reconstruct the same light from an object and satisfies all visual cues for autostereoscopic vision, such as motion parallax, binocular disparity, vergence and accommodation. Moreover, it enables natural autostereoscopic displays [1-4]. 3D holographic images are reconstructed from hologram patterns displayed on a spatial light modulator (SLM). However, the pixel pitch of conventional SLMs may not be sufficiently small for holography images with a wide viewing zone angle. The viewing zone angle is described by the equation, θ = 2 sin–1 (λ/2p), where λ is the light wavelength and p is the pixel pitch of the display [5]. The latest commercial SLMs with a 3 μm pixel pitch generate 3D holographic images with a narrow viewing zone angle of 12° for displays [6]. An SLM with narrow pixel pitch of < 1 μm is required to realize a viewing zone angle wider than 30°, which may open up a new application (e.g., a personal terminal with 3D holographic images) [3]. Liquid crystal (LC) devices with a narrow pixel-pitch have recently been actively studied for holographic applications for smaller crosstalk with dielectric wall structures [7-10]. The pixel structure of LC SLMs is very simple having electrodes and LC layers compared to the pixel structure of DMD having electrodes, micromirrors and some mechanical systems to control micromirrors [21, 22]. This simple structure is very important for the high applicability for narrow pixel pitch. Isomae et al. showed that ferroelectric liquid crystal (FLC) could achieve a higher resolution compared to nematic liquid crystal (NLC) with narrow pixel pitches [8]. Chida et al. have showed that blurring the black/white pixel boundaries affects the decrease of the first-order diffraction efficiency on simulations with NLC devices [10]. The first-order diffraction efficiency is one of the most important factors for the quality of 3D holographic images. Thus, the quantitative evaluation of the firstorder diffraction efficiency of the FLC device with almost 1 μm pixel pitch is very important for SLM devices in 3D holographic displays. The first-order diffraction efficiency is one of the most important factors for the quality of 3D holographic images. So the light diffraction Abstract We compare the diffraction characteristics of ferroelectric (FLC) and nematic liquid crystal (NLC) devices with one-dimensional stripe patterns of 1–10 μm pixel pitches. The polarizing micrographs show pixel boundaries of black/white pixels blur as the pixel pitch becomes smaller. The blur of NLC is more remarkable than that of FLC. The first-order diffraction efficiency of NLC remains constant for the pixel pitch of 4–10 μm and sharply decreases for the pixel pitch of < 2 μm. By contrast, the FLC efficiency decreases with the pixel pitch decrease from 10 to 4 μm and remains constant for the pixel pitch of < 3 μm. The FLC efficiency (5.5%) is four times larger than that of NLC (1.4%) with a 1 μm pixel pitch. The Fourier transform calculation shows the efficiency degradation of FLC is caused by the blur at the pixel boundary, whereas that of NLC caused by the blur and contrast deterioration.