Abstract
Liquid crystal polarization gratings manifest several unique features, such as high diffraction efficiency, polarization selectivity, and fast switching time. However, few works address the chiral-doped liquid crystal alignment issue in such gratings. Here, we develop an improved relaxation method to analyze the liquid crystal director distribution in chiral-doped polarization gratings. Our simulation result agrees well with experimental data on a polarization volume grating. The criteria for forming planar or slanted polarization grating are discussed.
Highlights
Liquid crystal polarization grating (LCPG) is a critical optical element in near-eye displays because of its high diffraction efficiency and polarization selectivity [1,2,3,4,5,6]
The simplest half-wave polarization grating (HWPG) is composed of nematic liquid crystal (LC) that forms half-wave plate with spatially rotating optical axis
Some previous works address on the nematic LC alignment in LCPGs [16,17], to the best of our knowledge, no rigorous analysis dealing with the cholesteric liquid crystal (CLC) case and weak anchoring condition has been reported
Summary
Liquid crystal polarization grating (LCPG) is a critical optical element in near-eye displays because of its high diffraction efficiency and polarization selectivity [1,2,3,4,5,6]. The simplest HWPG is composed of nematic liquid crystal (LC) that forms half-wave plate with spatially rotating optical axis It usually has limited angular and spectral bandwidths. The optical performances of HWPG and PVG are different, their fabrication processes are rather similar: begin with a patterned alignment layer and overcoat a LC layer with different thickness and chiral concentration. In a LCPG with high chiral concentration, the director field is dependent on two highly coupled spatial variables, which makes analytically solving the Euler-Lagrange equations difficult. We accelerate the algorithm by seven times with momentum gradient descent method [26] Using this improved relaxation method, we explore the LC director field in PVG with various scenarios and confirm our simulation results with experiment. For a large deflection angle multi-layer HWPG with chiral dopants, the maximum thickness of each layer should not exceed ~20 nm, while for a small deflection angle HWPG the maximum thickness of each layer is about 600 nm
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