Combining Stokes Parameters Method and Genetic Algorithm for Measuring the Cell Thickness, Twist Angle, Pretilt Angle, and Azimuth Angle of Twisted-Nematic Liquid Crystal Cells

• Main Authors: Wei-liang Lin, 林威良
• Other Authors: Yu-lung Lo
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/43744580704789493579

碩士 === 國立成功大學 === 機械工程學系碩博士班 === 96 === Here, we proposed a method that combining stokes parameters method and genetic algorithm for measuring the cell thickness, twist angle, pretilt angle and azimuth angle of twisted-nematic liquid crystal cells. The Jones matrix of the TN cell rotated around the axis parallel to the cell surface and perpendicular to the ray direction is derived here. Unlike the existing methods, they need to know the alignment directions of liquid crystal molecules at the cell substrates or provide multiple wavelengths. We can measure cell parameters in the TNLC cell at any degree of the azimuth angle without adjusting the azimuth angle to be a known value. Instead of multiple wavelengths, we choose horizontal linear polarized light and linear polarized light at 45 degree with respect to the x-axis as our input light. The cell thickness, twist angle, pretilt angle and azimuth angle of twisted-nematic liquid crystal (TNLC) can be determined by genetic algorithm. As the results of the experimental data, the maximum standard deviations of the cell thickness Δd=0.0074μm, twist angle Δψ=0.1867 degree, pretilt angle Δθp=0.3457 degree and azimuth angle Δα=0.1648 degree at the azimuth angle α=90 degree. The maximum standard deviations of the cell thickness Δd=0.0084μm, twist angle Δψ=0.1982 degree, pretilt angle Δθp=0.3382 degree and azimuth angle Δα=0.1521 degree at the azimuth angle α=0 (180) degree.