Transcript Slide 1
System for Measuring Parameters of Liquid Crystal Cells Sergiy Valyukh1,2, Christian Adås2, Gustav Franklin2, and Kent Skarp1,2 1Dalarna University, Borlänge, Sweden 2Swedish LCD Center AB, Borlänge, Sweden Outline ♦ Introduction ♦ Measuring of empty LC cells Method - Results - ♦ Measuring of filled transmissive LC cells Method - Results ♦ Measuring of filled reflective LC cells Method - Results ♦ Conclusion - Purposes of measuring Why this is necessary? Industrial purposes achieve a high quality of LCD image, desired characteristics of optoelectronic LC devices Fundamental studies of LC physics determination of some LC properties (e.g. measuring anchoring energy, studying LC viscosity, etc.) Types of LC cells What types of LC cells can be measured? Empty cells (reflective, transmissive) Filled nematic LC cells (reflective, transmissive) Optical arrangement Spectrometer Exit Polarizer Computer Transmissive LC Cell Beam Splitter Light source Entrance Polarizer Reflective LC Cell Reflector Empty cells Method 1) Measure spectrum of light reflected from (or transmitted through) a LC cell 2) Cell gap is derived from interference Empty cells Empty cells Range of measurements: 1m ... 50 m Accuracy of measurements: 0.01m Advantages: automatic real-time measurements allows determination of nonuniformity includes simulation results are saved in database Filled transmissive cells Method K 1 K 1) Built the characteristic function S ( ) Ti ( ) T j ( ) t i 1 j i 1 2) Find wavelengths of the extremes of St(): min, max 1 K T ( ) i o K i 1 arcsin 3) Determine the twist angle max1 max2 4) Find retardation from equations N 2 and 2 dn min cot X 2 2X X 3 2 where dn X Point of touch max 2 (*) 2 min 5) Find dispersion from fitting A sin 2 X 1 2 to St() X 6) Find cell gap as the ratio between retardation and birefringence Filled transmissive cells Sr() Ti() Filled transmissive cells Range: cell gap 2m ... 300 m twist angle 00...3600 Accuracy: cell gap 0,01m twist angle 0,50 input director 0,50 Advantages: semiautomatic fast includes simulation results are saved in database Filled reflective cells Characteristic function: Sr()=R()+ R+45() 1.0 1max1 1max2 2max1 2max1 3max1 3max1 4max1 4max1 Sr() 0.8 0.6 Lmin1 0.4 Lmin3 Lmin2 0.2 Lmin4 N=1 N=2 N=3 N=4 0.0 1 2 dn/ 3 4 5 Filled reflective cells Coordinates of extremes of Sr() Lmin2 N=2 2max1 Twist angle (deg.) Lmin1 1max1 1max2 N=1 dn/ 2max2 N=3 Filled reflective cells Values of local minima versus twist angle Lmin1 Lmin2 Lmin3 Lmin4 1.0 Sr() 0.8 0.6 0.4 0.2 0.0 60 80 100 120 140 160 Twist angle (deg.) 180 200 220 240 260 Filled reflective cells Method 1) Built the characteristic function: S=R+R+45 2) Find wavelengths of the extremes of Sr(): min, max R() R+45() Sr() Filled reflective cells Method 3) Determine the twist angle from value of a global minimum of Sr() 4) Find retardation from wavelength of the extremes of Sr() 2 sin X 2 cos X sin 2 X 2 X X 2 5) Find dispersion from fitting where dn X 2 to Sr() 2 6) Find cell gap as the ratio between retardation and birefringence Filled reflective cells Range: cell gap 2m ... 100 m twist angle 00...3600 Accuracy: cell gap 0,01m twist angle 0,50 input director 0,50 Advantages: semiautomatic fast includes simulation results are saved in database Conclusion ♦ The system developed by us can measure important LC cell parameters such as cell gap, twist angle, wavelength dispersion of birefringence, and the orientation of the input director ♦ The system can test all types of nematic LC cells: empty as well as filled, reflective and transmissive, with large and small cell gaps, with big and small twist angles ♦ The system has good accuracy ♦ Easy to use Dalarna university, Conoptix AB Forskargatan 3, Teknikdalen SE-781 70 Borlänge, Sweden e-mail: [email protected]