Zhan He

A Novel Method for Determining the Cell Thickness and Twist Angle of a Twisted Nematic Cell by Stokes Parameter Measurement

A novel method of determining the cell thickness and the twist angle of twisted nematic liquid crystal (TNLC) cells by measurement of the Stokes parameters of light transmitted through the cell is presented. The relationships of the Stokes parameters of transmission light to the cell thickness and the twist angle are reduced by use of Jones matrix representation. The cell thicknesses and twist angles of some TNLC cells are determined practically by this simple method. The experimental results indicate that this method is valid. Furthermore, some properties of this method are discussed and an accuracy analysis by theoretical calculation is undertaken.

POLARIZATION PROPERTIES OF INVERSELY TWISTED NEMATIC LIQUID-CRYSTAL GRATINGS

Based on the Jones matrix representation of twisted nematic liquid crystals (LCs), we have carried out a theoretical analysis of the polarization properties of inversely twisted nematic (ITN) LC gratings. Some interesting polarization behaviors are expected in the ITN LC grating. When a linearly polarized light parallel or perpendicular to the grating direction is incident on the ITN LC grating, the diffracted light in the 0th order is linearly polarized with the same polarization direction of incident light, while the diffracted light in high orders is linearly polarized perpendicular to that of incident light. Using a multirubbing alignment technique, we have practically prepared an ITN LC grating with ?45 degrees inversely twisted structures. The experimental investigations of the optical characteristics of the ITN LC grating demonstrate agreement with theoretical expectations.

Polarization properties of an amplitude nematic liquid crystal grating

A nematic liquid crystal (LC) grating is prepared using an amplitude-type grating electrode structure and a homogeneous initial alignment parallel to the grating electrode direction. The polarization properties of the LC grating are investigated by measuring Stokes parameters of diffracted light under differently polarized incident light. The electrically variable polarization modulations of diffracted light are verified for the first time, as well as the diffraction light intensity modulations. Moreover, the LC grating exhibits some unique optical properties, such as symmetric diffraction light intensities but antisymmetric polarization states in corresponding positive and negative diffraction orders when the incident light is linearly polarized parallel or perpendicular to the grating direction. A polarization grating model is proposed to clarify the unusual polarization properties, which suggests that it may be related to the antisymmetric LC molecular orientation domains induced by the grating electrode structure.

Diffraction and Polarization Properties of a Liquid Crystal Grating

Diffraction properties of an amplitude liquid crystal grating with a periodic electrode structure are studied under different polarizer configurations. Based on these experimental results, polarization characteristics of light diffracted from this grating are discussed. Both diffraction light intensities and polarization states of this liquid crystal grating can be controlled electrically. Symmetrical diffraction light intensities but antisymmetrical polarization states in corresponding negative and positive diffraction orders are demonstrated.

A Two-Dimensional Stokes Parameter Method for Determination of Cell Thickness and Twist Angle Distributions in Twisted Nematic Liquid Crystal Devices

In order to determine 2-dimensional (2D) cell thickness and twist angle distributions in twisted nematic (TN) liquid crystal (LC) devices, we propose a 2D Stokes parameter method (2DSPM). A 2DSPM system is set up using a polarizing microscope, in which some preliminary experiments are conducted to demonstrate the validity of this 2DSPM. Experimental results of 2D distributions of cell thickness and twist angle in TN LC sample cells are given for the first time. The measurement accuracy of the 2DSPM system is analyzed.

An Improved Stokes Parameter Method for Determination of the Cell Thickness and Twist Angle of Twisted Nematic Liquid Crystal Cells

Based on the method previously proposed by us, an improved Stokes parameter method (ISPM), which is independent of the liquid crystal (LC) molecular alignment direction at the front substrate of the cell, is presented here to determine the cell thickness and twist angle of twisted nematic liquid crystal (TNLC) cells. The function equations of the Stokes parameters with the cell thickness and twist angle are deduced, and the experimental method is introduced. The preliminary experimental results verify the ISPMs validity. This method is very simple basically, only four transmission intensities of the TNLC cell are required to be measured. Furthermore, the theoretical analyses indicate that a high level of accuracy can be obtained by means of this method.

Cylindrical Liquid Crystal Lens and Its Applications in Optical Pattern Correlation Systems.

The optical characteristics of a cylindrical liquid crystal (LC) lens are investigated with voltages applied to LC cells. We show that the focusing performance of cylindrical LC lenses, such as focal length, can be varied by voltage application. With this kind of cylindrical LC lens, optical correlation architectures are achieved for the first time using a holographic matched spatial filter. The influence on correlation results of different reference light distributions from a LC lens under various applied voltages is also discussed.

Generation of optical Haar wavelets by zone plates.

Optical Haar wavelets are generated by zone plates that are designed to realize the bipolar nature of Haar wavelets. We present a circular Haar wavelet in two-dimensional space, which can extract the edge and corner features simultaneously, and characterize its properties with computer simulations. A comparison with rectangular Haar wavelets is also given.

Generalized Relation Theory of Torque Balance Method for Azimuthal Anchoring Measurements

The theory of the torque balance method for azimuthal anchoring energy measurements is investigated in detail under a general case of anchoring strength relationships between two substrates and a generalized relationship equation is deduced. As an example, azimuthal anchoring energies of several polyimide (PI) materials in magnetically aligned twisted-nematic (TN) cells are determined and the experimental results are discussed.

Molecular Orientations and Optical Transmission Properties of Liquid Crystal Cells with Slit-Patterned Electrodes

The molecular orientations in slit-patterned electrode liquid crystal (LC) cells with homogeneous initial alignment parallel to the slit pattern are investigated in detail using a 3-dimensional polarization observation method. In addition to conventional observations of interference fringes, we study the molecular orientations from cross sections of the LC cells using photoelasticity experimental techniques and a UV-curable LC material. A model of LC molecular orientations referred to as the electrically induced hybrid twisted nematic (EHTN) molecular orientation, is proposed. Moreover, optical transmission properties of such LC cells with different structural parameters are measured as a function of the applied voltage. The possibility of application of these kinds of LC cells to LC display devices is discussed.