Birefringence of Thin Uniaxial Polymer Films Estimated Using the Light Polarization Ellipse

A simple method for determining the linear birefringence of the thin layers based on the determination of the orientation of the polarization ellipse of totally polarized light is proposed and it is applied to PVA thin foils. Theoretical notions and the experimental procedure are described. The linear birefringence of polymer thin foils with different degrees of stretching is determined and the applicability of the method is discussed.

Inner helical waveplate with angle-insensitive retardation

The angle-sensitivity is a serious defect of birefringent waveplate, and it draws lots of interest from researchers. In this paper, an angle-insensitive waveplate with inner helix structure is proposed. The super-twisted nematic liquid crystal polymer is used to fabricate the inner helical waveplate, and the retardation-shift is measured and analyzed. In the measured result, the retardation-shift is in the range from -0.311% to 0.194% at 45° polar angle, which is 2 orders of magnitude lower than that of the conventional waveplate. Theoretically, the retardation-shift is less than 0.5% in the polar angle range from 0° to 60°, and it will be less if the material with high refractive index is used. The analysis of the self-compensation effect explains the principle of angle-insensitivity, and the influence of tilt angle on angle-sensitivity is also investigated to guide the better design. At last, the application of the inner helical waveplate in wide color gamut display is taken as an example to show the broad application prospects.

Liquid Crystal Displays with Variable Viewing Angles Using Electric-Field-Driven Liquid Crystal Lenses as Diffusers

We propose a novel method for appropriately controlling the luminance distribution of liquid crystal displays (LCDs) for different usage environments by using electric-field-driven liquid crystal (ELC) lenses. The LCD systems are composed of quasi-collimated backlights (QCBLs), LC panels, and ELC lenses that are used as diffusers. To achieve a wide viewing angle, light is diffused with the ELC lenses by controlling its retardation with the voltage applied to the electrodes. For private use, a narrow viewing angle is achieved by turning the ELC lenses off so that the collimated light from the QCBLs passes directly through the liquid-crystal layer of the ELC lens and travels without diffusion. To validate the proposed method, we simulated the luminance distributions of the wide-view and narrow-view modes by using a finite difference method (FDM) and Taguchi’s design of experiments method. The simulation results show that the light distribution of the wide-view mode was 84.3% similar to the ideal Lambertian distribution and was wider than that of IPS-LCDs with wide viewing angle characteristics. In addition, the light distribution of the narrow-view mode had a full width at half maximum of 7°. The luminance of the exiting light at viewing angles of 20° and above was calculated to be close to 0.

Bending effect on the circular polarizer of an organic light-emitting diode display

We investigated the retardation change of a reactive-mesogen-type quarter-wave plate (QWP) by bending. We measured the retardation of the QWP when the slow axis of the QWP was perpendicular or parallel to the bending axis. We simulated the effect of the retardation change on the antireflection property of a quasi-circular polarizer used for an organic light-emitting diode display. The light leakage was diminished with bending in the vertical viewing direction, while it was increased in the horizontal viewing direction regardless of the orientation of the slow axis.

Dependence of the birefringence of polystyrene film on the stretching conditions

We investigated the dependence of the birefringence of polystyrene (PS) film with a negative optical birefringence on the stretching conditions. We varied the stretching ratio (SR), stretching speed (SS), and stretching temperature (ST), and measured the inplane birefringence and the N_z coefficient of the PS film. The inplane birefringence was increased with greater SR and SS but decreased with greater ST. The N_z coefficient of the stretched PS film was around zero and showed similar dependence on the stretching conditions like inplane birefringence.

Analysis of Crosstalk in 3D Circularly Polarized LCDs Depending on the Vertical Viewing Location

Crosstalk in circularly polarized (CP) liquid crystal display (LCD) with polarized glasses (passive 3D glasses) is mainly caused by two factors: 1) the polarizing system including wave retarders and 2) the vertical misalignment (VM) of light between the LC module and the patterned retarder. We show that the latter, which is highly dependent on the vertical viewing location, is a much more significant factor of crosstalk in CP LCD than the former. There are three contributions in this paper. Initially, a display model for CP LCD, which accurately characterizes VM, is proposed. A novel display calibration method for the VM characterization that only requires pictures of the screen taken at four viewing locations. In addition, we prove that the VM-based crosstalk cannot be efficiently reduced by either preprocessing the input images or optimizing the polarizing system. Furthermore, we derive the analytic solution for the viewing zone, where the entire screen does not have the VM-based crosstalk.

Polarizing grating color filters with large acceptance angle and high transmittance

We design and simulate a polarizing color filter with a sub-wavelength metal-dielectric grating. It manifests several advantages: a large acceptance angle (up to ±50°), high transmittance (74.3%-92.7%), low absorption loss (∼3.3%), and a high extinction ratio. This polarizing color filter can be integrated into a liquid-crystal display (LCD) backlight system to simultaneously recycle the light according to its color and polarization. In combination with a specially designed directional backlight, this newly proposed LCD system can theoretically improve optical efficiency up to ∼2.5×, and also provides a large ambient contrast ratio and a wide view. Our approach enables an ultra-low-power LCD without using the complicated field-sequential-color technique.

Achromatic wide-view circular polarizers for a high-transmittance vertically-aligned liquid crystal cell

We propose an optical compensation scheme through which we can eliminate the off-axis light leakage in a vertically-aligned liquid crystal cell with circular polarizers. In this scheme, four uniaxial films with complementary dispersion characteristics are used to compensate one another, resulting in achromatic effective phase retardation for off-axis angles. By using the proposed optical compensation, a contrast ratio higher than 2000:1 can be realized over the entire 55° viewing cone in a multi-domain vertical-alignment liquid crystal cell with circular polarizers.

Elimination of light leakage over the entire viewing cone in a homogeneously-aligned liquid crystal cell

We propose an optical compensation scheme that uses uniaxial films for perfect elimination of light leakage over the entire viewing cone in a homogeneously-aligned liquid crystal cell. Uniaxial films with different dispersion characteristics are used so that they can compensate one another to achieve achromatic optical compensation. Owing to the rotational symmetry of the polarization change on the S(2)-S(3) plane of the Poincaré sphere, we can eliminate the light leakage at all azimuth angles. The contrast ratio of the proposed configuration for white light is higher than 3000:1 at a polar angle of ± 85°, irrespective of the azimuth angle.

Achromatic optical compensation using dispersion of uniaxial films for elimination of off-axis light leakage in a liquid crystal cell

We propose an achromatic optical-compensation method using uniaxial films to eliminate the off-axis light leakage at the dark state in a homogeneously aligned liquid crystal cell. Three uniaxial films with different dispersion characteristics are used so that they can compensate each other to achieve achromatic effective phase retardation at off-axis. The retardation values are optimized with the aid of the Poincaré sphere and through numerical research. A contrast ratio of higher than 2000∶1 is predicted over the entire ±60° viewing cone for a homogeneously aligned LC cell with zero pretilt angle.

A vertical-field-driven polymer-stabilized blue phase liquid crystal mode to obtain a higher transmittance and lower driving voltage

We demonstrate a vertical-field-driven polymer-stabilized blue phase liquid crystal (PS-BPLC) mode for solving low transmittance and high driving voltage problems in conventional in-plane-switching (IPS) PS-BPLC modes. By controlling the ray directions of incident beams by means of two prism sheets attached to the top and bottom substrates, continuous grayscale properties can be achieved with a vertical field, where the transmittance of the proposed structure can be increased to become twice as high as that of a IPS PS-BPLC cell, and its driving voltage can also be lowered by about 20 V. With the vertical-field-driven PS-BPLC mode, the hysteresis problem of the IPS PS-BPLC mode can also be solved due to a reduction of the electric field required to achieve sufficient field-induced retardation.

Wideband and wide-view circular polarizer for a transflective vertical alignment liquid crystal display

We propose an optical configuration for a transflective mode with a circular polarizer for the vertical alignment liquid crystal cell, which can show the wideband property of high contrast in oblique incidence. The proposed configuration consists of a biaxial film and two uniaxial films for satisfying both the transmissive and the reflective modes. Optimization of the optical configuration of the circular polarizer has been performed on the Poincaré sphere in the entire visible wavelength range using the Stokes vector and the Mueller matrix method. We also verify the excellent optical characteristics of the proposed configuration by comparing the viewing angle and contrast ratio in the oblique direction with a conventional optical configuration in calculation.

Viewing angle controllable displays with a blue-phase liquid crystal cell

We demonstrate a controllable viewing angle liquid crystal display (LCD) using an inserted blue-phase liquid crystal (BPLC) cell. The BPLC layer functions as a tunable positive C-film or a negative C-film, depending on whether the employed LC has a positive or negative dielectric anisotropy. Therefore, the viewing angle of the LCD panel can be controlled continuously by the applied voltage of the BPLC cell.

Optimization of an optical configuration in a vertical alignment liquid crystal cell for wide viewing angle

We propose an optical structure for a vertical alignment (VA) liquid crystal (LC) cell with a wide viewing angle. The proposed LC cell consists of an A-plate and two C-plates for optical compensation. Optical compensation and optimization to eliminate off-axis light leakage in the entire visible wavelength range are performed on a Poincaré sphere using the Stokes vector and the Muller matrix method. After optimizing the wavelength dispersion of the retardation films that are used, we prove that the proposed VA LC cell can improve the viewing angle and contrast ratio by calculating optical characteristics, particularly in diagonal directions.