Byung-June Mun

Optical approach to improve the γ curve in a vertical-alignment liquid-crystal cell.

In this Letter, we propose an optical configuration of a four-domain vertical-alignment (VA) liquid-crystal (LC) cell, which can improve the γ-curve distortion by using a pair of patterned A plates, without any change in cell structure. In order to find the optimal parameter value of the patterned A film, we calculated the polarization difference between the normal direction and the all-viewing direction as functions of the optical axes and the retardation (Δnd) under the voltage applied state. Based on the calculated results, the proposed LC cell showed an improvement in γ-curve distortion of more than 80% in each oblique viewing angle compared to a conventional wide-view VA LC cell, without any loss of optical performance in the dark state.

Optimal design of quarter-wave plate with wideband and wide viewing angle for three-dimensional liquid crystal display

In this paper, we propose an optical structure for a circular polarizer-containing film patterned retarder (FPR), which has wideband and wide-view properties in a stereoscopic three-dimensional (3D) display. The FPR consists of a patterned λ/4 A-plate, a biaxial λ/2 plate, and a positive C-plate. We calculate the phase retardation of each film in the entire visible wavelength with the Stokes vector and the Muller matrix method. We demonstrate the excellent 3D characteristics of the proposed polarizer in the oblique direction by comparing the calculated light leakage of the proposed optical configuration with that of the conventional configuration. We calculate that the crosstalk of the proposed configuration is reduced to 0.39% for the left image and 0.29% for the right image in the horizontal oblique direction and to 0.37% for the left image and 0.29% for the right image in the vertical oblique direction (polar angle = 70°). These results indicate that the proposed configuration improves crosstalk by app...

A high transmittance color liquid crystal display mode with controllable color gamut and transparency

In this paper, we propose a color transparent liquid crystal (LC) mode that can control the properties of the color gamut and transparency in a single panel. To achieve high transmittance in the transparent LC mode, a reactive mesogen (RM) with embedded color dichroic dyes was applied instead of a color filter. Basically, the LC mode applied a 3-terminal electrode structure to switch between the transparent LC mode and the conventional color LC mode. Depending on the direction of the applied voltage, we can operate both the color mode and the transparent mode in a single panel, and modulate the transparency and color purity of the cell through appropriate voltage control. In the experiments, we confirmed that the transmittance and the color gamut of the cell were 39.4% and 2% in the transparent LC mode and 14.9% and 34% in the color LC mode, respectively. Modulation of the color gamut and transparency between each LC mode are also demonstrated in the paper.

A wide-view twisted nematic liquid crystal cell with improved image quality obtained by decreasing γ-curve distortion

Wide-view (WV) film, which was introduced by Fuji Co., has been commercialized to block light leakage of twisted nematic (TN)-liquid crystal (LC) cells in a dark state when the viewing angles are in the off-axis direction. In this investigation, we designed an optical compensation structure of a TN-LC cell with an improved γ-curve, as well as a viewing angle property in the dark state. Basically, we used a pair of optical films consisting of a positive and a negative A-plate in order to avoid affecting the viewing angle property in the dark state. Then, we optimized the positive and negative A-plate to improve the viewing angle property in the gray levels by calculating polarization variations as a function of the optical axis and the retardation of the pair of the A-plates. From this calculation, we were able to show that the proposed normally white (NW) WV-TN cell exhibits wide viewing angle performance, including good γ-curve stability.

Low Cell Gap Polymeric Liquid Crystal Lens for 2-D/3-D Switchable Auto-Stereoscopic Display

We propose a planar polymeric liquid crystal (LC) lens with a low cell gap (~ 4.6 μm) for a 2-D/3-D switchable auto-stereoscopic display. The proposed lens consists of two LC layers, one is a photopolymerized LC lens layer with a non-uniform refractive index with parabolic curve distribution, and the other is a half-wave LC switching layer of the vertical alignment type, which performs the 2-D/3-D image switching. The optimized refractive index of the LC lens layer was simply realized by polymerizing the LC molecules using a reactive mesogen. The proposed LC lens allow fast 2-D/3-D switching with low voltage and a simple fabrication process because of a low cell gap of the switching layer. We verified the electro-optical characteristics of the proposed LC lens by fabricating each layer after optimizing the cell structure. The measured focal length as a function of the applied voltage in the 3-D mode was compared with the calculated focal length and we confirmed that the measured results agreed with the calculated results.

Band-Separated UV Exposure on a Photosensitive Polyimide Layer With Embedded Reactive Mesogen for a High-Speed Liquid Crystal Display Device

In general, surface anchoring energy is one of the most important parameters that strongly affect electrooptical performance, especially the optical response time of liquid crystal (LC) displays. In this paper, we proposed a photoalignment method for strong surface anchoring energy by applying double ultraviolet (UV) exposure with a separated bandwidth to a photosensitive polyimide layer with embedded reactive mesogens (RMs) that can increase the anchoring energy during polymerization. We first polymerized the embedded RM molecules using long wavelength UV rays (over 340 nm), and then achieved the ordered photosensitive alignment layer using short UV rays (between 254 and 340 nm). We compared the measured surface anchoring energy and the optical response time by the proposed method with the conventional UV exposure using the in-plane switching LC mode for verification. As a result, we confirmed that the anchoring energy increased two times and the optical response time improved by 22% compared with the conventional pure UV exposure method.

The Optical Technology to Improve the Gamma-Curve in Liquid Crystal Display Modes

We introduce an optical approach, which can improve the γ-curve distortion using a pair of positive and negative A-type retardation films only for various liquid crystal display (LCD) modes. Optimization of a pair of A-plates was performed by calculating the polarization difference (Δp) between the normal and oblique incidence under a voltage applied state as functions of the retardation and the optical axis of the used A-plates. From the calculated results, LCD modes show an improvement of the γ-curve distortion over the 60% without any loss of optical performance in the dark state.

Fast Switching and Low Operating Vertical Alignment Liquid Crystal Display With 3-D Polymer Network for Flexible Display

Vertical alignment liquid crystal (LC) cell driven by in-plane field with 3-D polymer network exhibited no pooling mura under an external mechanical pressure; however, the operating voltage of the device was increased, because the polymer network hinders field-induced reorientation of LC. In this paper, we adopted a modified cell structure in which a counter electrode on top substrate of the conventional mode is existed, to improve upon this drawback. The proposed device in which the polymer network is formed in bulk of vertically aligned LC layer shows a very fast response time of 2 ms (rise + decay), 57% reduction in operating voltage, and also keeps image quality although the cell is curved.

Time-Sequential Ultraviolet Exposure to Alignment Layers Embedded With Reactive Mesogen for High-Speed In-Plane Switching Liquid Crystal Cell

We propose a time-sequential ultraviolet (UV) exposure process that can improve the surface anchoring energy of photopolyimide (PI) embedded with reactive mesogen (RM) in high-speed liquid crystal (LC) display devices. To increase the anchoring energy of the PI layer, a separated UV exposure process of polymerization for the embedded RM material and PI layer is required [1]-[8]. In this paper, we propose a novel single-frequency UV exposure method that can perform the separated polymerization of the UV alignment layer and the embedded RM material by optimizing the intensity of the exposure UV light. Using the proposed UV exposure method, we polymerize the RM material during the first 4 s, and then accomplish the polymerization of the UV alignment layer sequentially. To demonstrate the electro-optical performance, we measure the surface anchoring energy and the optical response time of in-plane switching LC cell. The measured results show that the surface anchoring energy and the optical response time are improved by more than 2.5 times and 28.2%, respectively, compared with the conventional UV exposure.

Multidimensional calculation of ray path in a twisted nematic liquid crystal cell

In general, light propagating an inhomogeneous liquid crystal (LC) cell can be modeled as ‘bundle rays’ because the LC cell consists of many birefringence layers. In order to calculate the optical path of the propagating light in the inhomogeneous LC cell, we multidimensionally calculated the wavevector, k, and the Poynting vector, S, of an ordinary and an extraordinary ray at LC grid interfaces, which are isotropic to a uniaxial medium and a uniaxial-to-uniaxial medium, by using the phase matching method. Furthermore, we also investigated the transmission coefficients and transmittance of the ordinary and the extraordinary rays as a function of difference of the optical axes of the facing birefringence medium at the interface to obtain the significant rays in the LC cell. Finally, we could calculate the exact path of the significant rays in the inhomogeneous LC cell, and compared the ray path in an electrically controlled birefringence (ECB) mode and a twisted nematic (TN) LC mode.