Computer-generated holograms: Reconstruction of curves in 3-D

The complex amplitude of a wave which gives rise to a focal curve of desired shape and position in space is determined in an analytical form and stored in a computer-generated hologram. Optical reconstructions of continuous foci are shown. The resolution limit due to diffraction effects is discussed.     

Novel cell parameter determination of a twisted-nematic liquid crystal display

In this paper a novel method is proposed to determine the cell parameters including the twist angle, optic retardation and rubbing direction of twisted-nematic liquid crystal displays （TNLCD） by rotating the TNLCD. It is a single-wavelength method. Because using subtraction equation of transmittance as curve fitting equation, the influence of the light from environment and the absorption by polarizer, the sample of TNLCD and analyser on the transmittance is eliminated. Accurate results can also be obtained in imperfect darkness. By large numbers of experiments, we found that not only the experimental setup is quite simple and can be easily adopted to be carried out, but also the results are accurate.     

Nanoparticles-doped guest-host liquid crystal displays

The technique, nanoparticles-induced vertical alignment (NIVA), was applied to fabricate a guest-host liquid crystal display (GH-LCD) without conventional alignment layers. The GH-LCD produced by NIVA exhibited a high reflectance of approximately 59% in the voltage-off state and a low threshold voltage of approximately 2.1 V(rms). NIVA is very suitable to be applied for fabricating a plastic LCD requiring a low temperature process, and a flexible timepiece by using NIVA was demonstrated.     

Driving matrix liquid crystal displays

Liquid crystal displays had a humble beginning with wrist watches in the seventies. Continued research and development in this multi-disciplinary field have resulted in displays with increased size and complexity. After three decades of growth in performance, LCDs now offer a formidable challenge to the cathode ray tubes (CRT). A major contribution to the growth of LCD technology has come from the developments in addressing techniques used for driving matrix LCDs. There are several approaches like passive matrix addressing, active matrix addressing and plasma addressing to drive a matrix display. Passive matrix LCD has a simple construction and uses the intrinsic non-linear characteristic of the LCD for driving. Departure from conventional line by line addressing of a passive matrix has resulted in improved performance of the display. Orthogonal functions have played a crucial role in the development of passive matrix addressing. Simple orthogonal functions that are useful for driving a matrix LCD are introduced. The basics of driving several rows simultaneously (multi-line addressing) are discussed by drawing analogies from multiplexing in communication. The impact of multi-line addressing techniques on the performance of the passive matrix LCDs in comparison with the conventional technique will be discussed.     

Displaying gray shades in liquid crystal displays

Quality of image in a display depends on the contrast, colour, resolution and the number of gray shades. A large number of gray shades is necessary to display images without any contour lines. These contours are due to limited number of gray shades in the display causing abrupt changes in grayness of the image, while the original image has a gradual change in brightness. Amplitude modulation has the capability to display a large number of gray shades with minimum number of time intervals [1,2]. This paper will cover the underlying principle of amplitude modulation, some variants and its extension to multi-line addressing. Other techniques for displaying gray shades in passive matrix displays are reviewed for the sake of comparison.     

Advancements of vertically aligned liquid crystal displays

This review describes the recent advancements in the field of the vertical aligned (VA) liquid crystal displays. The process and formation of different vertical alignment modes such as conventional VA, patterned VA, multi-domain VA, and polymer stabilised VA etc are widely discussed. Vertical alignment of liquid crystal due to nano particle dispersion in LC host, bifunctional PR-SAM formed by silane coupling reaction to oxide surfaces, azo dye etc., are also highlighted and discussed. Overall, the article highlights the advances in the research of vertical aligned liquid crystal in terms of their scientific and technological aspects.     

Modelling and characterization of ferroelectric liquid crystal displays

Modelling of liquid crystal displays is useful to predict their optical properties and dynamic behaviour. An integrated modelling system for ferroelectric liquid crystal displays has been developed. The system employs data from real FLC materials, polarizers, glasses, backlights, and colour filters, aiming to describe actual devices accurately. Optical transmission dependence on light wavelength and angle of incidence is obtained as a function of the liquid crystal director profile. This profile is in turn derived from energy minimization of bulk and glass surface conditioning contributions.The above static model has been extended to study sample switching in multiplexed displays. Usual slot times in actual displays are quite close to time response of FLC materials, hence no energy-minimized configurations are obtained upon switching. A dynamic model has been formulated to derive the director profile evolution with time, according to the employed driving scheme, and the rotational viscosity of the material.Predicted dynamic and optical results have been compared to experimental measurements on FLC test cells. It has been found that the behaviour of FLC cells depends on a large number of physical and optical parameters. Some of them may be obtained from FLC data sheets, and manufacturing conditions. Other parameters related to director profiles in relaxed states may be experimentally obtained by sample characterization through optical transmission measurements. A few little known parameters (e.g. specific elastic constants) remain; fortunately their influence on cell dynamics is low.     

Three-dimensional vector holograms in photoreactive polymer dissolved liquid crystal composite

A detailed analysis of three-dimensional vector holograms is presented which were recorded in a photoreactive polymer dissolved liquid crystal. The diffraction properties of resultant periodic anisotropic structures were investigated. Experimental observations confirmed that the diffraction efficiencies of the structures varied with slight changes of the grating pitch, and also that they strongly depended on the incident angle of the probe beam. These diffraction properties were explained by the finite-difference time-domain optical simulations.     

Achromatic diffractive lens written onto a liquid crystal display

We propose a programmable diffractive lens written onto a liquid crystal display (LCD) that is able to provide equal focal lengths for several wavelengths simultaneously. To achieve this goal it is necessary that the LCD operate in the phase-only regime simultaneously for the different wavelengths. We design the appropriate lens for each wavelength, and then the lenses are spatially multiplexed onto the LCD. Various multiplexing schemes have been analyzed, and the random scheme shows the best performance. We further show the possibility of finely tuning the chromaticity of the focal spot by changing the relative weights of the multiplexing among the various wavelengths.     

Effects of recording wavelength on three-dimensional vector holograms in photoreactive liquid crystal composites

Effects of recording wavelength on the recently proposed (Sasaki, 2008) three-dimensional vector holograms, in which the optical anisotropy is three-dimensionally modulated, are presented experimentally and theoretically. The polarization states of the interference light are three-dimensionally modulated due to both the polarization interference and optical anisotropy in the recording medium. These spatial distributions of the polarization states and the resulting diffraction properties in the three-dimensional vector holograms are strongly dependent on the recording wavelength. Theoretical consideration based on the finite-difference time-domain (FDTD) method reveals the mechanism of the optical characteristics of the three-dimensional vector holograms recorded by various kinds of light sources with different wavelengths.     

Analysis of Fabry-Perot interference effects on the modulation properties of liquid crystal displays

In this paper, we present the analysis of Fabry-Perot interferences in a twisted nematic liquid crystal display (LCD), and its influence on the modulation properties of the device. We develop a theoretical analysis based on the Jones matrix formalism and compare the results with the experimental response of a commercial display. The developed theory considers multiple reflections to derive a new Jones matrix for the display, which accounts for both polarization and Fabry-Perot interference effects. The validity of this treatment is limited to normal incidence illumination, but it is much simpler than other 4 × 4 matrix treatments developed for a general oblique incidence. It is shown that the existence of multiple reflections can be added to previously existing simplified models for the display, resulting in a modified Jones matrix with two new parameters: the Fresnel reflection coefficient r and the voltage independent phase Φ. In addition, a calibration procedure is proposed where the calculation of these two new parameters related with the multiple reflections, can be uncoupled from the calculation of the rest of the parameters, related with the modulation properties. We remark the good agreement between the theoretical results and the experimental measurements.     

Optical particle trapping with computer-generated holograms written on a liquid-crystal display

Computer-generated holograms written on a liquid-crystal display can be used to generate dynamic light fields of arbitrary shape. This method was used to simultaneously trap polystyrene particles laterally and to displace them independently of one another.     

Bistability and spatial hysteresis in an Nd:GdVO4 laser with an intracavity twisted-nematic liquid crystal

In this study, optical bistability accompanied by spatial hysteresis was demonstrated in an Nd:GdVO₄ laser with an intracavity twisted-nematic liquid crystal. The low branch of power hysteresis mainly has the spatial distribution of the fundamental mode as the pump power increases, whereas a four-mode and varying transverse pattern exist in the high branch of power hysteresis as the pump power decreases. The result revealed that the power and spatial hysteresis is controlled by the director axis reorientation and the order parameter modification in twisted-nematic liquid crystals, which is determined by the non-uniform transverse distribution of the intracavity laser intensity.     

Generation of three-dimensional optical structures by dynamic holograms displayed on a twisted nematic liquid crystal display

Reconstruction of computer generated holograms (CGHs) addressed on a spatial light modulator (SLM) is an effective way to dynamically generate designed light field distributions. Based on the classic Gerchberg–Saxton (GS) algorithm, we proposed a technique, which can greatly reduce the computation cost to about 60 % in calculating CGHs for three-dimensional (3D) structures but with little degradation of reconstructed light field compared with the classic GS algorithm. The CGHs calculated by our method were displayed on a twisted nematic liquid crystal display, working as a phase-only-modulation SLM, and 3D structures of optical fields, e.g., 3D array of optical traps and vortices, were reconstructed with high efficiency and high quality. Besides, the possibility for 3D holographic display or projection was also demonstrated with this algorithm by reconstruction several images simultaneously in distinct axial planes.     

Leakage of light in liquid crystal displays and birefringent thin film compensators

This paper elucidates the physical origin of leakage of light in the dark state of liquid crystal displays (LCDs) and describes birefringent thin film compensators to mitigate the problems. There are two fundamental sources of leakage of light in LCDs. They are the leakage of light through a pair of ideal crossed polarizers, and the leakage of light due to elliptical state of polarization after transmitting through the liquid crystal (LC) cell. The leakage of light in the dark state leads to poor contrast ratios and color instability, particularly at large viewing angles. The paper then describes the employment of sixth-wave (λ/6) plates as well as various wave plates that function as birefringent compensators for eliminating the leakage of light in LCDs.     

A polarized laser backlight using a zero-zero-birefringence polymer for liquid crystal displays

We have demonstrated a polarized laser backlight for liquid crystal displays and have investigated its basic polarization properties. To maintain the state of polarization of light propagating through the light-guide plate (LGP) of the backlight, we fabricated the LGP by injection molding of a zero-zero-birefringence polymer, poly(methyl methacrylate-co-2,2,2-trifluoroethyl methacrylate-co-benzyl methacrylate) (52: 42: 6 by mass) that is free of both orientational and photoelastic birefringence. The degree of polarization of light from the resulting backlight (average: 92.4%) was much higher than that from a backlight with a polycarbonate LGP (average: 8.0%) in the defined effective range of the backlight. A laser speckle pattern was observed but the speckle contrast on the output surface of the backlight was reduced from 68 to 10% by vibrating a diffuser sheet situated in front of the output surface of the LGP. We also manufactured a white surface light source [chromaticity (value: x, y) = (0:310, 0:314)] by mixing the outputs from three primary-color-emitting lasers in the backlight.