We propose a low-driving-voltage multifocal liquid crystal (LC) lens such as a concave lens inside a convex lens. The multifocal LC lens is prepared using a glass substrate with a transparent circularly hole-patterned electrode, an additional ring electrode inside, and a center electrode. The multifocal lens properties are attained, and the focal length of the concave lens and/or convex lens can be changed by applying low voltages to the electrodes.
Liquid crystal (LC) director distributions and optical phase profiles in LC micro-lens-array (LC-MLA) are studied by using a three-dimensional (3D) numerical calculation method. The LC-MLA design employs twodivided and tetragonally-patterned electrode structure in a flat nematic LC cell. The possibilities of prism and lenslike phase difference distributions in the rectangular aperture region of the LC-MLA are discussed. The LC molecular orientation distributions in the rectangular region can be estimated and its phase profile can be predicted fairly well by the calculations.
We study the electro-optical properties of the nematic liquid crystal (LC) cells such as a homogenously aligned nematic LC cell and twisted nematic (TN) LC cell fabricated with polished silicon wafers in a far-infrared wavelength region. The birefringence of the nematic LC material at the wavelength of about 10 μm is estimated by applying a voltage to the homogenously aligned LC cell under crossed infrared-wire-grid polarizers. The application of the TN LC cell into an optical shutter in the far-infrared region for electrically controlling the transmitted light intensity is demonstrated and discussed.
We propose a liquid crystal (LC) micro-lens array with two-divided and hexagonal-hole-patterned electrodes for varying a focal length and a beam deflection angle. The possibilities of lens-like refractive index distributions in the hexagonal region of the LC micro-lens array are discussed. We investigate the optical properties such as the focal length and beam deflection of the micro-lens array by measuring the refractive index distributions and the transmitted light intensity distributions.
We have proposed the multidomain patterning of a liquid crystal (LC) alignment by controlling the anchoring strength
of alignment surfaces. The azimuthal anchoring strength of rubbed polyvinyl cinnamate (PVCi) is increased by the
crosslinking reaction under the unpolarized UV light exposure. The multidomain patterning of twist angle from 0 to 90
degree has been successfully demonstrated in the LC cell using the polyimide coated substrate with strong anchoring and
PVCi coated substrate with multi anchoring strength, even though both substrate surfaces are uniformly rubbed and
rubbing directions cross at right angles. The twist angle of the LC orientation has been calculated using the torque
balance equation. The twist angle in the practical LC cell is consistent with the calculated one. The LC director
distribution has also been numerically and experimentally analyzed in the LC cell with one-dimensional periodic change
of the anchoring strength. The twist angle distribution is strongly affected by the periodic size, as well as the anchoring
strength, the cell thickness and elastic strain energies of K11, K22 and K33.
With hole-patterned electrodes separated from liquid crystal layers it becomes possible to fabricate liquid crystal lens of
high quality and large size. The properties of the lens of this kind of electrode structure are discussed. The modifications
to the original structure to realize lenses of improved quality, that are polarization-independent and having focus
movable in focal plane are also discussed.
A novel optical manipulation system for controlling three-dimensional positions and rotation of
trapped microscopic rods is proposed by using a liquid crystal (LC) device with unique functions such as
an anamorphic lens property in addition to both variable-focusing and deflection properties. Arranging
the control voltages of the LC optical device, the laser beam can be focused with any elliptical cross
section. The trapped slender object is aligned along the rotatable major axis of the elliptically shaped
laser beam spot and can be shifted three-dimensionally.
A two-voltage-driving technique is applied to build liquid crystal (LC) lens and LC microlens. One bias voltage is fixed and the other one varies to control the focal length of the LC lens or the LC microlens. The range of the variable focus is wide, and in the entire focus range the optical quality is preserved. The application of the LC lens as a focusing lens for cameras is demonstrated.
Studies on the liquid crystal lens with curved electrode are reported. The lens power is dependent on the applied voltage, and the lens size is nearly that of the curved electrode and therefore can be changed arbitrarily. The influences of material property and lens geometry on the properties of the LC lens are studied numerically. The properties of the lens of different geometries are investigated experimentally.
We propose optical phase-control devices using a liquid crystal (LC) material without applying a voltage, and demonstrate a composite alignment of LC molecules on a substrate with a patterned photo-resist film, where LC molecules are partly aligned parallel and perpendicular directions divided into very small areas on the substrate. The patterned film such as randomly distributed circular areas of small diameter size is fabricated by using a photo-mask and a photolithography technique. The LC cells are prepared using the locally composite alignment substrate and a perpendicular alignment substrate. The optical phase of the transmission light through the different pattern density regions was measured. Then, it is found that the optical retardation of the higher pattern density region is larger than that of the lower one.
Several types of liquid crystal (LC) lenses with variable focusing functions by applying an external electric field have been reported. We propose a new type of LC lens using the molecular orientation effects and resulting elastic force of LC director. The hole-patterned alignment area is treated for LC molecules to align parallel or perpendicular to the substrate coated with transparent electrodes, and outside area is treated to be an inverse alignment state. The surface of another substrate is coated with a homeotropic alignment layer. When the diameter of the hole pattern is nearly equal or less than the LC thickness, the distribution of the refractive index becomes bell-shaped and the LC cell behaves like an optical lens in the absence of the applied voltage. The focal length can also be varied by applying a voltage across the transparent electrodes.
We propose a laser manipulation (optical tweezers) system for controlling microscopic objects by using a liquid crystal (LC) optical device with variable focusing and beam deflection properties. The focused spot, that is the position of the trapped particles can be controlled and moved by the change of the optical properties of the LC optical device by applying the voltage to the LC cell.
We propose a high-speed optical measurement method for determining cell parameters such as cell thicknesses and twist angles of reflective liquid crystal (LC) cells. A polarization-converting device prepared using a circularly-homogeneously aligned LC (CH-LC) cell and a charge couple device (CCD) camera are used. The spatial light intensity distribution from the reflective LC cell through the CH-LC cell and the local minimum point are measured. Then the cell parameters can be derived by using the coordinate values of the point and the Jones matrix analysis.
Liquid crystal (LC) lens with voltage and azimuth dependent focus is realized by using divided electrode structure. By applying appropriate potentials on the divided electrode, the LC cell behaves like an optical lens having astigmatic properties; the phase retardation of an incident light beam takes an elliptical shape in the cross-section. The axes of the elliptical shape of the phase retardation are electrically controllable.
Techniques of polarized latent image formations on liquid crystal (LC) cells have been proposed for optical security devices. The glass plate coated with a photo-reactive polymer film is prepared as a substrate of the LC cell. The polymer surface is rubbed and subsequently modified by exposing with a non-polarized UV light through the photo-mask. The LC cell using the patterned substrate surface is homogeneously transparent under the normal condition (without polarizers). However, the image with continuous grey levels appears when the cell is set between two polarizers. The latent image can also be optically and thermally written on the cell filled with the LC. The guest-host LC cell which has dual latent images is also demonstrated using another photo-reactive polymer. The LC alignment on both substrate surfaces are respectively patterned by the photo modification and rubbing. The latent image can individually be visible and selected by replacing the polarizer in front or behind the LC cell. Our LC patterning process is very simple compared to other patterning methods and the patterning technique which is utilized the mechanical rubbing and photo modification gives great advantages of not only the large area but also the high density patterning.
Stokes parameter methods to determine cell parameters such as a pretilt angle, thickness and twist angle in reflective liquid crystal (LC) cells have been developed by measuring Stokes parameters of reflected light at plural wavelengths. The cell thickness can be determined by measuring one-wavelength Stokes parameters including a near-infrared wavelength, and both the cell thickness and twist angle can also be determined by calculating the Stokes parameter at two wavelengths. Furthermore, these cell parameters containing the pretilt angle as well as cell the cell thickness and twist angle can be determined by using Stokes parameters at three wavelengths. These methods can be applied to determine two-dimensional (2D) cell parameter distributions of the reflective LC cell by using a high resolution CCD camera.
First, a new method of voltage application is proposed. With the new drive method, disclinalion lines do not appear in the cell. Secondly, a liquid crystal lens with focus moveable along and off the axis is reported. The movements of the focus are controlled by the potentials of electrodes and sub-electrodes in the cell.
An optical measurement method to determine the cell thickness of reflective liquid crystal (LC) cells is prepared using a polarization-converting device such as a circularly-homogeneously aligned LC (CH-LC) cell and a charge couple device (CCD) camera. Since the minimum point of the spatial light intensity distribution from the reflective LC cell is measured in real time through the CH-LC cell, and then the cell thickness can be derived by the Jones matrix analysis. This method has an advantage that the measurement of the cell thickness is not affected by the reflection component from the surface and interface of glass substrates.
We develop the novel optical device for controlling the polarization state using liquid crystal (LC) and eight-divided hole-patterned electrodes which are coated with weak anchoring alignment films. The LC director can be reoriented by applying in-plane electric fields and the other electric fields across a cell thickness layer, and then polarization state of light transmitted trough the hole-patterned region can be controlled. The design and the electrical and optical properties of the LC device are briefly discussed.
We propose a two-dimensional (2D) and hyperfine measurement method for precisely determining cell parameter distributions such as a cell thickness and twist angle in color liquid crystal (LC) displays. The 2D cell thickness and twist angle distributions can easily be determined by measuring Stokes parameters of all pixels for red, green and blue in LCD panel at a wavelength of near-infrared region, because the transmission light at the wavelength is not absorbed by each color filter. In addition, the spatial resolution can be improved by increasing the magnification of the objective lens in front of a high resolution CCD camera. These cell parameters of each pixel in the practical LCD panel are compared and discussed.
A detail description of a new liquid crystal lens is presented. The focal length of the lens is a function of the applied voltage. The working mechanism of the liquid crystal lens is explained. The lens acts as a magnifying glass is demonstrated as an example.
Relatively large electro-optic effects of nematic liquid crystal (LC) in the millimeter wavelength region have the possibility of an application to the electrically controlled millimeter-wave devices. The millimeter-wave transmission properties of the conventional nematic LC cells with a grating-patterned electrode structure are described. Novel LC cells with a stack-layered structure using metal substrates, which have a large effective path length, are prepared and large millimeter-wave transmission modulation of 50% can be attained by applying an external electric field to the LC cell. The stack-layered structure is useful for an application to the millimeter-wave devices. Then, the LC prism and LC lens as the quasi-optical millimeter-wave devices using the stack-layered structure are proposed. Deflection and focusing effects of the millimeter-wave are observed by applying an external electric field to the LC cells.
Optical properties in the liquid crystal (LC) microlenses are studied on molecular orientations with large and axially symmetrical electric field. The LC microlenses with a thick LC layer are also investigated by experiments and simulations of 3 dimensional finite difference method (3D-FDM). The LC microlens has a converging property with low applied voltage as well as a diverging property with high applied voltage. The dependence of converging property on D/t is investigated in the LC microlenses, where D/t is the ratio between a hole-pattern diameter D and LC thickness t, and the simulation by the 3D-FDM in terms of the molecular orientation state is successfully carried out. It is found that the lateral distribution of the LC molecular orientation in the thickness direction is not uniform and changes depending on the D/t ratio, and good converging properties can be obtained when the D/t value is around 2.
Geometric type of liquid crystal (LC) lens can be obtained by using the spherical substrate in a liquid crystal cell. The LC lens can have a potential application to a kind of light wave controlling device by utilizing the electronic variable focusing properties. However, it shows a particular aberration properties induced by the molecular orientation related with a curved substrate structure. In this study, LC molecular orientation states in the LC lens and the optical properties are investigated by the experimental and the theoretical approaches. Interference fringe patterns induced by the LC layer are observed and optical path distribution properties are compared between the rubbing direction and the direction perpendicular to the rubbing. One dimensional model is applied to the molecular orientation calculation, and the optical path difference in the 2D area and the wave aberrations are calculated for normal incidence. It is confirmed that a particular wave aberration dependent upon the rubbing direction appears, and the influence of the curved substrate strongly depend upon the thickness of the LC layer. Therefore, the aberration phenomena of the convex and concave lens are quite different even though they have the spherical substrate with the same magnitude of curvature. When a voltage is applied to the LC lens, reverse tilted disclination lines tend to appear and they usually cause a fatal degradation of lens properties. The disclination lines can be eliminated by introducing a small pretilt angle to the alignment layer within a smaller inclination of substrate. However, even in the disclination free state, there is some influence on the wavefront through the LC lens; that is, large inclination of the wave front causes in the lower applied voltage.
Liquid crystal (LC) molecular orientations and optical properties of LC polarization-converting devices are discussed. It is found that two stable LC molecular orientation states appear (we define them at the +/- 90 degree(s) and +/- 180 degree(s) twist modes), and the switching method between the two modes are discussed. Fourier transforms (FT) of the transmitted light of the LC polarization- converting device are performed by computer simulations. It is confirmed from the simulated FT results that both distribution profiles of the transmitted light beams in the +/- 90 degree(s) and +/- 280 degree(s) twist modes can be regarded as wavelets. Wavelet transforms using the LC polarization- converting device are simulated and feature extraction properties are discussed. It is found that the +/- 90 degree(s) and +/- 180 degree(s) twist modes can perform corner and edge extractions, respectively.
Numerical simulation of temporal evolution and spatial distribution of directors in a liquid crystal (LC) microlens is presented. We show that splay deformation and twist deformation obtained for the LC microlenses with a pre-tilt angle and without one are quite different. Details of director orientation in both types of LC microlenses are discussed.
The optical properties of the liquid crystal (LC) polarization-converting device, which can convert a uniformly-distributed polarization state to a radially- distributed one (a radially polarized light), are measured. The availability of such the unique device for optical wavelet transforms is discussed experimentally and theoretically. It is found from the observation of Fourier images that the radially polarized light can be regarded as a 1D Haar wavelet and a circular Haar wavelet in the case with and without an analyzer, respectively. Therefore, we can select two types of Haar wavelets by attaching or removing the analyzer. To discuss the edge extraction properties, the wavelet transforms are implemented by using computer simulations. It is confirmed that the radially polarized light produced by the LC polarization-converting device is useful for extracting edge features of 1D and 2D images in the case with and without the analyzer, respectively.
A graded index type lens can be attained by utilizing the liquid crystal molecular orientation effects in an axially symmetrical electric field which is produced by the circular hole-patterned electrode. The liquid crystal (LC) microlens has a variable focusing property and is easy to make large scale of lens array because of its simple structure. Excellent lens properties can be obtained by optimizing the electrode structure, driving voltage and etc., and the focusing spot size is as small as the diffraction limit. We can expect a new type of lens as an active device for light control by the LC microlens. However, time response of the LC microlens is usually very slow and it has a large aberration caused by the liquid crystal molecular orientation. In this paper, fabrication and fundamental properties of the LC microlens are briefly reviewed, and then the improvement of response and optical properties are discussed. The response and recovery time can be extremely reduced by introducing the polymer stabilization technique using UV curable LC materials. In addition, the aberration can be eliminated by introducing divided electrode structure. The new electrode structure can also provide free space focusing and deflection properties to the LC microlens.
The multi-sensing system for detecting external electric fields and decomposition products of SF6 is proposed by using a nematic liquid crystal (LC) cell sandwiched with two cholesteric LC cells and a corner cube prism coated with dye films. The electric field and the decomposition products can be measured as changes in optical retardations of the nematic LC cell at a selective reflection band of the cholesteric LC and as the absorption changes of the dye films at different wavelength regions outside the selective reflection band, respectively. Furthermore, we discuss the dependence of the sensitivity to the electric field on the molecular orientation and the anchoring strength of the alignment layer in the nematic LC cells.
A fabrication method and optical properties of a double- layer polymer/liquid-crystal (LC) grating are reported. The double-layer polymer/LC grating is fabricated by a simple single-step process with UV irradiation through a grating photomask, using a mixture of liquid crystal and prepolymer materials. This liquid crystal grating consists of two polymer/LC layers with a periodic relief structure. The alignment directions of liquid crystal molecules for the two layers are orthogonal to each other. The diffraction properties of the double-layer polymer/LC grating have been measured and compared with that of a single-layer one. Behaviors of the disclination lines have been also investigated under a voltage application. The results indicate that the double-layer polymer/LC grating has voltage-controllable polarization direction-independent diffraction properties.
Uniaxial crystal properties can easily be obtained by using a nematic liquid crystal (LC) with suitable substrate treatment.A liquid crystal lens, which has bifocal properties, is fabricated wit a concave lens and a pane substrate to attain a convex lens shape LC layer, and is used as the key component of the double focusing interferometer. Liquid crystal materials are selected for the refractive index matching between the plano-concave lens and no value of the LC material. In this case, an incident ordinary ray as a test beam passes just through the lens without focusing. On the other hand, an extraordinary ray as a reference beam is focusing on the test piece with the same general path, and the common path configuration can easily be achieved. Basic properties as a novel optical test system using the LC lens are demonstrated, and it is confirmed that a thickness of an Al evaporated film can successfully be measured by introducing phase shifting technique.
The anamorphic liquid crystal (LC) microlens are prepared using elliptically-patterned electrode structures and nematic LC materials, and their optical properties are demonstrated. The interference fringe patterns of the LC microlens can be varied by applying voltages. Focal length and astigmatic focal distance properties are estimated as a function of applied voltage and it is confirmed that an astigmatism of the anamorphic LC microlens can easily be controlled by an ellipticity of a patterned electrode and an applying voltage. Coupling of a laser diode beam to a multimode optical fiber is also demonstrated using the anamorphic LC microlens.
We have investigated the electrooptical characteristics and viewing-angle properties of liquid crystal (LC) display devices referred as the electrically induced hybrid twisted nematic (EHTN) LC display devices, in which LC molecular orientation effects in inhomogeneous electric fields induced by grating electrode structures are utilized. The properties of EHTN display devices are studied in a measurement setup with an actual backlight unit as a light source. We have demonstrated that these devices have high contrast ratios, wide and symmetrical viewing-angle properties, specially in the direction perpendicular to the grating direction. Since there are diffraction effects from the gratings of periodic LC molecular orientations, we discuss the influence of the diffraction effects on viewing-angle properties by evaluating two kinds of EHTN LC cells fabricated by Al metal thin film (obscure) and ITO (transparent) grating electrode structures, show the possibility of realizing good viewing- angle properties by appropriate grating structures.
By determining Stokes' parameters of light diffracted from a nematic liquid crystal grating fabricated with a grating electrode structure, polarization modulation properties of this LC grating are characterized. The electrically controllable polarization modulations of its diffracted light are demonstrated as well as its diffraction light intensity modulations. A unique property of symmetrical diffraction light intensities but antisymmetrical polarization states in corresponding negative and positive diffraction orders is shown.
Liquid crystal cells with a radial molecular orientation is proposed using a UV curable liquid crystal material. A radially and homogeneously aligned LC cell (RH-LC cell) and an LC cell with a radial molecular orientation on both substrates (RR-LC cell) are fabricated and their optical properties are investigated. A polarization converting function of the RH-LC cell and detecting function of the polarization direction in the dye doped RR-LC cell are confirmed. Furthermore, an optical alignment of liquid crystal on the PVC surface is demonstrated using RH-LC cell.
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