Toshiaki Nose

A liquid crystal microlens obtained with a non-uniform electric field

Abstract A homogeneously aligned nematic liquid crystal cell with a hole-patterned electrode and with an indium-tin oxide (ITO-) coated counter-electrode has been prepared. A non-uniform electric field can be produced by the asymmetrical electrode structure. The liquid crystal director can be reoriented by applying a voltage across the electrodes, and this produces an axially symmetrical profile of the refractive index. This liquid crystal cell is expected to have a lens effect and so its optical properties have been investigated. The profile of the output light intensity was measured by using a detecting system with an optical fibre. Some relationships between the lens properties, the diameter of the hole and the thickness of the liquid crystal layer have been examined. The liquid crystal cell becomes a convex (converging) lens with a relatively low voltage. A focal length of several millimetres can be obtained by applying voltages of 3-4 V. As the applied voltage increases, the focal length becomes long...

Liquid-crystal microlens with a beam-steering function

A novel beam-steering device that makes use of a nematic liquid crystal (LC) is proposed and demonstrated. The beam-steering function is attained with a LC microlens with a divided hole-patterned electrode structure (DE-LC microlens). Optical properties of the DE-LC microlens are investigated and three-dimensional variable-focusing and beam-steering properties are verified experimentally for the first time, to our knowledge.

Effects of Low Polymer Content in a Liquid-Crystal Microlens

A small number of bifunctional monomers are mixed with a nematic liquid crystal (LC) and cured with a distributed electric field, which is produced by a circular-hole-patterned electrode structure. A gradient type of lens, that is, a LC microlens, is investigated for various polymer concentrations. Addition of 3% polymer is enough to freeze the gradient-index properties of the structure in the form of a convex lens, and a polymer-stabilized LC microlens is demonstrated. Although a lower concentration of polymer cannot hold the distribution properties in a curing process, it can maintain the variable focus as a nematic material can. The polymer networks can also eliminate the disclination line that usually appears and causes the lens in this type of LC device to deteriorate.

Refractive index of nematic liquid crystals in the submillimeter wave region

Large electro-optic effects of liquid-crystal materials are attractive in applications to various optical devices in a wider wavelength region. Fundamental optical properties in the submillimeter wave region, such as refractive indices and transmission losses for some cyanobiphenyl nematic liquid crystals, have been investigated for the first time, to our knowledge, with a submillimeter laser. Refractive indices of the liquid crystal materials for ordinary and extraordinary rays are a little larger than those in the visible region, and a larger birefringence comparable with the visible region can also be obtained. Although the loss level is larger by ~2 orders of magnitude than that of quartz plate, which is an excellent window in the submillimeter wave region, the transmission of the liquid crystal cell is high enough.

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.

Optical Properties of a Hybrid-Aligned Liquid Crystal Microlens

Abstract Microlens effects have been obtained in homogeneously aligned liquid crystal cells prepared using a hole-patterned electrode and a plane electrode. In the asymmetric electrode structure, an axially symmetric non-uniform electric field is produced and a radial distribution of refractive indices can be obtained by the molecular orientation effects in the non-uniform electric field. However, a disclination line which makes the optical properties worse is observed in the homogeneously aligned microlens when a voltage is applied across the cell. In order to improve the lens properties, hybrid-aligned liquid crystal microlens cells are prepared. Their optical properties are investigated and discussed in terms of a molecular orientation model in the non-uniform electric field of the hybrid-aligned cell.

Relationship between lens properties and director orientation in a liquid crystal lens

Abstract Lenses with a homogeneously aligned liquid crystal having a Fresnel structure have been prepared by using a nematic with a positive dielectric anisotropy. Their focal length can be varied continuously from the value fe for an extraordinary ray to f o for an ordinary ray by applying an electric field across the lens cell. The effective refractive index of the lens where the director is aligned perpendicular to the grooves of the Fresnel structure becomes smaller than when the director is aligned parallel to the grooves. Then the liquid crystal lens has a characteristic aberration which could not be observed in a conventional glass lens; that is, the focal length of the lens becomes different according to the incidence of rays on the different parts of the lens. The properties of the liquid crystal lens can be improved by making the director orientation axially symmetric, in the form of a concentric circle, but the polarization component rotated 90° from the incident extraordinary ray appears when ...

Optical properties of an UV-cured liquid-crystal microlens array

We propose and demonstrate, for the first time to our knowledge, a microlens array of the gradient-index type using a novel liquid-crystalline material that possesses the property ofphotopolymerization by UV irradiation. Optical and electrical properties of the UV-curable liquid crystal are investigated to optimize UV curing conditions. The microlens array is prepared by use of an UV-curable liquid crystal, and gradient-index profiles are monitored during photopolymerization. As a result, relatively good focusing and imaging properties can be obtained even after photopolymerization. This technique affords us a very controllable way to fabricate the micro-optic components.

Cross-sectional observations of the cholesteric texture in a Cano wedge cell

Abstract A novel procedure for an observation of a liquid crystal texture is proposed by using a UV curable liquid crystal. Optical observations from a cross-section of the Cano wedge cell are demonstrated and layered structures of cholesteric LC are visualized clearly. The structures near the Grandjean lines are then revealed in detail from images. From the observations, it is confirmed that the texture near the Grandjean line is similar to fingerprint texture

Polarization Properties of a Liquid Crystal Phase Grating

Abstract By measuring Stokes parameters of diffracted light versus applied voltages, polarization and diffraction properties of a liquid crystal phase grating (LCPG) are investigated at the first time. With this kind of LC phase gratings, high diffraction efficiencies and contrast ratios can be realized readily. And its polarization properties can be electrically varied as well as diffraction light intensities. A unique property of symmetrical diffraction light intensities but antisymmetrical polarization states in corresponding positive and negative diffraction orders is shown.