Michinori Honma

Liquid Crystal Lens With Spherical Electrode

The variable focusing function of a liquid crystal lens (LCL) with a spherical electrode is demonstrated. One electrode is a transparent film of indium tin oxide (ITO) coated on the spherical surface of a plano-convex glass lens that is placed on a planar liquid crystal cell. The lower substrate of the cell is also coated with an ITO film acting as another electrode. A nonuniform electric field nearly symmetrical about the central line produces a gradient distribution of refractive index. The cell therefore behaves like an optical lens. The LCL exhibits good optical properties, and can be of any size, and its diopter is a function of the applied voltage.

Dependence of optical properties on the device and material parameters in liquid crystal microlenses

Liquid crystal microlenses are prepared using various liquid crystals and dependence of the optical properties on device and material parameters is investigated experimentally. Numerical apertures of the liquid crystal microlenses for different combinations of the structure parameters and the material parameters are measured. The numerical aperture of the LC microlens is maximum value when the ratio of the diameter and thickness is 3 and its spot size is less than 2 µm. Optical properties of the LC microlenses are mainly dominated by the birefringence property and dielectric anisotropy of liquid crystal materials. It is necessary to use a LC material with a large birefringence and a large dielectric anisotropy to design the LC microlens with a large numerical aperture and a low driving voltage performance.

Liquid-crystal blazed grating with azimuthally distributed liquid-crystal directors

We propose a novel formation method of arbitrary phase profiles of circular light by controlling azimuthal angles of liquid-crystal directors; its principle is described theoretically. A new liquid-crystal blazed grating is demonstrated by use of the proposed method. It is revealed that the first-order diffraction efficiency reaches the maximum value (theoretically 100%, experimentally approximately 90%) at an optimum applied voltage when the phase difference between the extraordinary and ordinary rays agrees with one-half the wavelength. Furthermore, the polarization states of the diffracted light beams are analyzed by Stokes parameter measurements, and unique polarization-splitting properties are revealed.

Liquid-Crystal Fresnel Zone Plate Fabricated by Microrubbing

A novel liquid-crystal (LC) Fresnel zone plate (FZP) is fabricated only by the LC molecular alignment process without the need for surface relief structures and patterned electrodes. It is theoretically described that the Fresnel-lens-like phase profile is achieved under optimum LC molecular orientation conditions and the polarization state of incident light, that is, the retardation of the LC cell is (n+1/2)λ (n is an integer) and the incident light is circularly polarized. The optical properties of the fabricated LC FZP are experimentally investigated. Good focusing properties are confirmed (the full width at half maximum of the spot is approximately 8% larger than that of the diffraction limit) and the light intensity of the focusing spot is found to be controllable by adjusting applied voltage.

Rotational Behavior of Stripe Domains Appearing in Hybrid Aligned Chiral Nematic Liquid Crystal Cells

The appearance of stripe domains is strongly affected by various cell conditions such as thickness, applied voltage, and surface alignment. In this work, we adopt hybrid surface alignment to investigate the appearance of stripe domains under asymmetric surface anchoring. It is observed that the stripe direction rotates continuously according to the cell thickness and applied voltage, which has potential as a unique diffraction grating. It is also found that the rotational response time is always several seconds for any size of cell, because a large area rotation is achieved by the sum of small poly domain rotations related to defect creation–extinction processes on their boundaries.

Simple method for the determination of refractive indices and loss parameters for liquid-crystal materials in the millimeter-wave region

A reflection-type liquid crystal (LC) test cell is prepared with a rectangular waveguide for investigation of a novel method to determine refractive indices and loss parameters of nematic liquid-crystal materials. As the bottom of the test cell is sealed with a glass window and the top of the cell is capped with a metal-tipped movable reflector after the LC materials are injected, both ends of the waveguide test cell have large reflectance. Thus the reflection properties of the LC test cell can be well described by a multiple-beam interference model. A simple method for the determination of refractive indices from the reflection measurement data is proposed based on results of some investigations with the theoretical model. Commercially available LC materials have been measured with this method at a millimeter-wave frequency (50 GHz) by use of a simple experimental setup with a Gunn oscillator and a diode detector.

Influence of Elastic Constants on the Optical Properties of Liquid Crystal Microlenses

Use of liquid crystal (LC) microlenses prepared from various types of LC materials is demonstrated for clarification of the influence of material parameters on the optical performance experimentally. Spherical aberration in the LC microlens is reduced by optimization of structure parameters, and the correlation between astigmatic aberration and elastic constants is investigated. The astigmatic aberration in the LC microlens strongly depends on the elastic constants and is explained by use of molecular orientation models calculated by a finite element method.

Light-emitting liquid-crystal cells with polarization switching function: Electrochemiluminescent method

A unique light-emitting liquid-crystal (LC) cell that emits polarized light is developed by an electrochemiluminescent (ECL) method; sandwich-type LC cells filled with a nematic LC doped with an organic fluorescent dye are constructed. Luminance and current density characteristics as a function of an applied voltage are investigated under different sample preparation conditions such as mixing temperature and time. It is shown that luminance strongly depends on the abovementioned conditions. From the results of ECL and photoluminescent measurements, we conclude that a significant increase in luminance by heating is attributed to an increase in the molecularly dissolved rubrene concentration. Furthermore, attempts were made to develop a dynamic polarization switch by introducing a pair of crossed interdigitated electrodes. As a result, although a not so high polarization ratio smaller than 2 was obtained, the polarization direction of the emitted light was switched by changing the direction of the in-plane ...

Periodic reverse-twist nematic domains obtained by microrubbing patterns

A method for forming periodic 90° reverse-twist domains using a microscale rubbing pattern has been proposed; that is, an isolated 90° twist domain is surrounded by a 45° twist domain. Since liquid crystal (LC) materials exhibit elastic nature, the twist sense of the inner 90° twist domain prefers to be the same as that of the surrounding 45° twist domain. Two factors are investigated to obtain periodic 90° reverse-twist domains; (i) the injection process of LC material (isotropic or nematic phase) and (ii) the ratio of the area of the surrounding 45° twist domain and the whole area (the normalized area of the 45° twist domain). In the case of the injection in isotropic phase, it is revealed that periodic 90° reverse-twist domains can be obtained only when the area of the 45° twist domain is sufficiently large. On the other hand, in the case of injection in nematic phase, periodic 90° reverse-twist domains can successfully obtained regardless of the area of the 45° twist domain. Thus, the injection rocess...

Liquid-crystal depolarizer consisting of randomly aligned hybrid orientation domains

A novel depolarization method for linearly polarized incident light that uses a liquid-crystal (LC) cell with randomly aligned hybrid orientation domains is theoretically described by use of Mueller matrix calculations. The depolarization effect of the incident linear polarization is confirmed with Stokes parameter measurements. The unique optical properties of the fabricated LC depolarizer are revealed; that is, the intensity of the transmitted light is independent of the rotation of the analyzer. The degree of polarization becomes zero when the retardation of the LC depolarizer coincides with a half-wavelength.