Foreword. Series Editor's Foreword. Preface. 1. Liquid crystal physics.* Introduction.* Thermodynamics and statistic physics.* Orientational order.* Elastic properties of liquid crystals.* Response of liquid crystals to electro-magnetic fields.* Anchoring effects of nematic liquid crystal at surfaces. 2. Propagation of light in anisotropic optical medium.* Electromagnetic wave.* Polarization.* Propagation of light in uniform anisotropic optical media.* Propagation of light in cholesteric liquid crystals. 3. Optical modeling methods.* Jones matrix method.* Mueller matrix method.* Berreman 4x4 method. 4. Effects of Electric field on Liquid Crystals.* Dielectric interaction.* Flexoelectric Effect.* Ferroelectricity in liquid crystals. 5. Freedericksz transition.* Calculus of variation.* The Fredeericksz transition: statics.* The Freedericksz transition: dynamics. 6. Liquid Crystal Materials.* Introduction.* Refractive indices.* Dielectric constants.* Rotational Viscosity.* Elastic constant.* Figure-of-merits.* Refractive index matching between liquid crystals and polymers. 7. Modeling of liquid crystal director configuration.* Electric energy of liquid crystals.* Modeling electric field.* Simulation of liquid crystal director configuration. 8. Transmissive liquid crystal display.* Introduction.* Twisted nematic cells.* In plane switching (IPS) mode.* Vertical alignment (VA) mode.* Multi-domain Vertical Alignment (MVA) Cells.* Optically compensated bend (OCB) cell. 9. Reflective and Trasreflective display.* Introduction.* Reflective liquid crystal displays.* Transflector.* Classification of Transflective LCDs.* Dual-cell-gap Transflective LCDs.* Single-cell-gap Transflective LCDs.* Performance of transflective LCDs. 10. Liquid crystal display matrices, drive schemes and bistable displays.* Segmented displays.* Passive matrix displays and drive scheme.* Active Matrix Displays.* Bistable ferroelectric liquid crystal displays and drive scheme.* Bistable nematic displays.* Bistable cholesteric reflective display. 11. Liquid crystal/polymer composites. * Introduction.* Phase separation.* Scattering properties of liquid crystal/polymer composites.* Polymer dispersed liquid crystals.* Polymer stabilization liquid crystals.* Displays from liquid crystal/polymer composites. 12. Tunable liquid crystal photonic devices. * Introduction.* Laser beam steering.* Variable Optical Attenuators.* Tunable-Focus Lens.* Polarization-Independent LC Devices. Index.

Fundamentals of Liquid Crystal Devices

We present SLIM, a new optical method measuring optical pathlength changes of 0.3 nm spatially and 0.03nm temporally. SLIM combines two classic ideas in light imaging: Zernike’s phase contrast microscopyand Gabor’s holography.

Spatial light interference microscopy (SLIM)

A method of patterning surfaces for liquid-crystal alignment using a polarization holography exposure on a linear photopolymerizable polymer alignment layer is demonstrated. Three configurations are demonstrated which include registered planar-periodic surface boundary conditions on both surfaces (true polarization gratings), planar-periodic and uniform planary surface boundary conditions, and planar-periodic and homeotropic boundary conditions. Two-dimensional polarization gratings are also demonstrated by orientating planar-periodic alignment layers orthogonally. Passive polarization gratings are also demonstrated using reactive mesogens to capture the periodic order indefinitely. The underlying structure of the configuration is discussed, including the nature of their switching transition (threshold or thresholdless), for all three configurations. A simple phenomenological model is presented to describe the Freedericksz transition for the registered planar-periodic boundary condition case.

Liquid-crystal diffraction gratings using polarization holography alignment techniques

Patterned chiral liquid crystals operate as configurable optical elements. Reflective metasurfaces based on metallic1,2,3 and dielectric4,5 nanoscatterers have attracted interest owing to their ability to control the phase of light. However, because such nanoscatterers require subwavelength features, the fabrication of elements that operate in the visible range is challenging. Here, we show that chiral liquid crystals6,7 with a self-organized helical structure enable metasurface-like, non-specular reflection in the visible region. The phase of light that is Bragg-reflected off the helical structure can be controlled over 0–2π depending on the spatial phase of the helical structure; thus planar elements with arbitrary reflected wavefronts can be created via orientation control. The circular polarization selectivity and external field tunability of Bragg reflection open a wide variety of potential applications for this family of functional devices, from optical isolators to wearable displays.

Planar optics with patterned chiral liquid crystals

A tunable-focus spherical lens using two flat substrates and inhomogeneous electric field over a homogeneous liquid crystal (LC) layer is demonstrated. The top flat substrate has an imbedded spherical indium–tin–oxide (ITO) electrode and the bottom has a planar ITO electrode on its inner surface. The inhomogeneous electric field generates a centrosymmetric gradient refractive index profile within the LC layer which causes the focusing behavior. The focal length of the LC lens can be tuned continuously from infinity to 0.6 m by the applied voltage.

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Tunable-focus flat liquid crystal spherical lens

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.

https://iopscience.iop.org/article/10.1143/JJAP.41.L1232/pdf

Liquid Crystal Lens with Spherical Electrode

A novel rubbing process for generating a very fine liquid crystal (LC) alignment pattern is proposed: we term this the "microrubbing process". An alignment film (polyimide) is rubbed using a metal ball and the thicknesses of rubbed lines are controlled by the normal load. It is described that the maximum line thickness is restricted by the ball diameter and thickness of the alignment film. An LC grating with homogenous and twisted-nematic orientation domains is proposed and is successfully fabricated using the microrubbing process. Polarization-independent diffraction efficiency is confirmed in the low applied-voltage region below the threshold voltage of the electro-optical effect and the high applied-voltage region above 2 V. The diffraction efficiency almost reaches the theoretically maximum value at an optimum applied voltage and is electrically controllable while maintaining polarization-independent diffraction properties.

https://iopscience.iop.org/article/10.1143/JJAP.42.6992/pdf

Polarization-Independent Liquid Crystal Grating Fabricated by Microrubbing Process

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.

Dependence of Optical Properties on the Device and Material Parameters in Liquid Crystal Microlenses.

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.

https://iopscience.iop.org/article/10.1143/JJAP.44.287/pdf

Liquid-Crystal Fresnel Zone Plate Fabricated by Microrubbing

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.

Michinori Honma

Papers

Liquid Crystal Lens with Spherical Electrode

Polarization-Independent Liquid Crystal Grating Fabricated by Microrubbing Process

Dependence of Optical Properties on the Device and Material Parameters in Liquid Crystal Microlenses.

Liquid-Crystal Fresnel Zone Plate Fabricated by Microrubbing

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