摘要:

An electrically controlled birefringence liquid crystal display has a problem over narrow viewing angle. To solve this problem, the authors proposed a double-layer electrically controlled birefringence liquid crystal display with a wide-viewing-angle cone under an applied voltage. In this device, each liquid crystal layer compensates the variation of retardation as a function of viewing angle. However, the optical compensation occurs only when certain voltages are applied. The objective of this paper is to propose a novel film compensated double-layer electrically controlled birefringence liquid crystal display that has a wide cone of view in any state. This device is based on the concept of compensation of retardation.

ISSN:0267-8292    

DOI:10.1080/02678299308027641

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

We present a conception of two optical modulators. One of these, which we have called the scattering liquid crystal cell seems to be promising with a view to possible applications. We assumed that the modulator could be used in optical logic as a gate element, but other applications in optoelectronics would appear also to be possible. Some preliminary results of an experimental examination of the modulators are also presented.

ISSN:0267-8292    

DOI:10.1080/02678299308027642

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A new method for producing tilt angle in liquid crystal cells is proposed. The method requires a SiO vacuum deposition layer which is subsequently covered with a polyvinyl alcohol (PVA) layer, obtained by dipping in a solution. It was possible to obtain tilt angles between 7 and 30° by changing the concentration of PVA in the solution.

ISSN:0267-8292    

DOI:10.1080/02678299308027643

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Experimental results are presented on the optical response of chiral smectic C cells of various thicknesses (between 2 and 9 μm) on AC voltages. For part of the voltage and frequency range the electric field induces patterns of disclination lines. The threshold voltages for these electrohydrodynamic instabilities turn out to be independent of the cell thickness for 4, 6, and 9 μm cell gaps. In the 2 μm cells, structural changes of the chiral smectic C texture are found at voltages below the threshold for the instabilities. The applicability of the Carr-Helfrich model for electrohydrodynamic instabilities in nematics to these chiral smectic C layers is discussed.

ISSN:0267-8292    

DOI:10.1080/02678299308027644

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

This paper reviews liquid crystal optical devices including tunable filters, photonic switches and spatial light modulators, and examines their application to optical communication and information processing systems. Optical processing has three major advantages: massive parallelism, high speed and broad wavebands. Compared with typical optical materials including silica, semiconductors and inorganic electrooptic crystals used in communication systems, a liquid crystal has a number of outstanding features including its large refractive index change and large polarization rotation power at a low voltage. These features make it possible to develop new optical components.

ISSN:0267-8292    

DOI:10.1080/02678299308027645

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A new and simple electric charge interaction mechanism has been proposed to explain the behaviour of the tilt angle of liquid crystals by rubbing. The mechanism of the molecular alignment is elucidated based on the effect of a static electric charge on a substrate surface treated by rubbing. An electric field which is dependent on the topology of a substrate surface allows a planar orientation of molecules with positive dielectric anisotropy. With increasing rubbing strength, the tilt angle varies slowly. The director of molecules with negative dielectric anisotropy is uniform and has a tilt angle determined by the molecular permanent dipole direction. The air-liquid crystal interface case is also considered. This model enables us to give a unified picture of the molecular alignment mechanism.

ISSN:0267-8292    

DOI:10.1080/02678299308027646

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Many liquid crystals are found to have relatively high birefringence (Δn) values in the microwave and millimeter wave regions, as calculated from the phase shift induced by their reorientation by magnetic or electric fields. At 30 GHz, Δnvalues were obtained in the range of 0.08 to 0.18 for eleven liquid crystal mixtures of various types. The most favourable liquid crystal structures for high millimeter wave birefringence are highly conjugated rod-like molecules containing biphenyl, terphenyl, phenylpyrimidine, biphenylpyrimidine, and tolane groups in nematics of positive dielectric anisotropy (Δε). However, other liquid crystal structures including Schiffs base, azoxybenzene, and aromatic ester groups also have substantial birefringence, including nematics with negative and crossover Δε, as well as cholesteric nematics. The Δnvaried only slightly at different frequencies of microwave millimeter wave in the 15–94 GHz range. Studies on magnetic and electrical field liquid crystal orientation in specially designed waveguides provide a basis for new types of modulators and scanning array antennae in the millimeter wave region, where more compact liquid crystal modulation media can be used than in the microwave region. These scanners can be used for both sending and receiving radar signals for potentially low cost radar systems.

ISSN:0267-8292    

DOI:10.1080/02678299308027647

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Results are presented which show that the on-state clarity of a UV cured polymer dispersed liquid crystal (PDLC) film depends on the refractive index of the final polymer in the PDLC film, the ordinary refractive index of the liquid crystal, the solubility of the liquid crystal in the prepolymer and the rate at which the film is cured. Liquid crystal mixtures for use in PDLC films are chosen such that the ordinary refractive index of the liquid crystal is equal to the refractive index of the polymer matrix. It has been shown previously that a large quantity of liquid crystal remains dissolved in the polymer matrix, thus increasing the mismatch between the refractive index of the polymer and the ordinary refractive index of the liquid crystal and therefore reducing the on-state clarity. For liquid crystal mixtures which have high solubility in the prepolymer (>60 per cent) the mismatch in the refractive indices can be very large and the on-state clarity of the resulting film can be very poor (Ton<70 per cent). Results are presented which show that it is possible to increase the on-state clarity of such films by increasing the rate at which these films cure. If the liquid crystal is less soluble in the prepolymer (<45 per cent), a PDLC film formed from such a liquid crystal/ prepolymer system often has very good on-state clarity (Ton>75 per cent) be it cured slowly or quickly. Results are also presented which show that in order to achieve a true measure of on-state clarity it is necessary to use a small collection angle (<3°) in the detecting optics. If larger collection angles are used, the photodetector collects light which is scattered out of the specular beam, thus leading to a false measure of on-state clarity.

ISSN:0267-8292    

DOI:10.1080/02678299308027648

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The problems of photoinitiator contamination are addressed for the liquid crystal phase in polymer dispersed liquid crystal films formed by photopolymerization induced phase separation of liquid crystal from monomer solutions. Initiator contamination lowers the clearing point of the liquid crystal phase, and decreases the photostability and resistivity of the polymer dispersed liquid crystal. These problems are minimized by replacing the conventional photoinitiators with copolymerizable initiators which become incorporated in the polymer phase as it separates. Copolymerizable photoinitiators are studied and used to form polymer dispersed liquid crystals with higher clearing point liquid crystal phases, higher resistivity, and better photostability than polymer dispersed liquid crystals formed with conventional photoinitiators. These improvements provide very significant advantages for many polymer dispersed liquid crystal applications.

ISSN:0267-8292    

DOI:10.1080/02678299308027649

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Microtubule particles and metal-coated microtubules were dispersed in various host liquid crystal mixtures. Dispersion effects were evaluated as a function of liquid crystal type, viscosity, dielectric anisotropy and surface interaction. Experimental results indicated that all the types of liquid crystals studied were aligned perpendicular to the microtubule surfaces, regardless of liquid crystal composition or various surface coatings used on the metal-coated microtubules. Low concentrations of the metal-coated microtubules in nematic liquid crystal hosts were aligned by flow or cell surface alignment conditions, and could be modulated by electric or magnetic fields. We observed better microtubules dispersion uniformity in high viscosity liquid crystal host mixtures and in liquid crystal-monomers than in isotropic fluids. Microtubules particles dispersed in ROTN-404 liquid crystal mixture had a much higher birefringence in the microwave region than dispersion in a paraffin oil.

ISSN:0267-8292    

DOI:10.1080/02678299308027650

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor