Electrically controlled birefringence effect

Optical Characteristics of the Electrically Controlled Birefringence Effect... 

The many different kinds of LCDs " based on electrically controlled birefringence (ECB) are variants of the Freedericksz effect first reported in the 1930s. These related display types based on the same electro-optical effect, but a slightly different display configuration are denominated by a multitude of names. However, current versions of this type of display are now often referred... 

The most important geometries of electrically controlled birefringence (ECB) are shown in Fig. 4.1. A compromise between dielectric and elastic torques results in director reorientation from the initial alignment 0(z) with the maximum deviation 0m at the center of the layer (the Prederiks transition). The effect occurs when the electric field exceeds a certain threshold value... 

The electrically controlled birefringence (ECB) effect is observed both in the homogeneous (S-effect, Fig. 4.1(a)) and in the homeotropic (B-effect, (Fig. 4.1(b))) nematic cells (Fig. 4.7). Let us consider the example shown in Fig. 4.7. In its initial position the director is oriented along the ar-axis and... 

The light beam with the aperture a iZo passes parallel to the FLC layers through an FLC cell placed between the polarizer and analyzer. In an electrical field the FLC helical structure becomes deformed, so that the corresponding dependence of the director distribution cos as a function of coordinate 2 /110, oscillates symmetrically in E electric fields (Fig. 7.18). These oscillations result in a variation of the effective refractive index, i.e., electrically controlled birefringence appears. The effect takes place up to the fields of FLC helix unwinding... 

Light valves were first produced on the basis of the classical semiconductors, ZnS, CdS, ZnSe, CdTe, and GaAs, in contact with nematic or chiral nematic liquid crystal [18]. The basic effects in liquid crystals included electrically controlled birefringence, dynamic scattering, and the cholesteric-nematic phase transition with the frequency response limited to a few Hertz. 

Perpendicular Orientation DAP — Effect (Electrically Controlled Birefringence)... 

When a voltage U > is applied, the sample is deformed. The retardation between the wavefronts of the ordinary and the extraordinary rays of transmitted light is dependent on the applied voltage. The effect is called DAP-effect (Deformation of Aligned Phases) or electrically controlled birefringence and can be applied in display devices [52—55] (see third part of this book). 

Electric field is also expected as an effective external field to drive finite and fast deformation in LCEs, because, as is well known for low molecular mass LCs (LMM-LCs), an electric field is capable of inducing fast rotation of the director toward the field direction [6]. This electrically driven director rotation results in a large and fast change in optical birefringence that is called the electro-optical (EO) effect. The EO effect is a key principle of LC displays. Electrically induced deformation of LCEs is also attractive when they are used for soft actuators a fast actuation is expected, and electric field is an easily controlled external variable. However, in general, it is difficult for LCEs in the neat state to exhibit finite deformation in response to the modest electric fields accessible in laboratories. Some chiral smectic elastomers in the neat state show finite deformation stemming from electroclinic effects [7,8], but that is beyond the scope of this article we focus on deformation by director rotation. 

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