Transmission voltage curve

Gray scale inversion is explained in Fig. 9.9. Figure 9.9a shows a transmission voltage curve for normal incidence angles. For normal incidence the... 

Fig. 13.24 Tri-stable switching of an antifenoelectric liquid crystal. Typical hysteresis-type dependence [34] of the total polarization P as a function of the external field (a) and optical transmission-voltage curves [35] measured at three different Imiperatures (Tj > T2 > T ) in the...

The optical threshold voltage Vthr is obtained by extrapolating the linear portion of the transmission/voltage curve (with the polarizers parallel or perpendicular to the rubbing directions) as shown in Fig. 1. 

Otherwise, the changes in general appearance of the transmission-voltage curves with varying 3q look identical to those calculated here (Fig. 2). 

The viscoelastic properties of liquid crystals are very important, and mainly determine the behavior of liquid crystals in external electric fields, defining such characteristics as controlling voltages, steepness of the transmission-voltage curve, response times, etc. Now only the phenomenological theory of the viscoelastic properties of nematic liquid crystals is essentially complete [18, 28]. 

Transmission-Voltage Curve for Normal Light Incidence... 

The typical transmission-voltage curve (TVC) of the twist effect for normal light incidence is shown in Fig. 4.12 for the twist cell placed between parallel polaroids. As mentioned above, the deformation of the director, measured by birefringence [66] or capacity [73], begins for smaller voltages U = C/tw then visible variations of the twist cell transmission. In view of the Mauguin requirement (4.53), the optical threshold of the twist effect decreases for the smaller values of the cell thickness [74] and the optical anisotropy of the liquid crystal as well as for director pretilt on the boundaries [76]... 

The corresponding dependence of the steepness of the transmission-voltage curve (TVC) on physical parameters of the chiral nematic mixture and geometry of the supertwist display is shown in Table 4.8. The correlations, mentioned in Table 4.8 are used in the practical development of supertwist mixtures for highly informative displays [129-133]. 

Steepness of the transmission-voltage curve (TVC) at normal incidence, which defined the multiplexing capability of the display (4.61). 

Since the threshold of the reorientation is defined by the size of the droplet, which is randomly distributed, the transmission-voltage curve begins at very small voltages and assumes a nonthreshold behavior. The contrast of switching strongly depends on the viewing angle [264] (Fig. 4.47). 

Calculations of the twist structure resolution in a nonuniform field are very cumbersome and, for this reason, have not been attempted until recently [173, 174]. The direct minimization algorithm of the free energy functional proposed by Levov et al. stimulated progress in this field [174]. The idea of the calculations is as follows. A twist cell is considered as a linear optical unit for the corresponding values of voltages when the transmission-voltage curve is linear [2]. It enables us to determine the Optical Transfer Function (OTF) of a twist cell which characterizes the transformation of a spatially nonuniform field at the input of the cell to the corresponding variation of the optical transmission at the output (Fig. 5.33). OTF is defined as the... 

---