Anisotropy of the electro-optic Kerr effect in polymer-stabilized blue phases

Liquid crystalline polymer stabilized blue phases (PSBPs) are candidate materials for next generation electro-optic switching devices because they form a self-organized three-dimensional periodic structure and exhibit a fast response time of submillisecond order. Considering the crystallographic structures of PSBPs, it is intuitive to believe that the electro-optic effect would depend on the direction of the applied electric field; however, this relationship has not yet been investigated. In this study, we prepared two kinds of samples in which the (110) and (200) planes were oriented parallel to the substrates, and investigated the electro-optic Kerr effect as a field was applied between the two substrates. The two samples exhibited differing behaviors, with the Kerr coefficient of the (110)-oriented sample being larger by 20% than that of the (200)-oriented sample. These results imply that the electro-optic Kerr effect of PSBPs is not isotropic but anisotropic, just like cubic optical crystals.

Figure 1

Phase sequence of the sample for heating and cooling processes before UV irradiation (0.1 ${}^{\circ }\text{C/min}$).

Figure 2

(i) POM images and (ii) reflection spectra of the (a) (110)- and (b) (200)-oriented samples through crossed polarizers after the thermal recycle process and UV irradiation.

Figure 3

Kossel patterns and theoretical calculation results of the (a) (110)- and (b) (200)-oriented samples after the thermal recycle process and UV irradiation at room temperature.

Figure 4

Transmitted spectra and fitting results for (a) off (0 V/$\mu \mathrm{m}$) and (b) on (6.7 V/$\mu \mathrm{m}$) states.

Figure 5

Electric field-induced birefringence plotted against the square of the applied electric field and the curve by the fitting of the extended Kerr effect formula.

Figure 6

The model of (a) the double twisted cylinder and the BP I unit cells as the (b) (110) and (c) (200) planes oriented along the direction of the applied field.

Figure 7

Change in the field-induced birefringence of the cholesteric liquid crystal perpendicular to the applied electric field.