Bistability of splay and π twist states in a chiral-doped dual frequency liquid crystal cell

Abstract

A bistable liquid crystal cell with splay and π twist stable states is obtained by doping a chiral additive in a splay cell filled with dual frequency liquid crystals. The switching between the two states is achieved by using a sequential waveform of low and high frequencies. The switching mechanisms are proposed by using the backflow effect together with the anisotropic properties of dual frequency liquid crystals. As a result, the two stable states have the superior memory characteristics due to the topological inequivalence.

Tunable and Memorable Optical Devices with One-Dimensional Photonic-Crystal/Liquid-Crystal Hybrid Structures

“…Or it becomes negative if the frequency is higher than fc. Based on this mechanism, various types of MMLC cells composed of DFLC are demonstrated in the literature (Hsiao et al, 2011b;Hsu et al, 2004;Jhun et al, 2006;Yao et al, 2009). Among them, the bistable chiralhomeotropic nematic (BHN) LC and dual-frequency cholesteric LC (DFCLC) have been used as defect layer in the 1D PC/MMLC cell (Hsiao et al, 2011a(Hsiao et al, , 2011cWu et al, 2011).…”

Dynamic Tuning and Memory Switching of Defect Modes in a Hybrid Photonic Structure

“…Note that there is no polarizer employed in the measurements unless explicitly specified. Figure 1 illustrates the state transitions and the corresponding optical textures of the PC/CD-DFLC cell under crossed polarizers [30]. Here, f 1 and f 2 represent the frequencies fulfilling the criteria of f 1 < f c and f 2 > f c , and thus corresponding to the conditions of ∆ε > 0 and ∆ε < 0 of the DFLC, respectively.…”

“…Based on this mechanism, the CD-DFLC can operate in two optically stable states-the memorable splay and π-twist states-and in a voltage-sustained state-the dynamic bend state-at frequency of 1 kHz. The switching between the bistable states is achieved by the frequency-revertible dielectric anisotropy of the DFLC together with the electrohydrodynamic flow effect of LC molecules [30]. In order to make a photonic device that enables not only the electrical tunability but also the multistability in its optical properties, we propose in this work a 1D hybrid photonic structure incorporated with a dual-mode CD-DFLC as the defect layer.…”

“…In recent years, dual-mode LC cells have widely been studied from the point of view of practical applications because they possess both the dynamic and memory functions in a single device [25][26][27][28][29][30]. Specifically, a dual-mode chiral-agent-doped dual-frequency LC (CD-DFLC) unites the bistable chiral-splay nematic (BCSN) and optically compensated bend (OCB) as the memory and dynamic modes in one cell, respectively [29].…”

“…Specifically, a dual-mode chiral-agent-doped dual-frequency LC (CD-DFLC) unites the bistable chiral-splay nematic (BCSN) and optically compensated bend (OCB) as the memory and dynamic modes in one cell, respectively [29]. The DFLC is a LC material whose dielectric anisotropy ∆ε can be varied by the frequency of the applied electric field [30]. The DFLC exhibits a characteristic frequency, known as the crossover frequency f c , to discriminate the sign of ∆ε.…”