Nematic liquid crystal devices with sub-millisecond response time

Conventional nematic liquid crystal devices exhibit switching times that are in the order of several milliseconds. In this work we focus on two types of nematic liquid crystals that can overcome the limitations of conventional nematic liquid crystals and allow sub-millisecond switching times for both switching on and off: nano-pore polymer-liquid crystals and dual-frequency liquid crystals

Fast polarization insensitive optical shutters using dual frequency liquid crystals

Most of the existing displays and optical shutters based on liquid crystals work in combination with linear polarizers. This implies that often more than half of the light is lost due to optical loss in the polarizers and/or the fact that the incoming light is unpolarized. For a number of shutter and filter applications it is important to have a high transmission, while it is not necessary to have a very high contrast. When considering nematic liquid crystals for use in fast optical shutters or filters, a number of possibilities exist. Dual-frequency liquid crystals offer faster switching possibilities because they can be switched from one state to another with a low frequency voltage and switching back can be achieved with the aid of a high frequency voltage. One of the limiting factors for the switching speed of dual-frequency nematics is the appearance of backflow. As in vertically aligned nematic devices, a certain threshold voltage exists above which the switching speed increases drastically [1]. Above the backflow threshold, the liquid crystal ends up in a meta-stable twisted orientation as shown in the figure below

Infiltration of a photonic crystal fiber with cholesteric liquid crystal and blue phase

Photonic crystal fibers (PCF) have been selectively filled with a cholesteric liquid crystal (ChLC) with special interest in the blue phase (BP) of the liquid crystal. It has been observed thermal tuning of the guided light in the visible region. A dramatically enhance appears when the phase of the liquid crystal changes from cholesteric to blue phase I (BPI). When a thermal range of the blue phase I is achieved, no changes are observed while increasing temperature from BPI through BPII and to the isotropic phase

Liquid crystalline blue phase in mixtures of fluorinated compounds with positive and negative dielectric anisotropy and its electro-optic performance

Dependence of a blue phase temperature range on a chiral dopant and cyano compound addition as well as character of nematic base mixture was investigated. Base nematic mixtures of fluorinated compounds, one with positive and the other one with negative dielectric anisotropy, were chosen. Various fluoro compounds, chiral compounds and cyano compound were added in order to evaluate the relationship between blue phase stability and molecular structure of components. The stability of a blue phase in selected mixtures has been extended by polymer network formation. Fundamental electro-optic properties such as Kerr constant, operating time and switching voltage of a polymer-stabilised blue phase with positive and negative dielectric anisotropy are given, too. It has been confirmed that blue phase temperature range and its electro-optic performance strongly depends on molecular structure of mixture components as well as chiral dopants and their helical twisting power. Specifically, it was found that the cyano compound addition causes destabilisation of blue phase in mixtures consisted of fluorinated compounds

Liquid Crystalline Blue Phase In Mixtures Of Fluorinated Compounds With Positive And Negative Dielectric Anisotropy And Its Electro-Optic Performance

Dependence of a blue phase temperature range on a chiral dopant and cyano compound addition as well as character of nematic base mixture was investigated. Base nematic mixtures of fluorinated compounds, one with positive and the other one with negative dielectric anisotropy, were chosen. Various fluoro compounds, chiral compounds and cyano compound were added in order to evaluate the relationship between blue phase stability and molecular structure of components. The stability of a blue phase in selected mixtures has been extended by polymer network formation. Fundamental electro-optic properties such as Kerr constant, operating time and switching voltage of a polymer-stabilised blue phase with positive and negative dielectric anisotropy are given, too. It has been confirmed that blue phase temperature range and its electro-optic performance strongly depends on molecular structure of mixture components as well as chiral dopants and their helical twisting power. Specifically, it was found that the cyano compound addition causes destabilisation of blue phase in mixtures consisted of fluorinated compounds. © 2014 © Taylor & Francis