Blue phases are types of liquid crystal phases that appear in a temperature range between a chiral nematic phase and an isotropic liquid phase. Because blue phases have a three-dimensional cubic structure with lattice periods of several hundred nanometres, they exhibit selective Bragg reflections in the range of visible light corresponding to the cubic lattice. From the viewpoint of applications, although blue phases are of interest for fast light modulators or tunable photonic crystals, the very narrow temperature range, usually less than a few kelvin, within which blue phases exist has always been a problem. Here we show the stabilization of blue phases over a temperature range of more than 60 K including room temperature (260-326 K). Furthermore, we demonstrate an electro-optical switching with a response time of the order of 10(-4) s for the stabilized blue phases at room temperature.

Optical shutters whose operation is based on the Kerr effect, which is a quadratic electro-optic effect generated in optically isotropic substances, have extremely fast response times. However, the magnitude of the induced birefringence in conventional Kerr materials is too small for them to be used in flat-panel displays. We show that a polymer-stabilized blue phase has a Kerr constant which is about 170 times larger than that of nitrobenzene. We also demonstrate microsecond electro-optical switching over a wide temperature range for flat Kerr cells containing the polymer-stabilized blue phase. These achievements can contribute to providing fast-response flat-panel liquid-crystal displays that need not undergo a rubbing process during manufacture.The Kerr effect is the development of birefringence in an optically isotropic substance, such as a liquid, when the substance is placed in an electric field. The magnitude of the birefringence induced via the Kerr effect, Dn, can be expressed bywhere Dn is the induced birefringence, k is the wavelength of light, and K is the Kerr constant. The Kerr cell, which is used as an optical shutter, consists of a Kerr substance (usually a polar, organic liquid) placed in an insulating container with two electrodes. This is positioned between crossed linear polarizers whose transmission axes are at ±45 to the applied electric field. In order to obtain the half-wavelength retardation at which maximum contrast can be obtained, the cell needs to have a thickness (optical path length), d k/2 , ofFor example, a Kerr cell containing nitrobenzene, which is generally known to have a very large Kerr constant (K = 2.2 10 ±12 m V ±2 ), [1] requires a cell thickness of about 45 mm for application of an electric field, E, of strength E = 5 10 6 V m ±1 . Fast optical shutters can be used in flat-panel liquid-crystal displays, as these displays consist of arrays of small light shutters. However, Kerr shutters made of nitrobenzene are too thick to be used. Blue phases are liquid-crystalline phases that appear in a very small temperature range between the cholesteric phase (Ch) and the isotropic phase (Iso).[2±5] There are three types of blue phasesÐBPI, BPII, and BPIII. The BPI and BPII phases are characterized by cubic symmetry of the director field, with lattice constants that are comparable to the wavelength of visible light. [6,7] Since blue phases are optically isotropic in zero electric field due to their structural symmetry, surface treatment to obtain a specific molecular orientation, e.g., rubbing to obtain twisted alignment, is redundant. This is a great advantage for device fabrication, because the rubbing process introduces degradation of the display quality and increases manufacturing costs. Recently, we reported that the temperature range over which BPI exists, usually a few degrees Kelvin, was successfully extended to more than 100 K in the polymer±liquid crystal (blue phase) composite system, referred to as the ªpolymer-stabilized blue phaseº. [8,9] In this study, the Kerr effe...

Key challenges in achieving higher-quality liquid crystal displays for future generations are developing new liquid crystal materials with faster electro-optical response and simplifying the fabrication process of devices. Blue phases 1-4 , kinds of liquid crystal phases, have two major advantages over commonly used nematic phases. First, the response is much faster 5-8 . Second, the zero-electric field state is optically isotropic unlike nematic phases, that is, no surface treatment (no rubbing) is necessary, leading to a simplification of the fabrication process. One of the problems of blue phases that the available temperature range is very narrow has been overcome by our recent achievement, the polymerstabilized blue phases 9, 10 . Here we show that the polymer-stabilized blue phases surmount another problem that the blue phase is very fragile to an electric field. We also demonstrate the sufficiently large electric field-induced birefringence and the micro-second response of the polymer-stabilized blue phases without any surface treatment.

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