Blue Phase Liquid Crystal Research Articles

Reduced off-axis gamma shift of liquid crystal display by intercepting transmittance method

Generally, the brightness and color of one image on a large-area flat panel display are different when people watch a display image under different viewing angles. The gamma shift is used to evaluate the difference of electro-optical performances under different viewing angles, namely the gray-scale display distortion. In order to reduce the gamma shift under the oblique viewing angle, the intercepting transmittance method is proposed and illustrated based on the single-domain in-plane switching blue-phase liquid crystal display (IPS-BPLCD). The results show that the off-axis image distortion index (the quantitative evaluation index of gamma shift) can be reduced by ~72% if the transmittance ratio reduces from 100% to 80% for the IPS-BPLCD with a straight electrode structure. Moreover, the zigzag electrode structure is used as the reference to illustrate the merits of the proposed method. As a result, the operating voltage of the IPS-BPLCD can be reduced by >20%, and the off-axis image distortion index is reduced by ~47% compared with the zigzag electrode structure. Besides this, the effects of the proposed method on contrast ratio, operating voltage and color difference of IPS-BPLCD are investigated as well. In fact, the proposed method is also useful for other LCD modes and electro-optical devices to achieve wide and uniform viewing angles.

Fast self-assembly of macroscopic blue phase 3D photonic crystals.

Blue phase (BP) liquid crystals are materials with unique self-assembling properties. They can be regarded as 3D photonic crystals as they organize in 3D cubic structures with sub-micrometer range periodicity and display selective optical bandgaps. Yet, the obtained BP crystals are usually polycrystalline or micrometer-sized monocrystals. Producing large BP monocrystals has proven to be a challenging and time-consuming endeavor, due to BP crystal growth being notoriously slow and the complex requirements for achieving a reasonable size and monocrystalline structure. In this work we successfully obtained large BP monocrystals (single lattice orientation) by fast self-assembly. Our fabrication process, which is about 100× faster than in previous reported research, uses relatively simple techniques, therefore demonstrating a considerable improvement towards the manufacturing of 3D photonic crystals.

Electrically switchable band-edge laser based on polymer-stabilized blue phase liquid crystal

ABSTRACT An electrically switchable band-edge laser has been demonstrated in a dye-doped polymer-stabilised blue phase liquid crystal. The light intensity of the laser can be tuned in three-dimensional space with a switching time of submillisecond, which promotes this band-edge laser widespread use in displays, point-of-care biomedical analysis, and optical security coatings.

Electrically tunable photonic band gap structure in monodomain blue-phase liquid crystals

Photonic band gap materials have the ability to modulate light. When they can be dynamically controlled beyond static modulation, their versatility improves and they become very useful in scientific and industrial applications. The quality of photonic band gap materials depends on the tunable wavelength range, dynamic controllability, and wavelength selectivity in response to external cues. In this paper, we demonstrate an electrically tunable photonic band gap material that covers a wide range (241 nm) in the visible spectrum and is based on a monodomain blue-phase liquid crystal stabilized by nonmesogenic and chiral mesogenic monomers. With this approach, we can accurately tune a reflection wavelength that possesses a narrow bandwidth (27 nm) even under a high electric field. The switching is fully reversible owing to a relatively small hysteresis with a fast response time, and it also shows a wider viewing angle than that of cholesteric liquid crystals. We believe that the proposed material has the potential to tune color filters and bandpass filters.

Electrically Controlled Lasing in Supercooled Liquid Crystal Blue Phase I Microdroplets

We have prepared the liquid crystal blue phase (BP) microdroplets emulsified in the glycerol environment and investigated their electro-optical properties upon the applied electric field. We showed...

Polymer‐Stabilized Monodomain Blue Phase Diffraction Grating

AbstractThe structural beauty of liquid crystalline blue phases is attested not only by their colorful optical micrographic textures but also by optical isotropy. More importantly, the homogeneity of the structures influences greatly to the electro‐optic properties. In this work, how the lattice orientation in polymer‐stabilized blue phase liquid crystal (PS‐BPLC) diffraction grating affects phase‐modulated diffraction efficiency is elaborated. A well‐arranged monodomain structure of blue phase is achieved and its diffraction capability is compared with multidomain PS‐BPLC. The diffraction efficiency in the zeroth order of monodomain PS‐BPLC is improved by 9% compared to that of multidomain structure. In addition, both driving and threshold voltages in monodomain PS‐BPLC are decreased by 29% and 30%, respectively, compared to those in multidomain PS‐BPLC owing to the regular arrangement of cubic lattices that give rise to increase in the coherence length and unified response in molecular reorientation under electric fields. Furthermore, the monodomain PS‐BPLC shows an efficient polarization conversion of linear polarization into circular polarization. It is believed that the device exhibits great potential to be used as a polarization converter or beam steering devices.

Cylindrical fiber cored by a blue phase liquid crystal

We consider an electromagnetic field propagating within a cylindrical waveguide whose core consists of a material in which the elongated molecules have the tendency to rotate helically along all directions perpendicular to a given vector which we chose to be along the axis of the fiber. This type of structure can be found in some chiral nematic materials such as blue phases. We establish the electromagnetic equations governing the dynamics of all the orders of propagating modes and solve them numerically. We found the band structure of the mentioned modes and show that they can be classified in quasi-transverse magnetic and electric modes whose corresponding cut-off frequencies are in some cases degenerated. Also, the profile field amplitudes versus the radial axis of the fiber are depicted and analyzed. Finally, we discuss how the modes are conformed and their conditions to propagate electromagnetic waves.

Electrically tunable and reversible selective reflection due to the transition between simple cubic and tetragonal blue-phase liquid crystals

ABSTRACT In this paper, we present experimental results on electrically tunable reflected wavelength in the full visible spectral range from 460 nm to 620 nm in one simple cubic blue-phase cell due to the simple-cubic–tetragonal lattice transition, confirmed by Kossel lines. The reflected wavelength is switched less than few hundreds milli-second and it is reversible. From the experimental observations in the reflection spectra and Kossel lines, we can see the following phenomena as increasing the applied field: the lattice-plane realignment in the simple-cubic blue phase (BPII), the transition between BPII and tetragonal blue-phase liquid crystal (BPX), and the lattice deformation of the BPX. Among them, the lattice deformation of the BPX shows larger electrostriction coefficient to shift the wavelength in a wider range, but it takes the longest response time. Because the reflected wavelength in each applied field exhibited extraordinarily sharp photonic bandgaps (less than 20 nm) with high reflectivity, the BP cell here shows a great potential to be a tunable photonic device.

Electrically-Tunable Blue Phase Liquid Crystal Microlens Array Based on a Photoconductive Film.

This paper proposes an effective approach to fabricate a blue phase liquid crystal (BPLC) microlens array based on a photoconductive film. Owing to the characteristics of photo-induced conducting polymer polyvinylcarbazole (PVK), in which conductivity depends on the irradiation of UV light, a progressive mask resulting in the variation of conductivity is adopted to produce the gradient distribution of the electric field. The reorientations of liquid crystals according to the gradient distribution of the electric field induce the variation of the refractive index. Thus, the incident light experiences the gradient distribution of the refractive index and results in the focusing phenomenon. The study investigates the dependence of lens performance on UV exposure time, the focal length of the lens, and focusing intensities with various incident polarizations. The BPLC microlens array exhibits advantages such as electrically tunability, polarization independence, and fast response time.

Crystal structures and structural colors of blue phase liquid crystals

Crystal structures and structural colors of blue phase liquid crystals

Stabilization of liquid crystal blue phases by carbon nanoparticles of varying dimensionality.

The thermal stabilization of blue phases is a subject that has been of scientific and technological interest since their discovery. Meanwhile, carbonaceous nanomaterials such as C60 fullerenes, carbon nanotubes and graphene have generated interdisciplinary interest spanning across solid-state physics, organic chemistry, colloids, all the way to soft matter physics. Herein, the stabilization of liquid crystal blue phases by doping with C60, single-walled carbon nanotubes and graphene oxide is described. All three types of particles are found to extend the combined temperature range of blue phases I and II by a factor of ∼5. Furthermore, mixtures of pairs of different materials, and all three types are shown to stabilize the blue phases. The temperature range of the blue phases is shown to grow at the expense of the cholesteric phase. This leads to a blue phase-cholesteric-smecticA phase triple-point in all cases except that of doping with carbon nanotubes. The mechanisms of this thermal stabilization are discussed in light of theoretical descriptions for other established systems.

Reflective blue phase liquid crystal display with triangular dielectric layer

ABSTRACT We propose a reflective blue-phase liquid-crystal display (LCD) with triangular dielectric layers and a diffuse reflector electrode. The triangular dielectric layers with a high dielectric coefficient on the top and bottom indium tin oxide glass substrates are equivalent to the conductive plates, forming a corrugated electrode structure. This type of reflective blue-phase LCD based on planar electrode and diffuse mirror electrode can offer relatively high reflectance (~74.5%) and low operation voltage (9.2 Vrms) compared to most other devices due to its fairly strong and uniform horizontal electric field component along the whole blue-phase liquid crystal bulk. This design has the advantages of fast response time, easy manufacturing process, a high resolution and full-colour capability. It is a promising future high-quality reflective full-colour microdisplay.

A polarization-independent blue phase liquid crystal on silicon with low operation voltage

A polarization-independent blue phase liquid crystal on silicon (BPLCoS) device with low operation voltage for 2π phase depth is demonstrated. With optimized reflection structure and two reflection films, the incident light may experience multifold optical path and 2π phase depth can be obtained. For the polarization-independence, an inclined electric field made by periodical gradient voltage is applied on the blue phase liquid crystal (BPLC) to match the light propagation direction. With the structure, the operation voltage can be lowered to 5.5 V in simulation and 5.9 V in experiment for 2π phase modulation at 1550 nm. The proposed device shows great potential for communication and imaging systems.

Temperature tunable omnidirectional lasing in liquid crystal blue phase microspheres

In this work, we demonstrate micro resonators made of liquid crystal blue phase (BP) microspheres, embedded in a polymer/water matrix. The omnidirectional 3D lasing from BPII and BPI microspheres and the temperature-controlled laser tuning within the range of 55 nm from the BPI microspheres were observed for the first time. The potential applications of BPs microlasers range from temperature-controllable, omnidirectional, coherent light micro sources to informational displays and micro sensing devices.

Reconfiguration of three-dimensional liquid-crystalline photonic crystals by electrostriction.

Natural self-assembled three-dimensional photonic crystals such as blue-phase liquid crystals typically assume cubic lattice structures. Nonetheless, blue-phase liquid crystals with distinct crystal symmetries and thus band structures will be advantageous for optical applications. Here we use repetitive electrical pulses to reconfigure blue-phase liquid crystals into stable orthorhombic and tetragonal lattices. This approach, termed repetitively applied field, allows the system to relax between each pulse, gradually transforming the initial cubic lattice into various intermediate metastable states until a stable non-cubic crystal is achieved. We show that this technique is suitable for engineering non-cubic lattices with tailored photonic bandgaps, associated dispersion and band structure across the entire visible spectrum in blue-phase liquid crystals with distinct composition and initial crystal orientation. These field-free blue-phase liquid crystals exhibit large electro-optic responses and can be polymer-stabilized to have a wide operating temperature range and submillisecond response speed, which are promising properties for information display, electro-optics, nonlinear optics, microlasers and biosensing applications.

Spatially and electrically tunable random lasing based on a polymer-stabilised blue phase liquid crystal-wedged cell

ABSTRACTWe demonstrate a spatially and electrically tunable random lasing based on polymer-stabilized blue phase liquid crystal (PS-BPLC)-wedged cell. The spatially tunable random lasers can be obtained from the laser dye-doped PS-BPLC-wedged cell through changing the pump positions, where the emission wavelength of the random laser can be tuned due to the thickness gradient of the wedged cell, which affects the scattering mean free path. Additionally, applying different electric fields can also tune the laser emission wavelength. The changing of refractive index due to the Kerr effect leads to a change in the scattering mean free path, resulting in shift of lasing wavelength. This PS-BPLC-wedged cell device has a great potential in applications of speckle-free imaging, document coding, biomedicine and other photonic devices.

Hysteresis-free and fast response polymer-stabilised blue phase liquid crystals

ABSTRACTThe electro-optical properties of γ-Fe2O3 nanoparticles doped polymer-stabilized blue phase liquid crystals are investigated. The experimental results show that the hysteresis were effectively suppressed by doping γ-Fe2O3. When doped with γ-Fe2O3 of 1.0 wt. %, hysteresis-free and fast response were achieved by the coupling effect of polymer and nanoparticle. Our research provides excellent guidance for the development of electro-optical devices with high grey scale accuracy and fast response.

32.2: Invited Paper: Fast Switching Blue Phase Liquid Crystals

Several recent advances to improve the optical‐electrical properties of blue phase liquid crystals (BPLCs) were proposed. A critical temperature is demonstrated in the phase transition of BPLC, which affects the lattice formation process. Polymer materials with the reactive diluent was investigated which may increase the Kerr constant and decrease the response time. And a conductive polymer dopant was introduced into PS‐BPLCs which may much improved driving capacity without degradation response time, hysteresis and residual birefringence.

19.1: Invited Paper: Driving frequency effect on blue phase liquid crystal photonic crystals

19.1: <i>Invited Paper:</i> Driving frequency effect on blue phase liquid crystal photonic crystals

P‐11.6: A blue phase liquid crystal lens with large tunable focal length range using different birefringence materials

P‐11.6: A blue phase liquid crystal lens with large tunable focal length range using different birefringence materials