Light Shutter Research Articles

Electro-optical Performance Investigation of Cholesteric Liquid Crystal Containing Azo Dye: Light Shutter Device Application

In this study, the effect of chiral dopant concentration on electro-optical and dielectric properties of a cholesteric liquid crystal (CLC) composite was investigated, and a dye-doped cholesteric liquid crystal (DDCLC) light shutter was developed. The electro-optical properties of samples were investigated by electro-optical switching method without the use of a polarizer. The dielectric characterization of the composites were also realized using dielectric spectroscopy technique with a wide frequency range. Significant electro-optical and dielectric parameters, such as transition voltages, complex dielectric constant, dielectric anisotropy and light transmission values of composites were found from the experimental data. The obtained results show that the chiral dopant causes changes in electro-optical and dielectric parameters of CLC, and the developed DDCLC light shutter can be used in optoelectronic device applications.

Spectral Peculiarities of Multilayer Cholesteric Wedge-Cell System with Dye-Doped Polymer Layer

Spectral properties of the three-layered wedge-cell system of two identical cholesteric layers with an isotropic defect (dye-doped polymer layer) between them were investigated experimentally and theoretically. It was shown that multiple defect modes can be observed in this kind of system’s photonic band gap which widen the application range of system mentioned above such as low threshold lasing, multi-position trigger, multiwavelength filters, light shutters, etc. The supporting simulation was also provided showing an agreement between experimental results and theoretical calculations. The problem was solved by Ambartsumian’s layer addition modified method.

Low-driving-voltage, polarizer-free, scattering-controllable liquid crystal device based on randomly patterned photo-alignment.

In this work, a polarizer-free, electrically tunable liquid crystal device is presented. This device is based on randomly patterned photo-aligned boundaries generating light scattering in an adjacent liquid crystal film. Its transparent on state requires only 7.5Vrms driving voltage. Switching from a 49.5% hazy off state into the transparent on state occurs at 1.25 V, with only 1.2% residual haze. The effect exhibits fast rise and decay times of 0.3 ms and 7.2 ms, respectively. Thanks to its field-effect nature and the surface preparation process, zero ohmic low power consumption, fast response times, and steep transmission-voltage characteristics result. Applications are smart windows, light shutters, and/or transparent displays, as well as complementary metal-oxide-semiconductor driven multiplexed displays.

1550 nm infrared/visible light switchable liquid optical switch.

In this paper, a liquid optical switch is proposed, and the 1550 nm infrared/visible switching function based on hydraulic control can be realized. An infrared light switch cavity, a visible light cavity and a liquid control cavity are stacked to form the main framework of the device. The glycerol, dyed liquid, and transparent liquid are filled in the cavities, respectively. Two elastic films are fabricated between the cavities for controlling the liquid volume of the cavities. With such a structure, in the initial state, the 1550 nm infrared light and visible light are absorbed by the glycerol and dyed liquid, respectively. The device shows infrared light-off and visible light-off states. When the elastic film is actuated by the liquid pressure, the shape of the elastic film can be changed. Once the elastic film touches to the substrate, a light channel can be formed so that the infrared light or visible light can pass through it. It shows infrared light-on or visible light-on states. In this way, the device can be worked as an infrared light and visible light switchable optical switch. The experiments show that the device can obtain the optical attenuation from ∼1.02 dB to ∼18.24 dB for 1550 nm infrared light optical switch and ∼0.66 dB to ∼8.70 dB @ λ=450 nm; ∼0.62 dB to ∼8.74 dB @ λ=532 nm; ∼0.77 dB to ∼9.00 dB @ λ=633 nm for visible light optical switch. The device has potential applications in the fields of optical fiber communications, variable optical attenuators, and light shutters.

Spectral Peculiarities of Multilayer Cholesteric Wedge-Cell System with Dye-Doped Polymer Layer-=SUP=-*-=/SUP=-

Spectral properties of the three-layered wedge-cell system of two identical cholesteric layers with an isotropic defect (dye-doped polymer layer) between them were investigated experimentally and theoretically. It was shown that multiple defect modes can be observed in this kind of system.s photonic bandgap which widen the application range of mentioned above system such as low threshold lasing, multi-position trigger, multiwavelength filters, light shutters, etc. Supporting simulation was also provided showing an agreement between experimental results and theoretical calculations. The problem was solved by Ambartsumian.s layer addition modified method. Keywords: cholesteric liquid crystals, chirality, photonic bandgap, defect modes, tuning, laser dye, polymer layer.

Dye-doped liquid crystal light shutter fabricated by thermally-induced phase separation

Dye-doped liquid crystal light shutter fabricated by thermally-induced phase separation

Dye-doped liquid crystal light shutter fabricated by thermally-induced phase separation

Dye-doped liquid crystal light shutter fabricated by thermally-induced phase separation

Ion-doped liquid crystal light shutter switchable among transparent, haze-free opaque, and high-haze opaque states

Ion-doped liquid crystal light shutter switchable among transparent, haze-free opaque, and high-haze opaque states

Ion-doped liquid crystal light shutter switchable among transparent, haze-free opaque, and high-haze opaque states

Ion-doped liquid crystal light shutter switchable among transparent, haze-free opaque, and high-haze opaque states

A Single‐Step Dual Stabilization of Smart Window by the Formation of Liquid Crystal Physical Gels and the Construction of Liquid Crystal Chambers

AbstractSmart windows are very attractive because they not only provide comfortable indoor conditions for cars and buildings, but also protect privacy. However, current smart windows have problems such as high energy consumption, slow response time, and poor stability. To solve these problems, a single‐step dual stabilization (SSDS) is newly proposed for the fabrication of robust liquid crystal (LC) smart windows switching fast at low voltage. Upon irradiating ultraviolet light on the selected area of the nematic (N) LC optical cell with photoisomerizable macrogelators (B3AZ) and photopolymerizable monomers, NLC physical gels (LCPGs) and partition walls are simultaneously constructed. LCPGs play a role of light shutter under a low electric field (9.6 Vpp) which is ten times lower than that of the conventional polymer‐stabilized LC‐based smart windows. Partition walls constructed by the selected area photopolymerization significantly enhance the mechanical stabilities. Based on the experimental results, it is realized that the NLC layer generated near the partition walls makes the LCPGs respond to a low voltage. Robust SSDS smart windows could open new doors for the development of high‐performance smart windows.

An electrically light-transmittance-switchable film with a low driving voltage based on liquid crystal/polymer composites

ABSTRACTAs a typical class of electrically light-transmittance-switchable (ELTS) composites materials, polymer dispersed liquid crystal (PDLC) films have been widely used in displays, smart windows, light shutters, etc. However, the commercialised PDLC film still requires a comparatively high voltage to maintain its transparent state, leading to huge power consumption and even a potential safety risk. In this regard, we proposed a ‘heat followed UV’ stepwise polymerisation strategy for preparing a kind of ELTS film with a low driving voltage (~20.7 V) through constructing a coexistent system of polymer dispersed and polymer stabilised liquid crystal (PD&SLC). In this new PD&SLC system, vertically orientated polymer networks were formed within LC domains to induce the vertical alignment of LC, thereby reducing the driving voltage. Also, the as-made PD&SLC film exhibited good flexibility due to the high content of polymer. Moreover, the effects of the liquid crystalline polymerisable monomers content on the polymer morphologies as well as the electro-optical properties of the as-made PD&SLC films were elaborately investigated.

Novel easy to fabricate liquid crystal composite with potential for electrically or thermally controlled transparency windows

Switchable liquid crystal (LC) composites are a unique and attractive class of functional materials due to their extensive use in various applications including smart and privacy windows. Demand for developing smart windows with good switchable performance has steadily increasing in the past decades due to their importance in energy saving. Herein, we present the use of novel and highly active switchable LC composite material-octadecanol-doped LC-prepared via a facile, low-cost, and scalable process, for thermally or electrically controlled transparency windows. A systematic study of the switchable behavior reveals the formation of a reversible molecular arrangement between the LC and the octadecanol, which allows control of the transparency through scattering modulation of the device by voltage or temperature. The devices fabricated by sandwiching the LC composite material between two ITO-covered glass slides present switchable performance with high potential for cost-effective utilization in various applications, such as light shutters, smart or privacy windows.

P‐106: Guest‐Host Liquid Crystal Devices Utilizing Dichroic Dye and Its Application

Wide application of dichroic dye‐doped liquid crystal device (DLCD) devices has been proposed, which removes conventional film‐type polarizer in reflective LCD and OLED. Combination of DLCD, quarter‐wave film and reflector can realize effective reflective LCD. In addition, by replacing conventional polarizer to switchable DLCD in OLED, the proper level of a low reflection is achieved, and more interestingly high brightness OLED can be realized if the optic axis of DLC is switched to vertical alignment when there is no ambient light, which could save power consumption and life time of OLED. Further DLCD can be applied to bi‐functional device functioning as both smart mirror and light shutter.

66‐4: Late‐News Paper: Fast Dichroic‐Dye‐Doped Cholesteric Liquid Crystals Light Shutter

We demonstrate a dichroic‐dye‐doped cholesteric liquid crystal light shutter device with fast response time, achromatic dark state, and polarization independence. The liquid crystal director is switching between the transparent homeotropic state to a dark transient planar state without scattering, and continually to focal conic state with little scattering. The device fabrication process is simple because of no alignment is needed and a simple electrodes structure used. It has potential to be applied in automotive applications to block oncoming headlight glare, and in AR real world image occlusion.

Electrically switchable bistable dual frequency liquid crystal light shutter with hyper-reflection in near infrared

ABSTRACTBistable light shutter based on dual frequency cholesteric liquid crystals (LCs) have attracted intensive interests due to low energy consumption. Herein, we demonstrated an electrically switchable bistable dual frequency LC light shutter with a hybrid structure of cholesteric LC and chiral polymer film. The fabricated device can be switched between planar state which is transparent and focal conic state which is opaque in visible light through voltage pulse while keeping hyper-reflection in near infrared light in both states. The increase of reflection in near infrared light dramatically reduces the interior heat from solar energy, thus making it quite useful in temperature control. In addition, the reflection of near infrared light can be further improved by using cholesteric LC with larger birefringence. The proposed device is useful in smart windows of automobiles, energy-saving buildings and other photonic applications.

Voltage controlled scattering from porous silicon Mie-particles in liquid crystals

Creating novel liquid crystalline (LC) photonic metamaterial structures is a highly promising approach for the development of tunable photonic devices particularly when nanoporous structures are used in which the LC can infiltrate and modify their properties. In the present work, a tunable scattering device made of partially oxidized porous silicon microparticles mixed with LC is proposed and demonstrated. Being porous in nature, the microparticles trap the LC molecules and enhance the scattering in the voltage OFF state. Due to the random orientational order inside the particles, the averaged refractive index (RI) inside these nanopores is close to that of the isotropic LC RI in the OFF state. Averaging between this LC and the oxidized porous Si brings the average RI of the microparticle down and maximizes the index mismatch with the surrounding LC regions. When the porosity is large enough, a high RI mismatch between the particles and its surrounding in the OFF state is obtained. In the ON state, the molecules orient along the electric field direction, decreasing the RI mismatch and increasing the transparency of the system. The scattering decreases gradually and reversibly with the applied voltage while at zero voltage state it decreases with temperature. At the high voltage state the scattering increases with temperature with some enhancement at the clearing point due to the LC order parameter fluctuations. A slight decrease of the clearing point is observed as a result of weakening the intramolecular interaction and lowering the order parameter. Using fluorescent confocal microscopy the changes in the LC and microparticles domains are monitored showing some reversible dragging of the microparticles towards one of the substrates as the voltage increases. Being a tunable light scattering device, it has a great potential for smart window and light shutter applications.

Formation of polymer structure by thermally-induced phase separation for a dye-doped liquid crystal light shutter

A dye-doped LC/polymer light shutter with a polymer structure that is formed using the thermally-induced phase separation (TIPS) method is demonstrated. The TIPS method does not include any chemical reaction, and thus there is no degradation of the dye during the fabrication process. The light shutter can be fabricated quickly because the optical performance is not affected by the cooling time. The fabricated TIPS cell exhibits excellent optical performance, such as a low haze value of 0.5% in the initial transparent state, and a high haze value of 99.1% in the opaque state with a superior black color. This approach can be used for the high image quality of see-through displays using organic light-emitting diodes.

Low-Threshold-Voltage and Electrically Switchable Polarization-Selective Scattering Mode Liquid Crystal Light Shutters.

Low-threshold-voltage (Vth) and electrically switchable, polarization-selective scattering mode light shutters (PSMLSs) using polymer-dispersed liquid crystals (PDLCs) are demonstrated in this work. The optimized weight ratio of the nematic liquid crystals (LCs) to the adopted monomer (NBA107, Norland Optics) in the low-Vth PDLCs based on NBA107 is 7:3, [7:3]-PDLCsNBA107. The properties of the low-Vth PDLCsNBA107, such as light-scattering performance, initial transmission, Vth, and droplet size were investigated. Experiment results show that the surface anchoring (threshold-voltage) of NBA107 is weaker (lower) than or equal to that of the common NOA65. The cost is that the response time of the proposed PDLCsNBA107 is relatively long. A method to reduce the decay time, which can be applied to all other PDLC devices, will be elucidated. In addition to the low Vth of the proposed PDLCsNBA107, the operation voltage (~6 Vrms) to approach the maximum transmission is relatively low in a 7 μm-thick PDLCsNBA107 cell. Moreover, the polarization-selective light-scattering performances of the proposed PSMLSs based on the [7:3]-PDLCsNBA107, mainly driven by in-plane and vertical fields, are also demonstrated.

Scattering-/absorption-mode light shutters based on dye-doped fingerprint chiral textures

Scattering-/absorption-mode light shutters based on dye-doped fingerprint chiral textures (DdFCTs) are demonstrated. DdFCTs in a liquid crystal (LC) cell treated with homeotropic alignment are initially stable FCTs due to the vertical surface anchoring force (SAF). The LCs completely rotate to homeotropic orientation from stable FCTs by applying a suitable operation voltage (Vop). Furthermore, when the Vop is switched off, the LCs transform into temporary focal conic textures with lifetimes of few seconds from the homeotropic orientation, the LCs then transform into unstable FCTs. Finally, the unstable FCTs spontaneously return to the initial stable FCTs. The light absorption of DdFCTs in the stable FCTs/unstable FCTs/field-induced multi-domain FCTs is independent of the polarization of the incident light. The operation mechanism of the proposed DdFCTs is also discussed. Most importantly, the response time and the required Vop to rotate all LCs to homeotropic orientation in DdFCTs from stable FCTs in LC cells treated with homeotropic alignment layers are respectively shorter and lower than those in common dye-doped cholesteric LCs (DdCLCs) from stable planar textures in LC cells treated with homogeneous alignment layers. Comparing with DdCLCs, about 20% Vop can be reduced in DdFCTs. The cause can be understood since the Vop applied onto the DdFCTs is fully dedicated to unwind the helical structures.

Electrowetting optical switch with circular tunable aperture

We propose an optical switch with a circular tunable aperture based on electrowetting effect. The device is composed of two immiscible liquids. One liquid is dye-doped and conductive, while the other is transparent and insulating. The dye-doped water droplet is placed in the center of the bottom substrate, surrounded by transparent oil. In our experiment, in the voltage-off state, the light beam cannot pass through the aperture. When the voltage is applied, the black liquid expands in the radial direction because of the effect of electric field force and a circular aperture appears in the center of the device. Therefore, the device can achieve the function of light-on and light-off. Our device can provide a reasonable attenuation (∼582 ∶ 1). The aperture can be tuned from ∼0 to ∼5.8 mm. It requires ∼260 ms and ∼2.4 s for the device to switch on and off, respectively. Potential applications of this tunable optical switch are wide, for example, in adaptive irises, light shutters, and optical beam controls.