A blue-phase liquid crystal lens array based on dual square ring-patterned electrodes

We propose a blue-phase liquid crystal (BPLC) lens array based on dual square ring-patterned electrodes. A high dielectric constant layer is used to smoothen out the horizontal electric field and reduce the operating voltage. By creating a potential difference between the dual square ring-patterned electrodes, gradient electric fields are generated and lens-like phase profile is obtained. Besides, the focal length of the BPLC lens is adjustable with voltage changes and all simulation results indicate that the BPLC lens array is polarisation-insensitive.     

A multifunctional blue phase liquid crystal lens based on multi-electrode structure

A blue phase liquid crystal (BPLC) lens with multifunction using multi-electrode structure and a dielectric layer with high dielectric constant is proposed. The refractive index of the BPLC can be changed flexibly in different regions. Some functional or technical requirements such as switch between positive and negative lenses can be achieved. The lens reveals a good parabolic refractive index distribution and focus adjustment capacity simultaneously. The applied voltage on the electrodes is regular and computable. To decrease the applied voltage of the proposed lens with a large diameter, a drive-type adopted Fresnel lens is introduced.     

A polarisation-independent blue-phase liquid crystal lens array using gradient electrodes

A polarisation-independent blue-phase liquid crystal lens array using gradient electrodes is proposed. A high dielectric constant layer helps to smoothen out the horizontal electric field and reduce the operating voltage. With gradient electrodes and a planar top electrode, gradient electric fields are generated and lens-like phase profile is obtained. When the applied voltage is changed, the focal length of the lens can be tuned from ∞ to 5.94 mm. Besides, the simulation results show that the lens is insensitive to polarisation while keeping parabolic-like profile.     

High-diffraction-efficiency Fresnel lens based on annealed blue-phase liquid crystal–polymer composite

We demonstrated a relatively simple and effective method to fabricate a periodically isolated polymer wall of blue-phase liquid crystal Fresnel lens (BPLCFL) by employing a single-masking process of the ultraviolet (UV) irradiation, leading to excellent photopolymerisation-induced phase separation between blue -phase liquid crystal (BPLC) molecules and UV-curable monomers. Nevertheless, some uncured monomers would inherently reside in the BPLC-rich area and slightly inhibit the BPLC molecules realigned under the external electric field. To enhance the optical properties of the polymer-wall BPLCFL considerably, a novel technique for fabricating a pure BPLC zone is proposed that successfully expels the residual monomers from the BPLC volume using a thermal annealing process. Experimental results show that the maximum diffraction efficiency reaches ~36%, which approaches the theoretical limit of ~41%. Consequently, the annealing technique to purify phase-separated composite films has a strong potential to construct the BPLCFL in light of polarisation-free applications.     

Switchable polarisation-independent blue phase liquid crystal Fresnel lens based on phase-separated composite films

A simple method for fabricating a polarisation independent blue-phase liquid crystal Fresnel lens (BPLCFL) is demonstrated by utilising the photo-polymerisation-induced phase separation. The BPLC/polymer binary Fresnel zones is obtained well by periodic UV illumination with phase separation of the BPLC molecules and UV-curable pre-polymer mixture. The diffraction efficiency can be controlled when applying a uniform electric field which modulates the phase difference between even and odd Fresnel zones. Experimental results show that the maximum diffraction efficiency reaches 24.3%, which is close to the measured diffraction efficiency of the used Fresnel zone-plate mask of 25%. We also characterise the tunable lens performance at different applied voltages.     

Polarisation-independent blue-phase liquid crystal microlens array with different dielectric layer

A fast response (sub-milliseconds) and polarisation-independent blue-phase liquid crystal (BPLC) microlens array with periodical double layer electrodes using different dielectric layers is proposed. The bottom double layer electrodes are coated with transparent and different dielectric layers to generate linearly varying electric potential from the centre to the edge, while the top planar electrode iridium tin oxide (ITO) electrode has a constant potential. As a result, gradient vertical electric fields are generated, and a gradient refractive index profile is obtained. When the applied voltage is changed, the focal length of the BPLC microlens array can be tuned from ∞ to 12.05 mm while keep a low operating voltage (~35V_rms). Besides, the driving mode (simplification driving) and fabrication process (using printing method or mold-pressing method) of the BPLC microlens array is very simple. The simulation results show that the BPLC microlens array is insensitive to the polarisation of incident light while keeping parabolic-like phase profile.     

Analysis of focal length of blue-phase liquid crystal (BPLC) cylindrical lens for the light of the various incident angles and polarisations

Horizontally non-uniform electric field along the vertical direction inside blue-phase liquid crystal (BPLC) layer induces the Gradient index (GRIN) lens effect. Dependence of lens performance on the incident angle and polarisation is investigated by calculating the spatial phase distribution and the direction of wave front for lights passing through the BPLC layer. The calculated trajectories of light rays show that the focal distance for e-wave is less affected by the incidence angle than the focal distance of the o-wave. This can be attributed to the fact that steepness of spatial distribution of the effective refractive index for e-wave decreases for the larger incident angles.     

Coaxially bifocal liquid crystal lens with switchable optical aperture

An electrically tunable liquid crystal (LC) lens with dual hole-patterned electrodes is demonstrated. When the LC lens is operated at low voltages, the dual hole-patterned electrodes with different diameters impart the lens with a coaxial bifocal characteristic. At high voltages, the proposed LC lens functions as a conventional lens with a single focal length but with a switchable optical aperture. The demonstrated LC lens is free of disclination lines because of the presence of voltage-assisted high pretilt angles created from the upmost hole-patterned electrode with small diameter.     

Relationship between lens properties and director orientation in a liquid crystal lens

Lenses with a homogeneously aligned liquid crystal having a Fresnel structure have been prepared by using a nematic with a positive dielectric anisotropy. Their focal length can be varied continuously from the value f_e for an extraordinary ray to f_o for an ordinary ray by applying an electric field across the lens cell. The effective refractive index of the lens where the director is aligned perpendicular to the grooves of the Fresnel structure becomes smaller than when the director is aligned parallel to the grooves. Then the liquid crystal lens has a characteristic aberration which could not be observed in a conventional glass lens; that is, the focal length of the lens becomes different according to the incidence of rays on the different parts of the lens. The properties of the liquid crystal lens can be improved by making the director orientation axially symmetric, in the form of a concentric circle, but the polarization component rotated 90° from the incident extraordinary ray appears when the voltage is applied across the lens cell. This phenomenon is discussed in relation to the optical properties and the director orientation in a liquid crystal prism cell.     

Relationship between lens properties and director orientation in a liquid crystal lens

Lenses with a homogeneously aligned liquid crystal having a Fresnel structure have been prepared by using a nematic with a positive dielectric anisotropy. Their focal length can be varied continuously from the value f_e for an extraordinary ray to f _o for an ordinary ray by applying an electric field across the lens cell. The effective refractive index of the lens where the director is aligned perpendicular to the grooves of the Fresnel structure becomes smaller than when the director is aligned parallel to the grooves. Then the liquid crystal lens has a characteristic aberration which could not be observed in a conventional glass lens; that is, the focal length of the lens becomes different according to the incidence of rays on the different parts of the lens. The properties of the liquid crystal lens can be improved by making the director orientation axially symmetric, in the form of a concentric circle, but the polarization component rotated 90° from the incident extraordinary ray appears when the voltage is applied across the lens cell. This phenomenon is discussed in relation to the optical properties and the director orientation in a liquid crystal prism cell.     

Double-layer liquid crystal lens array with composited dielectric layer

ABSTRACT

A double-layer liquid crystal (LC) lens array with composited dielectric layer is proposed. In our design, a spatially non-uniform electric field is generated between the strip electrodes, resulting in a gradient refractive index distribution in the LC layer. Since the upper and lower parts of the LC lens array both adopt a composite dielectric layer, the operation voltage of the LC lens array is effectively reduced. In terms of LC lenslet, the double-layer design doubles the phase difference between the centre and the periphery of the LC layer, thereby reducing the focal length of the LC lens array. In addition, the shortest focal length (~1.78 mm) of the LC lens array is obtained at V = 3.3 V, and the LC lens array has a large focusing range.     

A polarisation-independent blue-phase liquid crystal microlens using an optically hidden dielectric structure

A polarisation-independent blue-phase liquid crystal microlens using an optically hidden dielectric structure is proposed. In this design, the non-uniform electric field across the lens aperture is obtained by the modulation of the effective dielectric constant of an optical hidden layer. As the applied voltage varies from 0 to 150V_rms, the focal length of the lens can be tuned from ∞ to 16.6 mm. Simulation results show that this device has a parabolic-like profile and exhibits polarisation-independent property.     

A liquid crystal microlens obtained with a non-uniform electric field

Abstract

A homogeneously aligned nematic liquid crystal cell with a hole-patterned electrode and with an indium-tin oxide (ITO-) coated counter-electrode has been prepared. A non-uniform electric field can be produced by the asymmetrical electrode structure. The liquid crystal director can be reoriented by applying a voltage across the electrodes, and this produces an axially symmetrical profile of the refractive index. This liquid crystal cell is expected to have a lens effect and so its optical properties have been investigated. The profile of the output light intensity was measured by using a detecting system with an optical fibre. Some relationships between the lens properties, the diameter of the hole and the thickness of the liquid crystal layer have been examined. The liquid crystal cell becomes a convex (converging) lens with a relatively low voltage. A focal length of several millimetres can be obtained by applying voltages of 3-4 V. As the applied voltage increases, the focal length becomes longer, and the cell changes to a concave (diverging) lens when a high voltage is applied (? 20 V). These properties are discussed from the viewpoint of the director orientation effects resulting from the non-uniform electric fields in the cell.     

A liquid crystal microlens obtained with a non-uniform electric field

A homogeneously aligned nematic liquid crystal cell with a hole-patterned electrode and with an indium-tin oxide (ITO-) coated counter-electrode has been prepared. A non-uniform electric field can be produced by the asymmetrical electrode structure. The liquid crystal director can be reoriented by applying a voltage across the electrodes, and this produces an axially symmetrical profile of the refractive index. This liquid crystal cell is expected to have a lens effect and so its optical properties have been investigated. The profile of the output light intensity was measured by using a detecting system with an optical fibre. Some relationships between the lens properties, the diameter of the hole and the thickness of the liquid crystal layer have been examined. The liquid crystal cell becomes a convex (converging) lens with a relatively low voltage. A focal length of several millimetres can be obtained by applying voltages of 3-4 V. As the applied voltage increases, the focal length becomes longer, and the cell changes to a concave (diverging) lens when a high voltage is applied (≳ 20 V). These properties are discussed from the viewpoint of the director orientation effects resulting from the non-uniform electric fields in the cell.     

Using of a microcapillary refractive X-ray lens for focusing and imaging

The microcapillary lens, formed by air bubbles in a hollow core glass capillary filled with epoxy, is a novel design of a compound refractive lens for X-rays. The epoxy enclosed between two air bubbles has the form of a biconcave lens and acts as a positive lens for X-rays. Each individual lens is spherical with radius of curvature equal to the inner radius of the capillary. Up to 500 individual biconcave lenses can be formed in a single capillary with diameters from 50 to 500 μm. Due to the small radius of curvatures that can be achieved, microcapillary lenses typically have shorter focal lengths than those made by compression or injection molding. For example, microcapillary lenses with a focal length about 5 cm for 8 keV X-rays and 50-micron aperture are readily available.We have produced a set of lenses in a 200-micron inner-diameter glass capillary with 100–350 individual microlenses and measured their parameters at the Stanford Synchrotron Radiation Laboratory and at the Advanced Photon Source.Our investigations have also shown that the lenses are suitable for imaging applications with an X-ray tube as a source of X-rays. A simple X-ray microscope is discussed. The microscope consists of a copper anode X-ray tube, X-ray lens and CCD-camera. The object, lens and CCD-camera were placed in-line at distances to satisfy the lens formula. It is shown that the field of view of the microscope is about 1 mm and resolution is equal to 3–5 μm.     

Low-voltage blue-phase liquid crystal display with diamond-shape electrodes

We propose a new electrode configuration, called diamond-shape in-plane switching, to lower the operation voltage of polymer-stabilised blue-phase liquid crystal (BPLC) displays (BPLCDs). The electrode structure is modified from conventional protruded IPS, where the strip protrusion is changed to diamond shape. By optimising the electrode gap and diamond length, we are able to obtain peak transmittance over 75% at 15 V. It enables single thin-film transistor (TFT) driving, and more importantly, this is based on an industrially proven BPLC material. That means good long-term stability, adequate TFT charging time for high-resolution displays and sub-millisecond response time and acceptable voltage-holding ratio for field sequential displays can be achieved simultaneously. Our device design helps accelerate the emergence of the long-awaited BPLCDs.     

Wide-viewing-angle switchable image splitter obtained using varied-line-spacing H-PDLC Bragg grating

We propose the use of a varied-line-spacing (VLS) holographic polymer-dispersed liquid crystal (H-PDLC) Bragg grating as a switchable image splitter to generate a compatible three-dimensional (3D) stereogram and to increase the viewing angle of the observer. To fabricate the VLS grating, a cylindrical lens is adopted to form a cylindrical wave, which interferes with a plane wave, generating an H-PDLC grating with a continuously varying period. The proposed holographic optical element (HOE)-based image splitter comprises two VLS H-PDLC gratings. It can be attached on a designed pattern, with two rectangles taking the place of conventional liquid crystal display panel pixels, and can separate them into right and left viewing fields with a wider range. Experimental results show that the movement of the eyes of the observer can reach 37.6 mm. A theoretical simulation indicates that a shorter focal length of the cylindrical lens can yield a larger movement range. Switching between two-dimensional and 3D modes can be performed by applying an external alternating-current voltage at ~80 V. The contrast ratio of the diffracted images induced by crosstalk is greater than 60%, which indicates the feasibility of the proposed HOE for 3D image splitting.     

The effects of silica nanoparticles on blue-phase liquid crystals

We investigate the effects of hydrophobic silica nanoparticles (SNs) on blue-phase liquid crystals (BPLCs). The optical microscope and reflection spectra observation reveal that a tiny hydrophobic SN dopant stabilises the BPLC phase, and widens the temperature range of the BP I phase. Furthermore, the doped dilute SNs can fine-tune their positions to relax the formation stress of the BPLC lattices, and slightly increase the platelet sizes of the BPLCs. The doped SNs also decrease the driving voltage and response time of the BPLC cell, because the added SNs decrease the elastic constant of the LC host and the relaxation time constant of the BPLC mixture.     

Actuation of adaptive liquid microlens droplet in microfluidic devices: A review

A significant growth of research on adaptive liquid lens is achieved over the past decades, and the field is still attracting increasing attentions, focusing on the transition from the current stage to the commercialized stage. The challenges faced are not limited to fabrication, material, small tuning range in focal lengths, additional control systems, limitations in special actuation methods and so on. In addition, the use of external driving parts or systems induce extra problem on bulky appearance, high cost, low reliability etc. Therefore, adaptive liquid lens will be an interesting research focus in both microfluidics and optofluidics science. This review attempts to summarize and focus on the droplet profile deformation under different driving mechanisms in tunable liquid microlens as well as the application in cameras, cell phone and so on. The driving techniques are generally categorized in terms of mechanisms and driving sources.     

High-Throughput Preparation and Machine Learning Screening of a Blue-Phase Liquid Crystal Based on Inkjet Printing

Blue-phase liquid crystal (BPLC) is considered as the next-generation liquid crystal display material, but its practical application is seriously affected by a narrow temperature range and a long research period. In this paper, we used inkjet printing technology to prepare BPLC materials with high throughput, and try to use machine vision technology to test BPLC with high throughput. The “standard curve method” for establishing each printing channel and the “vector matching method” for searching the chromaticity value of the minimum distance were proposed to improve the accuracy of inkjet printing BPLC materials. For a large number of sample-phase images, we propose a machine learning method to identify the liquid crystal phase. In this paper, for the first time, the high-throughput preparation and high-throughput detection of 1080 BPLC samples with five common components by a comprehensive experimental method has been successfully realized. The results are helpful to improve the research efficiency of blue-phase materials and provide a theoretical basis and practical guidance for rapid screening of multi-component BPLC materials.