Liquid Crystal Microlens Array Research Articles

Polarization-insensitive liquid crystal microlens array with dual focal modes.

We demonstrate a liquid crystal (LC) microlens array (MLA) fabricated by LCs possessing negative dielectric anisotropy, in conjunction with a cell with a three-electrode structure. The presented LC MLA is polarization-insensitive and can be operated in both concave and convex modes. The shortest focal length of the LC MLA is -2.54 and 2.22 mm in concave and convex mode, respectively. Disclination lines that are usually observed in conventional hole-patterned LC lens can also be avoided because of the vertical alignment treatment of LCs.

Simulation Study on Polarization-Independent Microlens Arrays Utilizing Blue Phase Liquid Crystals with Spatially-Distributed Kerr Constants

Polarization independent liquid crystal (LC) microlens arrays based on controlling the spatial distribution of the Kerr constants of blue phase LC are simulated. Each sub-lens with a parabolic distribution of Kerr constants results in a parabolic phase profile when a homogeneous electric field is applied. We evaluate the phase distribution under different applied voltages, and the focusing properties of the microlens arrays are simulated. We also calculate polarization dependency of the microlenses arrays at oblique incidence of light. The impact of this study is to provide polarizer-free, electrically tunable focusing microlens arrays with simple electrode design based on the Kerr effect.

51.4: Dielectric Force Induced Liquid Crystal Lenticular Microlenses

AbstractWe demonstrated a liquid crystal (LC) microlens array by assembling the phase separation morphology of liquid crystal (LC) and liquid monomer using a fringing field. The prepared lenticular microlenses can present a switchable focus with good optical characteristics. Our lenticular microlens array has promising applications in imaging processing and switchable 2D/3D displays.

Ommatidia structure based on double layers of liquid crystal microlens array

We present a new liquid crystal (LC) microlens structure having ommatidia function, which consists of the overlapped patterned electrode layers. Each electrode layer has a circular electrode array with a different size. Two electrode layers are deposited on the surface of a glass substrate and insulated by thin SiO₂ coating, which act as controlling electrodes. A plane electrode layer deposited on the surface of another glass substrate acts as the base electrode. Two glass substrates are made into a LC cell filled with nematic LC material. When a voltage signal is applied to the controlling electrode and base electrode, each circular unit of the array can focus along the optical axis and has good focusing character, and it behaves as a common microconvex lens. The whole circular array achieves ommatidia optical characters because of many microconvex lenses imaging to the objects simultaneously. Two circular arrays can both image to the objects and have different fields of view, which have extraordinary ommatidia effects. The common optical properties of the LC microlens are also demonstrated experimentally.

Modeling the carbon nanofiber addressed liquid crystal microlens array from experimentally observed optical phenomena

This paper presents a novel method of using experimentally observed optical phenomena to reverse-engineer a model of the carbon nanofiber-addressed liquid crystal microlens array (C-MLA) using Zemax. It presents the first images of the optical profile for the C-MLA along the optic axis. The first working optical models of the C-MLA have been developed by matching the simulation results to the experimental results. This approach bypasses the need to know the exact carbon nanofiber–liquid crystal interaction and can be easily adapted to other systems where the nature of an optical device is unknown.Results show that the C-MLA behaves like a simple lensing system at 0.060–0.276V/µm. In this lensing mode the C-MLA is successfully modeled as a reflective convex lens array intersecting with a flat reflective plane. The C-MLA at these field strengths exhibits characteristics of mostly spherical or low order aspheric arrays, with some aspects of high power aspherics. It also exhibits properties associated with varying lens apertures and strengths, which concur with previously theorized models based on E-field patterns. This work uniquely provides evidence demonstrating an apparent “rippling” of the liquid crystal texture at low field strengths, which were successfully reproduced using rippled Gaussian-like lens profiles.

Liquid-crystal micro-lens array with two-divided and tetragonally hole-patterned electrodes

We propose a liquid crystal (LC) micro-lens array with the structure of two-divided and tetragonally hole-patterned electrodes. Each LC cell in the lens array behaves like cylindrical or spherical lens properties by electrically adjusting the applied voltages. The LC micro-lens array is useful for tuning optical properties such a focal length and deflection angle of a light emitting diode (LED) illumination system.

Liquid Crystal Microlens Array Using Double Lenticular Electrodes

A liquid crystal (LC) microlens array using double lenticular electrodes is proposed. Two identical substrates with a lenticular electrode on each surface are prepared. The two lenticular electrodes are placed in parallel position with a gap. When a voltage is applied across the electrodes, a periodically inhomogeneous electric field can be generated. Such an electric field can cause a homogeneous LC with a gradient refractive index distribution. Our experiment results show that the lens cell can present good focusing property. The shortest focal length (~ 1.1 mm) of the lens cell can be obtained at a low operating voltage (18 Vrms).

Polymer-stabilized liquid crystal microlens array with large dynamic range and fast response time

We report a polymer-stabilized liquid crystal (LC) microlens array with a large dynamic range and fast response time. The top substrate has a planar indium-tin oxide (ITO) electrode, while the bottom substrate has two patterned ITO electrodes for generating a fringing field and uniform longitudinal field. The fringing field is utilized to create the desired gradient refractive index profile in the LC/monomer layer, which is later stabilized by UV curing to form polymer networks. To tune the focal length, we apply a longitudinal field to change the lens shape. This microlens array offers several attractive features, such as large dynamic range, fast response time, and good mechanical stability.

Modeling and design of an optimized patterned electrode liquid crystal microlens array with dielectric slab

To eliminate the occurrence of disclination lines in the hole patterned electrode liquid crystal microlens array (LC MLA), inserting an ultrathin dielectric slab was proved to be an effective method. The thickness of the dielectric slab played an important role in effecting the optical performance of the liquid crystal microlens array device, including the dynamic focal range, focus diameter and symmetry of phase profile. In this paper, we studied the effect of dielectric slab thickness on the optical performance of the liquid crystal microlens array by numerical simulation. It is indicated that the optical performance of the device could be improved by reducing the dielectric slab thickness, assuming that the dielectric slab thickness was larger than the threshold thickness. The dependence of the threshold thickness on some key parameters was investigated and the associated effect on the optical performance by changing these key parameters was also studied. In the end, the approaches to enhance the optical performance, namely the dynamic focal range of the liquid crystal microlens array was proposed and proved to be in effect by numerical simulation results.

64.2: Objective LC Lens Array for a Near‐to‐Eye Display

AbstractAn objective liquid crystal microlens array enables one to see a microdisplay located at the immediate vicinity of the eye, e.g. such that built into a contact lens or glasses. However, implementation of this microlens array is associated with two problems — correct conjugation of the image provided by the microdisplay with the retina of the eye and the light leakage to a microlens from the adjacent pixels that causes the image blur. In this work, we consider these problems and their possible solutions.

A microlens array based on polymer network liquid crystal

Using UV light to expose a homogeneous cell containing liquid crystal (LC)/monomer mixture through a patterned photomask, we prepared a polymer network liquid crystal (PNLC) microlens array. In each microlens, the formed polymer network presents a central-symmetrical inhomogeneous morphology and LC exhibits a gradient refractive index distribution. By applying an external voltage to the cell, the gradient of the LC refractive index is changed. As a result, the focal length of the microlens can be tuned. Our PNLC microlens array has the advantages of low operating voltage, easy fabrication, and good stability. This kind of microlens array has potential applications in image processing, optical communications, and switchable 2D/3D displays.

Tunable liquid crystal microlens array using hole patterned electrode structure with ultrathin glass slab

A configuration of hole patterned electrode liquid crystal microlens array with an ultrathin glass slab was fabricated. To reduce the fringing electric field effect and avoid the occurrence of disclination lines, an ultrathin glass slab was introduced between the patterned electrode and liquid crystal layer. The glass slab thickness played an important role in effecting the optical performance of the liquid crystal microlens array. An optimum thickness of 30 μm was selected employing numerical simulation method. Using this method, we demonstrated a microlens array that greatly improved the phase profile and focus power. The dynamic focal range of the liquid crystal microlens array may extend from <1.2 mm to >8 mm and the minimum diameter of the focus spot could be as small as 15 µm.

Numerical analysis and design of patterned electrode liquid crystal microlens array with dielectric slab

The phase profile of hole patterned electrode liquid crystal (LC) microlens array (MLA) was studied by a numerical method. It indicated that the formation of inverse domain and tilt wall in the liquid crystal cell limits the optical performance of the microlens array. The physical mechanism that determines the formation of inverse domain and tilt wall was elucidated by analyzing the phase profile and the liquid crystal director distribution. According to our numerical results, a new configuration for hole patterned electrode liquid crystal microlens array was proposed by introducing a dielectric slab between the patterned electrode and the liquid crystal. The physical parameters that influence the optical performance of this new configuration LC MLA were studied, which provide fundamental information for the design. The results indicate that the phase profile and focusing power of the new configuration is greatly improved.

P‐212L: Late‐News Poster: Adaptive Liquid Crystal Lens for Integral Image 3D Display

AbstractA new integral image (InIm) 3D display with an adaptive liquid crystal (LC) microlens array is proposed. By optimizing the InIm system parameters, our LC lens could achieve video rate and a large dynamic range.

A negative–positive tunable liquid-crystal microlens array by printing

A tunable microlens array by printing was demonstrated. An UV-curable adhesive, NOA65, was printed and cured to form a lens array profile on an ITO glass. Then this microlens array ITO glass was assembled with a normal ITO glass to form a cell, which was later filled with a liquid crystal. The focal length of the lens array can be tuned by an electric field, which changes the index difference between liquid crystals and NOA65 due to the reorientation of the LC molecules. In our experiment, the focal length varied from -2.29 cm to 3.12 cm when the applied voltage was increased from 0 V to 13.26 V.

Wavefront correction based on a reflective liquid crystal wavefront sensor

A novel wavefront sensor (WFS) based on liquid crystal on silicon (LCOS) is demonstrated. The design of the liquid crystal microlens array with LCOS is given in detail. To save the energy of the incident light, an optimized optical design of the WFS is also considered. In addition, closed loop wavefront correction experiments were conducted based on the designed LC WFS with square and hexagonal microlens arrays, respectively. In the experiment, the corrector was a tilt and tip mirror. The results indicated that the Zernike coefficients of the tilt and tip were decreased to less than 0.1λ(633 nm) after correction.

Fast Bistable Microlens Arrays Based on a Birefringent Layer and Ferroelectric Liquid Crystals

We fabricated a fast bistable ferroelectric liquid crystal (FLC) microlens array by combining a focusing unit with a tuning unit. The focusing unit with birefringent liquid crystalline polymer focuses the incident light depending on the polarization. The tuning unit with ferroelectric liquid crystal controls the polarization state of the incident light. The resultant microlens array shows fast switching time of the order of 10 µs and bistable characteristics which are not possible with nematic liquid crystal microlens arrays.

Liquid crystal polarization-converting devices for edge and corner extractions of images using optical wavelet transforms

Optical properties of radially polarized light generated by liquid crystal (LC) polarization-converting devices with two LC molecular orientations (+/-180 degrees and +/-90 degrees twist modes) are measured and the applicability to optical wavelet transforms (WTs) are discussed. It is found that the radially polarized lights in both the +/-180 degrees and +/-90 degrees twist modes can be regarded as wavelets. Based on the principle of WT, feature extractions of a simple binary image are carried out by applying the LC polarization-converting device to a shadow-casting system. Unique feature extraction properties of the shadow-casting system using the LC polarization-converting device and a LC microlens array are discussed. It is experimentally confirmed that edge and corner features are successfully extracted using the LC polarization-converting device with +/-180 degrees and +/-90 degrees twist modes, respectively.

Fabrication of electrically controllable microlens array using liquid crystals

Electrically controllable liquid-crystal (LC) microlens arrays have been fabricated using the process of anisotropic phase separation of the LC from its solution in a ultraviolet curable prepolymer. The focal length of nematic LC-based microlens arrays can be changed in milliseconds with an applied electric field. The ferroelectric LC microlens array exhibits the memory effect and modulates the transmitted light within a few microseconds, i.e., /spl sim/1000 times faster than the nematic LC-based microlens. Having no internal substructures to scatter light, these devices offer high efficiency and high light throughput that is different from polymer-dispersed devices.

Fast Switchable and Bistable Microlens Array Using Ferroelectric Liquid Crystals

Fast-switching ferroelectric liquid crystal microlens arrays have been fabricated using the anisotropic phase separation of liquid crystal from its solution in an ultra violet-curable prepolymer. The microlenses can be electrically controlled to modulate the transmitted light and change their focal length within a few microseconds, i.e., ∼1000 times faster than nematic liquid-crystal-based microlenses. These microlenses also exhibit the memory effect.