Liquid Crystal Lens Research Articles

Shortening Focal Length of 100‐mm Aperture Flat Lens Based on Improved Sagnac Interferometer and Bifacial Liquid Crystal

AbstractConventional lens technologies face great challenges in applications requiring large apertures and small f‐numbers, while a liquid crystal (LC) lens based on geometric phase is a potential solution. However, the challenge of manufacturing a large size LC flat lens with high efficiency and high phase gradient still remains. Here, an improved interferometric exposure system is proposed to acquire a large‐size vectorial optical field for photo‐alignment. Bifacial LC layers are applied to reduce the focal length while maintaining a large aperture, high diffraction efficiency, and light weight. LC layers are deposited on both sides of the substrate with the same vector system. Finally, a bifacial LC flat lens with a 10 cm diameter and 88.37% diffraction efficiency is fabricated by using optical elements smaller than 2 in., while the effective focal length is reduced from 91.5 cm to 46 cm comparing to the single side LC lens. This work demonstrates the great advantages of LC‐based flat lenses for flat optical systems with large aperture.

Robust Fastener Detection Based on Force and Vision Algorithms in Robotic (Un)Screwing Applications.

This article addresses how to tackle one of the most demanding tasks in manufacturing and industrial maintenance sectors: using robots with a novel and robust solution to detect the fastener and its rotation in (un)screwing tasks over parallel surfaces with respect to the tool. To this end, the vision system is based on an industrial camera with a dynamic exposure time, a tunable liquid crystal lens (TLCL), and active near-infrared reflectance (NIR) illumination. Its camera parameters, combined with a fixed value of working distance (WD) and variable or constant field of view (FOV), make it possible to work with a variety of fastener sizes under several lighting conditions. This development also uses a collaborative robot with an embedded force sensor to verify the success of the fastener localization in a real test. Robust algorithms based on segmentation neural networks (SNN) and vision were developed to find the center and rotation of the hexagon fastener in a flawless condition and worn, scratched, and rusty conditions. SNNs were tested using a graphics processing unit (GPU), central processing unit (CPU), and edge devices, such as Jetson Javier Nx (JJNX), Intel Neural Compute Stick 2 (INCS2), and M.2 Accelerator with Dual Edge TPU (DETPU), with optimization parameters, such as the unsigned integer (UINT) and float (FP), to understand their performance. A virtual program logic controller (PLC) was mounted on a personal computer (PC) as the main control to process the images and save the data. Moreover, a mathematical analysis based on the international standard organization (ISO) and patents of the manual socket wrench was performed to determine the maximum error allowed. In addition, the work was substantiated using exhaustive evaluation tests, validating the tolerance errors, robotic forces for successfully completed tasks, and algorithms implemented. As a result of this work, the translation tolerances increase with higher sizes of fasteners from 0.75 for M6 to 2.50 for M24; however, the rotation decreases with the size from 5.5° for M6 to 3.5° for M24. The proposed methodology is a robust solution to tackle outliers contours and fake vertices produced by distorted masks present in non-constant illumination; it can reach an average accuracy to detect the vertices of 99.86% and the center of 100%, also, the time consumed by the SNN and the proposed algorithms is 73.91 ms on an Intel Core I9 CPU. This work is an interesting contribution to industrial robotics and improves current applications.

Liquid crystal lens with a shiftable optical axis.

A liquid crystal (LC) lens with a laterally shiftable optical axis is proposed and demonstrated. The optical axis of the lens can be driven to shift within the lens aperture without compromising its optical properties. The lens is constructed by two glass substrates with identical interdigitated comb-type finger electrodes on the inner surfaces, and they are oriented at 90° with respect to each other. The distribution of voltage difference between two substrates is determined by eight driving voltages, and is controlled within the linear response region of LC materials, thereby generating a parabolic phase profile. In experiments, an LC lens with an LC layer of 50 µm and an aperture of 2 mm × 2 mm is prepared. The interference fringes and focused spots are recorded and analyzed. As a result, the optical axis can be driven to shift precisely in the lens aperture, and the lens maintains its focusing ability. The experimental results are consistent with the theoretical analysis, and good performance of the LC lens is demonstrated.

P‐12.9: Self‐powered Large Aperture Liquid Crystal Lens for Light Field Imaging Based on Fur Triboelectric Nanogenerators

Liquid crystal (LC) is an intermediate state compound between liquid and crystal, which has the anisotropy of crystal molecules while having the fluidity of liquid. It is a cutting‐edge technology in optoelectronics. LC lens is an electrically controlled focusable gradient refractive index lens. In light field displays, LC lenses with diameters in the millimetre range can cover more areas. Therefore, we propose a large aperture (LA) liquid crystal (LC) lens with an electrically controlled focal length of 4 mm in diameter. LC lenses with large apertures require large voltages and there are certain safety issues and equipment requirements. We have therefore utilised a triboelectric nanogenerator (TENG) that can harvest energy from the environment and convert it into usable electrical energy. TENG has the advantages of being small and portable and enables the use of renewable energy. In this paper, we propose a new type of feather TENG (F‐TENG) with a positive friction electrode of feathers and a negative electrode of polytetrafluoroethylene (PTFE) mixed with graphene, which enables the use of F‐TENG to power LC lens systems, thus providing a new application idea for the display field.

Achromatic polymer-dispersed liquid crystal lens with diffractive–refractive hybrid structure

The focal length of liquid crystal Fresnel lens is electrically controllable, but the disadvantage is the chromatic aberration is obvious. In this paper, the electrically controlled zoom characteristics of liquid crystal lens and the basic theory of Fresnel lens achromatic are analyzed, and a diffractive–refractive hybrid lens model made of polymer-dispersed liquid-crystal (PDLC) material is proposed. Fresnel liquid crystal lenses and PDLC hybrid lenses are tested with light at R (700.0 nm), G (546.1 nm) and B (435.8 nm) wavelengths, respectively. The simulation results show that the hybrid lens provides a greater range of adjustment of the focus position. After voltage modulation, the measured light with three different wavelengths have the same focal length, which means that the axial chromatic aberration is eliminated. In addition, with the elimination of axial chromatic aberration, the zoom range of the hybrid lens is doubled by further accurately controlling the electrode, which breaks through the limitation that the traditional liquid crystal lens can only work in monochromatic light spectrum.

54.3: A Hybrid Neural Network Approach for Phase Optimization of Liquid Crystal Lens in Three‐dimensional Display

Liquid crystal(LC) lenses are widely applied in three‐dimensional(3D) display, augmented reality/virtual reality (AR/VR) and machine vision system due to the advantages of electrical controllability and high flexibility. However, LC lenticular display technology is limited by the material characteristics of LC materials, because it is difficult to overcome the shortcomings of low resolution and high crosstalk at the same time. In this paper, a phase distribution optimization scheme based on the neural network is proposed, which may realizes the complex phase distribution of LC lens through machine learning and improve the optical properties of lenticular 3D display technology.lujg@sjtu.edu.cn

7.2: Invited Paper: Vari‐focal Near‐eye Displays Based on Geometry Phase Liquid Crystal Lenses

The development of metaverse has the potential to revolutionize people's life. As the entry to metaverse, virtual reality (VR) and augmented reality (AR) technologies are gaining ever‐increasing attention. However, there is vergence‐accommodation conflict problem for most VR or AR 3D displays. In this paper, we propose to realize vari‐focal near‐eye displays based on tunable geometry phase liquid crystal lenses to address this problem. Experimental results validate that images can be rendered at different depth as the tunable lenses change their focal lengths. Thus, correct accommodation cue can be induced, and 3D visual fatigue could be significantly suppressed.

Compact Foveated AR Displays with Polarization Selective Planar Lenses

The rapid development of powerful microprocessors, high-pixel density display panels, thin and small formfactor optics, and precise device fabrication capabilities enable wearable near-eye displays for augmented reality (AR) and virtual reality (VR) applications. However, in traditional near-eye displays, there is often a trade-off between field of view (FoV) and angular resolution when a single microdisplay light engine is employed. A high-resolution display panel helps overcome this conflict, but the device fabrication remains a challenge, not to mention the issues like huge data transfer, circuit overheating, and high computational load. Here, we propose a Maxwellian-type foveated AR display based on a single microdisplay light engine by using a temporal polarization multiplexing method, enabled by two polarization selective flat cholesteric liquid crystal lenses. One polarization lens provides a large FoV while the other realizes a high angular resolution imaging in a small fovea region. Moreover, the vergence-accommodation conflict issue is inherently nonexistent in the Maxwellian display, and the aberration can be eliminated for each view by matching the recording and reconstructing signals. In an experiment, we constructed a display breadboard and demonstrated that the angular resolution of the foveal view is enhanced by 3.12× while maintaining a compact formfactor. This work paves the way for implementing high-performance foveated AR displays while keeping a compact formfactor.

How to fix an ultrasonic variable-focus liquid crystal lens for substrate-mountable applications

This paper proposed a board-mounted ultrasonic variable-focus liquid crystal (LC) lens. The lens controls the focus using the acoustic radiation force generated by the resonant flexural vibration mode. The LC lens was fixed to an aluminum substrate with a hole whose aperture corresponded to the inner diameter of the transducer. The part of the LC lens attached to the substrates functioned as a fixed condition, and the flexural vibration mode was successfully generated. The fixed lens exhibited a gradual focal change with current, confirming that fixing the condition affected the rate of focal change.

A novel radial orientation treatment of nematic liquid crystals using magnetic field lines with permanent magnet and applying the assisted electric field

AbstractRecently, there has been considerable research on optical devices, such as liquid crystal (LC) lenses and special optical plates, using LCs. In such devices, relatively small LC cells are frequently used, or unique LC orientations are required. As an LC orientation process, we focused on the LC director's orientation induced by the magnetic force line distribution of a small neodymium magnet. We propose a simple method for obtaining radial orientation, which is rather difficult to obtain using the ordinary rubbing method. The initial orientation in the LC cell is a vertical orientation cell with almost zero azimuth anchoring. With the proposed method, the reorientation process is performed with an assisting electric field and a small permanent magnet, unlike the conventional magnetic field orientation process that requires a large electromagnet. Furthermore, a polymer stabilization treatment is used to fix the obtained radial orientation pattern in the LC cell. After the treatment, the applying voltage can control the tilt angle of the director in weak polymer treatment, and a completely fixed orientation pattern can be obtained that in strong.

How to construct liquid-crystal spectacles to control vision of real-world objects and environments

A major challenge in studying naturalistic vision lies in controlling stimulus and scene viewing time. This is especially the case for studies using real-world objects as stimuli (rather than computerized images) because real objects cannot be “onset” and “offset” in the same way that images can be. Since the late 1980s, one solution to this problem has been to have the observer wear electro-optic spectacles with computer-controlled liquid-crystal lenses that switch between transparent (“open”) and translucent (“closed”) states. Unfortunately, the commercially available glasses (PLATO Visual Occlusion Spectacles) command a high price tag, the hardware is fragile, and the glasses cannot be customized. This led us to explore how to manufacture liquid-crystal occlusion glasses in our own laboratory. Here, we share the products of our work by providing step-by-step instructions for researchers to design, build, operate, and test liquid-crystal glasses for use in experimental contexts. The glasses can be assembled with minimal technical knowledge using readily available components, and they can be customized for different populations and applications. The glasses are robust, and they can be produced at a fraction of the cost of commercial alternatives. Tests of reliability and temporal accuracy show that the performance of our laboratory prototype was comparable to that of the PLATO glasses. We discuss the results of our work with respect to implications for promoting rigor and reproducibility, potential use cases, comparisons with other liquid-crystal shutter glasses, and how users can find information regarding future updates and developments.

Low aberration and fast response liquid crystal lens with optically compensated bend structures

A hole-patterned electrode (HPE) liquid crystal (LC) lens with positive (0 D – 0.7 D) and negative focal lengths (0 D - −1.1 D) is demonstrated. The lens uses an optically compensated bend (OCB) cell filled with dual-frequency LC materials and alignment films with an intermediate pretilt angle. Better reduction in tilt and coma aberration can be achieved using this simple one-layer structure with its symmetric LC orientation in an OCB cell than can be obtained with a complicated two-layer HPE LC lens. The use of dual-frequency switching together with the reduction of the backflow effect in the OCB cell also improves the response by about 7 times compared with the conventional HPE LC lens.

Extended Depth of Field Imaging Using Liquid Crystal Lenses

Extended Depth of Field Imaging Using Liquid Crystal Lenses

Tunable Fresnel Liquid Crystal Lens with Large Aperture

Tunable Fresnel Liquid Crystal Lens with Large Aperture

Characteristics of liquid crystal lens with concentric ring electrode structure

Characteristics of liquid crystal lens with concentric ring electrode structure

Liquid crystal lens array based on polymer protrusion

Liquid crystal lens array based on polymer protrusion

Self-powered liquid crystal lens based on a triboelectric nanogenerator

Liquid crystal (LC) is an intermediate state compound between liquid and crystal, which has the anisotropy of crystal molecules while having the fluidity of liquid. It is a cutting-edge technology in optoelectronics. The large-aperture LC lens require larger voltages, and there are certain safety issues and equipment requirements. This situation indicates a great need for a safe and portable low-power device. A triboelectric nanogenerator (TENG) can collect the energy in the environment and convert it into usable electric energy. It has the advantages of small size and convenient portability, and can realize the use of renewable energy. This paper proposes a novel feather TENG (F-TENG) using feathers as friction materials. The approximate values of open-circuit voltage and short circuit current of the manufactured F-TENG can reach 247 V and 27 μA, respectively. After simple processing of the device, the performance can be further improved. We realized the use of F-TENG to power a LC lens test system, thus providing a new application idea for the display field. This study provides a simple and inexpensive method for harvesting mechanical energy to power experimental test equipment and facilitate the large-scale, intelligent practical application of TENG systems.

Design of Tunable Liquid Crystal Lenses with a Parabolic Phase Profile

An electrode pattern design generating a parabolic voltage distribution, in combination with usage of the linear response range of the liquid crystal (LC) material, has been recently proposed to obtain nearly ideal phase profiles for LC lenses. This technique features low driving voltages, simple structure, compact design, and the absence of high-resistivity (HR) layers. In this work, the universal design principle is discussed in detail, which is applicable not only to LC lens design, but also to other LC devices with any phase profile. Several electrode patterns are presented to form a parabolic voltage distribution. An equivalent electric circuit of the LC lens based on the design principle is developed, and the simulation results are given. In the experiments, an LC lens using the feasible parameters is prepared, and its high-quality performance is demonstrated.

Effects of the interlayer thickness on the optical characteristics of an ultrasound multilayered liquid crystal lens

Ultrasound multilayered variable-focus liquid crystal (LC) lenses have better optical performance compared to conventional ultrasound LC lenses. This paper investigates the effect of the distance between two LC layers on the optical characteristics of the lens. The LC molecular orientation in the lens was altered by the acoustic radiation force generated by the lens’ resonance flexural vibration mode, causing a change in the focal length. The focal length change was increased dramatically, and the electrical consumption was reduced in lenses with thinner interlayers.

A Depth Sensor Based on Transient Property of Liquid Crystal Lens

The property of maintaining the lens state of the liquid crystal (LC) lens during the switching between positive and negative lens states is made use of in the fast acquirement of multi-focus images without magnification change. A depth from focus (DFF) pipeline that can generate a low-error depth map and an all-in-focus image is proposed. The depth of the scene is then obtained via DFF pipeline from the captured images. The depth sensor proposed in this paper has the advantages of simple structure, low cost, and long service life.