Liquid Crystal Lens Research Articles

A polarisation-free blue phase liquid crystal lens with enhanced tunable focal length range

ABSTRACTA polarisation-free blue phase liquid crystal (BPLC) lens with enhanced tunable focal length range is proposed. A matched conventional glass lens is introduced on a BPLC lens to increase the range of the tunable focal length. The focal length of the BPLC lens can be switched from positive to negative, the negative lens-like phase profile can be neutralised by the conventional glass lens to get an infinity focal length and the positive lens-like phase profile can be enhanced by the conventional glass lens to get a shorter focal length. The minimum focal length can be decreased to almost half of that after the proposed method is adopted in our simulation. Moreover, the proposed BPLC lens exhibits a good polarisation-free feature and the optical effect is relatively good.

Liquid crystal lens with optimized wavefront across the entire clear aperture

Abstract Comparative theoretical analysis of performances of three electrically variable liquid crystal lens designs is conducted. Traditional hole patterned electrode, additional floating and inner-ring electrode configurations are considered within the framework of a modal control lens. The control mode of those electrodes and the choice of the voltage and frequency values of the driving electric signals are optimized to obtain spherical profile of the optical phase retardation across the entire clear aperture of the lens. This would allow the effective use of the tunable lens in combination with larger aperture fixed focus lenses. It is shown that we can improve significantly the acceptable (with low aberrations) dynamic variation range of the optical power of the lens by switching the control mode of electrodes.

Depth from defocus measurement method based on liquid crystal lens.

This paper describes a depth from defocus (DFD) method to recover the depth of scene from two images taken by a liquid crystal (LC) lens imaging system. The system is composed of a camera module and an LC lens. The system's focal length is electrically adjusted by the voltages that are applied on the LC lens. We use two images that are taken at maximum positive and negative, respectively, and the LC lens's optical power, to obtain the depth information via DFD. The principle is described and the experimental results are successfully obtained. The method is simple in that it needs not to involve any mechanical lens movements in the imaging system.

LC lens systems to solve accommodation/convergence conflict in three-dimensional and virtual reality displays

Accommodation–convergence mismatch is still an unsolved issue within the field of augmented reality, virtual reality, and three-dimensional systems in general. Solutions suggested to correct the focus cue in recent years require additional bandwidth, or compromise the image resolution. Our simple approach to overcome this issue is by using an eye-tracking system and electronic lenses. We propose an electronic hybrid lens system composed of segmented phase profile liquid crystal and Pancharatnam phase lenses. For practical application, eye tracking is necessary for measuring the toe-in of the user’s pupil to calculate the object depth. This information is used to determine the required diopteric power of the hybrid system. The optical performance and imaging quality of the proposed hybrid system are evaluated.

Dynamic compensation of gradient index rod lens aberrations by using liquid crystals.

An electrically variable liquid crystal lens is used to compensate the aberrations of commercial gradient index rod lenses used for deep brain endoscopy. This is achieved by the use of a weakly conductive layer in the so-called "modal control" lens approach with a segmented peripheral electrode. The root mean square aberrations of the system are reduced by a factor of 4.3. The proposed solution can be used in many photonic applications using fixed optical components with high aberrations that have significant sample-to-sample variability.

New Photo-Crosslinkable Benzaldehyde Polymers for Creating Liquid Crystal Lenses

We have studied new photo-crosslinkable benzaldehyde polymers with fragments including long hydrocarbon substituents in a side chain, as materials for creating a specified distribution of the pretilt angle of the director in a liquid crystal cell. We show that by changing the UV radiation exposure dose after rubbing the polymer layers, we can specify any pretilt angle in the range 0–90o. We have obtained the distribution of pretilt angles needed for creating liquid crystal lenses, where the maximum azimuthal anchoring energy of the liquid crystal with the alignment layer is increased to 2.5·10–5 J/m2, which allowed us to substantially reduce the number of defects and to improve the optical quality of the liquid crystal lens.

Trifocal lens system with liquid crystal Fresnel lens

In this paper, we present the construction of a trifocal lens system by combining a liquid-crystal (LC) lens and an ordinary lens. The focusing properties of the proposed system can be controlled by changing the polarization state of the incident light wave. The characteristics of the fabricated lens system were evaluated and it was confirmed that the system converged light at three focal points. It was also confirmed that the intensity of the light collected at each focal point could be regulated by controlling the polarization state of incident light and the retardation of the LC Fresnel lens in the proposed trifocal lens system.

Driving liquid crystal lens to extend focus range

A new driving method for a liquid crystal (LC) lens with a hole-patterned electrode is proposed to increase the range of the variable power of the lens. The optical properties of the LC lens are analyzed by an interferometer, and the combination of the driving parameters including the amplitudes and the frequency of the driving voltages are optimized to extend the focus range and keep the aberration below 0.07 wave. For the LC lens used in the experiment with an aperture of 2.0 mm diameter and an LC (Δn = 0.2) layer of 15 µm thickness, the focus range is extended from approximately 3.4 to 5.7 diopters.

Liquid crystal lens with corrected wavefront asymmetry.

We propose a simple technique allowing the correction of the inherent wavefront asymmetry in electrically variable liquid crystal lenses with relatively small diameters. This is achieved by splitting the peripheral hole patterned electrode of the lens in the direction of the ground-state anisotropy axis. Optical aberrations are measured before and after the split. It is demonstrated that a significant correction is achieved with a trade-off of trefoil increase in the direction of the split. This increase is then eliminated by the further segmentation of the peripheral electrode.

Motor affordance for grasping a safety handle

Mere observation of objects in our surroundings can potentiate movement, a fact reflected by visually-primed activation of motor cortical networks. This mechanism holds potential value for reactive balance control where recovery actions of the arms or legs must be targeted to a new support base to avoid a fall. The present study was conducted to test if viewing a wall-mounted safety handle – the type of handle commonly used to regain balance – results in activation of motor cortical networks. We hypothesized that the hand area of the primary motor cortex would be facilitated shortly after visual access to a safety handle versus when no handle was visible. Here, we used transcranial magnetic stimulation (TMS) to measure corticospinal excitability in hand muscles directly following access to vision while participants performed a seated reach-grasp task. Vision was controlled using liquid crystal lenses and TMS pulses were time-locked to occur shortly after the goggles opened but prior to any cue for movement. Between trials the response environment was unpredictably altered to present either a handle or no handle (i.e. covered). Our results demonstrated a rapid motor facilitation in muscles of the right hand when participants viewed a handle versus trials where this handle was covered. This effect was selective both in terms of the muscles activated and the timing at which it emerged. The First Dorsal Interosseus and Opponens Pollicus muscles (synergists in closing the hand) were facilitated 120 ms after viewing the handle. Interestingly, this effect was absent at earlier (80 ms) and later (160 ms) points. Conversely, Abductor Digiti Minimi, which moves the little finger out from the rest of the hand, tended to diminish when viewing the handle. These findings suggest a rapid engagement of muscles suitable for grasping a handle based on vision. This is consistent with the concept of affordances where vision automatically translates viewed objects into appropriate motor terms. The fact that this affordance effect was present for a wall-mounted safety handle commonly used to regain balance has implications for automatically priming recovery actions with upper limbs suited to our surroundings, even before postural perturbation is detected.

Focal stack camera in all-in-focus imaging via an electrically tunable liquid crystal lens doped with multi-walled carbon nanotubes.

A focal stack camera, based on an electrically tunable-focusing liquid crystal (LC) lens doped with multi-walled carbon nanotubes, is proposed to generate a single all-in-focus image of a 3D scene without depth map in a relatively short time. Focal sweep strategy of the camera is devised. Both its depth of field (DOF) and focal sweep speed are analyzed and deduced. Nano doping method is adopted to improve electro-optical features of the LC lens. To efficiently produce all-in-focus image, a weighted average algorithm for all images in the focal stack is utilized. The experiments show that the result is a high contrast at sensor resolution. It is greatly potential in optical compact 3D imaging system.

P‐148: A Continuous Variable Lens System to Address the Accommodation Problem in VR and 3D Displays

The focus cue is a continuing concern within the field of Virtual Reality (VR), Augmented Reality (AR) and 3D displays. Although liquid crystal (LC) based lens is an excellent candidate for tunability, a major problem with VR/3D application is a need for large aperture not inhibiting the field of view, but that also maintains a reasonable switching time. In this paper we discuss results with two systems that can be used for such application. We present the result of user preference for an approach using a Fresnel lens structure, and propose a second design that is a hybrid system comprised of refractive Fresnel and Pancharatnam‐Berry LC lenses. Our study presents a compact, large aperture, fast and tunable optic that can be used in numerous applications including VR/3D systems.

65‐5: Invited Paper: Resolving the Vergence Accommodation Conflict in VR and AR via Tunable Liquid Crystal Lenses

Virtual reality (VR) and augmented reality (AR) head mounted displays project stereoscopic virtual images to the eyes to obtain a three‐dimensional illusion. The mismatch between the vergence and accommodation focus cues, known as the vergence‐accommodation conflict (VAC), can cause physical discomfort and limit the immersive experience of these systems. In AR systems, even monocular vision is affected by the focus mismatch, since the eye cannot focus simultaneously on a close real object and a close virtual object. We present a dynamic focus compensation approach to resolve VAC in which an electronically controlled dynamic lens is used to correct the focus of the virtual content. The dynamic lens is implemented using a pixel grid, enabling rapid lateral movement of the lens, thus increasing the lens quality and field of view.

P‐149: A Polarization‐independent Blue Phase Liquid Crystal Lens Array with Multi‐electrode

A polarization‐independent blue‐phase liquid crystal lens array using multi‐electrodes is proposed. A high dielectric constant layer helps to smoothen out the horizontal electric field and reduce the operating voltage. With multi‐electrodes and a planar top electrode, the gradient electric fields are generated, and the lens‐like phase profile is obtained. When the applied voltage is changed, the focal length of the lens can be tuned from ∞ to 6.7 mm. Besides, the simulation results show that the lens is insensitive to polarization while keeping parabolic‐like profile.

Variable wide range of lens power and its improvement in a liquid-crystal lens using highly resistive films divided into two regions with different diameters

The variable range of lens power of a liquid-crystal (LC) lens driven by two voltages is discussed on the basis of calculated and experimental results. The LC lens has two electrodes, which are a circularly hole-patterned electrode and a circular electrode, in addition to a common electrode, and highly resistive transparent films. The variable range of lens power increases with increasing driving voltage applied across the circularly hole-patterned electrode and the common electrode, and with decreasing diameter of highly resistive films. However, the optical-phase retardation profile tends to deviate from a parabolic curve in these cases. As a method to improve the trade-off properties, the highly resistive film is divided into two regions with different diameters, where the sheet resistance of an outer film is larger than that of an inner one. The improved LC lens has a lens power that varies in a wide range, and it exhibits a good parabolic phase retardation profile.

Large aperture liquid crystal lens array using a composited alignment layer.

A liquid crystal (LC) lens array with high light control power and a large aperture using a composited alignment layer is proposed. In our design, the alignment layer is not only used for getting a uniform arrangement of LC molecule, but also for getting a lens-like refractive index distribution in the LC layer when a voltage is applied. Through simple technology processes, a tunable focal length LC lens array with a millimeter scale diameter can be achieved. Furthermore, the maximum phase difference of the proposed LC lens array can achieve 105.38π. So, the proposed LC lens array has a high light control power.

An optical system via liquid crystal photonic devices for photobiomodulation

Photobiomodulation or low-level light therapy (LLLT) has extensive applications based on light-induced effects in biological systems. Photobiomodulation remains controversial because of a poorly understood biochemical mechanism limited by the well-known biphasic dose response or Arndt-Schulz curve. The Arndt-Schulz curve states that an optimal dose of light is a key factor for realizing a therapeutic effect. In this report, we demonstrate a tunable optical system for photobiomodulation to aid physicians in overcoming the constraints of light due to biphasic dose response. The tunable optical system is based on a white light-emitting diode and four liquid crystal (LC) photonic devices: three LC phase retarders, and one LC lens. The output light of the tunable optical system exhibits electrical tunability for the wavelength, energy density and beam size. The operating principle is introduced, and the experimental results are presented. The proposed concept can be further extended to other electrically tunable photonic devices for different clinical purposes for photobiomodulation.

Switchable Liquid Crystal Contact Lenses for the Correction of Presbyopia

Presbyopia is an age-related disorder where the lens of the eye hardens so that focusing on near objects becomes increasingly difficult. This complaint affects everyone over the age of 50. It is becoming progressively more relevant, as the average age of the global population continues to rise. Bifocal or varifocal spectacles are currently the best solution for those that require near and far vision correction. However, many people prefer not to wear spectacles and while multifocal contact lenses are available, they are not widely prescribed and can require significant adaptation by wearers. One possible solution is to use liquid crystal contact lenses that can change focal power by applying a small electric field across the device. However, the design of these contact lenses must be carefully considered as they must be comfortable for the user to wear and able to provide the required change in focal power (usually about +2D). Progress towards different lens designs, which includes lens geometry, liquid crystal choices and suitable alignment modes, are reviewed. Furthermore, we also discuss suitable electrode materials, possible power sources and suggest some methods for switching the lenses between near and far vision correction.

Multi-electrode tunable liquid crystal lenses with one lithography step.

Electrically tunable lenses offer the possibility to control the focal distance by applying an electric field. Different liquid crystal tunable lenses have been demonstrated. In order to minimize lens aberrations, multi-electrode designs allow us to fine-tune the applied voltages for every possible focal distance. In this Letter, we provide a novel multi-electrode design in which only one lithography step is necessary, thereby offering a greatly simplified fabrication procedure compared to earlier proposed designs. The key factor is the use of a high-permittivity layer, in combination with floating electrodes.

梯形凸起电极液晶变焦透镜

梯形凸起电极液晶变焦透镜