Adaptive Lens

Dynamic projection mapping for non-planar objects with a variable focus lens and visual feedback

Dynamic projection mapping for moving objects has attracted much attention in recent years. However, conventional approaches have faced some issues, such as the target objects being limited to the moving speed of the objects, the limitation of the narrow depth-of-field optics, and the planar shape objects. This work proposed an adaptive three-dimensional projection prototype, and it could project an always in-focus image on a non-planar object based on liquid lens optics. The location of the non-planar object could be detected, and the mapped projection contents calculated; as a result, a stable "printed" projection mapping should be viewed on a moving object.

Large diameter electrically tunable lens for ophthalmic distance accommodation

Electrically tunable liquid crystal lens with 30 mm diameter is presented based on the refractive Fresnel concept. Relatively large optical power variation range (from - 0.74 to +0.71 Diopters) is demonstrated along with very low root mean square aberrations (≤0.15 µm). Optical characterizations, including with Snellen chart, show that good vision recovery may be obtained with fast response time (under 500 msec) and relatively low haze. The proposed design is very simple and may be fabricated by using single step lithography. Perspectives on its applications are discussed.

Parametric multiphysics study of focus-variable silicone lenses

By exploiting their inherent elasticity, focus-variable silicone lenses shift their focal length reversibly when deformed. Although biconcave and meniscus lenses contribute to optical systems just as well as biconvex lenses, studies primarily revolve around the latter. Thus, we aim to reveal the focal length shifting potential of all aforementioned lens types. Covering a wide parameter range of varying lens curvature radii, we present a coupled mechanical and optical simulation in which a lens deformation is applied. The results show significant differences in focal length shifting effectiveness for different lens types. Within the domains of specific lens types, trends in this effectiveness emerge for different combinations of curvature radii. Matching these radii when incorporating adaptive silicone lenses in optical systems may guide optics engineers toward more effective system designs through this study.

Simple electrically tunable liquid crystal spatial phase modulator

We describe multiple optical functionalities obtained with a simple electrically tunable liquid crystal element that can be controlled by 4 electrodes, which are connected to a serpentine shaped transparent indium tin oxide layer. We experimentally demonstrate that the device is capable of dynamically generating refractive index distributions corresponding to a standard spherical lens, axicon, cylindrical lens, and prism. The dynamic switching of the device between these different operation modes is done in a very simple electronic way. We think that this element has a significant potential for applications in adaptive imaging, optogenetics, photonic integrated circuits, etc.

Electrically tunable lens with a non-monotonic wavefront control capability

We describe an electrically tunable liquid crystal lens that can produce a rich variety of wavefronts, including sombrero-type (non-monotonic) phase modulation, enabling the focusing of light into a ring-shaped intensity distribution. The lens can also generate axicons or standard spherical lenses with a bipolar response (providing both positive and negative optical powers). The design of the lens requires only a single-step lithography process, dramatically simplifying its manufacturing. We describe various driving modes of this lens and present the first experimental results and discuss its possible applications in miniature cameras and microscopes. We think that this device can revolutionize the optical design in many areas of photonics.

Overview of Liquid Crystal Biosensors: From Basic Theory to Advanced Applications

Liquid crystals (LCs), as the remarkable optical materials possessing stimuli-responsive property and optical modulation property simultaneously, have been utilized to fabricate a wide variety of optical devices. Integrating the LCs and receptors together, LC biosensors aimed at detecting various biomolecules have been extensively explored. Compared with the traditional biosensing technologies, the LC biosensors are simple, visualized, and efficient. Owning to the irreplaceable superiorities, the research enthusiasm for the LC biosensors is rapidly rising. As a result, it is necessary to overview the development of the LC biosensors to guide future work. This article reviews the basic theory and advanced applications of LC biosensors. We first discuss different mesophases and geometries employed to fabricate LC biosensors, after which we introduce various detecting mechanisms involved in biomolecular detection. We then focus on diverse detection targets such as proteins, enzymes, nucleic acids, glucose, cholesterol, bile acids, and lipopolysaccharides. For each of these targets, the development history and state-of-the-art work are exhibited in detail. Finally, the current challenges and potential development directions of the LC biosensors are introduced briefly.

Electrically tunable liquid crystal lens with a serpentine electrode design

The design and operational principle of a new electrically tunable gradient index liquid crystal lens are described. The approach is based on linear serpentine electrodes and does not require a semiconductor layer. A preliminary validation is done for a lens with a 2 mm clear aperture, demonstrating 9.5 diopters of optical power and a root-mean-square wavefront error of 0.16 µm. The developed lens is tested with a miniature camera and the image quality improvement is demonstrated experimentally.

Electrically variable liquid crystal lenses for ophthalmic distance accommodation

We present the example of a specific design of an electrically tunable liquid crystal lens (TLCL) with floating electrode to analyze experimentally the potential of using TLCLs in intraocular implants. An optimized voltage-frequency driving technique is demonstrated to achieve high optical powers (up to 4 diopters) with very low aberrations (below 0.1μm) for an optical aperture of 3mm. In addition, the continuous character of distance accommodation and the absence of granularity across the aperture of the lens (pixel-free) make this component an excellent choice for various ophthalmic applications.

Dynamic control of polarization mismatch and coma aberrations in rod-GRIN assemblies

We describe the use of stacked electrically tunable liquid crystal lenses (TLCLs), along with rod gradient index (GRIN) fixed focus lenses, for endoscopic applications. Architectural and driving conditions are found for the optimization of total aberrations of the assembly. Particular attention is devoted to the coma and polarization aberrations. The coma aberration is reduced by stacking two TLCLs with "opposed" pre-tilt angles (all molecules are in the same plane), and then two such doublets are used with cross oriented molecules (in perpendicular planes) to reduce the polarization dependence. The obtained adaptive rod-GRIN lens enables a focus scan over 80μm (with exceptionally low RMS aberrations ≤0.16μm), making possible the high-quality observation of neurons at various depths.

A High-Efficiency Low-Power Chip-Based CMOS Liquid Crystal Driver for Tunable Electro-Optic Eyewear

A high-efficiency low-power chip-based liquid crystal (LC) driver has been successfully designed and implemented for adaptive electro-optic eyewear including tunable vision correction devices (eyeglass, contact lens, intraocular lens, occluder, and prism), phoropter, iris, head-mounted display, and 3D imaging. The driver can generate a 1 kHz bipolar square wave with magnitude tunable from 0 V to 15 V to change the lens focus adaptively. The LC driver output magnitude is controlled by a reference DC voltage that is manually tunable between 0 and 3 V. A multi-mode 1×/2×/3×/4×/5× charge pump is developed for DC-DC conversion to expand the output range with a fast-sink function implemented to regulate the charge pump output. In addition, a new four-phase H-bridge driving scheme is employed to improve the DC/AC inverter efficiency. The LC driver has been successfully implemented and tested as an IC chip (8.6 mm × 8.6 mm) using AMS 0.18 μm High-Voltage CMOS technology.

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.

Conjugation of Nanomaterials and Nematic Liquid Crystals for Futuristic Applications and Biosensors

The established role of nematic liquid crystals (NLCs) in the recent rapid development of displays has motivated researchers to modulate the electro-optical properties of LCs. Furthermore, adding nanomaterials into NLCs has led to enhancements of the properties of NLCs, like reduced threshold of the operating voltage, variation in pretilt angle, reduced switching time, etc. These enhanced properties, due to interfacial dynamics, are enabling wider applications of NLCs and nanomaterials. The recent literature of nanomaterial-doped NLCs is rich with various kinds of nanomaterials in a variety of NLCs. The light has been focused on the most widely used and studied gold nanoparticles in NLCs. The intrinsic inherent property of easy excitation of surface plasmons polaritons (SPP) is the mediating interaction of NLC electric dipoles and the polarization of charges in the GNP surface. The concepts and methods for the application of metal nanomaterials as dopants in NLCs are discussed for future applications, especially biosensors. The biosensing application of NLCs alone has already been proven in the literature. However, it is always desirable to further enhance the detection efficiency and selectivity, which have been achieved by the conjugation of GNPs and nickel nanoparticles with NLCs and their compatibility with biological materials. This aspect of future application of nanoparticles and NLC makes the point more selective to be included in the present manuscript.

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.

Paraxial design of an optical element with variable focal length and fixed position of principal planes

In this article, we analyze the problem of the paraxial design of an active optical element with variable focal length, which maintains the positions of its principal planes fixed during the change of its optical power. Such optical elements are important in the process of design of complex optical systems (e.g., zoom systems), where the fixed position of principal planes during the change of optical power is essential for the design process. The proposed solution is based on the generalized membrane tunable-focus fluidic lens with several membrane surfaces.

Lightweight Smart Autofocusing Eyeglasses

More than 100 million people in the United States of America alone suffer from age-related presbyopia caused by a loss of focal accommodation of the eye crystalline lens as the lens stiffens with age. The resulting accommodative error or lag produces blurred images of objects placed at different distances. Conventional fixed uniform or graded power eyeglasses cannot provide accommodation thus resulting in significant visual impairment. In this paper we will discuss the implementation of lightweight auto-focusing eyeglasses that augment the accommodative range thus partially or fully restoring normal vision function. The paper discusses some aspects of the construction of tunable power eyepieces and the implementation of accommodation correction algorithms.

Impact of titanium dioxide nanoparticles on purification and contamination of nematic liquid crystals

We have investigated the impact of titanium dioxide nanoparticles on the ionic contamination of liquid crystals. Nematic liquid crystals with high and low initial ionic contamination have been examined. It has been shown that titanium dioxide nanoparticles reduced the ion density of liquid crystals with high initial ionic contamination from 134.5 × 1012 cm-3 to 63.2 × 1012 cm-3. In the case of liquid crystals with low initial ionic contamination, the nanoparticles led to an insignificant increase of ion density from 19.8 × 1012 cm-3 to 25.7 × 1012 cm-3.

Double-sided telecentric zoom lens consisting of four tunable lenses with fixed distance between object and image plane

This work performs a paraxial analysis of the double-sided telecentric zoom lens consisting of four tunable lenses with fixed distance between the object and image plane. Equations enabling calculation of paraxial parameters of such optical systems are derived and the calculation is presented on examples. To our knowledge the presented analysis is novel and such optical systems have not been investigated yet.

Method of calculation of internal parameters of liquid lens

This paper is focused on the problem of determination of internal parameters of a fluidic lens composed of two immiscible liquids of different refractive index, which form a tunable refractive interface for changing the focal length of a lens. Formulas are derived for calculation of a radius of curvature of the internal interface between two liquids and refractive indices of liquids using the measurements of the focal length of the lens, positions of focal points, and transverse spherical aberration of the lens.

Isotropic Elastic Stress Induced Large Temperature Range Liquid Crystal Blue Phase at Room Temperature

A thermodynamically stable blue phase (BP) based on the conventional rod like nematogen is demonstrated for the first time at room temperature by only diluting a chiral-nematic mixture with the help of some nonmesogenic isotropic liquid. It is observed that addition of this isotropic liquid does not only stabilize the BPs at room temperature, but also significantly improves the temperature range (reversible during heating and cooling) of the BPs to the level of more than 28 °C. Apart from that, we have observed its microsecond electro-optic response time and, external electric field induced wavelength tuning, which are the two indispensable requirements for next generation optical devices, photonic displays, lasers, and many more. Here we propose that the isotropic liquid plays two crucial roles simultaneously. On one hand, it reduces the effective elastic moduli (EEM) of the BP mixtures and stabilizes the BPs at room temperature, and on the other hand, it increases the symmetry of the mutual orientation ordering among the neighboring unit cells of the BP. Hence, the resultant mixture becomes better resistive to some microscopic change due to the change in temperature, even over a large range.

Focal-length-tunable elastomer-based liquid-filled plano-convex mini lens

A liquid plano-convex lens with focal length tuning is proposed, which is formed by sinking an oil droplet onto the bottom of an elastomer. A simple and low-cost fabrication method is presented. The lens aperture and initial focal length can be controlled during the fabrication. Furthermore, focal length tuning is demonstrated. The lens made of a 40 mg oil droplet can achieve the tuning range from 12 to 17 mm. The effective aperture of the lens is about 2.8 mm. In the demonstration of an imaging system, the lens assists in focusing and a clear image can be observed.

Five-lens, easy-to-implement miniature objective for a fluorescence confocal microendoscope

A fluorescence confocal microendoscope requires a high-performance miniature objective. We present a miniature objective comprising four glass lenses and one plastic aspheric lens. The 0.5 NA objective is achromatized in the wavelength range of 488-550 nm, has a field of view (FOV) of 360 μm, and an outer diameter of 2.6 mm. The assembled miniature objective can resolve features separated by as little as 0.78 μm. The imaging quality of the fluorescence confocal microendoscope with the miniature objective is similar to that of a commercial confocal microscope. It can resolve cellular structures such as crypt structures and epithelial cells.

Solid electrically tunable dual-focus lens using freeform surfaces and microelectro-mechanical-systems actuator

In this Letter, a miniature solid tunable dual-focus (DF) lens, which is designed using freeform optical surfaces and driven by one microelectro-mechanical-systems rotary actuator, is reported. Such a lens consists of two optical elements, each having a flat surface and one freeform surface optimized by ray-tracing technology. By changing the relative rotation angle of the two lens elements, the lens configuration can form double foci with corresponding focal lengths varied simultaneously, resulting in a tunable DF effect. Results show that one of the focal lengths is tuned from about 30 to 20 mm, while the other one is varied from about 30 to 60 mm, with a maximum rotation angle of about 8.2 deg.

Design of high-performance adaptive objective lens with large optical depth scanning range for ultrabroad near infrared microscopic imaging

We report on the theory and design of adaptive objective lens for ultra broadband near infrared light imaging with large dynamic optical depth scanning range by using an embedded tunable lens, which can find wide applications in deep tissue biomedical imaging systems, such as confocal microscope, optical coherence tomography (OCT), two-photon microscopy, etc., both in vivo and ex vivo. This design is based on, but not limited to, a home-made prototype of liquid-filled membrane lens with a clear aperture of 8mm and the thickness of 2.55mm ~3.18mm. It is beneficial to have an adaptive objective lens which allows an extended depth scanning range larger than the focal length zoom range, since this will keep the magnification of the whole system, numerical aperture (NA), field of view (FOV), and resolution more consistent. To achieve this goal, a systematic theory is presented, for the first time to our acknowledgment, by inserting the varifocal lens in between a front and a back solid lens group. The designed objective has a compact size (10mm-diameter and 15mm-length), ultrabroad working bandwidth (760nm - 920nm), a large depth scanning range (7.36mm in air) - 1.533 times of focal length zoom range (4.8mm in air), and a FOV around 1mm × 1mm. Diffraction-limited performance can be achieved within this ultrabroad bandwidth through all the scanning depth (the resolution is 2.22 μm - 2.81 μm, calculated at the wavelength of 800nm with the NA of 0.214 - 0.171). The chromatic focal shift value is within the depth of focus (field). The chromatic difference in distortion is nearly zero and the maximum distortion is less than 0.05%.

Superior electro-optic response in multiferroic bismuth ferrite nanoparticle doped nematic liquid crystal device

A superior electro-optic (E-O) response has been achieved when multiferroic bismuth ferrite (BiFeO3/BFO) nanoparticles (NPs) were doped in nematic liquid crystal (NLC) host E7 and the LC device was addressed in the large signal regime by an amplitude modulated square wave signal at the frequency of 100 Hz. The optimized concentration of BFO is 0.15 wt%, and the corresponding total optical response time (rise time + decay time) for a 5 μm-thick cell is 2.5 ms for ~7 V(rms). This might be exploited for the construction of adaptive lenses, modulators, displays, and other E-O devices. The possible reason behind the fast response time could be the visco-elastic constant and restoring force imparted by the locally ordered LCs induced by the multiferroic nanoparticles (MNPs). Polarized optical microscopic textural observation shows that the macroscopic dislocation-free excellent contrast have significant impact on improving the image quality and performance of the devices.

Dielectrophoretically controlled Fresnel zone plate

Switchability is a highly sought after feature for planar optical systems. Suspensions of nanomaterials can be used for generating controllable changes in such systems. We report a planar diffractive microfluidic lens which integrates controlled dielectrophoresis (DEP) for trapping suspended nanomaterials. Silicon and tungsten oxide nanoparticle suspensions are used. These nanomaterials are trapped in such a way as to form alternating opaque and transparent rings using the DEP forces on demand. These rings form a planar diffractive Fresnel zone plate to focus the incident light. The Fresnel zone plate is tuned for the visible light region and the lens can be turned on (DEP applied) or off (DEP removed) in a controlled manner. This proof of concept demonstration can be further expanded for a variety of switchable optical devices and can be integrated with lab-on-a-chip and optofluidic devices.

rPLR: an imaging system for measuring pupillary light reflex at a distance

Pupillary light reflex (PLR) is a simple noninvasive neurological test that can reveal a great amount of information of the neural system. We report here a novel imaging system for measuring PLR without using any restraints to limit the subject's movement. Our system incorporates a tracking component that can locate the subject's eye position and redirect the pupillary imaging component to follow the subject's movement. This system can measure PLR, at a distance from the subject, with high spatial resolution (<50  μm) and temporal resolution (120 Hz). Because this new PLR device can accommodate the subject's movement, it is well positioned to test in young children and other people who have difficulty remaining voluntarily still during tests.

Paraxial analysis of zoom lens composed of three tunable-focus elements with fixed position of image-space focal point and object-image distance

This work performs a paraxial analysis of three-component zoom lens with a fixed position of image-space focal point and a distance between object and image points, which is composed of three tunable-focus elements. Formulas for the calculation of paraxial parameters of such optical systems are derived and the calculation is presented on examples.

Anisotropic shift of surface plasmon resonance of gold nanoparticles doped in nematic liquid crystal

Study of the liquid crystal (LC) director around nanoparticles has been an important topic of research very recently, since it allows design and fabrication of next-generation LC devices that are impossible in the past. In our experiment, alkanethiol-capped gold nanoparticles (GNPs) were dispersed in nematic LC. Analysis of the LC director around GNPs was performed by investigating the behavior of surface plasmon polariton (SPP) absorption peaks of the GNPs using spectrophotometry technique. It is found that the incident linearly polarized light orientated at 0°, 45°, and 90° angles with respect to the rubbing direction experiences varying interaction with the LC medium. The corresponding transmission of light reveals the anisotropic shift in wavelength of SPP peak. The anisotropic behavior of SPPs of the GNPs is in agreement with theoretical calculations.

Algebraic and numerical analysis of imaging properties of thin tunable-focus fluidic membrane lenses with parabolic surfaces

The theory of third-order aberrations for a system of rotationally symmetric thin tunable-focus fluidic membrane lenses with parabolic surfaces is described. A complex analysis of the third-order design of tunable fluidic lenses is performed considering all types of primary aberrations. Moreover, formulas are derived for the calculation of the change of aberration coefficients of the parabolic tunable fluidic membrane lens with respect to the wavelength. It is shown that spherical aberration of a simple tunable-focus fluidic membrane lens with parabolic surfaces can be corrected, which is not possible with a classical spherical lens. The presented analysis is explained on examples. Derived formulas make possible to calculate parameters of optical systems with fluidic membrane lenses with small residual aberrations.

Demonstration of focus-tunable diffractive Moiré-lenses

In an earlier publication [Appl. Opt. 47, 3722 (2008)] we suggested an adaptive optical lens, which consists of two cascaded diffractive optical elements (DOEs). Due to the Moiré-effect the combined optical element acts as a Fresnel zone lens with a refractive power that can be continuously adjusted by a mutual rotation of the two stacked DOEs. Here we present an experimental realization of this concept. Four designs of these Moiré-DOEs (MDOEs) were fabricated in thin (0.7 mm) glass slides by lithography and subsequent etching. Each element was realized as a 16 phase level DOE designed for 633 nm illumination. Our experimental investigation shows that the Moiré-lenses have a broad adjustable refractive power range with a high efficiency, which allows one to use them for flexible beam steering and for imaging applications.