Variable-focus Lens Research Articles

柔性变焦透镜发展现状

柔性变焦透镜发展现状

Multi-image acquisition-based distance sensor using agile laser spot beam.

We present a novel laser-based distance measurement technique that uses multiple-image-based spatial processing to enable distance measurements. Compared with the first-generation distance sensor using spatial processing, the modified sensor is no longer hindered by the classic Rayleigh axial resolution limit for the propagating laser beam at its minimum beam waist location. The proposed high-resolution distance sensor design uses an electronically controlled variable focus lens (ECVFL) in combination with an optical imaging device, such as a charged-coupled device (CCD), to produce and capture different laser spot size images on a target with these beam spot sizes different from the minimal spot size possible at this target distance. By exploiting the unique relationship of the target located spot sizes with the varying ECVFL focal length for each target distance, the proposed distance sensor can compute the target distance with a distance measurement resolution better than the axial resolution via the Rayleigh resolution criterion. Using a 30mW 633nm He-Ne laser coupled with an electromagnetically actuated liquid ECVFL, along with a 20cm focal length bias lens, and using five spot images captured per target position by a CCD-based Nikon camera, a proof-of-concept proposed distance sensor is successfully implemented in the laboratory over target ranges from 10 to 100cm with a demonstrated sub-cm axial resolution, which is better than the axial Rayleigh resolution limit at these target distances. Applications for the proposed potentially cost-effective distance sensor are diverse and include industrial inspection and measurement and 3D object shape mapping and imaging.

An improved low-optical-power variable focus lens with a large aperture.

We report an improved method of fabricating a variable focus lens in which an in-plane pretension force is applied to a membrane. This method realized a lens with a large optical aperture and high performance in a low-optical-power region. The method was verified by comparing membranes in a simulation using the finite element method. A prototype with a 26 mm-diameter aperture was fabricated, and the wavefront behavior was measured by using a Shack-Hartmann sensor. Thanks to the in-plane pretension force, the lens achieved an infinite focal length with a wavefront error of 105.1 nm root mean square.

TAG Lens: Revolutionizing Optical Microscopy With Ultra-High Speed Variable Focus

The Tunable Acoustic Gradient Lens, or TAG Lens, is a revolutionary innovation that uses sound waves in liquid to provide the fastest variable focus lens in the field of adaptive optics. Capable of scanning a wide range of focal lengths in microseconds, the TAG lens is orders of magnitude faster than other liquid lenses, optical membrane or mechanical scanning approaches presently available on the market [1]. The award-winning TAG Lens functions by using a piezoelectric element at the boundary of a cylindrical cavity to excite high frequency acoustic pressure waves in a confined liquid. The corresponding oscillations in liquid density create an index of refraction profile like that of a simple aspherical lens (Figure 1). However, unlike static devices that rely on the deformation of a surface or interface, the TAG Lens is a tunable gradient index of refraction (GRIN) lens that does not require any mechanical motion or redistribution of liquid to change its optical properties, allowing it to modulate focal length at very high speeds (70kHz to 1 MHz). Furthermore, the aspheric nature of the index of refraction profile results in a tunable lens with little to no spherical aberration, making it an ideal candidate for high-speed, high-precision applications [2].

The Research of a Variable-Focus Ultrasonic Liquid Lens

In this paper, a variable-focus ultrasonic liquid lens controlled by the external voltage is demonstrated. That is, the liquid lens can be reshaped with the external voltage, which will cause the focal length to change. The relationship between liquid lens’ shape and the control voltage was obtained. The influence factors of the response time were researched. And the distribution of the ultrasonic field after the lens under different external control voltages was simulated.

Intraocular lens based on double-liquid variable-focus lens

In this work, the crystalline lens in the Gullstrand-Le Grand human eye model is replaced by a double-liquid variable-focus lens, the structure data of which are based on theoretical analysis and experimental results. When the pseudoaphakic eye is built in Zemax, aspherical surfaces are introduced to the double-liquid variable-focus lens to reduce the axial spherical aberration existent in the system. After optimization, the zoom range of the pseudoaphakic eye greatly exceeds that of normal human eyes, and the spot size on an image plane basically reaches the normal human eye's limit of resolution.

电润湿双液体变焦透镜

An electrowetting-based double-liquid lens was developed to realize the small volume and automatic focusing without mechanical components for the focus-variation lens.The electrowettingbased double-liquid lens was designed and fabricated based on the dielectric wetting principle.Then,the focal length of liquid lens for different voltages was measured by a CCD image measurement system and it was compared with the theoretical value calculated by Gauss optical theory.Finally,COMSOL was employed to analyze the curvature radius of the double liquid interface at different voltages and to discuss the effect of dynamic viscosity on the response time and stability of the liquid lens.The results indicate that the double liquid interface bends to the conductive salt solution initially and then changes into a plane and finally bends to the insulating oil when the applied voltage is increased.Accordingly,the liquid lens changes from a concave lens to a convex lens,and the critical voltage is 50 V.However,the focal length of the liquid lens does not decrease any more when the applied voltage increases to65 V.The whole focal length of the lens ranges from-∞to-22.83 mm and from 33.47 mm to+∞,and it is adjusted continuously in a wider range.Moreover,when the dynamics viscosity of insulating oil is0.03,the response time is 0.015 sand the corresponding performance of the device is optimal.

Developments in the correction of presbyopia I: spectacle and contact lenses

To outline the refractive problems associated with presbyopia and to review the basis and relative merits of currently-available methods for their correction, with detailed consideration of spectacle and contact lens approaches. In the developed world, most of the present population will spend roughly half their lives as presbyopes. The well-known presbyopic changes with age in amplitude of accommodation and required near addition are briefly reviewed, together with the less widely acknowledged slow drifts that occur in distance refraction. The desirability of restoring to presbyopes clear vision for objects at any distance, ideally corresponding to vergences within the range of at least 0 to -5 D, in any viewing direction, is stressed. A general outline is given of possible corrective methods. Methods which satisfy the needs of a 50 year-old may not be suitable for the 80 year-old. Corrections may involve both fixed- and variable-focus lens systems, and surgical methods which modify the optics of the cornea, replace the crystalline lens with different fixed optics, or attempt to at least partially restore active accommodation. Some more recent methods of spectacle and contact lens correction are described in more detail. Particular attention is given to recent commercially-developed spectacles in which the corrective power can be varied actively by either mechanical (liquid-filled deformable lenses or Alvarez lenses) or electrical (liquid crystal lenses) means to allow objects at different distances to be seen clearly. Contact lens corrections show less progress and are still preferred only by a minority of older patients, most of whom are early presbyopes. The rising proportion of presbyopes in the population, covering an age span of around 40 years, represents both a problem for those concerned with giving their patients the best vision possible at both far and near viewing distances and a commercial opportunity. Traditional single-vision distance and near, bifocal, and progressive spectacle lens solutions, together with contact lens modalities for presbyopic correction, are being challenged by a variety of new approaches. It remains to be seen whether the latter will receive wide acceptance in practice.

Transparent actuator made with few layer graphene electrode and dielectric elastomer, for variable focus lens

A transparent dielectric elastomer actuator driven by few-layer-graphene (FLG) electrode was experimentally investigated. The electrodes were made of graphene, which was dispersed in N-methyl-pyrrolidone. The transparent actuator was fabricated from developed FLG electrodes. The FLG electrode with its sheet resistance of 0.45 kΩ/sq (80 nm thick) was implemented to mask silicone elastomer. The developed FLG-driven actuator exhibited an optical transparency of over 57% at a wavenumber of 600 nm and produced bending displacement performance ranging from 29 to 946 μm as functions of frequency and voltage. The focus variation was clearly demonstrated under actuation to study its application-feasibility in variable focus lens and various opto-electro-mechanical devices.

Dynamics of ADAMS Simulation for Continuous Zoom Infrared Lens and Analysis

This paper describes the basic structure of the continuously variable focus lens form. The movement in the form of the lens is simulated analysis through ADAMS software. Trajectory accurately restore the zoom group and compensation group. With the theoretical design of comparative analysis and validation process the lens structure design movement, save the latethe experiments verify the cost of the great significance of the production process.

Variable-focus lens with 30 mm optical aperture based on liquid–membrane–liquid structure

We report a liquid lens with a liquid–membrane–liquid structure in order to realize a variable-focus lens with a large optical aperture. We studied a typical liquid lens with a liquid–liquid structure and examined its physical limitation, namely, the capillary length, restricting the design of a larger-aperture liquid lens. We propose using elastic force instead of surface tension to acquire a much longer capillary length. We demonstrated that this approach can achieve sufficiently long capillary length when external pressure is loaded. A prototype lens with 30 mm aperture was constructed, and a resolution of 8.00 lp/mm was realized.

Focal length hysteresis of a double-liquid lens based on electrowetting

In this paper, an extended Young equation especially suited for an ideal cylindrical double-liquid variable-focus lens is derived by means of an energy minimization method. Based on the extended Young equation, a kind of focal length hysteresis effect is introduced into the double-liquid variable-focus lens. Such an effect can be explained theoretically by adding a force of friction to the tri-phase contact line. Theoretical analysis shows that the focal length at a particular voltage can be different depending on whether the applied voltage is increasing or decreasing, that is, there is a focal length hysteresis effect. Moreover, the focal length at a particular voltage must be larger when the voltage is rising than when it is dropping. These conclusions are also verified by experiments.

Ultrasonic variable-focus optical lens using transparent gel

Varifocal imaging using an optical lens that employs acoustic radiation force and a viscoelastic material and that has no mechanical moving parts is investigated. The lens has a simple and thin structure that consists of an annular ultrasonic transducer and silicone gel. An axially symmetric acoustic standing wave can be generated in the gel by exciting a vibration mode in the radial direction on the transducer. The lens profile can be altered by varying the acoustic radiation force of the transducer. The focal length can be controlled by varying the transducer input voltage so that the lens functions as a variable-focus lens.

Free vibrations of a spherical drop constrained at an azimuth

Two droplets coupled through a liquid filled (a) hole in a plate or (b) tube is referred to as a double droplet system (DDS) or a capillary switch. Such capillary systems are gaining increasing attention due to their utility in applications. A particularly exciting application is one where a DDS is employed as a liquid lens, one flavor of which entails using a DDS as a variable focus lens by keeping it under sustained oscillations at its natural frequencies. The natural modes of oscillation of a DDS are determined analytically here in the limit in which the plate thickness (or tube length) is vanishingly small and when the effect of gravity is negligible compared to that of surface tension. In this limit, a DDS at rest reduces to two spherical caps that are pinned to and coupled along a common circular ring of contact of negligible thickness. Here, the caps are taken to be complementary pieces of a sphere so that the equilibrium state of the system is a sphere that is constrained by a ring of negligible thickness at an azimuthal angle with respect to the center of the sphere. Both the constrained drop and the fluid exterior to it are taken to be inviscid fluids undergoing irrotational flow. Similar to the linear oscillations of a free drop first studied by Rayleigh, the analytical formulation of the linear oscillations of the constrained drop results in a linear operator eigenvalue problem but with one additional boundary condition, i.e., that which accounts for zero shape perturbation along the circle of contact. Exploiting properties of linear operators, an implicit expression is obtained for the frequency of each mode of oscillation, a feat that appears not to have been accomplished to date in any problem involving oscillations of constrained drops. An extension of a method based on Green's functions that was developed to analyze the linear oscillations of a drop in contact with a spherical bowl [M. Strani and F. Sabetta, “Free-vibrations of a drop in partial contact with a solid support,” J. Fluid Mech. 141, 233–247 (1984)]10.1017/S0022112084000811 is also employed to verify the aforementioned results. Results obtained from these two approaches are then compared to those reported by Bostwick and Steen [“Capillary oscillations of a constrained liquid drop,” Phys. Fluids 21, 032108 (2009)]10.1063/1.3103344. Careful examination of flow fields within drops reveals that by pinning a drop, it should be possible to selectively excite just a portion of a drop's surface.

Three-Dimensional Surface Profile Measurement of Microlenses Using the Shack–Hartmann Wavefront Sensor

We present a 3-D surface profiling method for microlenses that utilizes a Shack-Hartmann wavefront sensor. This method applies to both solid microlenses and liquid-liquid interfaces in liquid microlenses. The wavefront at the aperture stop of a microlens is measured by a Shack-Hartmann wavefront sensor and is then used to calculate the 3-D surface profile of the microlens. Three types of microlenses-a photoresist microlens, a hydrogel-driven tunable liquid lens, and an electrowetting-driven tunable liquid lens-were fabricated and measured. The variable-focus liquid lenses were tested within a wide focal length range. The obtained surface profiles were fitted to spherical and conical surface models to study their geometrical properties. The photoresist microlens was found to be approximately spherical. For the hydrogel-driven microlens, the profile was smooth and nearly spherical at the center but became steep and linear at the aperture edges. The electrowetting-driven liquid lens was also fitted better with the conical model, and its conic constant was determined. The obtained surface profiles were used to estimate the optical properties of microlenses in an optical analysis software package. The comparison between the simulation and experiment results indicated that the accuracy of the estimation is rough and the error could be due to the wavefront measurement and surface fitting approximation.

Electromechanically driven variable-focus lens based on transparent dielectric elastomer

Dielectric elastomers with low elastic stiffness and high dielectric constant are smart materials that produce large strains (up to 300%) and belong to the group of electroactive polymers. Dielectric elastomer actuators are made from films of dielectric elastomers coated on both sides with compliant electrode material. Poly(3,4-ethylenedioxythiophene) (PEDOT), which is known as a transparent conducting polymer, has been widely used as an interfacial layer or polymer electrode in polymer electronic devices. In this study, we propose the transparent dielectric elastomer as a material of actuator driving variable-focus lens system using PEDOT as a transparent electrode. The variable-focus lens module has light transmittance up to 70% and maximum displacement up to 450. When voltage is applied to the fabricated lens module, optical focal length is changed. We anticipate our research to be a starting point for new model of variable-focus lens system. This system could find applications in portable devices, such as digital cameras, camcorder, and cell phones.

Variable-Focus Liquid Lens Based on EWOD

A novel configuration of variable-focus liquid lens based on electrowetting-on-dielectric (EWOD) technique is presented, which consists of a glass slide coated with a conductive indium-tin-oxide (ITO) film and a hydrophobic dielectric film, a hollow conical metal ring suspended right above the gap between the slide and the ring, and the lens liquid (water). By varying the voltage applied to grounded metal ring and the ITO control electrode, both the position and curvature of the liquid meniscus can be reversibly adjusted, thus, tuning the focal length of the lens. The experimental results show that at a 40 V power supply, the liquid lens is able to focus on objects away from 2.5 cm up to infinity with a good imaging quality.

Characterization of adjustable fluidic lenses and capability for aberration correction of defocus and astigmatism

An adjustable, variable-focus fluidic lens is typically utilizing curvature change in the meniscus between two immiscible liquids or by adjusting the liquid pressure of the lens chamber. In addition, this curvature change can be used as a deformable mirror to correct the aberrations such as defocus and astigmatism. In this paper, we first fabricate a liquid lens prototype and experimentally characterize relevant optical performance such as focal length tunability over curvature change through adjusted liquid volume. Moreover, capability of adjustable fluidic lenses to correct the induced wavefront aberrations is investigated systematically, with particular attention placed on interpretation of Zernike modes and fully explores the potentials of fluidic lenses. Optically, various orders of wavefront aberrations are purposely induced by a commercial MEMS (micro-electrical–mechanical systems) DM (deformable mirrors) with 140 actuators. The optical properties of fluidic lenses are characterized by Shack–Hartmann measurements. It is experimentally shown that piston mode (Z1) can be significantly improved from 0.972μm to −0.031μm using fluidic lenses by injecting DI water as little as 0.02ml. Similar improvements can be found in defocus (Z5)/astigmatism (Z6) and aberrations are reduced for both modes from −0.15μm/−0.48μm to 0.02μm/0.085μm, respectively.

Variable-focus Liquid Lens Based on a Laterally-integrated Thermopneumatic Actuator

We report a focal-length tunable liquid lens based on thermopneumatically driven fluidic pressure. The fluidic pressure is generated by deformation of an elastomeric diaphragm induced by thermopneumaticity from a laterally integrated microheater sealed within an air chamber. The pressure is transmitted by a confined liquid to a lens diaphragm through an internal fluid channel. The liquid filling under the lens diaphragm functions as a liquid lens for dynamic focusing with properties depending on the curvature of the deformed diaphragm. The diaphragm area of the air chamber is designed five times larger than that of the lens cavity to yield high focal-length tunability by amplified deflection of the lens diaphragm. With our method, we achieved excellent focal-length tunability from infinity (without an input current) to 4 mm (with an input current of 12 mA) with a lens aperture diameter of 2 mm.

Ultrasonic variable-focus optical lens using viscoelastic material

A variable-focus lens that employs acoustic radiation force and a viscoelastic material and that has no mechanical moving parts is investigated. The lens has a simple and thin structure that consists of an annular ultrasonic transducer and silicone gel. An axially symmetric acoustic standing wave can be generated in the gel by exciting a vibration mode in the radial direction on the transducer. The lens profile can be altered by varying the acoustic radiation force of the transducer. The focal length can be controlled by varying the transducer input voltage so that the lens functions as a variable-focus lens.