Search

Electrowetting‐on‐dielectric (EWOD) devices have proven to be effective tools for precise microfluidic manipulation or in liquid lenses that surpass conventional solid lenses in versatility. However, the fabrication of these devices presents many challenges, such as their scalability or the growing concern on their environmental impact due to materials used in their fabrication. This review provides a comprehensive analysis of the materials currently used in the fabrication of EWOD devices and the characteristics they must meet. In addition, a discussion of future challenges in the fabrication of EWOD devices is presented, in particular the environmental problems presented by some of the materials currently in use. [ABSTRACT FROM AUTHOR]

Abstract Electrowetting‐on‐dielectric (EWOD) devices have proven to be effective tools for precise microfluidic manipulation or in liquid lenses that surpass conventional solid lenses in versatility. However, the fabrication of these devices presents many challenges, such as their scalability or the growing concern on their environmental impact due to materials used in their fabrication. This review provides a comprehensive analysis of the materials currently used in the fabrication of EWOD devices and the characteristics they must meet. In addition, a discussion of future challenges in the fabrication of EWOD devices is presented, in particular the environmental problems presented by some of the materials currently in use.

Microscope such as fluorescence microscope, confocal microscope and two-photon microscope plays an important role in life science, laser processing and other fields. However, most microscopes only have discrete zoom rates. In this paper, a continuous optical zoom microscope with extended depth of field and 3D reconstruction is demonstrated for the first time. It consists of a zoom objective lens, a microscope holder, an adjustable three-dimensional object stage, an Abbe condenser and an LED light source. The zoom objective lens is composed of several liquid lenses and solid lenses. By adjusting the applied voltage to the liquid lens, the proposed microscope can achieve a large continuous magnification from 10? to 60?. Moreover, an improved shape from focus (SFF) algorithm and image fusion algorithm are designed for 3D reproduction. Based on the liquid lenses, the axial focusing position can be adjusted to obtain images with different depths, and then the extended depth of field and 3D reconstruction can be realized. Our experimental results demonstrate the feasibility of the proposed microscope. The proposed microscope is expected to be applied in the fields of pathological diagnosis, biological detection, etc. [ABSTRACT FROM AUTHOR]

Why does a raindrop on a window pane show an image of the environment that is turned upside-down? And why does vision go blurry underwater, but is perfectly clear with diving goggles? Our everyday life is rich in optical phenomena. Unfortunately, these phenomena often play a subordinate role in Optics teaching, compared to ray constructions or mechanistic light models. In our new teaching-learning sequence designed for introductory physics courses at secondary schools, the observation of the phenomena assumes a more prominent position and the observer’s sense of sight becomes the starting point of learning about Optics. The centrepiece of our concept is the use of students’ self-made Optics inventory including liquid lenses in various experiments. [ABSTRACT FROM AUTHOR]

An electrowetting-on-dielectrics (EWOD) liquid lens, based on a flexible wire electrode, is proposed to avoid the defects prone to occur in the large area coating dielectric layer inside the cavity. A liquid lens cavity is formed by winding the flexible conductive wire with a thin dielectric layer (named EWOD wire) along the direction of light transmission in a circular wall uniformly. A tubular double-liquid electrowetting lens with a clear aperture of 7 mm is fabricated to demonstrate the practicality of this fabrication process. It can reach a focal length variation range of ($-\infty $ , −30 mm] $\cup $ [69 mm, $+\infty $) at a voltage of 0–190 Vrms and shows the other performance not inferior to those of liquid lenses fabricated by traditional methods. The EWOD wire can be assembled into any shape, performing the potential to produce other optofluidic components. [ABSTRACT FROM AUTHOR]

Wearable Video See-Through (VST) devices for Augmented Reality (AR) and for obtaining a Magnified View are taking hold in the medical and surgical fields. However, these devices are not yet usable in daily clinical practice, due to focusing problems and a limited depth of field. This study investigates the use of liquid-lens optics to create an autofocus system for wearable VST visors. The autofocus system is based on a Time of Flight (TOF) distance sensor and an active autofocus control system. The integrated autofocus system in the wearable VST viewers showed good potential in terms of providing rapid focus at various distances and a magnified view. [ABSTRACT FROM AUTHOR]

We report an electro-wetting liquid lens with dual apertures which consists of internal channel with two variable interfaces and external channel with a plano-concave solid lens. And we use LC cell and Polarizers to achieve switching between internal and external channel. The proposed lens can achieve a large turning range of focal length, and the shortest positive and negative focal length are ~24 mm and ~−16 mm, respectively. Meanwhile, the experimental results show that the angular resolution of the proposed lens can reach to $\sim 29^{\prime \prime }$. It has potential to be applied in cameras, microscopes and so on. [ABSTRACT FROM AUTHOR]

Wearable Video See-Through (VST) devices for Augmented Reality (AR) and for obtaining a Magnified View are taking hold in the medical and surgical fields. However, these devices are not yet usable in daily clinical practice, due to focusing problems and a limited depth of field. This study investigates the use of liquid-lens optics to create an autofocus system for wearable VST visors. The autofocus system is based on a Time of Flight (TOF) distance sensor and an active autofocus control system. The integrated autofocus system in the wearable VST viewers showed good potential in terms of providing rapid focus at various distances and a magnified view.

Graphical abstract Highlights • This paper presents a multifunctional liquid lens (MLL) for miniature camera modules. • The MLL provides concurrent variable-focus and variable-aperture functions. • Both optical functions are performed in a single module based solely on EWOD actuation. • The MLL not only offers a simple design structure but also covers a wide range of tunability. Abstract In this paper, we present a novel multifunctional liquid lens (MLL) for high-performance miniature cameras. The proposed MLL firstly offers concurrent variable-focus and variable-aperture functions in a single lens system solely using electrowetting-on-dielectric (EWOD) actuation. To perform both optical functions, the MLL employs two immiscible liquids and controls liquid–liquid interfaces directly through the application of voltage. The performances of both optical functions are experimentally verified by using a prototype of the MLL. Finally, as proof of concept, the simultaneous operation of the variable-focus and variable-aperture functions are demonstrated. The MLL has not only a wide range of tunability but also a simple design structure to be easily miniaturized for camera modules embedded in smart mobile devices and biomedical imaging systems. [ABSTRACT FROM AUTHOR]

Highlights • We demonstrate a dual functional optofluidic strategy where a single device can operate as either optical switch or liquid lens, or both the functions simultaneously. • Optical systems based on fluid-fluid interface offers advantages such as dynamic, reconfigurable and self-healing capabilities with less complex fabrication steps. • The principle relies on light-controlled volumetric change of an air plug confined in a minichannel filled with water. • For the optical switch, volumetric change of the air plug modulates total internal reflection. • For the liquid lens, the change of plug size acts as an actuator to control the meniscus shape of the liquid. Abstract Optical systems based on fluid-fluid interface are gaining great attention because they offer added advantages such as dynamic, reconfigurable, and self-healing capabilities with less complex fabrication steps compared to the solid based optical elements. Moreover, cost-effectiveness and ease of miniaturization pave a potential route towards the realization of portable optical and optofluidic devices. However, a single optofluidic device having remotely controlled multifunctional capabilities remains a challenge. We demonstrate an optofluidic multifunctional strategy, which could operate either as an optical switch or a tunable liquid lens. The principle relies on light-controlled volumetric change of an air plug confined in a minichannel filled with water. For the optical switch, volumetric change of the air plug modulates total internal reflection. A temperature difference of only 0.2 °C is sufficient for a subsecond switching time (0.6 ± 0.1 s). For the liquid lens, the change of plug size acts as an actuator to control the meniscus shape of the liquid. Upon heating or cooling, the meniscus develops a convex or a concave lens respectively. A temperature difference of 0.1–0.7 °C is sufficient for realizing tunability in the focal length. The demonstrated strategy is simple, cost-effective, non-contact and the device could be operated at room temperature. [ABSTRACT FROM AUTHOR]

This paper reports an electrically reconfigurable optofluidic lens with two air–liquid (silicone oil) interfaces actuated by dielectrophoretic (DEP) force. Initially, a symmetric biconcave air–liquid lens is formed by the surface tension in a microfluidic chip. Then, the DEP force deforms the air–liquid interfaces from biconcave to biconvex, tuning the focal length from −0.5 mm to infinite to +0.5 mm. The wide tunability of the focal length results from the large refractive index difference (∼0.4 at the air–liquid interface), which is only 0.1 in previous liquid–liquid lenses. In the experiment, the lens achieves an ° number of 0.91 while consuming only 6.7 nJ per circle. Some asymmetric working states, such as concave–convex and plano-convex lenses, have also been demonstrated. Compared with continuous liquid flow-sustained lenses, this stationary liquid lens holds promise of better compatibility and higher scalability. Its wide tunability, low power consumption and easy operation make it suitable for light manipulation in microfluidic networks. [ABSTRACT FROM AUTHOR]

Summary: Due to the large slope and complex geometry, it is difficult to measure the three‐dimensional parameters of cutting tools and drill bits by using general optical measurement method. A method that combines the multiview rotation scanning and nonmechanical focus variation by using a liquid lens is proposed in this paper. Firstly, the workpiece is rotated by using a rotation unit, and in every rotation position, a sequence of images of the workpiece are captured in the axial direction. Secondly, the relative degree of focus is measured for all pixels by using focus measure operators to obtain the depth value corresponding to each pixel. Thirdly, a multiview registration algorithm is designed to combine all the individual data sets at each rotation position into a whole three‐dimensional point cloud. Finally, the three‐dimensional parameters of the rake angle and clearance angle of the gear, screw tap and drills are measured. The proposed method is lateral shift‐free and no light intensity variation, so it can obtain better accuracy. The experimental results show that the accuracy of the axial measurement reaches 2.4 μm (2σ, Nikon 5×/0.1). Lay Description: This article is about a method that combines the multi‐view rotation scanning and non‐mechanical focus variation by using a liquid lens. [ABSTRACT FROM AUTHOR]

When a viscous liquid empties from an initially full, wide vertical tube, the drainage behaviour changes from a filament to a regime in which individual drops are shed by a lens formed at the end of the tube: liquid drains down the wall and the lens grows until it becomes unstable. This drop shedding regime was investigated for four Newtonian liquids (rapeseed oil, glycerol, honey and golden syrup) in three tube sizes and two tube materials (Bond number based on tube i.d. >1 in all cases). The drop mass increased modestly with flow rate and the equivalent sphere diameter, d , was strongly related to the capillary length L c  ≡ ( γ / ρg ) 1/2 rather than the tube diameter. The results were fitted to a correlation of the form d/L c  =  f (Bond, Reynolds, Morton, sine of the contact angle) derived from dimensional analysis. The data were compared with existing models for drop formation from filled narrow capillaries and a new, simple model based on a quasi-static model of the lens. Agreement with these models was poor, particularly for larger tubes, indicating the need for more detailed analysis. Insights into the dynamics, generated by video analysis of the lens shape, are presented. [ABSTRACT FROM AUTHOR]

A visualization technique was developed to accurately resolve the locations and phases of liquid and frozen water droplets naturally evolving on a subfreezing surface exposed to a humid air stream. The technique utilized the lens-like properties of unfrozen condensate droplets to focus reflected light in a manner that made it possible to reliably distinguish the unfrozen from frozen droplets. By inducing this lensing effect in all visible droplets on the surface prior to freezing, a small, high contrast region within each liquid droplet was produced. When freezing occurred, the higher opacity of the ice phase caused the frozen droplets to suddenly take on a darker appearance than the unfrozen droplets. A reflected light microscope and digital camera apparatus were used to feed data into an image analysis algorithm capable of mapping the time-evolution of the freezing water droplets on the surface. The algorithm processed raw image sequences into binary image stacks from which the light foci associated with the droplets could be reliably isolated into high contrast white pixel clusters on an otherwise black background. An edge detection method was employed within each binary image to locate the coordinates of the pixels residing along the periphery of each droplet's focal cone. Those data were subsequently used to compute the centroidal coordinates and state of each droplet over time. Compared with more laborious, frame-by-frame analyses with various commercially available software tools, this technique correctly identified the locations and states of the droplets through the entire growth and freezing processes with accuracies in excess of 99%. This technical approach also allowed for simultaneous tracking of all droplets and freezing events present within the region of interest-typically numbering in the hundreds or thousands-over time, paving the way for interdroplet coalescence and freezing interactions to be studied in detail. [ABSTRACT FROM AUTHOR]

Many consumers are interested in three-dimensional (3-D) technologies that make display images as real as possible. In response, a number of fairly mature 3-D technologies have already been introduced in various studies. Among them, we reviewed the integral imaging system and the multiview system, which can realize 3-D, from the past to the present. Those systems, however, suffer from problems such as depth range, two-dimensional (2-D) and 3-D conversions, and 3-D resolution. Therefore, a liquid lens is proposed as a technique to resolve the drawbacks. Using a liquid lens with variable focal length, the depth range was enhanced using a time-division multiplexing technique in an integral imaging system, and the function of 2-D and 3-D switching was enabled in a multiview system. Furthermore, methods were introduced to solve the problems of 3-D resolution reduction in multiview systems and vergence–accommodation conflicts in VR systems. [ABSTRACT FROM AUTHOR]

For the existent imaging devices, zooming is realized by varying either the distance or the curvature of the lenses. Therefore, the zoom system is either bulky or with a limited zoom range. To further minimize the structure and increase the zoom range, we propose an optofluidic zoom system using liquid optical path switchers. The liquid optical path switcher can be switched between liquid phase and air phase, which varies the refractive index of the optical path. Thus, for the system, zooming is realized by varying both curvature and refractive index, whose principle is quite different from the existent methods. We fabricate an optofluidic zoom system using liquid optical path switchers. The experiment results show that the proposed optofluidic zoom system can achieve a large zoom range from ~45 to ~70 mm. The system is very compact, and the light efficiency is high. The proposed system increases the zoom range greatly and has potential to be applied in cameras, endoscopes, microscopes, and so on. [ABSTRACT FROM AUTHOR]

We present a Variable Fiber-Optic Delay Line (VFODL) module capable of imparting long variable delays by switching an input optical/RF signal between Single Mode Fiber (SMF) patch cords of different lengths through a pair of Electronically Controlled Tunable Lenses (ECTLs) resulting in a polarization-independent operation. Depending on intended application, the lengths of the SMFs can be chosen accordingly to achieve the desired VFODL operation dynamic range. If so desired, the state of the input signal polarization can be preserved with the use of commercially available polarization-independent ECTLs along with polarization-maintaining SMFs (PM-SMFs), resulting in an output polarization that is identical to the input. An ECTL-based design also improves power consumption and repeatability. The delay switching mechanism is electronically-controlled, involves no bulk moving parts, and can be fully-automated. The VFODL module is compact due to the use of small optical components and SMFs that can be packaged compactly. [ABSTRACT FROM AUTHOR]

This paper presents a novel multifunctional liquid lens (MLL) for miniature camera modules integrated with smart devices such as smartphones and pads. MLL firstly offers concurrent variable-focus and variable-magnification functions in a single liquid lens system using two different actuation schemes: electrowetting-on-dielectric (EWOD) actuation for controlling the curvature of liquid interface and electromagnetic actuation for controlling the height of the liquid column. Imaging focus test is carried out using the prototype of MLL. When a target electrical voltage is applied to an electrode covered by a hydrophobic dielectric layer on the inside wall of a glass cylindrical lens chamber, the curvature of liquid interface is changed according to the principle of EWOD and the focal length of the lens is changed. As a result, an initially blurred check pattern image is clearly focused. Imaging magnification test is separately conducted. When an electrical voltage is applied to an electromagnetic system located beneath the prototype of MLL, a ring-shaped magnet presses an elastic membrane down. As a consequence, liquid residing in the actuation chamber is pumped into the lens chamber through open walls of a supporting frame, and the height of the liquid column in the lens chamber rises. The height change of the liquid column as a function of the applied voltage is measured by using a CCD camera. The height of the liquid column is linearly increased from 0 mm to 1.2 mm with the rise of applied voltage from 0 V to 50 V with 5 V increment. The average height variation per volt is about 24 μm. For the proof of concept, the sequential imaging focus and magnification test of MLL is demonstrated using simultaneous EWOD and electromagnetic actuation. Finally, the response time of MLL is measured by using a high-speed camera. The proposed MLL offers a simple design structure to be easily miniaturized but covers a wide range of imaging focus and magnification operations for high optical performance. [ABSTRACT FROM AUTHOR]

Optofluidics incorporates optics and microfluidics together to construct novel devices for microsystems, providing flexible reconfigurability and high compatibility. Among many novel devices, a prominent one is the in-plane optofluidic lens. It manipulates the light in the plane of the substrate, upon which the liquid sample is held. Benefiting from the compatibility, the in-plane optofluidic lenses can be incorporated into a single chip without complicated manual alignment and promises high integration density. In term of the tunability, the in-plane liquid lenses can be either tuned by adjusting the fluidic interface using numerous microfluidic techniques, or by modulating the refractive index of the liquid using temperature, electric field and concentration. In this paper, the in-plane liquid lenses will be reviewed in the aspects of operation mechanisms and recent development. In addition, their applications in lab-on-a-chip systems are also discussed. [ABSTRACT FROM AUTHOR]

The increased usage of liquid lenses motivates us to investigate surface waves on the liquid's surface. During fast focal switching, the surface waves decrease the imaging quality. We propose a model that describes the surface modes appearing on a liquid lens and predicts the resonance frequencies. The effects of those surface modes on a laser beam are simulated using Fresnel propagation, and the model is verified experimentally. [ABSTRACT FROM AUTHOR]

A simple and compact Depth-From-Defocus (DFD) setup, using telecentric illumination and liquid-lens based camera observation, was shown to perform well for 3D shape acquisition over extended measuring range. A further step to ameliorate the system performance is described in this paper. We focused on finding an algorithm to speed up the calibration step of the method, that automatically determines the minimum number of focal lengths to be used in the calibration and measurement procedure. As a result, the calibration is significantly shortened (up to 80% with respect to the original procedure), and the need to manually (and to some extent arbitrarily) select the focal length pairs is overcome. Measurement errors down to 0.73 mm over the measurement depth range of 130 mm, corresponding to 0.55% of the depth range are achieved, in total agreement with the original system. [ABSTRACT FROM AUTHOR]

We demonstrate an adaptive liquid lens controlled by laser-induced solutocapillary forces. The liquid droplet serving as a lens is formed in a thin layer of binary liquid mixture by surface tension driven flows caused by the thermal action of laser irradiation. The shape of droplet, its aperture and the focal length are reversibly changed without hysteresis by varying the intensity of the laser beam. The focal length variation range of the droplet-lens lies in between infinity (a flat layer) to 15 mm (a curved interface). The droplet-lens is capable to adjust the in-plane lateral position in response to a displacement of the laser beam. The proposed laser controlled droplet-lens will enable to develop smart liquid optical devices, which can imitate the accommodation reflex and pupillary light reflex of the eye. [ABSTRACT FROM AUTHOR]

Measurement of three-dimensional temperature field of a flame plays a significant role in in-depth insight into combustion process. This paper proposes a novel optical sectioning tomography for the measurement of three-dimensional temperature of flame through a single camera in combination with an ionic electrowetting-based variable focus liquid lens. Firstly, the optical sectioning imaging principle is introduced based on a variable focus liquid lens. Secondly, the calibration works are carried out on a liquid lens-based optical sectioning tomography system for three-dimensional flame temperature measurement to determine the relationship between the working voltages of the liquid lens and its focal planes in combination with entropy function. Further Gaussian model is taken as the defocused model to calibrate the point spread function of the system through edge method, and the CCD sensor is calibrated by a black body furnace to find out the relationship between the image gray and the received radiation energy. The reconstruction algorithms for three-dimensional flame luminosity distribution of the combustion flame are also developed. Finally experimental works are undertaken to evaluate the optical sectioning tomography system. Preliminary experimental results on an ethylene-air co-flow burner verified the feasibility of the optical sectioning tomography for the three-dimensional temperature distribution of a diffusion flame. The developed optical sectioning tomography system is capable of characterizing the structure and combustion characteristics of the diffusion flame. [ABSTRACT FROM AUTHOR]

We present a tunable, membrane-less, mechanical-wetting liquid lens that can be actuated manually using a linear actuator such as screw or piston. The operation of the liquid lens is based on deforming the interface separating two immiscible liquids with different refractive indices, while pinning the three-phase contact line at the sharp edge of lens aperture. Our lens design improves upon the existing designs of mechanical-wetting lenses by eliminating the use of complex actuation mechanisms, without compromising on the optical performance. We demonstrate the operation of the liquid lens by tuning its power back and forth from negative to positive by simple rotation of a screw. We also present an analytical description of the focal length of the lens and validate it with detailed experimental measurements. Our experiments show that the focal length of the liquid lens can be tuned repeatably without any adverse effects of hysteresis and gravity. [ABSTRACT FROM AUTHOR]

A novel depth from defocus (DFD) measurement system is presented, where the extension of the measurement range is performed using an emergent technology based on liquid lenses. A suitable set of different focal lengths, obtained by properly changing the liquid lens supply voltage, provides multiple camera settings without duplicating the system elements or using moving parts. A simple and compact setup, with a single camera/illuminator coaxial assembly, is obtained. The measurement is based on an active DFD technique using modulation measurement profilometry for the estimation of the contrast at each image point as a function of the depth range. Two different measurement methods are proposed, both based on a combination of multiple contrast curves, each derived at a specific focal length. In the first method (intensity contrast method), the depth information is recovered directly from the contrast curves, whereas in the second (differential contrast method), the depth is measured using contrast curve pairs. We obtained a measurement $\sigma _{{{0}}}$ of 0.55 mm over a depth range of 60 mm with the intensity contrast method (0.92% of the total range) and an $\sigma _{{{0}}}$ of 0.76 mm over a depth range of 135 mm with the differential contrast method (0.56% of the total range). Thus, the intensity contrast method is within the state-of-the-art DFD systems, whereas the differential contrast method allows, $\sigma _{{{0}}}$ being almost equal, a remarkable extension of the depth range. [ABSTRACT FROM AUTHOR]

A dual-beam laser autofocusing system is designed in this paper. The autofocusing system is based on a liquid lens with less moving parts and fast response time, which makes the system simple, reliable, compact and fast. A novel scheme “Time-sharing focus, fast conversion” is innovatively proposed. The scheme effectively solves the problem that the guiding laser and the working laser cannot focus at the same target point because of the existence of chromatic aberration. This scheme not only makes both guiding laser and working laser achieve optimal focusing in guiding stage and working stage respectively, but also greatly reduces the system complexity and simplifies the focusing process as well as makes autofocusing time of the working laser reduce to about 10 ms. In the distance range of 1 m to 30 m, the autofocusing spot size is kept under 4.3 mm at 30 m and just 0.18 mm at 1 m. The spot size is much less influenced by the target distance compared with the collimated laser with a micro divergence angle for its self-adaptivity. The dual-beam laser autofocusing system based on liquid lens is fully automatic, compact and efficient. It is fully meet the need of dynamicity and adaptivity and it will play an important role in a number of long-range control applications. [ABSTRACT FROM AUTHOR]

We proposed a method to create a tunable-focus cylindrical liquid lens using a liquid bridge between two narrow surfaces. Due to the surface edge effect, the interface of the liquid bridge (on the long side) was shown to be able to serve as a tunable-focus cylindrical liquid lens. The working distance of the lens can be adjusted by changing either or both of the height of the bridge (H) and the volume of the liquid (V). By varying H and V, the lens can serve as either diverging or converging lens, with a minimum working distance of 2.11 mm. [ABSTRACT FROM AUTHOR]

Insulating materials from the parylene family were investigated for use in low-power-consumption electrowetting-based liquid lenses. It was shown that for DC-driven operations, parylene C leads to hysteresis, regardless of the presence of a hydrophobic top coat. This hysteresis was attributed to the non-negligible time needed to reach a stable contact angle, due to charge injection and finite conductivity of the material. It was further demonstrated that by using materials with better insulating properties, such as parylene HT and VT4, satisfactory results can be obtained under DC voltages, reaching a low contact angle hysteresis of below 0.2°. We propose a simplified model that takes into account the injection of charges from both sides of the insulating material (the liquid side and the electrode side), showing that electrowetting response can be both increased and decreased. [ABSTRACT FROM AUTHOR]

The occurrence of freshwater lenses in saline aquifers adjoining gaining rivers has recently been demonstrated as being theoretically possible by way of analytical solution. However, physical evidence for freshwater lenses near gaining rivers is limited largely to airborne geophysical surveys. This paper presents the first direct observations of freshwater lenses adjacent to gaining rivers, albeit at the laboratory-scale, as validation of their plausibility. The experimental conditions are consistent with the available analytical solution, which is compared with laboratory observations of lens extent and the saltwater flow rate, for various hydraulic gradients. Numerical simulation shows that dispersion can account for the small amount of mismatch between the sharp-interface analytical solution and laboratory measurements. Calibration and uncertainty analysis demonstrate that accurate mathematical predictions require calibration to laboratory measurements of the lens. The results provide unequivocal proof that freshwater lenses can persist despite gaining river conditions concordant with theoretical lenses predicted by the analytical solution, at least within the constraints of the experimental setup. [ABSTRACT FROM AUTHOR]

In this paper, we design, fabricate and characterize a new electromagnetically actuated variable-focus liquid lens which consists of two polymethyl methacrylate (PMMA) substrates, a SU-8 substrate, a polydimethylsiloxane (PDMS) membrane, a permanent magnet and a planar electromagnetic actuator. The performance of this liquid lens is tested from four aspects including surface profiling, optical observation, variation of focal length and dynamic response speed. The results shows that with increasing current, the optical chamber PDMS membrane bulges up into a shape with a smaller radius of curvature, and the picture recorded by a charge-coupled device (CCD) camera through the liquid lens also gradually becomes blurred. As the current changes from −1 to 1.2 A, the whole measured focal length of the proposed liquid lens ranges from −133 to −390 mm and from 389 to 61 mm. Then a 0.8 A square-wave current is applied to the electrode, and the actuation time and relaxation time are 340 and 460 ms, respectively. The liquid lens proposed in the paper is easily integrated with microfluidic chips and medical detecting instruments due to its planar structure. [ABSTRACT FROM AUTHOR]

The evaporation behavior of toluene and hexane lenses on the surface of deionized (DI) water is studied. The toluene and hexane lenses during evaporation experience an advancing stage and a receding stage. There exists a significant difference of the evaporation behavior between the toluene lenses and the hexane lenses. The lifetime and largest diameter of both the toluene and hexane lenses increase with increasing the initial volume of the lenses. For the evaporation of the toluene lenses, the lifetime and largest diameter of the lenses decrease with increasing the temperature of DI water. The effect of the residual of the oil molecules on the evaporation of toluene lenses at a temperature of 21 °C is investigated via the evaporation of a series of consecutive toluene lenses being placed on the same position of the surface of DI water. The temporal evolution of the toluene lenses placed after the first toluene lens deviates significantly from that of the first toluene lens. Significant increase of the receding speed occurs at the dimensionless time in a range 0.7-0.8. [ABSTRACT FROM AUTHOR]

A low voltage driven electrowetting on dielectric liquid focus lens was fabricated based on a tiny glass tube which had been coated with ITO (indium tin oxide)–Al 2 O 3 –TiO 2 –Teflon multilayered thin films on the inside. Method of sol–gel/chemical solution dip coating was used for the film preparation. A cambered interface between silicon oil and aqueous solution containing NaCl and sodium dodecyl sulfate (SDS) was used for the lens refraction. The curvature of the interface was adjusted by changing the applied voltage. The contact angle of aqueous solution in oil atmosphere was reduced from 155° to 67° when − 10 V DC was applied. The leakage current was only 28 nA at that applied voltage and its focal length changed from − 2 mm to infinity then to 10 mm. [ABSTRACT FROM AUTHOR]

Optofluidics is a rapidly growing versatile branch of adaptive optics including a wide variety of applications such as tunable beam shaping tools, mirrors, apertures, and lenses. In this review, we focus on recent developments in optofluidic lenses, which arguably forms the most important part of optofluidics devices. We report first on a number of general characteristics and characterization methods for optofluidics lenses and their optical performance, including aberrations and their description in terms of Zernike polynomials. Subsequently, we discuss examples of actuation methods separately for spherical optofluidic lenses and for more recent tunable aspherical lenses. Advantages and disadvantages of various actuation schemes are presented, focusing in particular on electrowetting-driven lenses and pressure-driven liquid lenses that are covered by elastomeric sheets. We discuss in particular the opportunities for detailed aberration control by using either finely controlled electric fields or specifically designed elastomeric lenses. [ABSTRACT FROM AUTHOR]

Motivated by contaminant remediation, we study the volume of oil (oleic acid) removed from a liquid lens by a falling particle. When a spherical particle is dropped from a fixed height into an oil lens that floats on top of a water surface, a portion of the oil adheres to the sphere. Once the sphere comes to rest at the subsurface, the oil forms an equilibrium pendant drop that remains attached to the sphere. We find in experiments with spheres of different sizes and materials, that the pendant drop volume is an increasing function of sphere mass for each material and a decreasing function of sphere density. By contrast, the normalized droplet volume in all of our experiments scales with sphere mass following V oil / V sphere ∼ M −0.544 . Thus, for a given size, lighter spheres capture more oil relative to their own volume than do heavier spheres and are more efficient at removing oil from a water surface in our experiments. Estimates for the upper bound of the normalized droplet volume, determined from the continuous family of solutions of the Young–Laplace equation, show the same qualitative dependence on the sphere mass. [ABSTRACT FROM AUTHOR]

In this paper, a relatively fast-response liquid crystal (LC) lens was proposed, which was fabricated by a simple method. Multi-walled carbon nanotubes (MWCNTs) were utilized in fabricating the LC lens. As MWCNTs were doped into the LCs, the dielectric anisotropy of the mixture changed, which was the key factor in solving the technical barrier of slow response time. In experiments, the effects of doping with MWCNTs were demonstrated. The concentration of doped MWCNTs was discussed in detail, and the best concentration and doping method were analyzed. The relationship between the concentration and response time was also obtained. This LC lens had a sub-millisecond response time, which was a relatively fast response time in comparison to conventional LC lenses of pristine LCs. Thus, this proposed method could be considered as a new method to realize fast-response LC lens. [ABSTRACT FROM AUTHOR]

In this paper, a new kind of electrically controlled liquid crystal lens, which respond in a relatively fast time, is presented. The multiwalled carbon nanotubes are doped into liquid crystal to fabricate the liquid crystal lens. As 0.02 % concentration of multiwalled carbon nanotubes is uniformly distributed in the liquid crystal, the optical features of the liquid crystal lens are obviously improved. The liquid crystal lens with a diameter of 2.0 mm was fabricated with about 0.2 s response time and less than 5 Vrms applied voltage. The focal length can vary from 16 to 510 mm, and the operation voltage changes from 1.0 to 5.5 Vrms. This liquid crystal lens has the very attractive feature of submillisecond response time, which is a much faster response time in comparison with conventional liquid crystal lens. Thus, this kind of liquid crystal lens has high potential for implementation in many practical imaging applications and imaging commercialisation. [ABSTRACT FROM AUTHOR]

This paper presents a new design of tunable liquid lens. The lens was operated by electromagnetic actuation for autofocusing (AF) in miniature cameras and its optical performance was experimentally verified. An electrical voltage was applied to an electric coil inside an electromagnetic system beneath the liquid lens to generate a magnetic field around the electromagnetic system according to Faraday’s law of induction. The magnetic field was used to actuate a ring-type neodymium magnet placed on the top of an elastic membrane in the liquid lens. The sag (sagittal) height of the liquid lens was measured as a function of the applied voltage. The sag height of the lens increased linearly from −1 mm to 0.8 mm when the applied voltage was changed from 0 V to 50 V at 5 V increments. The average variation of the sag height per volt was about 32 μm. The focal length was also measured with respect to the applied voltage by using a custom-built testing system consisting of a laser, mirror, liquid lens, and detection screen. The measured focal length values were compared with the theoretical ones. For imaging tests, a single-object focusing test was first performed by using a sheet of paper with a check pattern. Furthermore, the ability of the liquid lens to distinguish two objects positioned at different distances by changing its focal plane was successfully tested. Finally, the response times of the liquid lens for actuation and relaxation were measured by a high-speed camera and were found to be about 900 ms. [ABSTRACT FROM AUTHOR]

This paper presents, for the first time, versatile and low-cost miniature liquid lenses with graphene as electrodes. Tunable focal length is achieved by changing the droplet curvature using electrowetting on dielectric (EWOD). Ionic liquid and KCl solution are utilized as lens liquid on the top of a flexible Teflon-coated PDMS/parylene membrane. Transparent and flexible, graphene allows transmission of visible light as well as large deformation of the polymer membrane to achieve requirements for different lens designs and to increase the field of view without damaging of electrodes. The tunable range for the focal length is between 3 and 7 mm for a droplet with a volume of 3 μL. The visualization of bone marrow dendritic cells is demonstrated by the liquid lens system with a high resolution (456 lp/mm). [ABSTRACT FROM AUTHOR]

When a liquid droplet is filled in the hole of a dielectric elastomer (DE) film, a liquid lens is prepared. By applying a DC voltage to the DE film, the liquid lens can be actuated. As a comparison, two liquid lenses, one in a millimeter scale and the other in a submillimeter scale, are demonstrated. In a relaxed state, the focal length of each liquid lens is the longest. In an actuated state, the diameter of each lens is reduced. As a result, their focal length is tuned. Here, the DE film functions as an actuator. Due to the biconvex shape and smooth liquid surface, each liquid lens can provide good optical performance. They also possess the merits of simple fabrication, compact structure, and easy operation. In contrast to the bigger liquid lens, the smaller one can present a better mechanical stability without the concern of the gravitational effect. [ABSTRACT FROM AUTHOR]

A four-group stabilized zoom system using two liquid lenses and two fixed lens groups is proposed. We describe the design principle, realization, and the testing of a 5.06:1 zoom system. The realized effective focal length (EFL) range is 6.93 mm to 35.06 mm, and the field of view (FOV) range is 8° to 40°. The system can zoom fast when liquid lens 1's (L1's) optical power take the value from 0.0087 mm-1 to 0.0192 mm-1 and liquid lens 2's (L2's) optical power take the value from 0.0185 mm-1 to-0.01 mm-1. Response time of the realized zoom system was less than 2.5 ms, and the settling time was less than 15 ms.The analysis of elements' parameters and the measurement of lens performance not only verify the design principle further, but also show the zooming process by the use of two liquid lenses. The system is useful for motion carriers e.g., robot, ground vehicle, and unmanned aerial vehicles considering that it is fast, reliable, and miniature. [ABSTRACT FROM AUTHOR]

A dielectric liquid lens is prepared based on our previous work. By optimizing the device structure, the liquid lens presents a converging focus with good resolution and changes its focal length over a broad range with a low driving voltage. For a liquid lens with ~2.3 mm diameter in the relaxed state, it can resolve ~40 1p/mm. The resolution does not degrade during focus change. Its focal length can be varied from ~12 to ~5 mm when the applied voltage is changed from 0 to 28 Vrms. The response time of one cycle is 22.5 s. Our liquid lens, with a low driving voltage for a large dynamic range, has potential applications in imaging, biometrics, optoelectronic, and lab-on-chip devices. [ABSTRACT FROM AUTHOR]

One specific kind of electrically tunable lenses is utilizing curvature change via adjusting input currents which electromagnetically exerts pressure on liquid volume to achieve variable-focusing properties. Nevertheless, the nature of curvature change and refractive index mismatch causes inherent spatial aberrations that severely degrade image quality. The novelty of the presented method lies in the experimental study of optical aberrations, such as root mean square (RMS), Strehl ratio and Zernike coefficients induced from electrically tunable lenses and use of adaptive optics to compensate for the wavefront errors. The optical properties of electrically tunable lens are quantitatively characterized by Shack – Hartmann measurements. Adaptive optics-based scheme is demonstrated for the current range 78–95 mA, resulting in a substantial reduction of the wavefront errors from 0.55, 0.53 to 0.22, 0.2 μm, respectively, corresponding to the focal power tunability of −2.52 to 0.2 diopters. It is experimentally showed that defocus ( Z 5 ) aberration is the most significant one since the changes of lens curvature varies in proportional with changing currents, and can be significantly improved from 0.328 μm to 0.156 μm with adaptive optics. Similar improvements can be found in piston ( Z 1 )/tip ( Z 2 )/tilt ( Z 3 ) aberrations with the integration of adaptive optics. [ABSTRACT FROM AUTHOR]