Liquid Lens Research Articles

Ultracompact optical microscopes made of liquid crystal Pancharatnam–Berry optical elements

Ultracompact optical systems are increasingly sought after for applications such as consumer electronics and medical imaging. Here, we present a design and manufacturing approach for ultracompact bright- and dark-field optical microscopes entirely made of flat liquid crystal optical elements. Both systems utilize liquid crystal PB lenses as objective and tube lenses, while the dark-field optical microscope incorporates an additional Q-plate with a +1 topological defect to filter zero-order light. We demonstrate two optical microscopic systems with a numerical aperture of 0.25 and overall thickness of just 5 mm. The system can achieve high imaging performance with a resolution better than 7 µm. We further demonstrate an exemplary application in biological imaging to effectively enhance edge contrast in imaging onion epidermal cells. This work presents an example in exploiting the flatness and high quality of liquid crystal optical elements to achieve compactness and high-quality imaging promising for various applications.

Electrowetting lens based on a conical aluminum cavity

A tunable liquid lens based on the electrowetting-on-dielectric effect is demonstrated using a machined aluminum substrate. A metallic substrate eliminates the need for deposited electrodes inside the droplet cavity and simplifies the fabrication procedures required to produce an electrowetting optic. Sloped sidewalls at 45° produce a large optical tuning range, with back focal length tuning from [−134, −18.5 mm] and [+11.3, +134 mm]. An input-shaped overdriven actuation voltage yields a response time of 149 ms. The aluminum substrate is machined using standard processes that allow the device geometry to be customized. A complete lens package is sealed with fluoroelastomer O-rings, enabling applications beyond the laboratory environment.

Tunable Lens Driven by Electrohydrodynamic Pumping

Developing soft actuators has emerged as one of the most promising areas in robotics, with a growing demand for tunable lenses driven by the rapid advancements in intelligent mobile devices and cameras. Traditional mechanical lens systems are characterized by their heaviness, complexity, and rigidity. To address these limitations, this research introduces a novel approach: a dual‐chamber liquid lens actuated by an electrohydrodynamic (EHD) pump. The study involves the fabrication of a planar EHD pump, with an experimental investigation into the impact of electrode gap, electrode width, and electrode‐pair gap on the pump's pressure. Following the optimization of the EHD pump, a dual‐chamber lens is constructed, comprising two chambers, a rigid transparent plate, and two prestretched elastic membranes, which are connected to the EHD pump via tubes. Additionally, a mathematical model is developed to predict the focal length of the lens. Both experimental and theoretical analyses are conducted to explore the effects of the prestretch ratio of the elastic membranes and the radius ratio of the two chambers on focal length variation. The theoretical predictions of the focal length–voltage curves align closely with the experimental findings, providing validation for the proposed theoretical model.

Simulation and experimental analysis of a double-liquid negative lens based on flat electrode

In order to carry out detailed research on focusing of liquid lens in negative optical power with simple structure, a double-liquid negative lens based on flat electrode is proposed. By adjusting voltage applied to indium tin oxide (ITO) conductive glass plates, the interface between glycerol and silicone oil can be changed to tune the focal length. With COMSOL, MATLAB and Zemax softwares, an optical model of the double-liquid negative lens based on flat electrode is established, its focal length at different voltages is simulated and analyzed, and it is found that when the flat exists with a small tilt (1°∼4°), the parallelism of the flat electrode has little influence on the focal length. In addition, through device fabrication and experimental analysis of this double-liquid negative lens, the focal length of the lens changes from -40.21622 mm to -24.2088 mm when operating voltage is 0V-320 V, which is basically consistent with the simulation results. And the maximum resolution of the proposed liquid lens can reach 71.838lp/mm. A lens with negative focal length holds great promise in diverse applications such as endoscopes, holographic imaging and adaptive optics.

Design and analysis of the liquid lens system for bionic human eye imaging

In this paper, the liquid lens system for bionic human eye imaging is designed based on the principles of dielectrophoretic drive and hydraulic drive. The core part of this lens system is the biconvex liquid lens of the bionic human eye crystalline lens. Based on this part, a PDMS membrane liquid lens module and a liquid chamber are added, which are combined with the biconvex liquid lens to form a structure that can be used to represent the cornea, the anterior chamber, the vitreous body and other parts of the human eye. It is a combined structural design to realize the whole human eye liquid lens system. The design of the system model and the analysis of ray tracing are mainly accomplished with COMSOL software, and the experimental research of the system is carried out. The whole liquid lens device for the bionic human eye is fabricated; its zoom characteristics and imaging resolution are measured at fixed volumes of liquid injection with different voltages and at fixed voltages with different volumes of liquid injection, respectively. The results show that the zoom range of the liquid lens system for bionic human eye imaging is 24.81mm-13.07 mm, which can reflect the zoom characteristics of general human eyes, and its imaging resolution can reach a maximum of 90.51lp/mm.

Polyelectrolyte mixture enables electrowetting liquid lens with large optical power tuning range

Electrowetting liquid lenses have aroused considerable interest among researchers in a variety of industrial applications and wetting sciences. However, conventional electrowetting liquid lenses face significant limitations in their optical power tuning range due to contact angle saturation. To address this issue, our research introduces a polyelectrolyte mixture (PM) composed of ammonium polyphosphate and potassium chloride, which enables a broad optical power tuning range for electrowetting liquid lenses. Through a comprehensive analysis involving viscosity, Raman spectrum, and contact angle measurements, we offer additional insights into the interdisciplinary mechanism of the PM in enhancing the electrowetting effect. Our investigation elucidates how the conformation of the polyelectrolyte and the formation of hydrogen bonds at varying concentrations can impact the electrowetting gain. By optimizing the electrowetting concentration of the PM (12.5 wt. % ammonium polyphosphate and 7.5 wt. % potassium chloride), we achieve a liquid lens with an extensive tuning range (−37.97 to +18.71 D) at 0–45 V, featuring a substantial aperture (6.4 mm) and a low threshold voltage (10 V). This PM formulation effectively mitigates contact angle saturation, thereby offering promising applications and paving the way for the development of liquid lenses with a significantly enhanced optical power tuning capacity.

Three-dimensional lattice Boltzmann flux solver for three-phase/component flow

In this article, an immiscible three-phase/three-component lattice Boltzmann flux solver (TPLBFS) based on diffusion interface method is proposed, which can achieve three-phase flow simulation with high density ratio (1:1000). This model quickly solved (1) the flux at the grid interface using the lattice Boltzmann method (LBM) solution format and (2) the Navier–Stokes (NS) equation and Cahn–Hilliard (CH) equation using a unified format. Compared to LBM, TPLBFS can be applied to unstructured networks. Moreover, TPLBFS can independently add or remove source items and has high secondary development features. Its outstanding computing power has been demonstrated by multiple two-dimensional/three-dimensional (2D/3D) examples, including 2D liquid lens as well as 3D bubble absorption and bubble rising in a three-phase system.

Optofluidic phase modulator based on electrowetting liquid lens

In this paper, a liquid optical phase modulator modified from a cylindrical two-liquid electrowetting liquid lens is presented. A movable optical plane is constructed by fixing a transparent sheet between two immiscible liquids. By using the electrowetting effect to flatten the optical plane along the through-light direction, the length ratio of the two liquids in the through-light direction can be fine-tuned to modify the optical path to realize phase modulation. To validate this concept, we experimentally fabricated a prototype phase modulator and tested its phase modulation capability. Experiments show that the phase shift range can be up to 5.82 π and the phase shift accuracy can be up to λ/60, a drive time of 72 ms and a relaxation time of 34 ms within the range of applied voltage 40–80 V DC voltage.

Investigation on liquid medium integration for piezoelectric MEMS tunable liquid lenses

In this paper, the design, fabrication and evaluation of a novel piezoelectric MEMS varifocal liquid lens are presented. The device consists of a thin film PZT actuator integrated with a liquid lens, featuring a new design with a modified disk-shaped actuator that enhances the overall displacement range. The primary innovation lies in simplifying the assembly process between the liquid/soft lens and the piezoelectric actuator, eliminating the need for vacuum bonding. Two types of liquid/soft lens materials, ionic gel and silicone oil, were investigated in different integration configurations to find the most suitable method. Analytical calculations and FEM simulations were conducted to optimize the actuator’s maximum displacement, which in turn maximizes the change in the device’s focal length. The developed actuator achieved around 15 µm of static displacement under a 40 V DC applied voltage, which matched well with simulation results. The shifting of the focus was clearly observed through a microscope, with the focal length estimated to change from infinity to about 31.6 mm at 35 V DC.

Design and fabrication of a large-aperture electrowetting liquid zoom system

In this paper, a continuous zoom system based on large-aperture electrowetting liquid lenses is designed and fabricated. The inner diameter of the electrowetting lens is up to 20 mm, which can tune stably from a focal length of −328.49mm to −∞ with applied voltages of 0 to 115 V. The zoom system mainly consists of two large-aperture electrowetting liquid lenses and a glass lens, getting continuous zoom images by adjusting the voltages applied to the two liquid lenses without any mechanical movement, ensuring a more compact structure than conventional zoom systems. The theoretical formulas of the zoom ratio and image plane stability condition for this optical system are systematically derived based on the matrix optics, laying the foundation for guiding system regulation and finding methods to improve zoom ratio, and corresponding influence factors on the zoom ratio are verified by experiments. The system zoom ratio can reach 1.52 at a fixed working distance, close to the theoretical derivation result. The system is expected to be used for imaging in a variety of scenarios, such as special photography, dynamic measurement, etc.

High-speed all-in-focus 3D imaging method based on liquid lens focus scanning

A large open aperture in an optical system can capture high-resolution images but yields a shallow depth of field. To overcome this issue, we propose a method for retrofitting microscopy imaging systems by using a variable-focus liquid lens to achieve 3D focus scanning. Specifically, the focal length of the imaging system was changed by controlling the liquid lens, and a sequence of images was captured at different focal planes in milliseconds. The image scale and phase were corrected. Then the in-focus pixels were abstracted by employing the Laplacian operator. These pixels were marked in the index table. According to the index table, the focused parts of multiple images were merged, and an all-in-focus image was generated. At the same time, a depth map was constructed based on the image number in the index table and the extracted depth information. Additionally, we have optimized the image processing flow; the processing speed was improved to around 6.5 fps.

FOV adjustable liquid lens driven by electrowetting effect.

In this paper, a FOV (field of view) adjustable liquid lens driven by electrowetting effect is demonstrated. The proposed lens consists of a window glass, a bottom electrode, four sidewall electrodes, two supporting shafts, and a deflectable aperture. The deflectable aperture is nested on the supporting shafts between the two liquids to limit the position of the liquid-liquid (L-L) interface. Different from the conventional FOV adjustable liquid lenses, the proposed lens can realize focal length adjustment and FOV deflection by applying voltages to the four sidewall electrodes, which has a simple structure and a miniaturized drive. The experiment shows that the aperture of the lens is 9 mm, the optical power range is -21 m-1 to -7 m-1 and the tilt angle of the L-L surface is ∼ 18° (± 9°). With a compact structure and easy drive, the proposed lens has great potential for applications in scanning, imaging, and inspection.

Large cell lymphoma through a liquid lens.

Liquid biopsy to provide a mutational snapshot of diffuse large B-cell lymphoma is an emerging technology of exciting potential utility. The report by Alcoceba etal. assesses the tractability of the EuroClonality-NDC assay to profile lymphoma using cell-free DNA and highlights the prognostic implication of attaining a major molecular response to therapy. Commentary on: Alcoceba etal. Liquid biopsy for molecular characterization of diffuse large B-cell lymphoma and early assessment of minimal residual disease. Br J Haematol 2024;205:109-121.

High-Magnification Object Tracking with Ultra-Fast View Adjustment and Continuous Autofocus Based on Dynamic-Range Focal Sweep.

Active vision systems (AVSs) have been widely used to obtain high-resolution images of objects of interest. However, tracking small objects in high-magnification scenes is challenging due to shallow depth of field (DoF) and narrow field of view (FoV). To address this, we introduce a novel high-speed AVS with a continuous autofocus (C-AF) approach based on dynamic-range focal sweep and a high-frame-rate (HFR) frame-by-frame tracking pipeline. Our AVS leverages an ultra-fast pan-tilt mechanism based on a Galvano mirror, enabling high-frequency view direction adjustment. Specifically, the proposed C-AF approach uses a 500 fps high-speed camera and a focus-tunable liquid lens operating at a sine wave, providing a 50 Hz focal sweep around the object's optimal focus. During each focal sweep, 10 images with varying focuses are captured, and the one with the highest focus value is selected, resulting in a stable output of well-focused images at 50 fps. Simultaneously, the object's depth is measured using the depth-from-focus (DFF) technique, allowing dynamic adjustment of the focal sweep range. Importantly, because the remaining images are only slightly less focused, all 500 fps images can be utilized for object tracking. The proposed tracking pipeline combines deep-learning-based object detection, K-means color clustering, and HFR tracking based on color filtering, achieving 500 fps frame-by-frame tracking. Experimental results demonstrate the effectiveness of the proposed C-AF approach and the advanced capabilities of the high-speed AVS for magnified object tracking.

Interference Mitigation in VLC Systems using a Variable Focus Liquid Lens

Interference Mitigation in VLC Systems using a Variable Focus Liquid Lens

Performance analysis of a liquid lens for laser ablation using OCT imaging

Laser ablation has been used in different surgical procedures to perform precise treatments. Compared with previous free-beam laser delivery systems, flexible-optical-fiber-based systems can deliver laser energy to a curved space, avoiding the requirement of a straight working path to the target. However, the fiber tip maintains direct contact with the tissue to prevent laser divergence, resulting in fiber damage, uneven ablation, and tissue carbonization. Here, a liquid lens is used to address the problem of laser defocusing when radiating targets at different depths for flexible-optical-fiber-based systems. The liquid lens focuses a laser with a maximum power of 3 W onto a medium-density fiberboard at a focal length of 40–180 mm. The relationships between the ablation crater diameter and depth with the radiation time and laser power have been quantitatively evaluated through OCT (optical coherence tomography) imaging. Experiments demonstrate that the liquid lens can continuously focus the high-power laser to different depths, with the advantages of compact size, fast response, light weight, and easy operation. This study explores liquid-lens-based focused laser ablation, which can potentially improve the performance of future medical image-guided laser ablation.

Measurement method of virtual image distance for a head-mounted display based on a variable-focus liquid lens

The distance from the virtual image to the human eye is an important factor in measuring the comfort of a head-mounted display (HMD). However, accurately measuring their distance is challenging due to the dynamic changes in virtual presence and distance. In this paper, we proposed a virtual image distance measurement prototype based on a variable-focus liquid lens and derived a virtual image distance calculation model. We built a variable-focus liquid lens experimental platform to verify the method’s correctness. In addition, we proposed an improved optimization algorithm that can efficiently and accurately search for the optimal focal length corresponding to the maximum sharpness moment of the virtual image within the focal length value space. Verified in an experimental scene of 0.5 m to 3.5 m, we observed that the error between the object image distance and the virtual image distance at the same focal length is about 5 cm. The proposed virtual image distance measurement method can accurately measure the distance value of the virtual image in the HMD. This method can be widely used in virtual and augmented reality, especially in the task of constructing realistic scenes.

Tunable liquid lens for three-photon excitation microscopy

We demonstrate a novel electrowetting liquid combination using a room temperature ionic liquid (RTIL) and a nonpolar liquid, 1-phenyl-1-cyclohexene (PCH) suitable for focus-tunable 3-photon microscopy. We show that both liquids have over 90% transmission at 1300 nm over a 1.1 mm pathlength and an index of refraction contrast of 0.123. A lens using these liquids can be tuned from a contact angle of 133 to 48° with applied voltages of 0 and 60 V, respectively. Finally, a three-photon imaging system including an RTIL electrowetting lens was used to image a mouse brain slice. Axial scans taken with an electrowetting lens show excellent agreement with images acquired using a mechanically scanned objective.

Research on Monocular Depth Sensing Method Based on Liquid Zoom Imaging

Monocular stereo vision has excellent application prospects in the field of microrobots. On the basis of the geometric model of bifocal imaging, this paper proposes a monocular depth perception method by liquid zoom imaging. Firstly, the configuration of a monocular liquid vision system for depth measurement is presented, and the working mechanism of the system is analyzed through theoretical derivation. Then, to eliminate the influence of optical axis drift induced by the liquid gravity factor on the measurement results, the target image area is used as the calculation feature instead of the image vector length. A target area calculation method based on chain code classification and strip segmentation is proposed. Furthermore, in response to the fluctuation problem of liquid lens focal power caused by factors such as temperature and object distance, a dynamic focal length model of the liquid zoom imaging system is constructed after precise calibration of the focal power function. Finally, a testing experiment is designed to validate the proposed method. The experimental results show that the average error of depth perception methods is 4.30%, and its measurement time is only on the millisecond scale. Meanwhile, the proposed method has good generalization performance.

Continuous optical zoom telescopic system based on liquid lenses

Telescopes play an essential important role in the fields of astronomical observation, emergency rescue, etc. The traditional telescopes achieve zoom function through the mechanical movement of the solid lenses, usually requiring refocusing after magnification adjustment. Therefore, the traditional telescopes lack adaptability, port-ability and real-time capability. In this paper, a continuous optical zoom telescopic system based on liquid lenses is proposed. The main components of the system consist of an objective lens, an eyepiece, and a zoom group composed of six pieces of liquid lenses. By adjusting the external voltages on the liquid lenses, the zoom telescopic system can achieve continuous optical zoom from ∼1.0× to ∼4.0× operating with an angular resolution from 28.648" to 19.098", and the magnification switching time is ∼50ms. The optical structure of the zoom telescopic system with excellent performance is given, and its feasibility is demonstrated by simulations and experiments. The proposed system with fast response, portability and high adaptability is expected to be applied to astronomical observation, emergency rescue and so on.