Liquid Lens Research Articles

Liquid crystal lens array based on polymer protrusion

Liquid crystal lens array based on polymer protrusion

Simulation of adjustable even aspheric liquid lens and zoom optical system

Simulation of adjustable even aspheric liquid lens and zoom optical system

Deep Reinforcement Learning Based System for Intraoperative Hyperspectral Video Autofocusing.

Hyperspectral imaging (HSI) captures a greater level of spectral detail than traditional optical imaging, making it a potentially valuable intraoperative tool when precise tissue differentiation is essential. Hardware limitations of current optical systems used for handheld realtime video HSI result in a limited focal depth, thereby posing usability issues for integration of the technology into the operating room. This work integrates a focus-tunable liquid lens into a video HSI exoscope, and proposes novel video autofocusing methods based on deep reinforcement learning. A first-of-its-kind robotic focal-time scan was performed to create a realistic and reproducible testing dataset. We benchmarked our proposed autofocus algorithm against traditional policies, and found our novel approach to perform significantly (p < 0.05) better than traditional techniques (0.070 ±.098 mean absolute focal error compared to 0.146 ±.148). In addition, we performed a blinded usability trial by having two neurosurgeons compare the system with different autofocus policies, and found our novel approach to be the most favourable, making our system a desirable addition for intraoperative HSI.

Measurement and Analysis of Transient Process of Electrowetting Liquid Lens

Measurement and Analysis of Transient Process of Electrowetting Liquid Lens

Design and Analysis of Aspheric Liquid Lens with Square Cavity Structure

Design and Analysis of Aspheric Liquid Lens with Square Cavity Structure

Axisymmetric lattice Boltzmann model for three-phase fluids and its application to the Rayleigh-Plateau instability

Based on the multi-component phase field theory, in this paper we propose an axisymmetric lattice Boltzmann model for three-phase fluids. The proposed model takes advantage of two particle distribution functions for capturing phase interface among three different fluids, and another particle distribution function for solving the hydrodynamic equations for flow field. In order to describe the axisymmetric effect arising from the coordinate transformation, we elaborately design the equilibrium distribution function and forcing distribution function in the evolution equation, which ensures that the model can accurately recover the macroscopic governing equation for three-phase fluids. Also, the introduced source terms accounting for the axisymmetric effect contain no additional gradient term, which makes it be simpler than the existing lattice Boltzmann model for axisymmetric three-phase fluids. To validate the proposed model, a series of axisymmetric multiphase benchmark examples are performed, including the static double droplets, the spreading of liquid lens, and the binary-fluid Rayleigh-Plateau instability. It is reported that the present model can accurately capture the phase interface, and the predicted steady shapes of the liquid lens agree well with the analytical profiles. Then, the proposed model is used to study the three-phase Rayleigh-Plateau instability and the effects of the wavenumber and the radius ratio of liquid column on the interfacial dynamic behaviour, the breakup time of liquid threads and the size of daughter droplet are investigated in detail. It can be found that the compound liquid thread at a high wavenumber could break up into one main droplet and one satellite droplet, but the multiple satellite droplets can be produced at a low wavenumber, which leads to that the sizes of main and satellite droplets increase with the wavenumber at first and then decrease with it. Besides, we can observe that the inner fluid undergoes the breakup at earlier time than the middle fluid, and the breakup time for both inner and middle fluids increases with the decrease of the wavenumber. Finally, we can find that increasing the radius ratio of liquid column accelerates the breakup of inner-fluid thread, but prevents the breakup of the middle-fluid thread. In addition, the size of the compound main droplet increases with the radius ratio of liquid column, while the size of the compound satellite droplet doest not change much with it.

Zoom liquid lens with switchable aperture

A zoom liquid lens with switchable aperture is demonstrated in this paper, which consists of a lens chamber, a circular truncated cone, a limit ring and two immiscible liquids. Different from conventional zoom liquid lenses, the curvature of the liquid-liquid (L-L) interface, the position of the L-L interface and the aperture size of the proposed liquid lens can be tuned by only one actuator. Then, two problems can be solved: a larger range of optical power is realized by the switchable size of the aperture, and the zoom function can be achieved by switchable position of the aperture. Thus, the proposed zoom lens has characteristics of large optical power tunable range and excellent zoom ability with only one actuator. However, due to a single actuator, the curvature, position and aperture of the proposed lens cannot be controlled arbitrarily and individually. With a large aperture of 10 mm and a small aperture of 5 mm, the range of optical power is -43 m−1 ∼ +43 m−1, the zoom ratio reaches ∼2 × and the angular resolution is 27"7. It is promising to promote the development of a new generation of miniaturized optofluidic imaging systems.

Design of Tunable Liquid Crystal Lenses with a Parabolic Phase Profile

An electrode pattern design generating a parabolic voltage distribution, in combination with usage of the linear response range of the liquid crystal (LC) material, has been recently proposed to obtain nearly ideal phase profiles for LC lenses. This technique features low driving voltages, simple structure, compact design, and the absence of high-resistivity (HR) layers. In this work, the universal design principle is discussed in detail, which is applicable not only to LC lens design, but also to other LC devices with any phase profile. Several electrode patterns are presented to form a parabolic voltage distribution. An equivalent electric circuit of the LC lens based on the design principle is developed, and the simulation results are given. In the experiments, an LC lens using the feasible parameters is prepared, and its high-quality performance is demonstrated.

Design and fabrication of a focus-tunable liquid cylindrical lens based on electrowetting.

In this study, a focus-tunable liquid cylindrical lens based on electrowetting was designed and fabricated. The cylindrical cavity usually used in common electrowetting zoom spherical lenses was replaced by a 20 mm × 10 mm × 8 mm cuboid cavity, in which the interface of two liquids formed a toroid owing to the electrowetting effect. The proposed liquid cylindrical lens can serve as either a converging or diverging lens with the response time under 110 ms by changing the supplied voltage. The zoom lens we fabricated worked stably under 0-110 V voltage for a long time, guaranteeing that the focal length of the liquid cylindrical lens can range within (-∞, -148.36 mm) ∪ (697.21 mm, +∞). By combining the liquid lens that we designed with a simple fixed cylindrical lens, a cylindrical lens system with an arbitrary focal length suitable for various tasks in beam manipulation can be realized.

Movable and Focus-Tunable Lens Based on Electrically Controllable Liquid: A Lattice Boltzmann Study.

Adjusting the focal length by changing the liquid interface of the liquid lens has become a potential method. In this paper, the lattice-Boltzmann-electrodynamic (LB-ED) method is used to numerically investigate the zooming process of a movable and focus-tunable electrowetting-on-dielectrics (EWOD) liquid lens by combining the LBM chemical potential model and the electrodynamic model. The LB method is used to solve the Navier-Stokes equation, and the Poisson-Boltzmann (PB) equation is introduced to solve the electric field distribution. The experimental results are consistent with the theoretical results of the Lippmann-Young equation. Through the simulation of a liquid lens zoom driven by EWOD, it is found that the lens changes from a convex lens to a concave lens with the voltage increases. The focal length change rate in the convex lens stage gradually increases with voltage. In the concave lens stage, the focal length change rate is opposite to that in the convex lens stage. During the zooming process, the low-viscosity liquid exhibits oscillation, and the high-viscosity liquid appears as overdamping. Additionally, methods were proposed to accelerate lens stabilization at low and high viscosities, achieving speed improvements of about 30% and 50%, respectively. Simulations of lens motion at different viscosities demonstrate that higher-viscosity liquids require higher voltages to achieve the same movement speed.

Wide field of view chiral imaging with a liquid crystal planar lens enabled by digitalized nanogratings.

To compensate for the inability for polarization imaging by conventional methods, metasurface optics with compactness and multi-function emerge as an approach to provide images with different linear and circular polarizations. Here, we propose a liquid crystal (LC) geometric phase-based chiral imaging lens (CIL) that simultaneously forms images of objects with opposite helicity. The CIL (Diameter 2.3 cm) was optimized by a spatial multiplexing algorithm and realized using the digital holography technique, where the LC domains were regulated by pixelated nanogratings with varied orientation. We investigated the potential of the patterning technique toward high order LC alignment by balancing the periodicity and depth of the nanogratings. The CIL exhibited a wide field of view of ±20°, which is attributed to the self- assembling effects of LC molecules. The compactness, lightness, and ability to produce chiral images of the LC CIL even at large angles have significant potential for practical polarization imaging.

A note on “Variable-focus liquid lens based on electrically responsive fluid”

A note on “Variable-focus liquid lens based on electrically responsive fluid”

Theoretical and Numerical Studies of Liquid Lens Evaporation with Coupled Fields

The evaporation of the liquid lens on an immiscible liquid is widely adopted in many industrial and scientific applications, so it is crucial to predict the evaporation rate and lifetime of the liquid lens. During the evaporation, the internal thermocapillary flow, external natural convection, and interfacial evaporative cooling are coupled together and affect the evaporation characteristics greatly. In this paper, the slow and fast evaporation with coupled fields are studied by theoretical analysis and numerical simulation, respectively. It is found that the evaporative cooling can always inhibit the liquid lens evaporation, while the thermocapillary flow and natural convection can enhance the liquid lens evaporation. The total evaporation rate is determined by the competence between the interfacial evaporative flux and upper surface of the liquid lens. With the increasing liquid lens volume, the total evaporation rate will generally increase for fast evaporation, while for slow evaporation that only considers the evaporative cooling effect, the total evaporation rate may decrease at a low tangential angle ratio. The evaporation of the liquid lens follows the constant contact angle mode, the transient variation of volume satisfies the “2/3 law”, independent of evaporative cooling, thermocapillary flow, and natural convection, and it is analogous to the sessile droplet evaporation in constant contact angle mode. These findings can provide guidance for the wide application of liquid lens evaporation.

Beam Steering and Divergence Control Using Variable Focus Liquid Lenses for WDM FSO Communications

Optical beam steering and divergence control is a critical function in free-space optical (FSO) communications. Variable focus liquid lenses (VFLLs) can be used for simultaneous realization of beam steering and adaptive beam divergence control. Two off-axis VFLLs are employed to steer the optical beam in 2 dimensional directions, while one on-axis VFLL adjusts the beam divergence adaptively to channel conditions. This VFLL-based system has been studied only for single-wavelength FSO communications. In this letter, we explore the possibility of using the VFLL-based system for wavelength-division-multiplexed (WDM) FSO communications. For this purpose, we investigate the wavelength dependence of VFLL-based optical beam steering and divergence control through experiment and theory. We also demonstrate the transmission of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times 10$ </tex-math></inline-formula> -Gb/s WDM signals over a 104-m FSO link.

Measurement of specular surfaces using electrically tunable lens in digital holography

In the field of industrial metrology, the 3D nondestructive imaging of reflective metallic surfaces is a delicate task. In this work, we propose a novel application of the electrically tunable lens (ETL) in digital holography for imaging specularly reflecting objects. The precise surface profile of the microscopic step height at different axial depths is obtained by tuning the liquid lens at different currents. Initially, the ETL’s focal length is set by tuning its control current to image the specular reflection observed from the surface of the reflecting sample. The current of the ETL is tuned accordingly as the sample is moved to different z-positions. In order to demonstrate the efficacy of the proposed setup, the object is kept at multiple axial distances within the depth of field of the ETL. The step height measurements are carried out and a measurement uncertainty of 0.083 µm is calculated for step height measurements at different axial positions ranging from 2 cm–21 cm. The axial range of the setup is validated by keeping two specularly reflecting samples in the field of view of the ETL. The experimental results demonstrate the ETL’s efficiency in a digital holographic system for accurately imaging specularly reflecting objects present at multiple axial depths. The setup is useful for precise step height measurements and for obtaining surface profiles of microstructures.

An automated fast neutron computed tomography instrument with on-line focusing for non-destructive evaluation.

A fast neutron tomography imaging instrument has been designed, built, and tested at The Ohio State University 500 kW Research Reactor on a fast neutron beamline with a peak neutron flux ≈5.4 × 107 n·cm-2·s-1 at 1.6MeV median neutron energy. The instrument and beamline are also configurable for thermal neutron imaging. The imaging apparatus is composed of a lens coupled, water-cooled Electron Multiplying Charge Coupled Device camera, a front-surface mirror, and a high light yield plastic Polyvinyl toluene scintillator. The instrument sits on a mobile cart. A total of 5 motion-control stages are built into the system for XYZ and rotational degrees of freedom for sample positioning; the fifth stage fine tunes the focal distance between the camera and the scintillator to achieve on-line focusing. A Python code with a user-friendly graphical user interface controls the fully automated image acquisition, not requiring user interaction, yet facilitating tracking of the image acquisition. A complete fast neutron computed tomography dataset with 360 projections requires less than 3 h, with 30s per projection. On-line focusing is accomplished with a commercial, off-the-shelf, dielectrically actuated liquid lens. Finally, tomographic reconstructions are visualized using the Livermore Tomography Tools software package. The effective pixel size (width and height) is ≈0.1058mm, yielding a minimum voxel size of 0.1058 × 0.1058 × 0.1058mm3, and produces a spatial resolution of 231μm when calculated from knife-edge measurements.

Adaptive liquid lens with a tunable field of view.

In this paper, we demonstrate an adaptive liquid lens with a tunable field of view (FOV). The proposed liquid lens consists of an actuator and a lens chamber, the annular sheet is just placed on the liquid-liquid (L-L) interface in order to change the curvature and steer the tilt angle of the interface. Different from the conventional FOV adjustable lens combined with a liquid lens and a liquid prism, the proposed lens requires only one L-L interface to achieve the focal length change and FOV deflection. Moreover, the proposed lens reduces aberrations while maintaining high resolution. The experiments show that the optical power range is -27 m-1 to 30 m-1. It can realize the FOV deflection while tuning the focal length, with an angular resolution of 37"05. The proposed lens can be applied to telescopic system and microscopic system.

Focus stacking in non-contact dermoscopy

Dermoscopy is the main tool for early detection of skin cancer. Non-contact dermoscopes often suffer from a small depth of field leading to images of skin topographies with regions that are not in focus. We aim to provide an easy-to-implement focus stacking-based approach to ensure all-in-focus images from a non-contact dermoscope. Further, we aim to extract additional information about the skin topography from the image stacks. The focus stacking procedure itself is implemented in a non-contact dermoscope with an electrically adjustable focus realized by using a tunable liquid lens. We show that all-in-focus imaging is possible for non-contact dermoscopy and deliver a method to extract topographical information for dermatologists from the acquired image stacks. Our finding indicate that the approach can be valuable for non-contact dermoscopic examination as well as for the early detection of skin diseases such as cancer as it possible to derive hyperfocus images and information on the skin topography. With this, we were able to develop a software for the acquisition of the raw image data and its processing into a high resolution hyperresolution dermoscopic image. In the next steps, we plan to apply the approach in the clinical environment for skin cancer diagnostics or imaging of inflammatory skin diseases.

Evaluation of a liquid membrane-based tunable lens and a solid-state LIDAR camera feedback system for presbyopia.

Presbyopia is an age-related loss of accommodation ability of the eye which affects individuals in their late 40s or early 50s. Presbyopia reduces the ability of a person to focus on closer objects at will. In this study, we assessed electronically tunable lenses for their aberration properties as well as for their use as correction lenses. The tunable lenses were evaluated in healthy subjects with cycloplegia by measuring visual acuity and contrast sensitivity for their use in presbyopia correction. Furthermore, we have developed and demonstrated the feasibility of a feedback mechanism for the operation of tunable lenses using a portable solid-state LIDAR camera with a processing time of 40 ± 5 ms.

A miniature fluorescence microscope for multi-plane imaging

Miniature fluorescence microscopes are becoming an increasingly established tool to investigate neural circuits in freely moving animals. In this work we present a lightweight one-photon microscope capable of imaging at different focal depths. The focal plane can be changed dynamically by modulating the pulse width of the control signal to a variable focus liquid lens, which is synchronized to the image sensor to enable changing focal plane between frames. The system was tested by imaging GCaMP7f expressing neurons in the mouse medial prefrontal cortex (mPFC) in vivo during open field test. Results showed that with the proposed design it is possible to image neurons across an axial scan of ~ 60 μm, resulting in a ~ 40% increase of total neurons imaged compared to single plane imaging.