Tunable Lens Research Articles

A Smartphone-Based Fluorescence Microscope With Hydraulically Driven Optofluidic Lens for Quantification of Glucose

The traditional method for early diagnosis of diabetes is to detect urine or blood glucose levels. However, the present clinical detection methods cause either cross-infection or require expensive instruments with complex procedures of operation. In this work, a handheld smartphone-based fluorescence microscope with the tunable optofluidic lens and microfluidic assay is demonstrated for the facile detection of glucose concentration for the first time to our knowledge. The tunability of the optofluidic lens is based on the dynamic deformation of an elastomeric membrane driven by adjustable hydraulic pressure. And the glucose sensor integrates a smartphone, a tunable optofluidic lens, a microfluidic chip, a customized holder and some easily accessible optics. A low detection limit of 0.33 mM of glucose was achieved subjected to a linear range of detection from 0 to 6 mM glucose, which is evaluated with an enzymatic fluoresce method. These results show that the cost-effective miniaturized system can be used for early screening and diagnosis of diabetes and potentially some other onsite applications of clinical diagnosis and environment monitoring.

Chiral Liquid Crystal Lenses Confined in Microchannels.

It is known that the liquid crystalline smectic-A phase has geometric defects, called focal conic domains, which can be used as gradient-index microlenses. Cholesteric (chiral nematic) phases also have topological defects with a central symmetry and a singularity at their center. We explore a weakly chiral system in which both types of defects can be present in the same material at different temperatures, and with this strategy we create lenses whose focal length is tunable with temperature. We measure the focal length of the tunable lenses, and we investigate the behavior of the defects near the phase transition. We identify the experimental conditions that make the simultaneous presence of the smectic focal conic domains and the circular cholesteric domains possible, such as the concentration of chiral dopant and the rate of heating and cooling. The transformation of focal conic domains into circular cholesteric domains is a new example of memory at the phase transition between smectic-A and nematic liquid crystals.

Diffractive tunable lens for remote focusing in high-NA optical systems.

Remote focusing means to translate the focus position of an imaging system along the optical axis without moving the objective lens. The concept gains increasing importance as it allows for quick 3D focus steering in scanning microscopes, leaves the sample region unperturbed and is compatible with conjugated adaptive optics. Here we present a novel remote focusing approach that can be used in conjunction with high numerical aperture optics. Our method is based on a pair of diffractive elements, which jointly act as a tunable auxiliary lens. By changing the mutual rotation angle between the two elements, we demonstrate an axial translation of the focal spot produced by a NA = 0.95 air objective (corresponding to NA = 1.44 for an oil immersion lens) over more than 140 µm with largely maintained focus quality. We experimentally show that for the task of focus shifting, the wavefront produced by the high-NA design is superior to those produced by a parabolic lens design or a regular achromatic lens doublet.

Dual-beam stealth laser dicing based on electrically tunable lens

In this paper, we present the development of a high-speed dual-beam stealth laser dicing (D-SLD) method for processing semiconductor wafers based on electrically tunable lenses (ETLs). An SLD system utilizes a laser beam to dice a wafer by inducing interior defects without modifying the surface characteristics of a wafer, thereby presenting significant advantages over conventional dicing methods, e.g., blade dicing or laser ablation. Currently, the throughput of SLD is limited by the serial scanning process; in addition, wafer misalignment and the warpage effects together deteriorate the dicing quality and yield and demand high-cost multi-axis precision stages. To address the issue, we parallelize the dicing process by splitting the laser focus into two foci, where the laser intensity at different depths are automatically adjusted to achieve optimal dicing condition. By combining the height sensor and ETLs, each laser focus, i.e., laser scan lines, can be rapidly controlled axially to compensate the wafer curvature and misalignment errors in real time, leading to substantially improved precision (kerf width < 2 μm) and speed, demonstrated by our experimental results. The new dual-beam laser dicing system presents an effective solution for high-speed wafer dicing as well as other important engineering applications, e.g., fabrication of micro-devices and optical components.

High-speed coherent diffraction imaging by varying curvature of illumination with a focus tunable lens.

A high-speed coherent diffraction imaging method is proposed by varying the curvature of illumination with a focus tunable lens. The imaging setup is free of conventional mechanical translation and takes only milliseconds to refocus by changing the electric signal applied on the lens. It is more compact and also an inexpensive alternative to coherent diffraction imaging with computerized translational stages. A detector that is kept at a fixed distance from the sample records diffraction patterns each time the spherical wavefront illuminations on the sample is changed with a control current. The complex wavefront of the object is then quantitatively recovered from the diffraction intensity measurements using an iterative phase retrieval algorithm. The feasibility of the proposed method is experimentally verified using various samples. Extremely short response time of the focus tunable lens makes the proposed method highly suitable for applications that requires high speed imaging.

Optimization of ultrafast axial scanning parameters for efficient pulsed laser micro-machining

Abstract In order to achieve high-resolution micro-machined features, tight focusing is traditionally adopted in laser micro-machining systems, at the cost of a narrow axial machining range. As the laser energy is confined in a single, fixed focal spot, machining throughput is significantly constrained by the writing speed of either translation stages or galvanometer scanners. We study an ultrafast axial scanning technique that asynchronously distributes laser pulses along the axial direction. Oscillation of the focal spot induced by the tunable acoustic gradient index lens is visualized in borosilicate glass with femtosecond laser pulses. By tuning frequency and amplitude of the acoustic field, machining parameters can be optimized, as demonstrated by the case of line machining on silicon. Multi-pass groove machining with axial scanning on silicon as well as femtosecond laser cutting of battery separators exhibit an extended effective machining range and an improved machining efficiency for both focused and defocused surfaces.

A MEMS lens scanner based on serpentine electrothermal bimorph actuators for large axial tuning.

Confocal microscopes and two-photon microscopes are powerful tools for early cancer diagnosis because of their high-resolution 3D imaging capability, but applying them for clinical use in internal organs is hindered by the lack of axially tunable lens modules with small size, high image quality and large tuning range. This paper reports a compact MEMS lens scanner that has the potential to overcome this limitation. The MEMS lens scanner consists of a MEMS microstage and a microlens. The MEMS microstage is based on a unique serpentine inverted-series-connected (ISC) electrothermal bimorph actuator design. The microlens is an aspheric glass lens to ensure optical quality. The MEMS microstage has been fabricated and the lens scanner has been successfully assembled. The entire lens scanner is circular with an outer diameter of 4.4 mm and a clear optical aperture of 1.8 mm. Experiments show that the tunable range reaches over 200 µm at only 10.5 V and the stiffness of the microstage is 6.2 N/m. Depth scan imaging by the MEMS lens scanner has also been demonstrated with a 2.2 µm resolution, only limited by the available resolution target.

A 3D-printed tunable fluidic lens with collagen-enriched membrane

We present a low-cost and biocompatible 3D-printed fluidic device composed of a main body and two lids with membranes in between forming a tunable lens. The main body and the lids of the device is manufactured using stereolithography (SLA) technology and comprises of one or two inlets. Collagen type-I enriched Sodium Alginate membranes are sandwiched between the main body and the top and the bottom lids. A syringe pump is employed to control the amount of liquid inside the chamber, thus tuning the radius of curvature of both membranes. The device dimensions are chosen as 15 × 10 × 7 mm3 (length × width × height), towards integration with previously developed miniaturized 3D-printed laser scanning imagers, offering focus adjustment capability. The extracted collagen, which is mixed with the membrane material, offers (1) a lens-mimicking structure, (2) biocompatibility, and (3) capability of tailoring membrane mechanical properties through adjusting collagen mass ratio. Using the manufactured device, we demonstrate focus tuning, hysteresis characterization and resolution target imaging experiments conducted at different target distances. The 3D-printed tunable lens structure is suitable for integration with a wide range of minimally invasive laser scanned imagers or ablation units presented in the literature.

Compact and tunable active-plasma lens system for witness extraction and driver removal

Plasma based technology will allow an unprecedented reduction of the size of accelerating machines. Both fundamental research and applied science and technology will take profit of this feature. The same compactness is required downstream the accelerator module, where the plasma-accelerated beams usually experience a large angular divergences growth. Therefore compact, strong and tunable focusing devices are needed. Active-plasma lenses have been demonstrated to be a compact and affordable tool to generate radially symmetric magnetic fields. We present a new scheme using active-plasma lenses and a metallic collimator to catch and transport the witness bunch while removing the driver. The considered case study is in the context of the EuPRAXIA project.

Measurement of a flow-velocity profile using a laser Doppler velocimetry coupled with a focus tunable lens

This paper reports on the measurement of a flow-velocity profile using a laser Doppler velocimetry (LDV) system having a focus tunable lens (FTL). In the system, the FTL is installed in the transmitting optics of the LDV; therefore, it can measure the flow velocity profile by changing the measurement position without any mechanical scanning system. To demonstrate the concept of the technique, the velocity profile measurement of Poiseuille flow was conducted, and the measured velocity profile showed good agreement with the theoretical value.

Positive-negative tunable liquid crystal lenses based on a microstructured transmission line

In this work, a novel technique to create positive-negative tunable liquid crystal lenses is proposed and experimentally demonstrated. This structure is based on two main elements, a transmission line acting as a voltage divider and concentric electrodes that distribute the voltage homogeneously across the active area. This proposal avoids all disadvantages of previous techniques, involving much simpler fabrication process (a single lithographic step) and voltage control (one or two sources). In addition, low voltage signals are required. Lenses with switchable positive and negative focal lengths and a simple, low voltage control are demonstrated. Moreover, by using this technique other optical devices could be engineered, e.g. axicons, Powell lenses, cylindrical lenses, Fresnel lenses, beam steerers, optical vortex generators, etc. For this reason, the proposed technique could open new venues of research in optical phase modulation based on liquid crystal materials.

Reducing the light scattering impact in liquid-crystal-based imaging systems.

We show an experimental method of quantifying the effect of light scattering by liquid crystals (LCs) and then apply rather simple image processing algorithms (Wiener deconvolution and contrast-limited adaptive histogram equalization) to improve the quality of obtained images when using electrically tunable LC lenses (TLCLs). Better contrast and color reproduction have been achieved. We think that this approach will allow the use of thicker LC cells and thus increase the maximum achievable optical power of the TLCL without a noticeable reduction of image quality. This eliminates one of the key limitations for their use in various adaptive imaging applications requiring larger apertures.

Electrically tunable liquid crystal lens in extreme temperature conditions

We investigate the potential of using electrically tunable liquid crystal lenses (TLCLs) to record the activity of small animals in the Canadian Arctic. This suggests extreme temperature conditions that may dramatically change the TLCL’s parameters. Our analysis is performed on the example of “modal-control” TLCLs. Temperature dependences of main parameters are presented for TLCLs made with 5CB and ultra-low viscosity LCs. We finally propose an approach allowing to “athermalize” such lenses by adjusting certain control parameters, to maintain good optical performance. Other factors and limitations that affect the lens performance with temperature change are also discussed.

Mechanics of dielectric elastomer structures: A review

In the past decade, the development of theory has deeply revealed the electromechanical coupling deformation mechanism of dielectric elastomer (DE). Many theoretical predictions on highly nonlinear deformation of dielectric elastomer have been verified by experiments. With the guidance of theory, the voltage-induced areal strain of dielectric elastomer has been increased from 100% in the pioneering work to the current record of 2200% and the energy density of a dielectric elastomer generator has reached 780 mJ/g. Much more developments have been realized on the applications of DE transducers in the fields of bioinspired artificial muscles, soft robotics, tunable lenses, and haptic interfaces. However, there is a gap between theory and application. Great potentials of developing DE transducers with the aid of a systematic theory have yet to be explored. This paper reviews the recent advances in the theory of dielectric elastomer and demonstrates some examples of using theory to design DE transducers. 9 boundary value problems of DE structures are analyzed from the simplest homogeneous deformation of a flat membrane to the highly complex bifurcations of a tube. Comparisons between theory and experiment are discussed. The viscous effect and the vibration of dielectric elastomer are reviewed. The developments of DE transducers and new dielectric materials are also reviewed. We summarize the performance of existing DE transducers with different configurations and make some discussions. It is hoped that the mechanics of DE structures can help to develop high-performance DE transducers in the future.

Computational Model and Design of the Soft Tunable Lens Actuated by Dielectric Elastomer

Abstract Inspired by the accommodation mechanism of the human eye, several soft tunable lenses have been fabricated and demonstrated the capability of controllable focus tuning. This paper presents a computational model of a dielectric elastomer-based soft tunable lens with a compact structure that is composed of a lens frame, two soft films, and the optically transparent fluid enclosed inside. The two soft films, respectively, serve as the active film and passive film. The active film is a dielectric elastomer film and can be coated with the annular electrode or circular electrode. The deformation of the lenses with both electrode configurations can all be formulated by a boundary value problem with different boundary conditions and be solved as the initial value problem using the shooting method. Two common failure modes of loss of tension and electrical breakdown are considered in the calculation of the lens. The computational results can well fit the experimental data. The focus tuning performances as well as the distributions of stretches, stresses, and electric field in the active films of the lenses with two different electrode configurations are compared. The influences of several parameters on the performances of the lenses are discussed, such that the tunable lens can be designed to have maximum focal length change or to be optimized based on different application requirements.

Surface and mechanical analysis of metallized poly(dimethylsiloxane) gel for varifocal micromirrors

Varifocal micromirrors are alternative and miniaturized mirror systems that are used for imaging procedures in biomedical diagnostics, mirror‐based tunable lenses, or the correction of spherical aberration. In this study, we demonstrate a new concept for focal length variation by electrostatic mirror deformation of a compact and integrated electroactive polymer actuator based on metallized poly(dimethylsiloxane) (PDMS) gel thin films. The varifocal micromirrors have a lateral size of 70 × 70 μm2 and are capable of deforming in either convex or concave direction, depending on a defined surface treatment by O2‐plasma or UV/ozone of the PDMS prior to metallization by physical vapor deposition (PVD). Surface and interface analysis by wetting experiments, sputter depth‐profiling X‐ray photoelectron spectroscopy (XPS) combined with scanning electron microscopy (SEM) on cross‐sections processed with focused ion beam (FIB) as well as polymer and metal surfaces are used to understand and to improve the metal film growth and quality with respect to high reflectivity and conductivity. In addition to the high quality of the metallic mirror layer, the mirror displacement is important and inevitably depends on the gel stiffness of the actuator. Therefore, we investigate the gel mechanics and the performance of the actuator with rheology, confocal microscopy, and image formation on the electrically deformed mirrors. Our concept of varifocal micromirrors offers a wide range of applications for tunable mirror‐based optics due to their simple and compact design.

Broadband tunable focusing lenses by acoustic coding metasurfaces

Acoustic tunable focusing lens has important applications in acoustic fast imaging and three-dimensional displays. Previously developed metasurface lenses suffer from narrow bandwidth and fixed geometric configuration, thereby limiting their further practical applications. Here, we design an acoustic coding metasurface (ACM) lens to achieve a broadband tunable focusing in air. This simple ACM lens only includes two coding bits: a space-folding structure is designed to act as the bit ‘1’ and an air unit with the same size is used as the bit ‘0’. By adjusting the coding sequence of the ACM, the focus location of the ACM lens can be modified efficiently and be steered in the whole working plane. Moreover, the focusing behaviors of the ACM lens are well performed in a large frequency range of ∼3.1 to ∼4.6 kHz. Our ACM lens may be beneficial to applications that traditionally need different and complicated structures for tunable acoustic focusing.

Hysteresis characterization of an electrically focus-tunable lens

Electrically focus-tunable lenses are a type of lens whose focal distance can be varied and controlled electronically and fast. These advantages are making them suitable for many optical applications and research experiments in fields like visual optics, optical metrology, optical information processing, nonlinear optical-properties measurements, among others. For most applications, the focal distance must be known with precision and reliability, becoming an important issue that the focal distance programmed on the tunable lens corresponds to the truly obtained focal distance. However, recently, a research article has presented evidence that these tunable lenses have hysteresis. In this work, we confirmed the hysteresis of three tunable lenses, determined how predictable is the focal distance programmed under different schemes, corroborated the existence of an optical-power time drift, and proposed two schemes to be able to predict the optical-power outcome with reliability. A case of study is presented to highlight the importance of the characterization.

Focusing with saw-tooth refractive lenses at a high-energy X-ray beamline.

The Advanced Photon Source 1-ID beamline, operating in the 40-140 keV X-ray energy range, has successfully employed continuously tunable saw-tooth refractive lenses to routinely deliver beams focused in both one and two dimensions to experiments for over 15 years. The practical experience of implementing such lenses, made of silicon and aluminium, is presented, including their properties, control, alignment, and diagnostic methods, achieving ∼1 µm focusing (vertically). Ongoing development and prospects towards submicrometre focusing at these high energies are also mentioned.

Comment on "Bioinspired Reversible Switch between Underwater Superoleophobicity/Superaerophobicity and Oleophilicity/Aerophilicity and Improved Antireflective Property on the Nanosecond Laser-Ablated Superhydrophobic Titanium Surfaces".

Laser-textured surfaces enabling reversible wettability switching and improved optical properties are gaining importance in cutting-edge applications, including self-cleaning interfaces, tunable optical lenses, microfluidics, and lab-on-chip systems. Fabrication of such surfaces by combining nanosecond-laser texturing and low-temperature annealing of titanium Ti-6Al-4V alloy was demonstrated by Lian et al. in ACS Appl. Mater. Inter. 2020, 12 (5), 6573–6580. However, it is difficult to agree with (i) their contradictory explanation of the wettability transition due to low-temperature annealing and (ii) their theoretical description of the optical behavior of the laser-textured titanium surface. This comment provides an alternative view—supported by both experimental results and theoretical investigation—on how the results by Lian et al. could be interpreted more correctly. The annealing experiments clarify that controlled contamination is crucial in obtaining consistent surface wettability alterations after low-temperature annealing. Annealing of laser-textured titanium at 100 °C in contaminated and contaminant-free furnaces leads to completely different wettability transitions. Analysis of the surface chemistry by XPS and ToF-SIMS reveals that (usually overlooked) contamination with hydrophobic polydimethylsiloxane (PDMS) may arise from the silicone components of the furnace. In this case, a homogeneous thin PDMS film over the entire surface results in water repellency (contact angle of 161° and roll-off angle of 15°). In contrast, annealing under the same conditions but in a contaminant-free furnace preserves the initial superhydrophilicity, whereas the annealing at 350 °C turns the hydrophobicity “off”. The theoretical calculations of optical properties demonstrate that the laser-induced oxide layer formed during the laser texturing significantly influences the surface optical behavior. Consequently, the interference of light reflected by the air–oxide and the oxide–metal interfaces should not be neglected and enables several advanced approaches to exploit such optical properties.