Deformable Lens Research Articles

Full-aperture extended-depth oblique plane microscopy through dynamic remote focusing.

The reprojection setup typical of oblique plane microscopy (OPM) limits the effective aperture of the imaging system, and therefore its efficiency and resolution. Large aperture system is only possible through the use of custom specialized optics. A full-aperture OPM made with off the shelf components would both improve the performance of the method and encourage its widespread adoption. To prove the feasibility of an OPM without a conventional reprojection setup, retaining the full aperture of the primary objective employed. A deformable lens based remote focusing setup synchronized with the rolling shutter of a complementary metal-oxide semiconductor detector is used instead of a traditional reprojection system. The system was tested on microbeads, prepared slides, and zebrafish embryos. Resolution and pixel throughput were superior to conventional OPM with cropped apertures, and comparable with OPM implementations with custom made optical components. An easily reproducible approach to OPM imaging is presented, eliminating the conventional reprojection setup and exploiting the full aperture of the employed objective.

Large field of view aberrations correction with deformable lenses and multi conjugate adaptive optics.

Optical microscopes can have limited resolution due to aberrations caused by samples and sample holders. Using deformable mirrors and wavefront sensorless optimization algorithms can correct these aberrations, but the correction is limited to a small area of the field of view. This study presents an adaptive optics method that uses a series of plug-and-play deformable lenses for large field of view wavefront correction. A direct wavefront measurement method using the spinning sub-pupil aberration measurement technique is combined with correction based on the deformable lenses. Experimental results using fluorescence microscopy with a wide field and a light sheet fluorescence microscope show that the proposed method can achieve detection and correction over an extended field of view with a compact transmissive module placed in the detection path of the microscope. This method could improve the resolution and accuracy of imaging in a variety of fields, including biology and materials science.

Microstructural evolution of the bonding zone in TRIP-TWIP laminate produced by accumulative roll bonding

For the first time a four-layered laminate made of X5CrMnNi-16-6-6 (TRIP steel) and X5CrMnNi16-6-9 (TWIP steel) was manufactured by accumulative roll bonding (ARB). An intermediate annealing between rolling passes allowed to achieve good bonding between the laminate layers. The microstructure of the laminate at each step of production was analysed with the main focus on the bonding interface and deformation lenses by means of scanning electron microscopy, including chemical and orientation mapping techniques, and microhardness measurements. Additionally, a special measuring routine was developed to reveal spatial distribution of the grain size along the cross section. Finally, tensile specimens were cut out from the laminate and tested under quasi-static loading with subsequent fracture surface analysis. Repeated rolling and annealing of the steel layers resulted in the alteration of the grain size and microhardness, whereas significant texture appeared only after tensile loading. The grain size in the layer of TWIP steel after first roll bonding and annealing was found to drop down near the surface, whereas no such effect was found in TRIP steel. The microstructure of a deformation lens was found to fully change from severely deformed brittle steel matrix with excessive oxygen content after rolling to a ductile mixture of sub-micron globular oxides and austenite grains after annealing. These ductile deformation lenses ensure excellent bonding of layers and microcrack blunting. This allowed to achieve a remarkable combination of mechanical properties of the four-layered TRIP-TWIP laminate with a yield strength up to 800 MPa and an elongation to failure up to 45%, which resulted in the work of deformation up to 41 GPa·%.

Aberration measurement and correction on a large field of view in fluorescence microscopy.

The aberrations induced by the sample and/or by the sample holder limit the resolution of optical microscopes. Wavefront correction can be achieved using a deformable mirror with wavefront sensorless optimization algorithms but, despite the complexity of these systems, the level of correction is often limited to a small area in the field of view of the microscope. In this work, we present a plug and play module for aberration measurement and correction. The wavefront correction is performed through direct wavefront reconstruction using the spinning-pupil aberration measurement and controlling a deformable lens in closed loop. The lens corrects the aberrations in the center of the field of view, leaving residual aberrations at the margins, that are removed by anisoplanatic deconvolution. We present experimental results obtained in fluorescence microscopy, with a wide field and a light sheet fluorescence microscope. These results indicate that detection and correction over the full field of view can be achieved with a compact transmissive module placed in the detection path of the fluorescence microscope.

All-Solid Ionic Eye

Abstract We describe the materials, design, experimental measurements, and simulations of a bio-inspired all-solid tunable optical device: ionic eye. A dielectric elastomer functions as an electroactive material. An ionogel functions as an ionic conductor. Both materials are stretchable and transparent. The ionic eye achieves a ∼50% relative change of the focal length, beyond that of the human eye. Our analysis also points out that the ionic eye can respond rapidly (3.6 ms) and be miniaturized in size. This all-solid deformable lens eliminates the risk of leakage of currently used encapsulated fluid lenses and can be integrated into other devices for diverse applications.

Deformable polyvinyl chloride gel for fabrication of varifocal microlens array

Limitations in further miniaturization of lenses and arrays to achieve varifocal capabilities in compact 2D/3D switchable imaging devices have spurred investigations into the use of alternative materials. To this end, we fabricated a new deformable microlens array (MLA) utilizing polyvinyl chloride (PVC) gel, containing 67–90 wt.% of dibutyl adipate (DBA), sandwiched between an anode with apertures, 20–300 μm in diameter, and a cathode made of a transparent conductive film. The effects of applied voltage and DBA content on the protrusion of the PVC gel were studied and the protrusion mechanism was investigated. The gel was deformed from a flat shape in the absence of voltage to a lens shape at 100–600 V. When a voltage was applied, the negatively charged PVC chains accumulated near the anode and induced deformation of the PVC gel, which rose along the aperture walls and protruded from the apertures. Furthermore, the protrusion level of the PVC gel increased with DBA content, which lowered its elastic modulus and increased the negative charge density. Thus, the deformation of the PVC gel was mainly governed by the effects of electrostriction and PVC chain dynamics. Additionally, aperture diameter was found to influence the shape of the lens. The protrusion profile was concave at aperture diameters of 50 and 100 μm but became convex at 20 μm. At an applied voltage of 600 V, the focal length of the MLA was −0.20 mm at aperture diameters of 50 and 100 μm, representing a concave lens, but +0.05 mm at 20 μm, representing a convex lens. The MLA functioned more as a deformable lens, which transformed from a flat shape into a lens shape, than as a variable lens whose focal length changed continuously. The roles of plasticizer content, PVC chain dynamics, and aperture diameter in achieving greater control over lens curvature merit further investigation.

Influence of edge effects on laser-induced surface displacement of opaque materials by photothermal interferometry

We demonstrate the influence of edge effects on the photothermal-induced phase shift measured by a homodyne quadrature laser interferometer and compare the experiments with rigorous theoretical descriptions of thermoelastic surface displacement of metals. The finite geometry of the samples is crucial in determining how the temperature is distributed across the material and how this affects the interferometer phase shift measurements. The optical path change due to the surface thermoelastic deformation and thermal lens in the surrounding air is decoded from the interferometric signal using analytical and numerical tools. The boundary/edge effects are found to be relevant to properly describe the interferometric signals. The tools developed in this study provide a framework for the study of finite size effects in heat transport in opaque materials and are applicable to describe not only the phase shift sensed by the interferometer but also to contribute to the photothermal-based technologies employing similar detection mechanisms.

Correction of non-common path aberrations in pyramid wavefront sensors to recover the optimal magnitude gain using a deformable lens.

Adaptive optics (AO) correction based on pyramid wavefront sensors (P-WFSs) has been successfully implemented in several instruments for astronomical observation due to the P-WFS advantages in terms of sensitivity with respect to other WFSs, such as the Shack-Hartmann. The correction of non-common path aberrations (NCPAs) between the sensing and the scientific arm, commonly performed introducing offsets to the Zernike coefficients of the measured wavefront in the AO closed loop, reduces the sensitivity of P-WFSs causing a loss in sky coverage and scientific throughput. We propose a technique to exploit the full capabilities of P-WFSs compensating the NCPAs up to the fourth order on the WFS channel by means of a multi-actuator adaptive lens (MAL). We show the preliminary results obtained in a dedicated laboratory test bench.

Simulation of heat–water–mechanics process in a freezing soil under stepwise freezing

AbstractFrost heave is a process coupling heat transfer, water migration, water–ice phase change and deformation. Frost heave forms various landforms, such as frost mounds, ice pitons, sorted polygons and stone circles, and potentially induces a variety of engineering failures, such as building inclination, differential engineering foundation and pavement cracking. To understand the mechanism of frost heave under complex freezing paths, we provide a numerical heat–water–mechanics model that incorporates shrinkage in an unfrozen zone and uses a water content criterion to judge the formation of the ice lens. The model is then used to simulate the moisture, temperature, deformation and ice lens of a freezing soil during stepwise freezing. The simulated results for temperature, displacement and the ice lens are in good agreement with measured data, indicating that the model can be used to describe the heat–water–mechanics process in freezing soils under a complex freezing path. The freezing path determines the soil's water content profile in a manner like that in a stepwise freezing process, where each step produces a water‐content peak at the frozen fringe of the step. The model must consider shrinkage of the unfrozen area, or the amount of frost heave would be overestimated and the predicted ice lens would unrealistically be found in the frozen zone.

A low-cost deformable lens for correction of low-order aberrations

Introducing a reflective deformable mirror into an existing optical system for aberration correction requires a folded optical path and relay optics, increasing of the bulk and cost. This paper proposes a low-cost deformable lens (DL) that can be easily integrated into the existing system for correction of low-order aberrations. It is formed by a transparent medium layer sandwiched between a thick glass plate and a piezo-actuated thin glass plate with a transparent area in the middle. The thin glass plate presses the underlying transparent medium to produce optical path difference for correcting the aberrations of the transmitted light. The fabricated DL prototype accurately reproduced the first 9 Zernike mode shapes. Furthermore, the DL was integrated into a customized microscopy imaging system to correct the aberrations, significantly improving the quality of microscopic images.

Antireflective structures on highly flexible and large area elastomer membrane for tunable liquid-filled endoscopic lens.

The antireflection coating on an optical lens plays a key role not only in minimizing specular reflection but also in maximizing light transmission. Antireflective structures (ARS) found in the eyes of moths have the same role as conventional antireflection coating, and they also provide many intriguing features such as broadband coverage, self-antireflection, and strong water repellence. In particular, ARS on a highly flexible membrane can effectively deliver antireflective properties, which are rarely achieved by conventional hard coating. Herein, we report antireflective structures on a highly flexible elastomeric lens membrane for tunable endoscopic imaging applications. A thin antireflective membrane was fabricated using a large-area nanohole template and replica molding. The thin membrane increases light transmittance up to 96.8% in the visible region while enhancing the image contrast up to 56%, higher than that of a smooth membrane during lens deformation. This antireflective, tunable, liquid-filled lens offers new opportunities for compact endoscopic laparoscopy enabling maximum transmittance and variable zoom imaging in narrow and low-illumination environments.

Extreme-ultraviolet refractive optics.

Refraction is a well-known optical phenomenon that alters the direction of light waves propagating through matter. Microscopes, lenses and prisms based on refraction are indispensable tools for controlling light beams at visible, infrared, ultraviolet and X-ray wavelengths1. In the past few decades, a range of extreme-ultraviolet and soft-X-ray sources has been developed in laboratory environments2-4 and at large-scale facilities5,6. But the strong absorption of extreme-ultraviolet radiation in matter hinders the development of refractive lenses and prisms in this spectral region, for which reflective mirrors and diffractive Fresnel zone plates7 are instead used for focusing. Here we demonstrate control over the refraction of extreme-ultraviolet radiation by using a gas jet with a density gradient across the profile of the extreme-ultraviolet beam. We produce a gas-phase prism that leads to a frequency-dependent deflection of the beam. The strong deflection near to atomic resonances is further used to develop a deformable refractive lens for extreme-ultraviolet radiation, with low absorption and a focal length that can be tuned by varying the gas pressure. Our results openup a route towards the transfer of refraction-based techniques, which are well established in other spectral regions, to the extreme-ultraviolet domain.

Bioinspired adaptive gradient refractive index distribution lens

Inspired by the soft, deformable human eye lens, a synthetic polymer gradient refractive index distribution (GRIN) lens with an adaptive geometry and focal power has been demonstrated via multilayer coextrusion and thermoforming of nanolayered elastomeric polymer films. A set of 30 polymer nanolayered films comprised of two thermoplastic polyurethanes having a refractive index difference of 0.05 were coextruded via forced-assembly technique. The set of 30 nanolayered polymer films exhibited transmission near 90% with each film varying in refractive index by 0.0017. An adaptive GRIN lens was fabricated from a laminated stack of the variable refractive index films with a 0.05 spherical GRIN. This lens was subsequently deformed by mechanical ring compression of the lens. Variation in the optical properties of the deformable GRIN lens was determined, including 20% variation in focal length and reduced spherical aberration. These properties were measured and compared to simulated results by placido-cone topography and ANSYS methods. The demonstration of a solid-state, dynamic focal length, GRIN lens with improved aberration correction was discussed relative to the potential future use in implantable devices.

Explicit computational model of dielectric elastomeric lenses

Deformable lenses have many advantages over traditional lens assemblies in respect of compactness, cost benefit, efficiency, and flexibility. We propose a computational model based on the nonlinear elasticity to characterize the performance of dielectric elastomeric lenses in terms of the focal length variation with respect to the actuation voltage, with theoretical predictions fitting well with experimental data. This model can also be used to predict the relationship between the maximum focal length change and parameters of the lenses including geometry and the internal liquid volume. It is expected that our work could provide insight into designing this particular type of lens for experimental researchers in the field of tunable lenses.

Aberration control in adaptive optics: a numerical study of arbitrarily deformable liquid lenses.

By means of numerical simulations, using a computational fluid dynamics software together with an optical ray tracing analysis platform, we show that we can tune various optical aberrations by electrically manipulating the shape of liquid lenses using one hundred individually addressable electrodes. To demonstrate the flexibility of our design, we define electrode patterns based on specific Zernike modes and show that aspherical, cylindrical and decentered shapes of liquid lenses can be produced. Using different voltages, we evaluate the tuning range of spherical aberration (Z11), astigmatism (Z5 and Z6) and coma (Z7), while a hydrostatic pressure is applied to control the average curvature of a microlens with a diameter of 1mm. Upon activating all electrodes simultaneously spherical aberrations of 0.15 waves at a pressure of 30Pa can be suppressed almost completely for the highest voltages applied. For astigmatic and comatic patterns, the values of Z5, Z6 and Z7 increase monotonically with the voltage reaching values up to 0.06, 0.06 and 0.2 waves, respectively. Spot diagrams, wavefront maps and modulation transfer function are reported to quantify the optical performance of each lens. Crosstalk and independence of tunability are discussed in the context of possible applications of the approach for general wavefront shaping.

Lens rigidity for manifolds with hyperbolic trapped sets

For a Riemannian manifold ( M , g ) (M,g) with strictly convex boundary ∂ M \partial M , the lens data consist of the set of lengths of geodesics γ \gamma with end points on ∂ M \partial M , together with their end points ( x − , x + ) ∈ ∂ M × ∂ M (x_-,x_+)\in \partial M\times \partial M and tangent exit vectors ( v − , v + ) ∈ T x − M × T x + M (v_-,v_+)\in T_{x_-} M\times T_{x_+} M . We show deformation lens rigidity for such manifolds with a hyperbolic trapped set and no conjugate points. This class contains all manifolds with negative curvature and strictly convex boundary, including those with non-trivial topology and trapped geodesics. For the same class of manifolds in dimension 2 2 , we prove that the set of end points and exit vectors of geodesics (i.e., the scattering data) determines the Riemann surface up to conformal diffeomorphism.

Mechanically tunable aspheric lenses via additive manufacture of hanging elastomeric droplets for microscopic applications

Mechanically deformable lenses with dynamically tunable focal lengths have been developed in this work. The fabricated five types of aspheric polydimethylsiloxane (PDMS) lenses presented here have an initial focal length of 7.0, 7.8, 9.0, 10.0 and 10.2 mm. Incorporating two modes of operation in biconvex and concave–convex configurations, the focal lengths can be tuned dynamically as 5.2–10.2, 5.5–9.9, 6.6–11.9, 6.1–13.5 and 6.6–13.5 mm respectively. Additive manufacturing was utilized to fabricate these five types of aspheric lenses (APLs) via sequential layering of PDMS materials. Complex structures with three-dimensional features and shorter focal lengths can be successfully produced by repeatedly depositing, inverting and curing controlled PDMS volume onto previously cured PDMS droplets. From our experiments, we empirically found a direct dependence of the focal length of the lenses with the amount (volume) of deposited PDMS droplets. This new mouldless, low-cost, and flexible lens fabrication method is able to transform an ordinary commercial smartphone camera into a low-cost portable microscope. A few microscopic features can be readily visualized, such as wrinkles of ladybird pupa and printed circuit board. The fabrication technique by successively applying hanging droplet and facile mechanical focal-length-tuning set-up can be easily adopted in the development of high-performance optical lenses.

Biomimetic Accommodating Intraocular Lens Using a Valved Deformable Liquid Balloon.

Presbyopia is a common age-related condition that prevents people from focusing on near objects. The etiology of presbyopia continues to be debated, but the end effect of all postulated mechanisms is the lack of deformation of the human lens. Using our understanding of the biomechanical properties of the natural human lens, we created a unique accommodating intraocular lens. Although this lens can be used for lenticular disease such as myopia and hyperoperopia, this study addresses the needs of cataract patients with presbyopia. The lens was implanted into presbyopic human cadaver eyes. Focal length of the lens was measured with simulated muscle contraction. Lens dimensions were measured using artificial tissue and a finite-element analysis (FEA) to simulate accommodation. Lens power was measured at various fill volumes. Accelerated soak testing for an equivalent of 7.4years was performed and lens weight and optical transmittance were measured. Previously presbyopic human eyes were able to accommodate between 2.0 and 7.4 diopters after lens implantation. FEA and lens measurements demonstrated a change in curvature of the anterior and posterior portions of the lens during accommodation. After accelerated aging, lens weight remained unchanged and optical transmission was 96%. Lens power increased with fill volume. A deformable liquid lens reversed presbyopia, can be individualized by optically adjusting for each patient, is stable for long periods of time, and is compatible with minimally invasive surgical techniques. A deformable liquid-filled lens can significantly improve accommodation over the presbyopic natural lens.

光刻物镜主动变形镜像差补偿分析

光刻物镜主动变形镜像差补偿分析

Tunable lens driven by dielectric elastomer actuator with ionic electrodes

A tunable lens driven by a dielectric elastomer actuator is developed. A solution of NaCl was used as the deformable lens and one of the electrodes for applying a bias voltage across the actuator. The dielectric elastomer actuator was made of a curved polydimethylsiloxane (PDMS) thin film sandwiched between a gold electrode and the NaCl solution. When a bias voltage was applied, the electrostatic force induced a radial compression, causing a lateral deflection of the PDMS. The radius of the curvature of the NaCl lens was consequently changed. The variation of the focal length under different bias voltages was characterised separately using two different approaches, and consistent results were obtained. The lens diameter was 4 mm. The focus lens can be tuned from 16.1 to 13.1 mm when the bias voltage is increased from 0 to 900 V.