Fluidic Lens Research Articles

Design and dynamic characterization of a phototunable optofluidic lens

Optofluidic devices that dynamically respond to light stimuli have the potential to impart modern adaptive optics with intrinsic optical logic without the need for external power sources or feedback control. While photo actuation is typically associated with low energy efficiency compared with alternative modes of actuation, fluid lenses can be tuned with minimal work by generating small differential pressures across the surface of the lens to drive a change in focal length. In this study, we developed a wide aperture (9.5 mm) photothermally actuated lens that leverages spatially and thermodynamically informed design principles developed for resistively heated thermo-pneumatically actuated lenses. Using experimentally validated models to describe the curvature of pressurized elastomer-bound interfaces, we demonstrated phototunable modulation of the focal length from 124 mm to 90 mm in real time using 233 mW of 405 nm light over 30 s of irradiation with an estimated 8.2 µJ of mechanical work (10−4% efficiency). The initial focal length recovered after 60 s in the dark over three consecutive cycles of actuation. Additionally, the photoactuated response is shown to correlate well with the light intensity.

Spectral characterization of optical aberrations in fluidic lenses

We report an extensive numerical study and supporting experimental results on the spectral characterization of optical aberrations in macroscopic fluidic lenses with tunable focal distance and aperture shape. By using a Shack–Hartmann wavefront sensor, we experimentally reconstruct the near-field wavefront transmitted by the fluidic lenses, and we characterize the chromatic aberrations in terms of Zernike polynomials in the visible range. Moreover, we further classify the spectral response of the lenses using clustering techniques, in addition to correlation and convolution measurements. Experimental results are in agreement with numerical results based on our theoretical model of the nonlinear deformation of thin elastic membranes.

A Message From the Pluriverse: The Spiritually Fluid Gift of Philip Cote’s Walls of Welcome

Called Walls of Welcome, Philip Cote—an Anishinaabe-Algonquin artist and spiritual elder—created a large-scale panorama inside the interior walls of the Roncesvalles United Church’s sanctuary in late 2021. Located in the west end of Tkaronto/Toronto—and believed to be the first Indigenous art mural inside a church in Turtle Island/North America (if not globally)—the wall painting visually narrates the Ojibway creation story and alludes to “The Eighth Fire.” The latter stems from an Anishinaabe prophecy that we (human beings) can unite in our shared humanity. Walls of Welcome gives us all a message from the pluriverse and a spiritually fluid lens for seeing our foundational stories. My paper explores how this mural brings communities together through the power of art and builds a new world for trust-building and healing that epitomizes truth and reconciliation.

Non-mechanical axial focus tuning by coherent beam combining technique

High-speed variable-focus optics brings new opportunity to the applications of fiber laser in the fields of advanced laser processing, laser three-dimensional (3D) printing, imaging and so on. As an emerging field, variable-z-focus optical elements have been developed rapidly. There are many approaches to achieve high-speed variable focus such as ferroelectric liquid crystal lens, acoustically driven fluid lenses and enhanced adaptive optical technologies. In this paper, a method of non-mechanical axial focus tuning by coherent beam combining (CBC) technique is investigated. The method does not depend on any made-to-order element to achieve the high-speed variable focus. We provide detailed design processes and theoretical basis of how to achieve focus tuning by CBC technique. Then, the influencing factors of the tunable range of focus are analyzed. We also propose a tilt modulation assisted method in this paper to extend the tuning range furtherly. Finally, a visual demonstration is carried out by spatial light modulators to verify the method and achieving 10 cm tuning range of focus point.

Accuracy of an objective binocular automated phoropter for providing spectacle prescriptions

ABSTRACT Clinical relevance Currently eye examinations are usually based on autorefraction followed by subjective refraction (SR) with a phoropter. An automated phoropter that can also perform autorefraction may facilitate the optometric workflow. Background The efficiency and feasibility of an objective autorefraction and correction system are assessed by comparing objective refractive measurements with SR on the same subjects and evaluating the visual acuity (VA) values obtained after the objective refractive measurement and correction. Methods Objective autorefraction and correction was performed on 41 subjects using an automated binocular phoropter system. The auto-phoropter performs autorefraction by wavefront measurement and corrects the spherical and cylindrical errors with tunable fluidic lenses while the patient looks at a visual display inside the instrument. The instrument outputs are optometric constants of spherical and cylindrical aberrations. After measurement and automated correction of the refractive errors, the VA values were assessed by having the subjects look at an integrated Snellen chart. The objective measurement results were statistically compared with their SR. Results The correlations between SR and objective autorefraction and correction spherical equivalents (M) were 0.98 (0.97–0.99) and 0.96 (0.93–0.98), the vertical Jackson cross cylinder (J0) were 0.96 (0.92–0.98) and 0.95 (0.91–0.97), and the oblique Jackson cross cylinder (J45) were 0.73 (0.55–0.85) and 0.82 (0.69–0.90), for the right and left eyes, respectively, with the 95% confidence interval (CI) values in parentheses. 89.0% of the 82 eyes had at least 6/7.5 VA. Conclusions A significant agreement between the SR and objective autorefraction and correction was observed. An all-objective refractive assessment with instantaneous verification may improve the precision of eye prescriptions and possibly reduce the procedure time.

Interplay of bulk soluble surfactants and interfacial kinetics governs the stability of two-layer channel flows.

The linear stability of two-layer channel flows in the presence of bulk-soluble surfactants is investigated here, taking into account the rheological properties of the interface. The interfacial stresses are quantified using the Boussinesq-Scriven model, while the surfactant kinetics is assumed to follow the Frumkin isotherm, which accounts for their non-ideal behavior. Our results show that in general, the bulk solubility of surfactants has a stabilizing effect on the interface, both with and without the presence of inertia. On the other hand, the interfacial viscosities play a more complex role, depending on the viscosity ratios of the two fluids, the thickness of the fluid layers, the strength of the surface tension gradients, and the extent of inertia. We show that depending on the strength of inertia and the variability in the surface tension, the interfacial rheology may either stabilize or destabilize the base flow. However, for sufficiently small Reynolds numbers, the surface viscosity always has a stabilizing influence. Our results may be used to better design stable co-flow systems with applications in various processes such as surface coating, preparation of fluid lenses, as well as in a host of multi-purpose microfluidic devices.

Performance analysis of a compact auto-phoropter for accessible refractive assessment of the human eye.

We present the performance analysis and specifications of a portable auto-phoropter system that can be employed for fast refractive assessment of a large population. A customized Shack-Hartmann wavefront sensor is developed to accurately measure the defocus and astigmatism of the eye within ±10D and ±6D, respectively. Three fluidic lenses are designed to correct the vision in real time. A digital Snellen chart is integrated into the system to validate the accuracy of the measurement and the correction by means of achieving 20/20 vision. The refractive error of eight subjects (16 eyes) has been measured objectively (without patient's feedback) using the proposed system and the results are compared with their clinical prescription through the Bland-Altman method. It is shown that the auto-phoropter takes less than 8 s to measure and correct the eye refractive error with an accuracy of ±0.25D.

High-Flexibility Control of Structured Light with Combined Adaptive Optical Systems

Combining the specific advantages of high-resolution liquid-crystal-on-silicon spatial light modulators (LCoS-SLMs) and reflective or refractive micro-electro-mechanical systems (MEMS) presents new prospects for the generation of structured light fields. In particular, adaptive self-apodization schemes can significantly reduce diffraction by low-loss spatial filtering. The concept enables one to realize low-dispersion shaping of nondiffracting femtosecond wavepackets and to temporally switch, modulate or deflect spatially structured beams. Adaptive diffraction management by structured illumination is demonstrated for piezo-based and thermally actuated axicons, spiral phase plates (SPPs) and Fresnel bi-mirrors. Improved non-collinear autocorrelation with angular-tunable Fresnel-bi-mirrors via self-apodized illumination and phase contrast of an SLM is proposed. An extension of the recently introduced nondiffractive Talbot effect to a tunable configuration by combining an SLM and a fluid lens is reported. Experimental results for hexagonal as well as orthogonal array beams are presented.

Tunable fluidic lens with a dynamic high-order aberration control.

Fluidic lenses based on electrowetting actuation are attractive for their wide focal tuning range, yet are limited by optical aberrations, either intrinsic to the lenses themselves or due to the optical imaging systems in which they are employed. However, the ability to control the meniscus shape that forms the lens refractive surface with a high degree of spatial accuracy will allow correction of and compensation for a wide range of these aberrations. We demonstrate here for what we believe, to the best of our knowledge, is the first time a tunable optofluidic lens controlled by 32 azimuthally placed electrodes for which most aberrations up to the fourth radial Zernike order may be corrected. Using both wavefront sensing and sensorless wavefront estimation techniques, it is shown that focal length tunability with a significant reduction in imaging aberrations and the ability to compensate for externally induced aberrations may be achieved using a single component.

Parametric dog-bone-shaped tunable cylindrical fluidic lens.

Tunable spherical fluidic lenses are among the most essential components in adaptive optics. However, fabricating cylindrical tunable lenses has proven more challenging, mainly due to the difficulty in eliminating the defocus component. We demonstrate a parametric approach to minimize the defocus in cylindrical tunable fluidic lenses. We theoretically model and experimentally verify that a dog-bone-shaped tunable cylindrical fluidic lens exhibits almost pure cylindrical performance within the range of ${\pm{\rm 5D}}$ of astigmatism. We anticipate these results will facilitate the use of tunable cylindrical fluidic lenses in adaptive optics applications and particularly ophthalmic devices, where rapid and reliable wavefront correction is required.

Accelerated electrowetting-based tunable fluidic lenses.

One of the limitations in the application of electrowetting-based tunable fluidic lenses is their slow response time. We consider here two approaches for enhancing the response speed of tunable fluidic lenses: optimization of the properties of the fluids employed and modification of the time-dependent actuation voltages. Using a tubular optofluidic configuration, it is shown through simulations how one may take advantage of the interplay between liquid viscosities and surface tension to reduce the actuation time. In addition, by careful designing the actuation pulses, the response speed of both overdamped and underdamped systems may be increased by over an order of magnitude, leading to response times of several ten milliseconds. These performance improvements may significantly enhance the applicability of tunable optofluidic-based components and systems.

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.

Long-term uveal and capsular biocompatibility of a new fluid-filled, modular accommodating intraocular lens.

To evaluate long-term uveal and capsular biocompatibility of a new fluid-filled modular accommodating intraocular lens (IOL) consisting of base and fluid lenses. John A. Moran Eye Center, University of Utah, Salt Lake City, UT, USA. Experimental study. Bilateral phacoemulsification was performed on 8 rabbits; 1 eye received the test IOL (Juvene) and the other a hydrophobic acrylic control IOL (SA60AT). Slitlamp examinations were performed at postoperative weeks 1 and 4, and at months 2, 3, and 6. The rabbits were killed humanely at 6 months. After gross examination from the Miyake-Apple view, IOLs were removed for implant cytology. All globes were then processed for histopathologic examination. Uveal biocompatibility was similar between test and control IOLs up to 6 months postoperatively. Anterior capsule opacification appeared absent in the test group, and posterior capsule opacification (PCO) was significantly less in comparison with the control group throughout the study. At 6 months, central PCO was scored as 0.12 ± 0.23 with test IOLs and as 4.0 ± 0 with control IOLs (P < .0001, 2-tailed t test: paired 2-sample for means). Histopathologic examination confirmed the relative lack of capsular opacification in test eyes in comparison to controls and the absence of toxicity in any eye. Six weeks in the rabbit model corresponds to approximately 2 years in the human eye for PCO. In this model, the Juvene IOL maintained an open and expanded capsular bag, preventing overall capsular bag opacification while retaining excellent uveal and capsular biocompatibility.

Explantation/exchange of the components of a new fluid-filled, modular, accommodating IOL.

To evaluate the ease of replacement and capsular stability of a new fluid-filled, modular, accommodating intraocular lens (IOL) system composed of a monofocal base lens with a fluid lens clipped inside of it. John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA. Experimental study. Five New Zealand rabbits underwent bilateral phacoemulsification with implantation of the test lens (Juvene, LensGen, Inc.) in both eyes (4 rabbits), or a control IOL in 1 eye (AcrySof, Alcon Laboratories, Inc.) and the test IOL in the other (1 rabbit). At 2 weeks, the 4 rabbits with bilateral Juvene IOLs had the clipped-in fluid lens exchanged for a new fluid lens in 1 eye, and the base and fluid lenses exchanged for a control lens in the contralateral eye. Slitlamp examinations were performed weekly for 4 weeks. The globes were enucleated and evaluated with ultrasound biomicroscopy, grossly from the posterior Miyake-Apple view, and histopathologically. Explantation/exchange of the fluid lens was considered straightforward by the surgeon. Explantation of the base lens (4) was also safely performed, albeit more demanding, without any signs of damage to the capsular bag under clinical, ultrasound biomicroscopy, and pathological examination in the exchanged eyes. Less capsular bag opacification was observed with the Juvene lens system. Explantation/exchange of the fluid lens component, or both fluid and base lenses, of this new lens system can be safely accomplished if necessary, because of its modular design and the relative lack of postoperative capsular bag opacification associated with it.

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.

Compound Drop Shape Analysis with the Neumann Number.

A compound droplet is composed of a traditional pendant drop (PD) or sessile drop (SD) sharing the interface with an immiscible phase of comparable sizes, which could be a solid particle, a gas bubble, or most often another droplet of an immiscible liquid. Over the past decade, the study of compound droplets has attracted increasing attention because of extensive applications in many research fields, such as complex fluids, microfluidics, foam and emulsion, and biomedical applications. Among all technical difficulties in characterizing compound droplets, a central problem in surface science is the prediction of its equilibrium shape, which requires knowledge of complicated boundary conditions. Existing dimensionless groups, such as the Bond number traditionally used to evaluate the shape of PDs and SDs, largely fail in predicting the shape of compound droplets. Here, we propose an alternative Bond number, termed the Neumann number, to characterize the shape of compound droplets. Using three dimensionless groups, that is, the Neumann number, the Bond number, and the Worthington number, we have quantitatively predicted and analyzed the shape of traditional PDs/SDs and various compound droplets, including a PD with a spherical particle suspending at the drop apex, a SD with its apex disturbed by a vertical cylinder, and a spherical SD (no gravity) with its apex disturbed by a fluid lens. It is found that the Neumann number can be readily adapted to quantitatively predict and analyze the shape of PDs/SDs and compound droplets.

Two-layer resist process for printing thick patterns by exploiting a maskless projection exposure system using a liquid-crystal-display panel

To utilize maskless lithography using a liquid-crystal-display (LCD) panel for printing thick resist patterns, a novel two-layer resist process was developed. In the past research, simple and low-cost maskless exposure system was developed using an LCD panel in place of a reticle. However, commercial LCDs were fabricated not to irradiate short-wavelength light rays for protecting human eyes. Therefore, only thin g-line resists have been applicable for printing patterns. Nevertheless, patterning in 10–100 μm thick resist is frequently required for fabricating fluidic devices, lens arrays, and others. For this reason, a conventional g-line resist was coated on a thick UV resist, and patterns of g-line resist formed using the LCD maskless lithography was used as exposure masks of the bottom layer UV resist. As a result, various test patterns with widths of down to 40 μm and almost vertical side walls were successfully printed in the 70 μm thick UV resist.

Tunable fluidic lenses with high dioptric power

We report a complete theoretical model and supporting experimental results on the fabrication and characterization of macroscopic adaptive fluidic lenses with high dioptric power, tunable focal distance, and aperture shape. The lens is 17 mm wide and is made of an elastic polydimethylsiloxane (PDMS) polymer, which can adaptively restore accommodation distance within several cm according to the fluidic volume mechanically pumped in. Moreover, the lens can provide for magnification in the range of +25 diopter to +100 diopter with optical aberrations within a fraction of a wavelength, and overall lens weight of less than 2 g. The agreement between the non-linear theoretical model describing the elastic membrane deformation and the experimental results is apparent. We stress that these features make the proposed lenses appropriate for the low vision segment, as well as for applications in video magnifiers, camera zooms, telescope and microscopes objectives, and other machine vision applications where large magnification is required.

Annexins induce curvature on free-edge membranes displaying distinct morphologies

Annexins are a family of proteins characterized by their ability to bind anionic membranes in response to Ca2+-activation. They are involved in a multitude of cellular functions including vesiculation and membrane repair. Here, we investigate the effect of nine annexins (ANXA1-ANXA7, ANXA11, ANXA13) on negatively charged double supported membrane patches with free edges. We find that annexin members can be classified according to the membrane morphology they induce and matching a dendrogam of the annexin family based on full amino acid sequences. ANXA1 and ANXA2 induce membrane folding and blebbing initiated from membrane structural defects inside patches while ANXA6 induces membrane folding originating both from defects and from the membrane edges. ANXA4 and ANXA5 induce cooperative roll-up of the membrane starting from free edges, producing large rolls. In contrast, ANXA3 and ANXA13 roll the membrane in a fragmented manner producing multiple thin rolls. In addition to rolling, ANXA7 and ANXA11 are characterized by their ability to form fluid lenses localized between the membrane leaflets. A shared feature necessary for generating these morphologies is the ability to induce membrane curvature on free edged anionic membranes. Consequently, induction of membrane curvature may be a significant property of the annexin protein family that is important for their function.

High-speed focal-distance-modulated fiber-coupled confocal sensor for coordinate measuring systems.

This article presents a new robust, precise, high-frequency focal-distance-modulated confocal point sensor for probing in coordinate measuring systems (CMSs). While maintaining the known advantages of the confocal measurement principle, the sensor represents an innovative combination of a fiber-coupled confocal illumination and detection with a tuneable, acoustically driven gradient-index fluid lens for modulation of the focus distance and a novel signal processing utilizing a lock-in amplifier. The new arrangement is able to achieve an approximately linear characteristic curve for the optimized feedback control of the CMS in scanning sample mode. This article emphasizes the optical application and the signal processing of the setup.