Microlens Formation Research Articles

Thermal mechanism-driven microlens formation in Ge–Sb–S glasses by direct laser writing: composition dependent insight

Microlenses were fabricated through a thermal process using laser-induced localized overheating on the surfaces of various bulk Ge–Sb–S glasses. These glasses spanned three distinct groups: (a) stoichiometric (GeS2)1−x(Sb2S3)x glasses with x = 0–0.88; (b) a series with a constant Sb content represented as GexSb0.17S0.83−x, x = 0.13–0.24, and (c) glasses with a constant Ge content denoted by Ge0.18SbxS0.82−x, x = 0.03–0.10. A continuous-wave laser emitting at 532 nm was used in the fabrication process. Both the photo-induced microlenses and the non-illuminated surfaces underwent characterization to determine their topography (via digital holographic microscopy), chemical composition (using EDX analysis), structure (through Raman spectroscopy), and mechanical properties (assessed by Nanoindentation). The influence of the chemical composition was studied to identify parameters that described the characteristics of the formed microlenses, such as the maximum achieved height and the threshold power density for microlens formation. For (GeS2)0.66(Sb2S3)0.34 glass, the effective focal length of the produced microlenses was calculated to be approximately 145–190 µm, potentially aiding in the miniaturization of optical devices that, in the context of Ge–Sb–S, working primarily in the near and/or mid-IR region.Graphical abstract

Fabrication of quartz microlenses using laser ablation

Various quartz microlenses were fabricated in two stages with two lasers. A fiber laser at 1.06 µm was employed for the laser ablation, while a CO2 laser at 10.6 µm was used for direct laser writing (DLW). The experimental data demonstrate the formation of spherical, cylindrical microlenses and microlens array (MLA) with an optimum numerical aperture (NA) of 0.55. Theoretical calculations and simulation were conducted to estimate the temperature at the quartz surface during ablation and simulation of the reshaping. A temperature of 2500 K is achieved in the ablation, and 2015 K was established during the reshaping. The ablation depth is 280 µm, the diameter is 150 µm, and the heat affected zone (HAZ) is approximately 1345 µm after 1 s. Due to the controllable laser micromachining, optoelectronics and biological imaging are viable applications for MLAs.

Scalable and Facile Formation of Microlenses on Curved Surfaces Enabling a Highly Customized Sustainable Solar‐Water Nexus

Solar‐driven water treatment suffers from low efficiency due to the solar energy loss during the energy conversion, especially in the scale‐up operation. One promising solution is using microlenses (MLs) to enhance the photodegradation of organic contaminants in water. However, most MLs fabrications apply to 2D planar surface only, which restricts their potential applications. In this study, a flexible and scalable technology is presented to fabricate MLs on curved surfaces. Precursor microdroplets form in a dilution process and are converted to MLs by photopolymerization. Optical simulations and experiments are combined to establish the correlation between optical properties of MLs and the performance of ML‐functionalized reactors in photodegradation. It is demonstrated that surface MLs on all‐shaped reactors significantly enhance the photodegradation efficiency of organic contaminants under simulated solar light or natural indoor light, with a maximum improvement of 83 folds. The surface coverage and size distribution of MLs can be adjusted by varying the solution concentration and the dilution rate when generating microdroplets. In addition, fabrication of MLs on a larger scale is achieved over an area up to 250 . MLs on 3‐dimensional curved surfaces fabricated by the technique enable significantly enhanced, highly customized, and sustainable solar‐driven water treatment.

Microlenses formation on surface of stoichiometric Ge-As-S bulk glasses by CW laser direct writing

Laser direct writing using continuous-wave laser emitting at 532 nm was successfully performed into stoichiometric (GeS2)x(As2S3)(1-x) bulk glasses, where 0 ≤ x ≤ 1. The illumination of the samples led to the microlenses and microcraters formation. The influence of chemical composition and illumination conditions was studied especially on the microlens formation in order to create the highest one. The created microlenses and non-illuminated area were characterized with the help of digital holographic and atomic force microscopies, energy-dispersive X-ray analysis, Raman and Force spectroscopies in order to find the potential differences in properties between them. The created microlenses have the potential applicability in miniaturization optics due to their radius of curvature and focal length. The increase in local temperature caused by the laser illumination was estimated by COMSOL software. For the comparison, in–situ microlens formation was studied by the modified thermo-mechanical analyzer.

Simulation and optimization of microlens hot-melting fabricating process based on finite element method

As an important optical element, the microlens array has received more and more attention. Due to the advantages of a short production cycle, low cost, high efficiency, and easy to transfer, the photoresist hot-melting method has been widely used to fabricate microlens. Fabricating microlenses with large aperture and curvature radius are the basic requirements to ensure image quality. However, due to the limitations of photoresist material properties and the hot-melting process, the shape of the microlens is not easy to control. In this paper, the finite element fluid simulation software Fluent was used to simulate the microlens hot-melting fabricating process. Through the simulation, we could understand the formation process of the microlens. By multiple groups of simulation comparison, the key parameter in the formation of microlens was discussed. Besides, the simulation result shows that when a layer of residual photoresist is left around the original photoresist cylinder, microlens with larger diameter can be easily obtained. The experimental results are in good agreement with the simulation results. The comparison imaging experiment also illustrates that the microlens fabricated by the improved process has better imaging ability. Through simulation, this paper not only explains the mechanism of the hot-melting method, but also optimizes its process. The related research could expand the application range of the hot-melting method in the fabrication of microlens.

A simplified method for producing human lens epithelial cells and light-focusing micro-lenses from pluripotent stem cells

Here we describe a modified method for harvesting tens-of-millions of human lens epithelial-like cells from differentiated pluripotent stem cell cultures. To assess the utility of this method, we analysed the lens cell population via: light microscopy; single cell RNA-sequencing and gene ontology analyses; formation of light-focusing micro-lenses; mass spectrometry; and electron microscopy. Both individually and collectively, the data indicate this simplified harvesting method provides a large-scale source of stem cell-derived lens cells and micro-lenses for investigating human lens and cataract formation.

Rapid fabrication of microlens arrays on PMMA substrate using a microlens array by rear-side picosecond laser swelling

Microlens arrays were fabricated on polymethyl methacrylate (PMMA) substrate using a microlens array (MLA) with rear-side ps laser swelling in this study. The modified beam energy can ensure the fabricated microlenses are uniform. Using the foci of a microlens array (MLA), approximately 630 microlenses were fabricated with a single series of pulses, which provides greater processing throughput compared to point-to-point direct laser writing. The formation of smooth microlenses is attributed to photolysis of methyl red (MR) and molecular relaxation. The dependence of height and diameter of the microlenses on laser fluence and irradiation time were investigated. The results show that the size of microlenses could be controlled using the appropriate fluence and irradiation time. Finally, an array of mirolenses with high uniformity was fabricated over a large area. The diameter and height of the microlenses were measured to be 55 and 12 µm, respectively.

73‐4: Distinguished Paper: Image Formation Modeling and Analysis of Near‐Eye Light Field Displays

The image formation of microlens array‐based near‐eye light field displays is modeled with near‐perfect accuracy by incorporating diffraction, ray aberration, defocusing, and pixel sampling. Based on this model, algorithms and hardware parameters are suggested for resolution optimization, and the resolution variations with FOV and image depth are analyzed.

Advanced technologies of microlenses production for robot system camcorders

The processes of formation of microlenses in photosensitive silicate and germanate glasses have been studied. A series of successive operations with samples of photosensitive glass activated by silver and cerium ions: irradiation, photolithography, secondary heat treatment, diffusion and ion exchange lead to the formation of various profiles on the glass surface, including convex or concave lens surfaces. On the basis of this effect, a promising technology for the production of raster microlenses and lenses for various optical devices and video cameras of a robotic system was developed.

Shape-controllable, bottom-up fabrication of microlens using oblique angle deposition.

This Letter reports a novel method for the simple fabrication of microlens arrays with a controlled shape and diameter on glass substrates. Multilayer stacks of silicon dioxide deposited by oblique angle deposition with hole mask patterns enable microlens formation. Precise control of mask height and distance, as well as oblique angle steps between deposited layers, supports the controllability of microlens geometry. The fabricated microlens arrays with designed geometry exhibit uniform optical properties.

Development of a continuous roll-to-roll processing system for mass production of plastic optical film

This paper reports a highly effective method for the mass production of large-area plastic optical films with a microlens array pattern based on a continuous roll-to-roll film extrusion and roller embossing process. In this study, a thin steel mold with a micro-circular hole array pattern is fabricated by photolithography and a wet chemical etching process. The thin steel mold was then wrapped onto a metal cylinder to form an embossing roller mold. During the roll-to-roll process operation, a thermoplastic raw material (polycarbonate grains) was put into the barrel of the plastic extruder with a flat T-die. Then, the molten polymer film was extruded and immediately pressed against the surface of the embossing roller mold. Under the proper processing conditions, the molten polymer will just partially fill the micro-circular holes of the mold and due to surface tension form a convex lens surface. A continuous plastic optical film with a microlens array pattern was obtained. Experiments are carried out to investigate the effect of plastic microlens formation on the roll-to-roll process. Finally, the geometrical and optical properties of the fabricated plastic optical film were measured and proved satisfactory. This technique shows great potential for the mass production of large-area plastic optical films with a microlens array pattern.

Application of tot'hema eosin sensitized gelatin as a potential eye protection filter against direct laser radiation

The optical limiting properties of tot'hema and eosin sensitized gelatin layer (short TESG) under continuous second harmonic Nd:YAG laser light were investigated. In contrast to classical eye protection filters the microlens formation and carbonization in TESG are the main mechanisms for eye protection from direct laser radiation. Results have shown that safety goggles made on TESG can protect the eye from up to 10 W of incident laser power. Filters for other wavelengths can be manufactured by varying the sensitizer.

Formation of Polymeric Hollow Microcapsules and Microlenses Using Gas-in-Organic-in-Water Droplets

This paper presents methods for the formation of hollow microcapsules and microlenses using multiphase microdroplets. Microdroplets, which consist of a gas core and an organic phase shell, were generated at a single junction on a silicon device without surface treatment of the fluidic channels. Droplet, core and shell dimensions were controlled by varying the flow rates of each phase. When the organic solvent was released from the organic phase shell, the environmental conditions changed the shape of the solidified polymer shell to either a hollow capsule or a microlens. A uniform solvent release process produced polymeric capsules with nanoliter gas core volumes and a membrane thickness of approximately 3 μm. Alternatively physical rearrangement of the core and shell allowed for the formation of polymeric microlenses. On-demand formation of the polymer lenses in wells and through-holes polydimethylsiloxane (PDMS) structures was achieved. Optical properties of the lenses were controlled by changing the dimension of these structures.

Chromatic control in coextruded layered polymer microlenses

We describe the formation, characterization and theoretical understanding of microlenses comprised of alternating polystyrene and polymethylmethacrylate layers produced by multilayer coextrusion. These lenses are fabricated by photolithography, using a grayscale mask followed by plasma etching, so that the refractive index alternation of the bilayer stack appears across the radius of the microlens. The alternating quarter-wave thick layers form a one-dimensional photonic crystal whose dispersion augments the material dispersion, allowing one to sculpt the chromatic dispersion of the lens by adjusting the layered structure. Using Huygen's principle, we model our experimental measurements of the focal length of these lenses across the reflection band of the multilayer polymer film from which the microlens is fashioned. For a 56 μm diameter multilayered lens of focal length 300 μm, we measured a ∼ 25% variation in the focal length across a shallow, 50 nm-wide reflection band.

Self-aligned process for forming microlenses at the tips of vertical silicon nanowires by atomic layer deposition

The microlens is a key enabling technology in optoelectronics, permitting light to be efficiently coupled to and from devices such as image sensors and light-emitting diodes. Their ubiquitous nature motivates the development of new fabrication techniques, since existing methods face challenges as microlenses are scaled to smaller dimensions. Here, the authors demonstrate the formation of microlenses at the tips of vertically oriented silicon nanowires via a rapid atomic layer deposition process. The nature of the process is such that the microlenses are centered on the nanowires, and there is a self-limiting effect on the final sizes of the microlenses arising from the nanowire spacing. Finite difference time domain electromagnetic simulations are performed of microlens focusing properties, including showing their ability to enhance visible-wavelength absorption in silicon nanowires.

Surfactant-mediated formation of polymeric microlenses from interfacial microdroplets.

Nano- and micro-scale lenses have a range of potential applications, such as in antireflective layers in photovoltaic or light emission devices, and in super resolution imaging in the near field modes. One of the protocols to mass produce polymeric microlenses is through the polymerization of microdroplets of a monomer precursor that are produced at solid–liquid interfaces by a solvent exchange technique. In this work, we have advanced this protocol by using surfactants. A cationic surfactant was added to the liquid phase for the control over the formation and morphology of polymerisable microdroplets and their resultant microlenses (i.e. the polymerized microdroplets). The results demonstrate that the surfactant could enable the production of polymerizable microdroplets on hydrophilic substrates by the solvent exchange technique, and eliminate the restriction by the substrate wettability on the microlens fabrication. Furthermore, the size distribution and aspect ratio of microlenses could be tuned by the surfactant concentration.

Formation of micro lens by laser polymerization

AbstractRecently, micro lenses have been in demand for uniting laser devices and optical fibers. We have fabricated a new type of plastic micro lens by laser polymerization. The amount of resin polymerized by exposure to laser light (light curing) depends on the laser power and the exposure time. The shape of the lens can be controlled by changing the conditions of laser irradiation. In this paper, the characteristics of the lens formed by this method are examined. The relation between the lens shape and the conditions of laser irradiation are investigated, and the conditions for reducing transverse spherical aberration are examined. A lens 390 μm in diameter was formed. The area that can be used for light coupling from a laser diode to a multimode fiber will be 81% of the total lens area. © 2012 Wiley Periodicals, Inc. Electron Comm Jpn, 95(2): 59–67, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10339

Ray tracing for the optics at nano‐textured ZnO–air and ZnO–silicon interfaces

AbstractWe investigate the scattering behavior of nano‐textured ZnO–Air and ZnO–Silicon interfaces for the application in thin film silicon solar cells. Contrary to the common approach, the numerical solution of the Maxwell's equations, we introduce a ray tracing approach based on geometric optics and the measured interface topography. The validity of this model is discussed by means of scanning near‐field optical microscopy (SNOM) measurements and numerical solutions of the Maxwell's equations. We show, that the ray tracing model can qualitatively describe the formation of micro lenses, which are the dominant feature of the local scattering properties of the investigated interfaces. A quantitative analysis for the ZnO–Silicon interface at λ = 488 and 780 nm shows that the ray tracing model corresponds well to the numerical solution of the Maxwell's equations, especially within the first 1.5 µm distance from the interface. Direct correlations between the locally scattered intensity and the interface topographies are found. Copyright © 2011 John Wiley & Sons, Ltd.

Dynamical formation of microlenses by the reflow method: numerical simulation and experimental study of the process fabrication

In order to study the dynamics of microlens formation by the reflow method, we develop a model based on the Navier–Stokes equation that describes the formation of a microlens from its initial state (photolithographic dot) up to its final shape (rounded microlens). In CMOS imagers, photoresists used to form microlenses contain crosslinkers in order to obtain chemically and thermally stable microlenses at the end of the process. This model takes into account the effect of surface tension as well as the viscosity evolution with bake time, due to the crosslinking reaction. The results of the dynamic modelling show that the microlens passes through different intermediate steps before achieving its expected final spherical shape. It also shows that fast crosslinking kinetics leads to non-spherical microlenses. Indeed the fast increase of viscosity has the effect of blocking the formation of the microlens and freeze the microlens profile in an intermediate shape. Thus, with such type of photoresist materials, contrary to what is reported in the literature, the final shape of the microlens does not depend only on the initial volume or the aspect ratio of the resist pattern. This is the competition, during the melting bake, between the microlens formation under the effect of surface tension and the crosslinking reaction that determines, over all, the final shape that the microlens will adopt.

Thermal analysis of microlens formation on a sensitized gelatin layer

We analyze a mechanism of direct laser writing of microlenses. We find that thermal effects and photochemical reactions are responsible for microlens formation on a sensitized gelatin layer. An infrared camera was used to assess the temperature distribution during the microlens formation, while the diffraction pattern produced by the microlens itself was used to estimate optical properties. The study of thermal processes enabled us to establish the correlation between thermal and optical parameters.