Fabrication Of Microlens Arrays Research Articles

3D OPC method for controlling the morphology of micro structures in laser direct writing.

A 3D optical proximity correction (OPC) method for controlling the morphology of micro-structures in laser direct writing is proposed, considering both the optical proximity effect and nonlinear response of a thick-film photoresist. This method can improve the manufacturability and optical performance of devices, and can be used for most 3D micro\nano structures. Its application in the fabrication of a quadratic curvature microlens array shows that the shape of the lens is well controlled; that is, when the height of the lens is 5.25 µm, the average height error of the lens shape is less than 5.22%.

Fabrication of Microlens Arrays with High Numerical Aperture Based on Femtosecond Laser Self-Modulating Processing Method

Fabrication of Microlens Arrays with High Numerical Aperture Based on Femtosecond Laser Self-Modulating Processing Method

A theoretical and experimental investigation into tool setting induced form error in diamond turning of micro-lens array

Micro-lens array (MLA) has been widely used for 3D imaging, etc., due to its excellent functional performances. Ultra-precision diamond turning (UPDT) offers a satisfying solution to the high-quality fabrication of MLA with sub-micrometric form accuracy and nanometric surface roughness. However, in UPDT tool setting, errors would deteriorate form accuracy as a crucial factor. This study focuses on discussing the tool setting effect on form error of MLA and proposes a new two-step tool setting method for UPDT. Firstly, a theoretical model was established for form error of MLA under tool setting errors. Moreover, a new two-step tool setting method was developed with high accuracy to control the tool setting errors. Finally, a series of experiments were carried out with different tool setting errors for the MLA fabrication, and its form error would be measured. The theoretical and experimental results are found that the proposed tool setting method is effective with a high-precision accuracy and the tool setting errors would crucially induce periodical form error at the MLA of UPDT. Significantly, the study draws up a comprehensive understanding of the tool setting effect on form accuracy of MLA in UPDT with the further improvement.

Symmetrical Coupling Multi-Cavity Bandpass Filter for CMOS Compatible Fluorescence Detection

Integration of functional components such as excitation light source, micro-fluidic chip, optical filters, and complementary metal–oxide–semiconductor (CMOS) sensors on a single photonics chip for fluorescence detection by advanced semiconductor process, is a future technology for rapid responding, high accuracy, and handheld point-of-care diagnosis protocol in field application of daily life. We designed a CMOS compatible bandpass filter on a glass substrate based on symmetrical coupling multi-cavity (SCMC) SiN/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film stacker aimed at detection of 5-carboxylfluorescein (5-FAM), a commonly used fluorescence probe in biotechnology and medicine diagnosis. The calculation based on transfer matrix method (TMM) and 2D finite difference time domain (FDTD) algorithm, revealed that there was an optimized number of cavities in the SCMC stacker, for the transmittance in the pass band decreasing with the increment of the number of cavities while the optical density in the stop band improving with it. For a SCMC stacker with 10 resonant cavities, both the TMM and 2D FDTD calculation, figured out that the fluorescence emission and the remained excitation source should be directed to incident on the SCMC stacker with an angle less than 18° for a good passing of fluorescence emission centered at 520 nm and blocking of excitation light of a wavelength of 488 nm. It provided new insights for future design and fabrication of micro-lens array and micro-apertures array for the highly integrated photonics chip aimed at detection of fluorescence on a single chip.

Flexible Superhydrophobic Microlens Arrays for Humid Outdoor Environment Applications.

A microlens array (MLA) is an essential optical imaging device in the applications of augmented and virtual realities. The imaging of MLA would become blurry in a humid outdoor atmosphere. While the incorporation of superhydrophobicity to MLA would prevent the adhesion of droplets, the complex structure and the multiple fabrication process reduce the capability of optical imaging of MLA. Herein, a flexible superhydrophobic MLA with good optical imaging capability is successfully fabricated by the combination of 3D direct laser writing (DLW) and soft lithography. 3D DLW allows the fabrication of MLA with a hierarchical pillar array (h-MLA) in one step, which ensures good optical properties of the resulting polydimethylsiloxane (PDMS) h-MLA. The resulting h-MLAs with pitches ranging between 50 and 100 μm are superhydrophobic from which water droplets slide away at a sliding angle smaller than 15.6° and bounce off from the surface. Meanwhile, the hierarchical pillar array has a limited impact on the imaging capability and the field of view of h-MLA. With an optimized pitch of 60 μm, h-MLA has a transparency as good as MLA. Moreover, PDMS h-MLA retains excellent optical and superhydrophobic properties when bent and in an extremely humid environment. We believe that the proposed h-MLA could find applications in outdoor environments.

A Theoretical and Experimental Investigation of High-Frequency Ultrasonic Vibration-Assisted Sculpturing of Optical Microstructures

Ultrasonic vibration-assisted cutting (UVAC) has been regarded as a promising technology to machine difficult-to-machine materials. It allows for a sub-micrometer form accuracy and surface roughness in the nanometer range. In this paper, high-frequency vibration-assisted sculpturing is used to efficiently fabricate quadrilateral microlens array with sharp edges, instead of using slow-slide-servo diamond turning with vibration. The machining principle of diamond sculpturing, the cutting dynamics of ultrasonic vibration, and the tool edge on the theoretical form error between the designed structure and the machined structure were investigated for this technique. Then, the quadrilateral microlens array was machined by means of conventional sculpturing (CS) and high-frequency ultrasonic vibration-assisted sculpturing (HFUVAS), respectively, followed by a study of the cutting performances including form accuracy, the surface morphology of the machined structure, and the tool wear. Results showed that conventional sculpturing fabricated microlens array with poor form accuracy and surface finish due to couple effect of material adhesion and tool wear, while the high-frequency ultrasonic vibration-assisted sculpturing achieved optical application level with sub-micrometer form accuracy and surface roughness of nanometer due to reduction of material adhesion and tool wear resulted from high-frequency intermittent cutting.

Rapid Fabrication of Silica Microlens Arrays via Glass 3D Printing.

Rapid manufacturing of high purity fused silica glass micro-optics using a filament-based glass 3D printer has been demonstrated. A multilayer 5 × 5 microlens array was printed and subsequently characterized, showing fully dense lenses with uniform focal lengths and good imaging performance. A surface roughness on the order of Ra = 0.12 nm was achieved. Printing time for each lens was <10 s. Creating arrays with multifocal imaging capabilities was possible by individually varying the number of printed layers and radius for each lens, effectively changing the lens height and curvature. Glass 3D printing is shown in this study to be a versatile approach for fabricating silica micro-optics suitable for rapid prototyping or manufacturing.

Defocus digital light processing stereolithography for rapid manufacture of microlens arrays

This study applied defocusing to digital light processing (DLP) stereolithography for the fabrication of microlens arrays (MLAs) within 1 s. We studied the effects of exposure energy, defocus distance, and a diameter adjustment algorithm to ensure printed MLAs with designed dimensions. Experiment results demonstrate that our simple fabrication method is applicable to the manufacture of various MLA designs, while achieving nanoscale surface roughness and good image quality. We determined that the height of the MLAs is proportional to the exposure energy. The highest height-to-diameter ratio achieved in this study was 0.63 (diameter = 200 µm; height = 126 µm). Our use of defocusing significantly reduced the average surface roughness (Ra) of the printed MLAs to 129 nm with a corresponding improvement in image resolution 45.3 lp/mm. Our use of a diameter adjustment algorithm in designing the digital mask helped preserve the dimensionality of the printed MLAs. The proposed manufacturing process was used to create a variety of MLAs with numerical apertures as high as 0.980, multiple focal lengths on a single substrate (from 21 µm to 199 µm), and fill factors as high as 77.98 %.

Fabrication of high aspect-ratio aspheric microlens array based on local spiral diamond milling

Ultraprecision mold machining combined with precision glass molding is the most promising technology for the mass production of glass microlens arrays (MLAs). However, fabricating an MLA with a high aspect-ratio (AR) (ratio of height to aperture), submicron scale profile accuracy, nanoscale surface finish, and good consistency remains a considerable challenge. A local spiral diamond milling (LSDM) method is proposed to generate a high AR MLA on a nickel-phosphorous (Ni-P) plated mold. A spiral toolpath generation algorithm that considers the tool edge radius and performs profile error (PV) compensation is developed. Each lenslet at any local position can be precisely machined by controlling the servo motions of the three translational axes. Then, the entire MLA can be generated by shifting the toolpath to go through the centers of all lenslets according to the MLA layout. The tool parameters are optimized to avoid local and global tool interference during machining. The generated toolpath provides steady slide axis movements to avoid dramatic changes in cutting speed and acceleration. An MLA with an AR of 0.166 is fabricated. The results show that the fabricated mold and the molded lenses have a profile accuracy (PV) of less than 1 μm and a surface roughness (Ra) of less than 14 nm. The cross-sectional profiles indicate that the fabricated MLA has high machining consistency.

Surface Topographical Control of a Liquid Crystal Microlens Array Embedded in a Polymer Network

A novel approach for fabricating a microlens array with a tunable surface topographical structure and focal length is proposed in the present study. The microlens array was manufactured through the photoinduced molecular reorientation of nematic liquid crystals (LCs) stabilized by a polymer network. The fabricated microlens array had a mountain-shaped topographical structure due to the accumulation of polymers and LC molecules. The molecular orientation of the LC inside the microlens was disordered, while the outer side of the microlens was ordered. The thermal expansion of the polymer network and the phase transition of the LC molecules within the microlens array allowed the surface topographical structure and the focal length to be reversibly tuned under heat treatment. The results of this research work will enable future implementations to provide a thermally tunable microlens array.

Rapid fabrication of large-area concave microlens arrays on silica glasses by femtosecond laser bursts.

An efficient and flexible method using femtosecond laser bursts assisted by wet etching is presented to fabricate large-area high-quality microlens arrays (MLAs) on a silica glass surface. In this method, femtosecond laser bursts can ablate micro craters on silica glass in a fast, single-step process by controlling the electron density and a high-speed scanning galvanometer, and the influence mechanism of the number of pulses within a burst on the accuracy and quality of micro craters is analyzed in detail. The experimental results show that the preparation efficiency of micro craters is significantly improved to approximately 32,700 per second. By subsequent acid etching, concave microlenses with controllable dimensions, shapes, and alignments are easily obtained. A large area close-packed hexagonal concave MLA is successfully fabricated by using this method and shows high surface quality and uniformity, which excellently demonstrates the feasibility and flexibility of rapidly fabricating MLAs in the burst regime.

Fabrication of Cylindrical Microlens Array on RB-SiC Moulds by Precision Grinding with MAWJ-Textured Diamond Wheels

Cylindrical microlens array (CMA) is applied widely in imaging, sensing, and laser machining fields. Among the many techniques for machining CMA, moulding is considered a mass-production method with low-cost and good accuracy. Aimed at the present problems in the machining of CMA moulds, which include low processing efficiency and the prediction of the surface topography, this paper focused on the fabrication of CMA on RB-SiC moulds by precision grinding with micro-abrasive water jet (MAWJ) textured diamond wheels. The combined rough–fine grinding strategy for ceramic mould materials was proposed. The grinding experiments of CMA were carried out. The ultra-precision grinding method was optimized to obtain high shape accuracy and a high-quality surface of RB-SiC moulds. It was found that by using MAWJ-textured diamond wheels, the profile error in the peak-to-valley value (PV) of the CMA moulds can be further reduced to 6.7 μm by using the combined rough–fine strategy grinding process.

Fabrication of Microlens Arrays with High Quality and High Fill Factor by Inkjet Printing

AbstractMicrolens arrays (MLAs) have a variety of applications in, e.g., display systems, projection optics, and sensors. They can be manufactured by various fabrication methods. Among all, inkjet printing stands out because it offers a straightforward, versatile, and low‐cost fabrication route. However, extra manufacturing steps such as photolithography are so far involved to pre‐structure the substrate in order to improve the uniformity of the printed MLAs and achieve a high fill factor (FF). In this study, the fabrication of MLAs is reported on unstructured substrates by inkjet printing using an optimized UV‐curable ink on top of self‐assembled monolayers (SAMs). The latter allows for tuning the surface free energy and thus the aspect ratio of the microlenses. The high uniformity of the printed MLAs is demonstrated by the automatic quantitative evaluations, where the standard deviations of the radii are below 2.5% and of the sag heights are less than 3.9%. An unprecedented FF of 88% amongst all inkjet‐printed MLAs on unstructured substrates is achieved. Digitally controlled large area fabrication is demonstrated, both, on rigid as well as on flexible substrates, opening a pathway for customized microoptics by additive manufacturing.

Fabrication of High Precision Silicon Spherical Microlens Arrays by Hot Embossing Process.

In this paper, a high-precision, low-cost, batch processing nanoimprint method is proposed to process a spherical microlens array (MLA). The nanoimprint mold with high surface precision and low surface roughness was fabricated by single-point diamond turning. The anti-sticking treatment of the mold was carried out by perfluorooctyl phosphoric acid (PFOPA) liquid deposition. Through the orthogonal experiment of hot embossing with the treated mold and subsequent inductively coupled plasma (ICP) etching, the microstructure of MLA was transferred to the silicon substrate, with a root mean square error of 17.7 nm and a roughness of 12.1 nm Sa. The average fitted radius of the microlens array units is 406.145 µm, which is 1.54% different from the design radius.

Comparative Additional Factor for Diffraction Loss On (TEM01) Mode from That of (TEM00) Mode

Comparative Additional Factor for Diffraction Loss On (TEM01) Mode from That of (TEM00) Mode

Fabrication of microlens arrays with high filling factors by combining a thermal reflow and parylene CVD technique and the applications on OLEDs.

In this paper, microlens array (MLA) templates with high filling factors were prepared by combining a thermal reflow method and parylene chemical vapor deposition (CVD). Then photoresist MLAs were replicated from the MLA templates by using ultraviolet nanoimprint technology. The surface morphology of the replicated photoresist MLAs was characterized by scanning an electron microscope and optical microscope. Results show that the photoresist MLAs have a relatively smooth surface, and the filling factor has been improved obviously. Also, the surface profiles of the MLAs were measured. The optical imaging properties of the MLAs were also characterized, and they had a relatively good imaging performance. Finally, the photoresist MLAs were applied on organic LEDs (OLEDs), and their luminance and current efficiencies were measured. Results show that the current efficiency of the OLEDs increased by about 42.41%, 29.01%, and 35.51%, respectively, for OLEDs with circular, hexagonal, and square MLAs. All the results above indicate that it is a simple and effective process to prepare MLA templates with high filling factors by combining thermal reflow and CVD techniques, and the prepared photoresist MLAs have great application potential in OLED areas.

Fabrication of a microlens array featuring a high aspect ratio with a swinging diamond tool

Microlens arrays are gaining wider applications due to their unique optical geometry and excellent optical properties. Ultra-precision diamond turning is preferable for fabricating microlens arrays with high form accuracy. However, the interference between the flank face of the diamond tool and the finished surface restricts its application in machining microlens arrays with a high aspect ratio. In this paper, a novel method based on the slow tool servo turning technique is proposed to fabricate these microlens arrays by introducing a rotational motion (A-axis) to swing the diamond cutting tool and adjust the actual tool clearance angle in real time, which can prevent tool interference effectively. The machining system and method principle are introduced first. Then, the toolpath is generated, and the influence of the tool nose radius is compensated for. Finally, machining experiments of cutting spherical lens arrays with high aspect ratios are conducted on a Nanotech 650UPL ultraprecision lathe, and the machined lenses are inspected with an optical microscope, a stylus profilometer and a white light interferometer. The measurement results of the spherical lens arrays machined by the proposed method and the conventional slow tool servo turning method are compared, which demonstrates the superiority of the proposed method in fabricating high-quality lens arrays featuring a high aspect ratio.

Morphology adjustable microlens array fabricated by single spatially modulated femtosecond pulse

AbstractSilica microlens arrays (MLAs) with multiple numerical-apertures (NAs) have high thermal and mechanical stability, and have potential application prospects in 3D display and rapid detection. However, it is still a challenge to rapidly fabricate silica MLAs with a larger range of NAs and how to obtain multiple NAs in the same aperture diameter. Here, a wet etching assisted spatially modulated femtosecond laser pulse fabricating technology is proposed. In this technology, Gaussian laser pulse is modulated in the axial direction to create a pulse with a large aspect ratio, which is used to modify the silica to obtain a longer modification distance than traditional technology. After that, a microlens with a larger NA can be obtained by etching, and the NA variable range can be up to 0.06–0.65, and even under the same aperture, the variable NA can range up to 0.45–0.65. In addition, a single focus is radially modulated into several focus with different axial lengths to achieve a single exposure fabricating of MLA with multiple NAs. In characterization of the image under a microscope, the multi-plane imaging characteristics of the MLA are revealed. The proposed technology offers great potential toward numerous applications, including microfluidic adaptive imaging and biomedical sensing.

High-speed, large-area and high-precision fabrication of aspheric micro-lens array based on 12-bit direct laser writing lithography

Aspheric micro-lens array (AMLA), featured with low dispersion and diffraction-limited imaging quality, plays an important role in advanced optical imaging. Ideally, the fabrication of commercially applicable AMLAs should feature low cost, high precision, large area and high speed. However, these criteria have been achieved only partially with conventional fabrication process. Herein, we demonstrate the fabrication and characterization of AMLAs based on 12-bit direct laser writing lithography, which exhibits a high fabrication speed, large area, perfect lens shape control via a three-dimensional optical proximity correction and average surface roughness lower than 6 nm. In particular, the AMLAs can be flexibly designed with customized filling factor and arbitrary off-axis operation for each single micro-lens, and the proposed pattern transfer approach with polydimethylsiloxane (PDMS) suggests a low-cost way for mass manufacturing. An auto-stereoscopic-display flexible thin film with excellent display effect has been prepared by using above technology, which exhibits a new way to provide flexible auto-stereoscopic-display at low cost. In brief, the demonstrated fabrication of AMLAs based on direct laser writing lithography reduce the complexity of AMLA fabrication while significantly increasing their performance, suggesting a new route for high-quality three-dimentional optical manufacturing towards simplified fabrication process, high precision and large scale.

On-demand liquid microlens arrays by non-contact relocation of inhomogeneous fluids in acoustic fields.

Microlens arrays (MLAs) are key micro-optical components that possess a high degree of parallelism and ease of integration. However, rapid and low-cost fabrication of MLAs with flexible focusing remains a challenge. Herein, liquid MLAs with dynamic tunability are presented using non-contact acoustic relocation of inhomogeneous fluids. By designing ring-shaped acoustic pressure node (PN) arrays, the denser fluid of miscible liquids is relocated to PNs, and liquid MLAs with ideal morphology are obtained. The experimental results demonstrate that the liquid MLAs possess a powerful reconfigurability with long-term stability and sharp imaging that can conveniently switch between the on and off state and can dynamically magnify by simply adjusting the acoustic amplitude. Moreover, the high biocompatibility inherited from liquids accompanied by the acoustic treatment allows cells to be within working distance of the MLAs without immersion, as would be required for a solid lens. This innovative liquid MLA is inexpensive to manufacture and possesses continuous focus, fast response, and satisfactory bioaffinity, and thus offers promising potential for microfluidic adaptive imaging and biomedical sensing, especially for live cell imaging.