Microlens Research Articles

Electrohydrodynamically printed microlens arrays with controllable curvature based on surface functionalization

Precisely controlling the optical characteristics of the microlens array (MLA) is a key issue for the MLA's fabrication and its applications. A cost-effective method for fabricating MLA with different curvatures and diameters by surface functionalization and electrohydrodynamic inkjet (E-jet) printing is proposed. The surface with self-assembled monolayers has low surface energy, which greatly improves the contact angle of the microlens. The UV-ozone treatment and neutral density filters with different optical densities are used to control the wettability of the substrates. Based on this method, the curvatures of the microlens can be controlled easily and the numerical aperture (NA) of the microlens can be adjusted from 0.18 to 0.49. Compared with traditional fabrication techniques, the method we demonstrated is flexible, low-cost, rapid, and capable of fabricating MLA with large area, high packing density, desirable NA, and diameters.

Laser-assisted direct roller imprinting of large-area microstructured optical surfaces

In this study, a high-throughput fabrication method called laser-assisted direct roller imprinting (LADRI) was developed to lower the cost of nanoimprinting large-area polymer films and to address problems associated with nanoimprinting, namely, microstructural damage and precision in flatness of entire film. With LADRI, the laser directly heats the microstructured surface of the roller mold, which heats and melts the surface of a polymethyl methacrylate (PMMA) film to replicate the microstructures on the mold rapidly. In this study, the effects of laser power density, scanning speed, size of the microstructures, and contact pressure on the replication speed were investigated experimentally. The replication speed increased as the power and scanning speed increased. However, because the film required heating until it filled the entire depth of the microstructure, an appropriate replication speed was necessary. This result was supported by simulation of the temperature distribution inside the mold and the PMMA using transient heat conduction analyses. To demonstrate the applications of LADRI, two different optical surfaces were replicated: an antireflection (AR) structure with conical structures sized several hundred nanometers and a light-extraction structure with a microlens array (MLA) comprising 10 μm lenses, for display and illumination, respectively. The replication degree of the MLA was governed by the contact pressure. Polymer flow simulation indicated that the heat conduction and flow speeds of the melted PMMA surface were comparable within several tens of micrometers. In addition, the reflectivity of the AR structure decreased from 4 to 0.5%, and the light intensity of the light-extraction structure increased by a factor of 1.47.

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.

Effect of rapid thermal annealing on the surface properties of the microlens arrays machined on monocrystalline silicon

Microstructure arrays, such as microlens arrays, play a significant role in optical systems, biomedical imaging, and telecommunications. However, the machining-induced subsurface defects deteriorate their performance and functionality. To address this issue, this study proposes a rapid thermal annealing method to heal the subsurface defects using different temperatures ranging from 200 °C to 1000 °C in a vacuum. Firstly, the ultra-precision diamond sculpturing process is employed to machine the high-quality microlens array on the monocrystalline silicon surface. Then, the effects of the rapid thermal annealing on the microlens array surface, such as surface roughness and subsurface defect, are comprehensively investigated. Experimental results show that the annealing temperature of >600 °C contributes to the decrease in surface roughness and subsurface defect. Furthermore, to reveal the healing mechanism, a molecular dynamics simulation of rapid thermal annealing is performed by controlling the bulk temperature of machined monocrystalline silicon from 500 K to 1300 K. The simulation results show that recrystallization always occurred on the interface between the amorphous layer and monocrystalline silicon substrate and the healing mechanism should be solid phase epitaxy rather than random nucleation. The research findings would contribute to fabricating the defect-free optical lens in the industry.

Controlling the size and curvature radius of concave microlens array on fused silica by wet-etching-assisted with picosecond laser

Controlling the size and curvature radius of concave microlens array on fused silica by wet-etching-assisted with picosecond laser

Quantitative real-time phase microscopy for extended depth-of-field imaging based on the 3D single-shot differential phase contrast (ssDPC) imaging method.

Optical diffraction tomography (ODT) is a promising label-free imaging method capable of quantitatively measuring the three-dimensional (3D) refractive index distribution of transparent samples. In recent years, partially coherent ODT (PC-ODT) has attracted increasing attention due to its system simplicity and absence of laser speckle noise. Quantitative phase imaging (QPI) technologies represented by Fourier ptychographic microscopy (FPM), differential phase contrast (DPC) imaging and intensity diffraction tomography (IDT) need to collect several or hundreds of intensity images, which usually introduce motion artifacts when shooting fast-moving targets, leading to a decrease in image quality. Hence, a quantitative real-time phase microscopy (qRPM) for extended depth of field (DOF) imaging based on 3D single-shot differential phase contrast (ssDPC) imaging method is proposed in this research study. qRPM incorporates a microlens array (MLA) to simultaneously collect spatial information and angular information. In subsequent optical information processing, a deconvolution method is used to obtain intensity stacks under different illumination angles in a raw light field image. Importing the obtained intensity stack into the 3D DPC imaging model is able to finally obtain the 3D refractive index distribution. The captured four-dimensional light field information enables the reconstruction of 3D information in a single snapshot and extending the DOF of qRPM. The imaging capability of the proposed qRPM system is experimental verified on different samples, achieve single-exposure 3D label-free imaging with an extended DOF for 160 µm which is nearly 30 times higher than the traditional microscope system.

Q -balls in the sky

There may exist extended configurations in the dark matter sector that are analogs of structures in the visible sector. In this work, we explore nontopological solitonic configurations, specifically Q-balls, and study when they may form macroscopic astrophysical structures and what their distinct characteristics might be. We study in some detail theoretical bounds on their sizes and constraints on the underlying parameters, based on criteria for an astrophysical Q-ball’s existence, gravitational stability and viability of solutions. Following this path, one is able to obtain novel limits on astrophysical Q-ball sizes and their underlying parameters. We also explore the gravitational lensing features of different astrophysical Q-ball profiles, which are more general than the simple thin-wall limit. It is seen that the magnification characteristics may be very distinct, depending on the actual details of the solution, even for astrophysical Q-balls having the same size and mass. Assuming that such astrophysical Q-balls may form a small component of the dark matter in the Universe, we place limits on this fraction from the gravitational microlensing surveys EROS-2, OGLE-IV, HSC-Subaru and the proposed future survey WFIRST. Exploring various astrophysical Q-ball profiles and sizes, it is found that while for most intermediate masses that we consider, the dark matter fraction comprising astrophysical Q-balls is at most subpercent, for other masses it may be significantly higher. Published by the American Physical Society 2024

Photografting of Surface‐Assembled Hydrogel Prepolymers to Elastomeric Substrates for Production of Stimuli‐Responsive Microlens Arrays (Adv. Funct. Mater. 3/2024)

Photografting of Surface‐Assembled Hydrogel Prepolymers to Elastomeric Substrates for Production of Stimuli‐Responsive Microlens Arrays (Adv. Funct. Mater. 3/2024)

A New Method to Detection of Laser Focal Position based on Microlens Array

A New Method to Detection of Laser Focal Position based on Microlens Array

Manufacturing reflection holographic couplers for see-through applications recorded in photopolymers without prisms: An experimental validation

In the present work, the viability of a novel recording geometry to produce reflection holographic couplers is analyzed. Recalling the idea of previous works, photopolymers are used as the recording material because they have been proven to be well-suited for the intended see-through application: the capability to provide a virtual image without compromising the information about the surrounding environment. Moreover, holography fundamentals give us the proper background to examine the proposed design, where no prisms or microlenses arrays are used. Aiming to support the analysis, we provide experimental evidence that the produced reflection holographic gratings exhibit the correct properties to work as a coupler, where the sensitivity of the material and its properties are studied and examined.

Micron-level processing technology of microlens array （MLA） photolithography based on convolutional neural network

Micron-level processing technology of microlens array （MLA） photolithography based on convolutional neural network

Microfluidics assisted optics manufacturing technique

The conventional micro/nano-manufacturing techniques can hardly process interior microstructures. The entire fabrication process is complex and requires large-footprint and high-cost equipment. The presented microfluidics assisted optics manufacturing technique is feasible to create the curved surface inside microstructure using various modified materials. The fabrication process is simple. Only small, low-cost devices are needed. In this paper, microfluidics assisted optics manufacturing technique is introduced in detail and compared with the current manufacturing techniques. A diversity of interesting micro-optics, including microlens array and compound eye, are demonstrated. These optical components are all fabricated by the microfluidics assisted manufacturing technique and possess their own outstanding features.

Micro-optical illumination properties of hierarchical microlens arrays formed by hot-embossing

Micro-optical illumination properties of hierarchical microlens arrays formed by hot-embossing

Design and characterization of microlens arrays for InGaAs single photon detectors

Design and characterization of microlens arrays for InGaAs single photon detectors

Research on Space Positioning Technology of Microlens Array Based on Multi-Camera

Research on Space Positioning Technology of Microlens Array Based on Multi-Camera

A liquid-crystal microlens with dual-layers arrayed pattern electrode for the effective modulation of incident light beams

In this paper, an electrically controlled liquid crystal (LC) microlens array based on dual-layer arrayed planar pattern electrode is reported for effective light wave modulation. By adjusting the voltages applied to two planar arrayed electrodes within one substrate of the LC microlens, an adjustable focused circular ring or point-shaped light spot can be formed. Dual-layers arrayed pattern electrode with a minimum interval spacing of approximately ~10μm and a maximum of 130μm are achieved on one substrate by using standard microelectronic lithography, etching, coating film, and other processes. Experimental results are presented and discussed to illustrate outstanding performance of electrically focusing and modulation capability of the proposed LC device. This approach will serve as inspiration for the continued development and design of LC optical elements, enabling applications such as light field imaging, wavefront detection/correction, and the advancement of imaging augmented systems.

Underwater wireless optical NOMA communication experiment system exploiting GaN-based micro-LED array grouping

Underwater wireless optical NOMA communication experiment system exploiting GaN-based micro-LED array grouping

Integrated Deep-Ultraviolet Micro-LED Array with Ultralow Contact Resistance and Ultrahigh Bandwidth for Intermixed Solar-Blind Optical Wireless Communication

Integrated Deep-Ultraviolet Micro-LED Array with Ultralow Contact Resistance and Ultrahigh Bandwidth for Intermixed Solar-Blind Optical Wireless Communication

Large modulation bandwidth GaN-based micro-LED arrays on Si Substrates with graded In composition barriers

Large modulation bandwidth GaN-based micro-LED arrays on Si Substrates with graded In composition barriers

Free-floating or Wide-orbit? Keck Adaptive-optics Observations of Free-floating Planet Candidates Detected with Gravitational Microlensing

Recent detections of extremely short-timescale microlensing events imply the existence of a large population of Earth- to Neptune-mass planets that appear to have no host stars. However, it is currently unknown whether these objects are truly free-floating planets or whether they are in wide orbits around a distant host star. Here, we present an analysis of high-resolution imaging observations of five free-floating planet candidates collected with the Keck telescope. If these candidates were actually wide-orbit planets, then the light of the host would appear at a separation of 40–60 mas from the microlensing source star. No such stars are detected. We carry out injection and recovery simulations to estimate the sensitivity to putative host stars at different separations. Depending on the object, the presented observations rule out 11%–36% of potential hosts assuming that the probability of hosting a planet does not depend on the host mass. The results are sensitive to the latter assumption, and the probability of detecting the host star in the analyzed images may be a factor of 1.9 ± 0.1 larger, if the exoplanet hosting probability scales as the first power of the host star mass, as suggested by recent studies of planetary microlensing events. We argue that deeper observations, for example with JWST, are needed to confidently confirm or refute the free-floating planet hypothesis.