Microlens Research Articles

Research on Characteristics Matching of Micro-LED Devices

This paper presents the design of a 40 × 40 micro-light-emitting (micro-LED) test array based on a 20 mm × 20 mm substrate. A study of the relationship between luminous brightness, driving current, and driving voltage revealed that the data voltages of the red, green, and blue micro-LED array from 0 to 255 grey levels are 0.31 V, 0.29 V, and 0.30 V, respectively, under the condition that the target brightness of the white field is 1000 nits and the color temperature is 9300 K. The brightness range of the red micro-LED array is 64.8–101.2%, the brightness range of the green micro-LED array is 66.5–102.8%, and the brightness range of the blue micro-LED array is 53.5–129.2%. In order to overcome the luminance nonuniformity, a grey level depth of 12 -bit is required. A 10T3C pixel driver circuit based on low-temperature polysilicon (LTPS) with a depth of 12 bits greyscale is designed and fabricated into the micro-LED display. A brightness uniformity of 84.1–97.1% can be achieved by brightness correction combined with a 12-bit greyscale depth system for micro-LED display. This provides a valuable reference point for subsequent improvements in the quality of micro-LED displays.

Infrared microlens formation on chalcogenide polymer surface via femtosecond laser pulse ablation

In this study, we introduced micro-optical surface formation via femtosecond (fs) laser pulse scanning to chalcogenide polymer (ChP), a promising material for cost-effective infrared applications. Employing this method, we successfully fabricated a large-area poly(sulfur-random-(1,3-diisopropenylbenzene)) (S-r-DIB) microlens array (MLA) component. Each micro-concave spherical surface was crafted with a single fs laser pulse, serving as a micro-concave lens surface. We achieved a quasi-periodic MLA sample with over 2 × 105 micro-lenslets within a 10 mm × 10 mm footprint. Additionally, precise locating of laser pulse irradiation enabled us to create a hexagonal MLA with a filling factor over 37 %. Morphological investigations and imaging tests confirmed the adequate surface quality of the fabricated components, with its uniformity revealed by the virtual foci grid in near infrared region. To elucidate the forming conditions and mechanisms, we studied the evolution of surface morphology under various laser irradiation conditions. Laser induced damage thresholds of S70-r-DIB30 were experimentally determined for both 800 nm and 400 nm wavelengths under single- and multi-pulse irradiation scenarios. We identified the optimal fabrication fluence window as 115–205 mJ/cm2 with 800 nm single-pulse irradiation. The bandgap of the S70-r-DIB30 was estimated as 2.06 eV, and energy band analysis confirmed distinctions in ablation morphology. Furthermore, we investigated sub-surface morphology evolution using orthogonal ultrafast pump–probe imaging, revealing diversity compared to traditional inorganic and polymeric optical materials due to differing absorption and etching mechanisms. The elastic wave velocity of 3.2 km/s in this ChP and etching velocity of 0.7 μm/pulse were experimentally determined. These findings deepen our understanding of ChP material interaction with fs lasers, offering insights for potential applications such as surface engineering, substrate cutting, and micro-structure formation.

Fabrication of a microfluidic system with in situ-integrated microlens arrays using electrohydrodynamic jet printing

Microfluidic systems with integrated microlenses enhance cellular analysis and observation and have gained significant attention in the biomedical field. However, the integration and design of microlenses in microfluidic systems remain challenging. In this study, we utilize a high-precision electrohydrodynamic jet (E-jet) printing system for in-situ integration of microlens. By incorporating a tilting illumination observation module into the E-jet printing system, the print nozzle can be accurately positioned 10 μm above the microchannel bottom, thereby mitigating the edge effect of the microfluidic channels. We have developed a microfluidic system embedding microlens arrays (MLAs) that enable parallel, multichannel cell counting. The microfluidic system comprises nine channels, each featuring a 50 μm diameter microlens printed along the central axis. Using microlenses enables non-contact cell counting by detecting light-intensity changes. Simulating and optimizing the microfluidic channel size enable cells to align on the centerline of the channel and pass over the focal region of the microlens via inertial forces. As the cells flow through the microlens, the intensity of the focal spots decreases by approximately 50 %. The microfluidic cell-counting system can function independently or be integrated with other microfluidic systems as a unit, thus enhancing the single-cell operational and analytical capabilities of microfluidic systems.

Assessing the 3D resolution of refocused correlation plenoptic images using a general-purpose image quality estimator

Correlation plenoptic imaging (CPI) is emerging as a promising approach to light-field imaging (LFI), a technique enabling simultaneous measurement of light intensity distribution and propagation direction from a scene. LFI allows single-shot 3D sampling, offering fast 3D reconstruction for a wide range of applications. However, the array of micro-lenses typically used in LFI to obtain 3D information limits image resolution, which rapidly declines with enhanced volumetric reconstruction capabilities. CPI addresses this limitation by decoupling the measurement of the light field on two photodetectors with spatial resolution, eliminating the need for micro-lenses. 3D information is encoded in a four-dimensional correlation function, which is decoded in post-processing to reconstruct images without the resolution loss seen in conventional LFI. This paper evaluates the tomographic performance of CPI, demonstrating that the refocusing reconstruction method provides axial sectioning capabilities comparable to conventional imaging systems. A general-purpose analytical approach based on image fidelity is proposed to quantitatively study axial and lateral resolution. The analysis fully characterizes the volumetric resolution of any CPI architecture, offering a comprehensive evaluation of its imaging performance.

Bioarchitectonic Nanophotonics by Replication and Systolic Miniaturization of Natural Forms.

The mimesis of biological mechanisms by artificial devices constitutes the modern, rapidly expanding, multidisciplinary biomimetics sector. In the broader bioinspiration perspective, however, bioarchitectures may perform independent functions without necessarily mimicking their biological generators. In this paper, we explore such Bioarchitectonic notions and demonstrate three-dimensional photonics by the exact replication of insect organs using ultra-porous silica aerogels. The subsequent conformal systolic transformation yields their miniaturized affine 'clones' having higher mass density and refractive index. Focusing on the paradigms of ommatidia, the compound eye of the hornet Vespa crabro flavofasciata and the microtrichia of the scarab Protaetia cuprea phoebe, we fabricate their aerogel replicas and derivative clones and investigate their photonic functionalities. Ultralight aerogel microlens arrays are proven to be functional photonic devices having a focal length f ~ 1000 μm and f-number f/30 in the visible spectrum. Stepwise systolic transformation yields denser and affine functional elements, ultimately fused silica clones, exhibiting strong focusing properties due to their very short focal length of f ~ 35 μm and f/3.5. The fabricated transparent aerogel and xerogel replicas of microtrichia demonstrate a remarkable optical waveguiding performance, delivering light to their sub-100 nm nanotips. Dense fused silica conical clones deliver light through sub-50 nm nanotips, enabling nanoscale light-matter interactions. Super-resolution bioarchitectonics offers new and alternative tools and promises novel developments and applications in nanophotonics and other nanotechnology sectors.

Frequency Shift in Binary Microlensing

Abstract Gravitational microlensing with binary lensing is one of the channels for detecting exoplanets. Due to the degeneracy of the lens parameters for the binary microlensing, additional features such as parallax and finite-size effects need to identify the lens parameters. The frequency-shift effect as the relativistic analogy of the gravity assist for the photons, is an extra observation that provides additional constraint between the lens parameters . In this work, we extend the application of the frequency shift effect to binary microlensing and derive the frequency shift during the lensing and caustic crossing. The frequency shift for the binary lens is of the order of Δν/ν ∼ 10−12. We also investigate the feasibility of detecting this effect by employing Cross-Correlation methods .

Random phase plate designed by the genetic algorithm for decoherence in energy homogenization units of a photolithography illumination system

The microlens array (MLA) is used in the flexible pupil shaping module of lithography illumination system for energy balance. However, the coherence of the light source can lead to interference patterns. Most of the decoherence methods are restricted for the pulse laser and the scanning exposure application. To solve this issue, a specific random phase plate (RPP) is designed to eliminate the interference patterns caused by the coherence of the light source. The model of partially coherent light propagation in the MLAs homogeneous system is established based on the mutual intensity theory, and the genetic algorithm is introduced to design a high-performance RPP. The corresponding measurement device is constructed, and the intensity of the image plane light field is measured. Experiment results indicate that the intensity integral non-uniformity is 32.14% in the x-direction and 66.04% in the y-direction without the RPP, and the intensity integral non-uniformity is 22.95% in the x-direction and 19.18% in the y-direction with the RPP, which verifies the feasibility of the proposed method.

Compact broadband high-resolution real-time four-dimensional imaging spectrometer

A broadband high-resolution real-time four-dimensional imaging spectrometer (HRRFDIS) is presented, which can acquire both broadband fine spectra and high-resolution three-dimensional (3D) spatial images of a 3D object in real time. The HRRFDIS consists of a first microlens array arranged in a plane to achieve orthographic view spatial imaging, a second microlens array arranged on a conical surface to measure the depth and to achieve 360-degree side-view spatial imaging, multiple optical fibers, a collimating microlens array arranged in a straight line, a parallel planar transmission grating pair to obtain high spectral resolution over a broadband spectral range, and an area-array detector. Compared with the scanning four-dimensional imaging spectrometer (FDIS), the HRRFDIS can obtain a broadband high-resolution four-dimensional dataset using only one frame of data, and it is more stable, compact, small-sized, and lightweight. Compared to the staring FDIS using a liquid crystal filter and requiring at least one modulation period of liquid crystal to acquire a complete hyperspectral image, the HRRFDIS can acquire a complete broadband hyperspectral image in real time. Compared to existing snapshot FDIS, the HRRFDIS can achieve much higher spectral resolution, especially over a broadband spectral range. The HRRFDIS is a unique concept that is the first to obtain both high-resolution broadband spectral information and high-resolution 3D spatial information in real time, to the best of our knowledge. The HRRFDIS will be suitable for real-time measurement of 3D objects in the ultraviolet to infrared spectral range.

Superhydrophobic quasi-periodic concave microlens array on fused silica prepared by spatially modulated picosecond laser parallel processing

Fused-silica-based microlens array (MLA) has excellent stability in the harsh environment. However, it is still a challenge to efficiently prepare superhydrophobic quasi-periodic MLA and keep the optical performance of the microlens. In this paper, we proposed spatial modulated picosecond laser parallel processing method to prepare a superhydrophobic quasi-periodic MLA on fused silica. By using a spatial light modulator, the picosecond laser was shaped to multi-focal spots and line-shape beam, respectively, which improved the fabrication efficiency. The line-shape beam was the key to induce micro-nanostructures on the smooth MLA and keep the optical performance of the microlens. The results showed that the surface roughness of the microlens region was less than 100 nm. Combing with shaping picosecond laser processing and chemical treatment, the superhydrophobic MLAs showed the excellent anti-fogging and self-cleaning properties. The average contact angle of the superhydrophobic MLAs was 162.3°. The superhydrophobic MLA showed low adhesion to water droplet (<10 μN) and low contact angle hysteresis (2.1° ± 0.7°). We believe shaping picosecond laser parallel processing method is a flexible and low-cost approach to prepare superhydrophobic micro-optical elements on fused silica.

Bio-inspired flat optics for directional 3D light detection and ranging

The eyes of arthropods, such as those found in bees and dragonflies, are sophisticated 3D vision tools that are composed of an array of directional microlenses. Despite the attempts in achieving artificial panoramic vision by mimicking arthropod eyes with curved microlens arrays, a wealth of issues related to optical aberrations and fabrication complexity have been reported. However, achieving such a wide-angle 3D imaging is becoming essential nowadays for autonomous robotic systems, yet most of the available solutions fail to simultaneously meet the requirements in terms of field of view, frame rate, or resistance to mechanical wear. Metasurfaces, or planar nanostructured optical surfaces, can overcome the limitation of curved optics, achieving panoramic vision and selective focusing of the light on a plane. On-chip vertical integration of directional metalenses on the top of a planar array of detectors enables a powerful bio-inspired LiDAR that is capable of 3D imaging over a wide field of view without using any mechanical parts. Implementation of metasurface arrays on imaging sensors is shown to have relevant industrial applications in 3D sensing that goes beyond the basic usage of metalenses for imaging.

Induced gravitational wave interpretation of PTA data: a complete study for general equation of state

We thoroughly study the induced gravitational wave interpretation of the possible gravitational wave background reported by PTA collaborations, considering the unknown equation of state w of the early universe. We perform a Bayesian analysis of the NANOGrav data using the publicly available PTArcade code together with SIGWfast for the numerical integration of the induced gravitational wave spectrum. We focus on two cases: a monochromatic and a log-normal primordial spectrum of fluctuations. For the log-normal spectrum, we show that, while the results are not very sensitive to w when the GW peak is close to the PTA window, radiation domination is out of the 2σ contours when only the infra-red power-law tail contributes. For the monochromatic spectrum, the 2σ bounds yield 0.1 ≲ w ≲ 0.9 so that radiation domination is close to the central value. We also investigate the primordial black hole (PBH) abundance for both monochromatic and log-normal power spectrum. We show that, in general terms, a larger width and stiffer equation of state alleviates the overproduction of PBHs. No PBH overproduction requires w ≲ 0.57 up to 2-σ level for the monochromatic spectrum. Furthermore, including bounds from the cosmic microwave background, we find in general that the mass range of the PBH counterpart is bounded by 10-5 M ⊙ ≲ M PBH ≲ 10-1 M ⊙. Lastly, we find that the PTA signal can explain the microlensing events reported by OGLE for w ~ 0.7. Our work showcases a complete treatment of induced gravitational waves and primordial black holes for general w for future data analysis.

Study on Deformation Behavior of Glass in High-temperature Molding for Massive Unit Microlens Arrays.

Microlens arrays (MLAs) with a large number of units, known as massive unit microlens arrays (MUMLAs), are increasingly sought after for their ability to achieve high-power conversion in infrared optical systems. Precision glass molding (PGM) is considered the ideal manufacturing method for MUMLAs. However, the stress distribution and deformation behavior during molding lack detailed understanding, resulting in poor filling consistency and forming accuracy. Consequently, this leads to inconsistent diffuse spot size and irradiance in MUMLAs. This study aims to comprehensively analyze the glass filling behavior during the molding process of MUMLAs using both simulation and experimental approaches. It explains the impact of glass filling behavior and consistency on the optical performance of MUMLAs. Additionally, the effects of molding parameters on the filling consistency of the lenses are investigated. By optimizing these parameters, a high-consistency 128 × 128 MUMLA is fabricated.

Exploring Fractional Pigment Toning: A Novel Approach for Treating Benign Pigmented Lesions in Asian Patients With Fitzpatrick Skin Types III-V.

Laser therapy has emerged as a widely favored treatment option for solar lentigines (SL). However, a significant challenge associated with this treatment, particularly among individuals with darker skin tones, is the notable risk of postinflammatory hyperpigmentation (PIH) induction. In response to these concerns, the authors conducted a prospective, self-controlled study to comprehensively evaluate the safety and effectiveness of 532-nm picosecond laser, both with and without a microlens array (MLA), for the management of SL in patients with Fitzpatrick skin types (FST) III-V. Twenty-seven patients with FST III-V and bilateral SL on the face underwent randomized treatment. One side of the face was treated with a 532-nm picosecond laser coupled with an MLA, utilizing the fractional pigment toning (FPT) technique, while the other side received treatment without the MLA, following the conventional technique (CT). The FPT technique utilized a 9-mm spot size with a fluence of 0.47 J/cm2 for two passes covering 40% of the area. In contrast, the CT used a 4.5-mm handpiece with fluence ranging from 0.3 to 0.7 J/cm2. Patients received a single treatment and were evaluated for pigment clearance, occurrence of PIH, and other adverse effects at 2 weeks, 1, 3, and 6 months posttreatment. Twenty-seven participants completed the study protocol. Analysis of pigment clearance, measured via 3D photography, showed significant improvement from 2 weeks to 6 months posttreatment for both the FPT technique (p < 0.001) and CT (p = 0.004). PIH occurred in 64%, 80%, 96%, and 88% of cases on the CT side, compared to 8%, 32%, 36%, and 16% on the FPT technique side at 2 weeks, 1, 3, and 6 months posttreatment, respectively. The incidence of PIH was significantly lower on the FPT technique side compared to the CT side throughout the follow-up periods. Additionally, transient and mild hypopigmentation occurred in one participant (4%) on the FPT technique side and in five participants (20%) on the CT side. No other adverse effects were observed during the study. The 532-nm picosecond laser emerges as a safe and efficacious treatment modality for SL in individuals with FST III-V. Particularly noteworthy is the efficacy of the FPT technique, which demonstrates comparable effectiveness while significantly reducing the incidence of PIH compared to the CT.

Template-Oriented-Assembly microsphere lithography for multi-type SiC microlens arrays

Silicon carbide (SiC) microlens arrays (MLAs) with a defined layout are used as an optical homogenizer in extremely high-temperature environments due to their excellent physicochemical properties. In this paper, a novel template-oriented-assembly microsphere lithography (TMSL) method is proposed to fabricate SiC MLA. Firstly, the metal micropyramid array (MPA) template was designed and fabricated by ultraprecision cutting and then converted to a polydimethylsiloxane (PDMS) surface. After that, the microspheres were assembled into a monolayer on the inverted MPA of PDMS. Subsequently, the microsphere array monolayer (MSM) was used as the stamper in the hot embossing process to create the photoresist MLA mask. Finally, the patterns on the photoresist mask were transferred to the SiC substrate by inductively coupled plasma (ICP) etching. The layout of lens units was determined by the MPA template and the positioning accuracy of MLA unit is mainly influenced by the form error in MPA mold manufacturing process. The transfer mechanism from the metal MPA template to SiC MLA was studied, and the transfer characteristics of theoretical analyses and experimental results were compared, confirming the feasibility and advantages of the TMSL method.

Photonic integrated interference imaging system based on front-end S-shaped microlens array and Con-DDPM

Aiming at the problems of uneven UV spatial frequency sampling and inverse Fourier transform (IFT) artifacts of the photonic integrated interference imaging system, this study proposes a new imaging system based on a front-end S-shaped microlens array, combined with a conditional denoising diffusion probabilistic model (Con-DDPM). The front-end S-shaped microlens array improves the uniformity of UV spatial frequency sampling, increasing the average peak signal-to-noise ratio (PSNR) and structure similarity index measure (SSIM) by approximately 5 dB and 0.16, respectively. In addition, the deep learning reconstruction algorithm based on Con-DDPM is employed to process the IFT images. This algorithm effectively removes artifacts and restores the detailed information of the images. As a result, the average PSNR and SSIM are improved by approximately 9 dB and 0.38, respectively. These enhancements have significantly improved the imaging quality, laying a solid foundation for the future development of space-based telescopes.

Primordial Black Hole Dark Matter Simulations Using PopSyCLE

Primordial black holes (PBHs), theorized to have originated in the early Universe, are speculated to be a viable form of dark matter. If they exist, they should be detectable through photometric and astrometric signals resulting from gravitational microlensing of stars in the Milky Way. Population Synthesis for Compact-object Lensing Events, or PopSyCLE, is a simulation code that enables users to simulate microlensing surveys, and is the first of its kind to include both photometric and astrometric microlensing effects, which are important for potential PBH detection and characterization. To estimate the number of observable PBH microlensing events, we modify PopSyCLE to include a dark matter halo consisting of PBHs. We detail our PBH population model, and demonstrate our PopSyCLE + PBH results through simulations of the Optical Gravitational Lensing Experiment-IV (OGLE-IV) and Nancy Grace Roman Space Telescope (Roman) microlensing surveys. We provide a proof-of-concept analysis for adding PBHs into PopSyCLE, and thus include many simplifying assumptions, such as f DM, the fraction of dark matter composed of PBHs, and m¯PBH , mean PBH mass. Assuming m¯PBH=30 M ⊙, we find ∼3.6f DM times as many PBH microlensing events than stellar evolved black hole events, a PBH average peak Einstein crossing time of ∼91.5 days, estimate on order of 102 f DM PBH events within the 8 yr OGLE-IV results, and estimate Roman to detect ∼1000f DM PBH microlensing events throughout its planned microlensing survey.

In Vivo Evaluation of Laser-Induced Optical Breakdown (LIOBS) by 1064-nm Nd:YAG Fractional Picosecond Laser With Reflectance Confocal Microscopy and Precise Histopathologic Correlation.

Picosecond lasers with a microlens array can cause laser-induced optical breakdown (LIOBS) and LIC (Intradermal laser-induced cavitation) within high-fluence areas. This study aimed to describe the clinical, reflectance confocal microscopy (RCM), histopathological findings, and the characteristics of vacuoles caused by LIOBS and LIC in individuals with skin types III and IV. This study was performed on six Chilean healthy volunteers, males and females, aged 35-65 years old with Fitzpatrick skin phototypes III-IV. The laser was applied in the inner proximal area of the nondominant arm. RCM evaluation was performed 24 h later; 48 h later, skin biopsies were performed on the laser-treated areas. Clinical, histological, and RCM findings were recorded. Every individual developed a 10 mm2 area of clinical erythema in the treated area. Under RCM, all six volunteers had hyporeflective spherical structures at the level of the epidermis, consistent with intraepidermal vacuoles. Histopathological evaluation revealed different sizes of vacuoles in both the epidermis and dermis. The LIOBS and LIC processes and the secondary production of vacuoles could be highly valuable for effective dermal remodeling treatment and aid in promoting the production of new collagen, elastic fibers, and growth factors that could improve skin texture. These structures were visible under RCM and histopathological evaluation.

Fabrication of liquid-filled zoom compound eyes with a tunable focal length

The conventional bionic compound eye system encounters challenges associated with a complex zoom structure, susceptibility to wear, and elevated costs. In this paper, a preparation method of liquid-filled zoom compound eyes is proposed. A polydimethylsiloxane (PDMS) film is integrated with a microfluidic chamber composed of polymethyl methacrylate (PMMA). The microlens array (MLA, hexagonal array, diameter 800 µm, center distance 850 µm) on the PDMS film is prepared by a wettability-guided dipping method. The sub-eye focal length on zoom compound eyes (ZCEs) is 1.42 mm. By controlling the volume of deionized (DI) water injected into the chamber from 2.41 to 2.71cm3, the focal length of the main lens is adjusted from infinity to 55.51 mm, and the FOV is adjusted from 32° to 58°. This large aperture ZCE combines the advantages of monocular and compound eyes. This method has great potential for advanced micro-optical devices with a wide field of view and tunable imaging capabilities.

Enlarge the dynamic range of Shack-Hartmann wavefront sensor based on biplanar image acquisition and segmentation method

In present paper, a simple and robust method to expand the SHWS dynamic range is proposed. The intensity patterns are obtained with biplanar image acquisition and segmentation. The process involves calculating the spot centroids of two images and then matching the centroid of the spots of light with the center of a micro-lens array. This also resolves the issue of mandating the determination of centroids exclusively within the corresponding detection area. It is performed a comparative analysis between our proposed method and the conventional method for measuring large wavefronts, utilizing both numerical simulations and experiments. Additionally, a statistical analysis of the dynamic range of the method for wavefront measurement was conducted. This study demonstrates that the biplanar image acquisition and segmentation method provided a larger dynamic range while ensuring accuracy relative to the single image acquisition of conventional algorithm

Microlens arrays for multichannel laser-to-waveguide coupling

An optical multichannel coupling system for coupling laser arrays to waveguide arrays is developed. Based on a microlens array, the system enables coupling of nine individual optical channels, with one aspheric microlens per channel at a lateral channel pitch of 100 µm. The design process criteria for the proposed microlenses, with 97 µm diameter and working distances from laser to lens and lens to waveguide of 150 µm and 275 µm, respectively, are described. The microlens array is fabricated on a 4mm×2mm×0.41mm fused silica chip and contains an orthogonal grid with 32×16 microlenses, of which a row of nine adjacent microlenses is used for coupling. Uniform coupling over all channels can be achieved, as well as specific coupling for each channel individually with less than −13.5dB crosstalk. The coupling system is designed for optical neural stimulators.