Microlens Research Articles

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.

Improving detection accuracy of extreme-few-pixel Shack-Hartmann wavefront sensor based on tilt modulation

Conventional high spatial resolution Shack-Hartmann wavefront sensors have difficulty realizing high-precision wavefront detection under extreme-few-pixel conditions. A method of Shack-Hartmann wavefront sensor based on tilt modulation is proposed. The proposed method first increases the amount of sub-spot image information. Then, the corresponding wavefront detection accuracy can be improved by tuning parameters such as modulation amplitude, modulation angle, and modulation number. Finally, the detection accuracy for different parameter settings is fitted statistically. As observed in numerical simulations and experiments, the tilt modulation-based method effectively improves detection accuracy. Moreover, there are obvious advantages over the conventional Shack-Hartmann wavefront sensors in 4 × 4 sub-aperture pixels and a short focal length of the microlens array, which improves detection accuracy by about 84% in the experiments. Realization of the need for high spatial resolution and high detection accuracy of Shack-Hartmann wavefront sensors.

Optical design and development of an underwater dual-channel microlens array integral field snapshot hyperspectral imager

Compared to push-scan hyperspectral imagers, snapshot hyperspectral imagers offer an advantage by minimizing sensitivity to attitude jitter in underwater mobile platforms. Here we present the optical design and development of an underwater microlens array integral field hyperspectral imager. The system comprises a panchromatic imaging channel with a high spatial resolution and a spectral imaging channel with a lower spatial resolution. Through the fusion of high-resolution panchromatic images and low-resolution spectral images, we achieve high spatial resolution hyperspectral images. Both the panchromatic imaging channel and the spectral imaging channel share a common front objective, featuring a 25 mm focal length and a wide 36° field of view angle. Utilizing prism dispersion, the spectral imaging system spans a band range from 465 to 700 nm with a spectral resolution of less than 10 nm. Specialized algorithms for spectral image reconstruction and image fusion have been developed. The experimental results across diverse scenes confirm the exemplary spectral imaging performance of the system, positioning it as a robust solution for underwater snapshot hyperspectral imaging.

Characterizing Biphoton Spatial Wave Function Dynamics with Quantum Wavefront Sensing.

With an extremely high dimensionality, the spatial degree of freedom of entangled photons is a key tool for quantum foundation and applied quantum techniques. To fully utilize the feature, the essential task is to experimentally characterize the multiphoton spatial wave function including the entangled amplitude and phase information at different evolutionary stages. However, there is no effective method to measure it. Quantum state tomography is costly, and quantum holography requires additional references. Here, we introduce quantum Shack-Hartmann wavefront sensing to perform efficient and reference-free measurement of the biphoton spatial wave function. The joint probability distribution of photon pairs at the back focal plane of a microlens array is measured and used for amplitude extraction and phase reconstruction. In the experiment, we observe that the biphoton amplitude correlation becomes weak while phase correlation shows up during free-space propagation. Our work is a crucial step in quantum physical and adaptive optics and paves the way for characterizing quantum optical fields with high-order correlations or topological patterns.

A piston and tilt wavefront sensor dedicated to the cophasing of segmented optics in low light level conditions

We present a new interferometer to measure piston, tip and tilt of segmented mirrors, using the combination of an optical grating and a microlens array. Since this interferometer is able to collect all the incident light and to operate with a large spectra bandwidth, it is particularly suitable to operate in low light level conditions, for example for the co-phasing of segmented primary mirrors like James Webb Space Telescope. We tested our new device on a 37-segment deformable mirror and obtained an accuracy better than λ/100. The measurement is self-referenced and errors can be estimated on the measurement itself thanks to closure relationships.

Gravitational lensing of gravitational waves: prospects for probing intermediate-mass black holes in galaxy lenses with global minima image

ABSTRACT This work studies microlensing effects in strongly lensed gravitational wave (GW) signals corresponding to global minima images in galaxy-scale lenses. We find that stellar microlenses alone are unable to introduce noticeable wave effects in the global minima GW signals at strong lensing magnification $( {\mu})\lt 50$ with match value between unlensed and lensed GW signals being above ${\sim }99.5~{{\ \rm per \, cent}}$ in ${\sim }90~{{\ \rm per \, cent}}$ of systems implying that GW signals corresponding to global minima can be treated as reference signal to determine the amount of microlensing in other strongly lensed counterparts. Since the stellar microlenses introduce negligible wave effects in global minima, they can be used to probe the intermediate-mass black hole (IMBH) lenses in the galaxy lens. We show that the presence of an IMBH lens with mass in the range $[50,10^3]~{\rm M_\odot }$ such that the global minima lies within five Einstein radius of it, the microlensing effects at $f\lt 10^2$ Hz are mainly determined by the IMBH lens for ${\mu} \lt 50$. Assuming that a typical strong lensing magnification of 3.8 and high enough signal-to-noise ratio (in the range ${\simeq }[10, 30]$) to detect the microlensing effect in GW signals corresponding to global minima, with non-detection of IMBH-led microlensing effects in ${\simeq }15~({\simeq }150)$ lensed GW signals, we can rule out dark matter fraction $\gt 10~{{\ \rm per \, cent}}~(\gt 1~{{\ \rm per \, cent}})$ made of IMBH population inside galaxy lenses with mass values $\gt 150~{\rm M_\odot }$ with ${\sim }$90 per cent confidence. Although we have specifically used IMBHs as an example, the same analysis applies to any subhalo (or compact objects) with lensing masses (i.e. the total mass inside Einstein radius) satisfying the above criterion.

Spatial light assisted femtosecond laser direct writing of a bionic superhydrophobic Fresnel microlens arrays

High quality imaging and self-cleaning function are two significant factors for Fresnel Microlens Arrays (FMLAs) to operate properly in outdoor environment. Bionic superhydrophobic FMLAs are explored for outdoor uses due to their ability allowing free rolling down of water droplets taking away dust particles. Current photolithographic method of fabricating FMLAs involves multi-processing steps, which increase the complexity of the microlens array structure as well as reduces the optical imaging capability of the lenses. In this study, we report a method for creating bionic superhydrophobic FMLAs by integrating the Nepenthes Alata crescent structures with FMLAs fabricated by spatial light assisted femtosecond laser direct writing, i.e. Two-Photon Polymerization (TPP). The fabricated FMLAs were further modified with Perfluorooctyltrimethoxysilane (F13) to enhance hydrophobicity and surface uniformity. Results show that the optimized bionic FMLAs exhibit superhydrophobicity in different liquid media and excellent self-cleaning ability. The water contact angle (CA) reached 156.3°, a low rolling angle of 4.7°, and surface adhesion force of 25.5 μN. The FMLAs designed have excellent imaging characteristics and focusing ability. This research provides insights into the fabrication and performance optimization of bionic superhydrophobic FMLAs, offering potential applications for outdoor optical systems.

Multi-lens component used for a LWIR field-integral gas spectral imager

This paper reports a miniature multi-lens component used for a LWIR field-integral gas spectral imager. The component is designed for crosstalk minimization and consists of a 4∗3 array of micro-lenses and a detector. To reduce the cost, the detector is uncooled and the optical parameters of the 12 micro-imaging lenses are identical. These include 3.38 mm focal length and 35° field-of-view. The F/# is designed to be 1.2 to increase the luminous flux of the imager. After image quality evaluation and tolerance analysis, the micro-imaging lens has good imaging quality, is insensitive to tolerances, and is easy to fabricate. To enhance the environmental stability of the component, a temperature control system was designed to depress the temperature drift. In addition, the athermalization of the micro-imaging lens was beneficial. The performance test of the component shows that the NETD of the 12 micro-imaging lenses is less than 90 mK and most of them are less than 65 mK, and an image of an ethylene gas cloud observed by the component is also shown. The component has been integrated to the spectral imagers, and crosstalk is analyzed.