Lens Array Research Articles

The design method and test of a Dual-Focused ultrasound transducer toward small and adjustable F-numbers

An ultrasound transducer with a F-number less than 1.0 has been used in many fields such as non-destructive testing, medical treatment, particle manipulation, and so on. Traditional focusing technologies such as self-focusing structure and lens sets suffer from undesired surface cavitation due to large cavity depth, difficulties in fabrication, and most of designs have a fixed focal depth. This paper presents a small F-number ultrasound transducer design using a combination of acoustic lens and phased array, its fabrication process is not complicated, and focal depth is adjustable when applying different time delays. The design methods, including analytical expression, empirical equation and numerical results, are elaborated in this paper, followed by fabrication and tests. Simulations and experimental results prove that this dual-focused transducer can reach a changeable F-number as small as 0.72. The cavity depth of the transducer is relatively small (1.1 λ) compared to existing focusing transducers (4 ∼ 10 λ), which is not prone to unexpected surface cavitation. Moreover, the array in transducer has no grating lobes with an expanded pitch of 1.43 λ, which not only increase the fill factor and effective area but also further reduces the fabrication difficulty, especially in high frequency applications.

Integral imaging systems using interleaved Fresnel lenses and transmissive display panels

Integral imaging reproduces the light-ray space of a scene to realize a 3D vision. In particular, a coarse integral imaging system, featuring elemental lenses large enough to cover more pixels than the number of views, holds promise in applications like interactive visualization systems and automobile head-up displays (HUDs) for 3D display. However, conventional coarse integral imaging and coarse integral volumetric imaging systems face challenges related to visible seams in the lens array and the emergence of moiré patterns caused by layered liquid crystal panels (LCDs), that significantly degrade image quality. This paper presents a solution to these problems by employing an integrated interleaved Fresnel lens sheet to achieve seamless 3D images with smooth motion parallax while using layered transmissive panels to generate volumetric images free from moiré.

Paired Treatment Using Radiofrequency Microneedling and 755-nm Picosecond Laser With Fractionated Lens Array for Facial Rejuvenation.

Patients frequently complain about fine lines, wrinkles, dyschromia, and photoaging, for which lasers and energy-based devices can treat each of these. Pairing various devices in a single treatment session can be safe and effective, but different technologies, mechanisms, histologies, parameters, and techniques must be considered. To examine the utility of a paired treatment regimen using radiofrequency microneedling and 755-nm picosecond laser with fractionated lens array to improve the clinical appearance of facial wrinkles and photoaging. A prospective clinical study investigated this paired treatment regimen using 4 monthly sessions. Twenty-five subjects were enrolled, while 18 subjects completed 3-month follow-up. The mean age was 54 years, and 92% were women. Fitzpatrick Skin Types I to IV were represented. Assessments compared baseline with the 3-month follow-up. Two of 3 blinded reviewers agreed in identifying pretreatment and post-treatment photographs for 94.4% of cases. For physician Global Aesthetic Improvement Scale, 100% of subjects had clinical improvement. Overall, 88.9% of subjects were considered to be satisfied with their treatment. No serious or unanticipated adverse events occurred. Paired treatment using radiofrequency microneedling and 755-nm picosecond laser with fractionated lens array can safely and effectively improve facial wrinkles and photoaging.

X-Ray Multibeam Ptychography at up to 20 keV: Nano-Lithography Enhances X-Ray Nano-Imaging.

Hard X-rays are needed for non-destructive nano-imaging of solid matter. Synchrotron radiation facilities (SRF) provide the highest-quality images with single-digit nm resolution using advanced techniques such as X-ray ptychography. However, the resolution or field of view is ultimately constrained by the available coherent flux. To address this, the beam's incoherent fraction can be exploited using multiple parallel beams in an X-ray multibeam ptychography (MBP) approach. This expands the domain of X-ray ptychography to larger samples or more rapid measurements. Both qualities favor the study of complex composite or functional samples, such as catalysts, energy materials, or electronic devices. The challenge of performing ptychography at high energy and with many parallel beams must be overcome to extract the full advantages for extended samples while minimizing beam attenuation. Here, that challenge is overcome by creating a lens array using cutting-edge laser printing technology and applying it to perform scanning with MBP with up to 12 beams and at photon energies of 13 and 20 keV. This exceeds the measurement limits of conventional hard X-ray ptychography without compromising image quality for various samples: Siemens star test pattern, Ni/Al2O3 catalyst, microchip, and gold nano-crystalclusters.

Continuous Optical Zoom Compound Eye Imaging Using Alvarez Lenses Actuated by Dielectric Elastomers.

The compound eye is a natural multi-aperture optical imaging system. In this paper, a continuous optical zoom compound eye imaging system based on Alvarez lenses is proposed. The main optical imaging part of the proposed system consists of a curved Alvarez lens array (CALA) and two Alvarez lenses. The movement of the CALA and two Alvarez lenses perpendicular to the optical axis is realized by the actuation of the dielectric elastomers (DEs). By adjusting the focal length of the CALA and the two Alvarez lenses, the proposed system can realize continuous zoom imaging without any mechanical movement vertically to the optical axis. The experimental results show that the paraxial magnification of the target can range from ∼0.30× to ∼0.9×. The overall dimensions of the optical imaging part are 54 mm × 36 mm ×60 mm (L × W × H). The response time is 180 ms. The imaging resolution can reach up to 50 lp/mm during the optical zoom process. The proposed continuous optical zoom compound eye imaging system has potential applications in various fields, including large field of view imaging, medical diagnostics, machine vision, and distance detection.

Microsphere lens array embedded microfluidic chip for SERS detection with simultaneous enhancement of sensitivity and stability

Surface enhanced Raman spectroscopy (SERS) utilizes the fingerprint features of molecular vibrations to identify and detect substances. However, in traditional single focus excitation scenarios, its signal collection efficiency of the objective is restricted. Furthermore, the uneven distribution of samples on the SERS substrate would result in poor signal stability, while the excitation power is limited to avoid sample damage. SERS detection system always requires precise adjustment of focal length and spot size, making it difficult for point-of-care testing applications. Here, we proposed a SERS microfluidic chip with barium titanate microspheres array (BTMA) embedded using vacuum self-assembled hot-pressing method for SERS detection with simultaneous enhancement of sensitivity and stability. Due to photonic nano-jets and directional antenna effects, high index microspheres are perfect micro-lens for effective light focusing and signal collecting. The BTMA can not only disperse excitation beam into an array of focal points covering the target uniformly with very low signal fluctuation, but enlarge the power threshold for higher signal intensity. We conducted a proof-of-principle experiment on chip for the detection of bacteria with immuno-magnetic tags and immuno-SERS tags. Together with magnetic and ultrasonic operations, the target bacteria in the flow were evenly congregated on the focal plane of BTMA. It demonstrated a limit of detection of 5 cells/mL, excellent signal reproducibility (error∼4.84%), and excellent position tolerance of 500 μm in X–Y plane (error∼5.375%). It can be seen that BTMA-SERS microfluidic chip can effectively solve the contradiction between sensitivity and stability in SERS detection.

Preparation of fused silica glass micropatterns via gel method using quartz fiber as reinforcer

The preparation of fused silica glass with microstructural patterns has attracted considerable interest, and the process chain of using nano-silica powders mixed with organic polymers to prepare composites for molding, degreasing, and sintering provides a good solution. However, the potential negative effects of organic residues cannot be avoided. In this study, a pattern stencil replication method with silica gel using high-purity quartz fibers as reinforcement is proposed for preparing micropatterned fused silica glass. The microscopic morphology and mechanical properties before and after silica gel drying and the optical properties of fused silica glass obtained by sintering were evaluated via transmission electron microscopy), three-point bending strength test, scanning electron microscopy, X-ray diffraction spectrum analysis, ultraviolet–visible and infrared measurements. The results showed that quartz fiber as a reinforcer could shorten the drying time of the gel and did not degrade the quality of the fused silica glass obtained by sintering. Laser confocal test results showed that microlens arrays were generated by template replication, demonstrating the feasibility of molding fused silica lens arrays with small feature sizes and providing new ideas for the preparation of bulk fused silica glass or micropatterned glass.

Extended depth-of-field wide-field fluorescence microscopy with a micro-mirror array lens system for versatile cellular examination.

We present a versatile extended depth-of-field (EDOF) wide-field fluorescence microscopy using a new, to the best of our knowledge, active device, micro-mirror array lens system (MALS) for calibration-free and orientation-insensitive EDOF imaging. The MALS changed the focal plane during image acquisition, and the system could be operated in any orientation. Two EDOF imaging modes of high-speed accumulation and low-speed surface sectioning were implemented. The performance was demonstrated in non-contact imaging of conjunctival goblet cells in live mice and depth-resolved cellular examination of ex-vivo human cancer specimens. MALS-based EDOF microscopy has potential for versatile cellular examination.

Ultrahigh precision laser nanoprinting based on defect-compensated digital holography for fast-fabricating optical metalenses.

The 3D structured light field manipulated by a digital-micromirror-device (DMD)-based digital hologram has demonstrated its superiority in fast-fabricating stereo nanostructures. However, this technique intrinsically suffers from defects of light intensity in generating modulated focal spots, which prevents from achieving high-precision micro/nanodevices. In this Letter, we have demonstrated a compensation approach based on adapting spatial voxel density for fabricating optical metalenses with ultrahigh precision. The modulated focal spot experiences intensity fluctuations of up to 3% by changing the spatial position, leading to a 20% variation of the structural dimension in fabrication. By altering the voxel density to improve the uniformity of the laser cumulative exposure dosage over the fabrication region, we achieved an increased dimensional uniformity from 94.4% to 97.6% in fabricated pillars. This approach enables fast fabrication of metalenses capable of sub-diffraction focusing of 0.44λ/NA with the increased mainlobe-sidelobe ratio from 1:0.34 to 1:0.14. A 6 × 5 supercritical lens array is fabricated within 2 min, paving a way for the fast fabrication of large-scale photonic devices.

P‐219: Research on the Direction of Luminance Modulation at Small Angles Based on Micro Lens

The study investigated the variations in luminance of active‐matrix organic light‐emitting diodes (AMOLED) when viewed at small angles, employing different micro lens arrangements. By examining the micro lens array (MLA) structure, we analyzed how luminance behaves at various angles. Concurrently, we explored the alignment of red, green, and blue (R/G/B) pixel apertures with the micro lens placement, aiming to achieve precise luminance modulation for acute viewing angles.Initially, micro lens arrays are crafted by utilizing materials with varying refractive indices above the pixel aperture, ensuring total internal reflection of light at thejunction between materials of high and low refractive indices. This arrangement also alters the emission angle of light. Within this architecture, the critical angle — determined by the disparity in refractive indices — and the variance in the angle at the reflective interface are crucial in influencing light emission reflection.Furthermore, we explored how the spacing of graphic openings with low refractive indices influences the angle of light emission. This spacing affects the reflection angle, as it is not produced by a singular interface but rather by a composite of multiple angles. The size of the pixel apertures and the spacing of these openings cause the point of total internal reflection to vary, altering the deflection angle of light. Thus, the design of pixel openings and the external expansion is crucial to controlling the light emission angle.Lastly, we examined the influence of the reflective interface and the external expansion design on the light output angle. This analysis highlighted the enhancement of light output at narrow angles and provided strategies to minimize luminance fluctuations at such angles, contributing to the development of high‐precision luminance control in AMOLED displays.

P‐120: Sub‐Pixel Marking Method for the Elimination of Voxel Drifting in Integral Imaging Display System

Integral imaging is a type of true three‐dimensional (3D) display technology that uses a lens array to reconstruct vivid 3D images with full parallax and true color. In order to present a high‐quality 3D image, it's vital to correct the axial position error caused by the misalignment and deformation of the lens array which makes the reconstructed lights deviate from the correct directions, resulting in severe voxel drifting and image blurring. We proposed a sub‐pixel marking method to measure the axial position error of the lenses with great accuracy by addressing the sub‐pixels under each lens and forming a homologous sub‐pixel pair. The proposed measurement method relies on the geometric center alignment of image points, which makes the measurement accuracy high. Additionally, a depth‐based sub‐pixel correction method was proposed to eliminate the voxel drifting. The proposed correction method takes the voxel depth into consideration. The experimental results well confirmed that the proposed measuring and correction methods can greatly suppress the voxel drifting caused by the axial position error of the lenses, and greatly improve the 3D image quality.

70‐3: Wide Field of View Flat Panel Light Field Display

Light field displays enable viewers to perceive true three‐dimensional (3D) images with the naked eye. A wide viewing angle would provide a more comfortable viewing condition and the possibility for multiple users. However, there is typically a trade‐off between the form factor and the viewing angle. Based on the previously developed lenticular‐type flat panel light field display, this paper proposes the use of an isolated micro lens array (i‐MLA) in conjunction with an extended coding pitch algorithm to address crosstalk issues. This solution not only reduces the constraints on the minimum viewing distance but also expands the field of view, all without increasing the thickness of the display panel.

Estimation of Mutual Coupling in Integrated Lens Arrays Using a Geometrical Optics-Based Technique With Bi-Directional Forward Ray-Tracing

Estimation of Mutual Coupling in Integrated Lens Arrays Using a Geometrical Optics-Based Technique With Bi-Directional Forward Ray-Tracing

33‐3: An Autostereoscopic Display with Time‐Multiplexed Directional Backlight Using an Electroluminescent Display as a Light Source

We propose an autostereoscopic display with a directional backlight unit using an interleaved lens array and an organic electroluminescent display as an active light source. In the proposed system, the screen luminance per unit of power consumption is enhanced and the uniformity of luminance is improved.

Evaluation of 755-nm Picosecond Alexandrite Laser With a Focus Lens Array for the Treatment of Enlarged Facial Pores.

This study aims to evaluate the use of 755-nm picosecond alexandrite laser with a focus lens array to treat facial pores. Laser treatment was performed on 129 patients between January 2021 and October 2022. VISIA imaging system was used for photographic assessments, the total average number and pore index was calculated, the physicians' assessment score and patient satisfaction score were collected, and the incidence of disadvantage effects was also documented. The mean patient age was 35.2±6.4 years (21-45y). The total average number of facial pores was 1614.1±412.8, and the total average number decreased to 1262.6±356.2 three months after the last treatment. The pretreatment baseline of pore index was 26.1±4.5, while the pore index was 21.3±3.7 three months after the last treatment. The physicians' assessment score was 2.7 on the 0-to-4 scale, and patient satisfaction score was 3.5 on the 1-to-5 scale. There were no adverse events, such as hyperkeratosis, scarring, and hypo-or hyperpigmentation. 755-nm picosecond alexandrite laser with a focus lens array was safe and effective in the treatment of facial pores with relatively few unanticipated adverse events. Level IV-observational study without controls.

Enhancement of pH imaging of light addressable potentiometric sensor by colloidal spherical lens array

Visualizing the distribution of pH in a solution is an important basis for monitoring reaction processes and metabolic changes in micro-biochemical species. Light addressable potentiometric sensor (LAPS), as a simple structure, flexible imaging, low-cost and label-free electrochemical sensor, has been widely used to pH imaging. However, its spatiotemporal resolution is greatly affected by the frequency of modulation light, thus limiting its imaging performance. In this study, LAPS device modified by well-ordered and low-cost polystyrene (PS) colloidal monolayer as spherical lens array is proposed to obtain higher available modulation frequency of the maximum photoresponse. The morphology, optical properties and the electric field distribution of PS colloidal spherical lens array were tested and analyzed. pH sensing, imaging of uniform pH solution, the spatiotemporal pH imaging and dynamic imaging of enzymatic reactions of LAPS modified by PS colloidal spherical lens array were tested and evaluated. The experimental results show that LAPS modified by PS colloidal spherical lens array not only has acceptable pH sensing, but also widens the modulation frequency of the maximum photoresponse to 40 kHz. LAPS modified by colloidal spherical lens array modulated at the frequency of 40 kHz shows acceptable sensitivity and linearity, good reproducibility and stability, high SNR and high-spatiotemporal pH imaging capability. This work can be suitable for high-spatiotemporal monitoring of the changes in electrolyte environmental pH caused by the reaction and metabolism of the biochemical species.

Bidirectional Optical Neural Networks Based on Free-Space Optics Using Lens Arrays and Spatial Light Modulator.

This paper introduces a novel architecture-bidirectional optical neural network (BONN)-for providing backward connections alongside forward connections in artificial neural networks (ANNs). BONN incorporates laser diodes and photodiodes and exploits the properties of Köhler illumination to establish optical channels for backward directions. Thus, it has bidirectional functionality that is crucial for algorithms such as the backpropagation algorithm. BONN has a scaling limit of 96 × 96 for input and output arrays, and a throughput of 8.5 × 1015 MAC/s. While BONN's throughput may rise with additional layers for continuous input, limitations emerge in the backpropagation algorithm, as its throughput does not scale with layer count. The successful BONN-based implementation of the backpropagation algorithm requires the development of a fast spatial light modulator to accommodate frequent data flow changes. A two-mirror-like BONN and its cascaded extension are alternatives for multilayer emulation, and they help save hardware space and increase the parallel throughput for inference. An investigation into the application of the clustering technique to BONN revealed its potential to help overcome scaling limits and to provide full interconnections for backward directions between doubled input and output ports. BONN's bidirectional nature holds promise for enhancing supervised learning in ANNs and increasing hardware compactness.

Research on key technology of cooled infrared bionic compound eye camera based on small lens array

Traditional 2D imaging technologies are limited by the need for a large field of view and their sensitivity to small target motion. Inspired by the characteristics of insect compound eye structure, we propose an infrared bionic compound eye camera based on a small lens array. The camera is composed of 61 small lens arrays mounted on a curved spherical shell and a relay optical system. The imaging device is a high-performance cooled mid-wave infrared detector. This is an innovative design for an infrared biomimetic compound eye camera system that provides a wide field of view and all-day detection capability. Aimed to meet the specified requirements. The optical system achieves a 100% cold-membrane match between the infrared optical system and the cooled detector, and the relay optical system optimizes the large-field aberration by introducing a higher-order aspheric surface and modifying the geometric surface of the lenses. Our entire system enables an observation field angle of 108∘×108∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$108^\\circ \ imes 108^\\circ$$\\end{document}. The experiments showed that the image quality of the system is high, each ommatidium was effective within the imaging range of the compound eye camera, resulting in an improved signal-to-noise ratio in various scenes.

Wide-viewing-angle holographic 3D display using lens array for point cloud data

A method using a lens array to expand the viewing angle of holographic three-dimensional displays endows simplicity to optical systems and offers robustness against misalignment. In this study, we develop a method for generating holograms from point cloud data using the lens-array method. The proposed method utilizes the fact that the lens array generates a sparse light field in a checkered pattern to accelerate computation. Numerical verification and optical experiments show that the proposed method can generate holograms with wide viewing angles of 30° and 17° at high speeds.

Dynamic Polarization Patterning Technique for High-Quality Liquid Crystal Planar Optics

The Pancharatnam–Berry (PB)-phase liquid crystal (LC) planar optical elements, featuring large apertures and a light weight, are emerging as the new generation optics. The primary method for fabricating large-aperture LC planar optical elements is through photo-alignment, utilizing polarization laser direct writing. However, conventional polarization direct writing suffers from an inertia-induced stopping step during splicing, leading to suboptimal optical effects. Here, we propose a novel highly efficient method for arbitrary polarization patterning, significantly reducing interface splicing errors in these optical elements. (We call it dynamic polarization patterning technology). This process involves simultaneous mobile splicing and real-time generation of different polarization patterns for exposure, eliminating the inertia-related splicing interruption. As a demonstration, we fabricated a lens with an aperture of approximately 1 cm within 30 min at 633 nm. Furthermore, we developed a 100% fill-factor lens array (3 × 3) with an element lens diameter of approximately 7 mm within 1.5 h at 532 nm. Their focal lengths were uniformly set at 30 cm, demonstrating superior convergence capabilities within their designated working wavelengths, alongside commendable performance in converging light across various other wavelengths. Our measurements confirmed the good focusing performance of these samples. The convergence spot size of the lens deviated by approximately 40% from the theoretical diffraction limit, whereas the lens array exhibited a deviation of around 30%. The dynamic polarization direct writing during uniform platform movement reduced splicing errors to a mere 100–200 nm. The enhancement in imaging quality can be primarily attributed to the innovative use of mobile polarization splicing exposure technology, coupled with the inherent self-smoothing properties of LC molecules. This synergy significantly mitigates the impact of seam diffraction interference.