Lens Array Research Articles

360-degree directional micro prism array for tabletop flat-panel light field displays.

Tabletop light field displays are compelling display technologies that offer stereoscopic vision and can present annular viewpoint distributions to multiple viewers around the display device. When employing the lens array to realize the of integral imaging tabletop light field display, there is a critical trade-off between the increase of the angular resolution and the spatial resolution. Moreover, as the viewers are around the device, the central viewing range of the reconstructed 3D images are wasteful. In this paper, we explore what we believe to be a new method for realizing tabletop flat-panel light field displays to improve the efficiency of the pixel utilization and the angular resolution of the tabletop 3D display. A 360-degree directional micro prism array is newly designed to refract the collimated light rays to different viewing positions and form viewpoints, then a uniform 360-degree annular viewpoint distribution can be accurately formed. In the experiment, a micro prism array sample is fabricated to verify the performance of the proposed tabletop flat-panel light field display system. One hundred viewpoints are uniformly distributed in the 360-degree viewing area, providing a full-color, smooth parallax 3D scene.

Multifocal acoustic radiation force-based reverberant optical coherence elastography for evaluation of ocular globe biomechanical properties.

Quantifying the biomechanical properties of the whole eye globe can provide a comprehensive understanding of the interactions among interconnected ocular components during dynamic physiological processes. By doing so, clinicians and researchers can gain valuable insights into the mechanisms underlying ocular diseases, such as glaucoma, and design interventions tailored to each patient's unique needs. The aim of this study was to evaluate the feasibility and effectiveness of a multifocal acoustic radiation force (ARF) based reverberant optical coherence elastography (RevOCE) technique for quantifying shear wave speeds in different ocular components simultaneously. We implemented a multifocal ARF technique to generate reverberant shear wave fields, which were then detected using phase-sensitive optical coherence tomography. A 3D-printed acoustic lens array was employed to manipulate a collimated ARF beam generated by an ultrasound transducer, producing multiple focused ARF beams on mouse eye globes ex vivo. RevOCE measurements were conducted using an excitation pulse train consisting of 10 cycles at 3kHz, followed by data processing to produce a volumetric map of the shear wave speed. The results show that the system can successfully generate reverberant shear wave fields in the eye globe, allowing for simultaneous estimation of shear wave speeds in various ocular components, including cornea, iris, lens, sclera, and retina. A comparative analysis revealed notable differences in wave speeds between different parts of the eye, for example, between the apical region of the cornea and the pupillary zone of the iris (). Moreover, the study also revealed regional variations in the biomechanical properties of ocular components as evidenced by greater wave speeds near the apex of the cornea compared to its periphery. The study demonstrated the effectiveness of RevOCE based on a non-invasive multifocal ARF for assessing the biomechanical properties of the whole eyeball. The findings indicate the potential to provide a comprehensive understanding of the mechanical behavior of the whole eye, which could lead to improved diagnosis and treatment of ocular diseases.

Melasma treatment with a 1064 nm, picosecond-domain laser with a fractionated multibeam lens array.

Picosecond-domain lasers have been fitted with fractionated optics for dermal remodeling. This study evaluates the safety and efficacy of a multiwavelength picosecond-domain laser, using a 1064 nm multibeam lens array, for improving the appearance of melasma. Twenty adults with a clinical diagnosis of melasma were enrolled and received 4 monthly 1064-nm, 450 ps laser treatments delivered with a 10 × 10 fractional array of 150 µm microbeams. Cosmetic units with melasma were treated with fluences ranging from 1.7 to 2.9 mJ/microbeam with a repetition rate of 6 Hz. Treatment effect was evaluation of digital images by dermatologists blinded as to the treatment conditions, comparing baseline and 3- and 8-month post-treatment images. Modified melasma area and severity index (mMASI) scores were determined by the study investigator based on clinical photography. Subject self-assessment of treatment effects was also recorded. Blinded reviewers correctly identified the post-treatment image in 16 of the 20 image sets (80%). Ratings demonstrated statistically significant (p < 0.001) improvement on an 11-point scale at both the 3- and 8-month timepoints for a mean improvement of 3.7 point (range -8 to 10) or 37% improvement at the 3-month follow-up, and 2.7 (range -8 to 9) or 27% at the 8-month follow-up for all subjects. The average mMASI score showed highly significant reduction at both the 3- and 8-month follow-ups compared to baseline (p < 0.01). Most subjects (90%) were satisfied with the treatment outcome in melasma at both follow-ups, which is consistent with the treatment outcome and mMASI scores. The fractionated, picosecond-domain, 1064 nm laser is safe and effective for improving melasma and should be considered as an adjunct to topical treatment regimens and sun-protection for management of melasma.

Laser - Produced Functional Surfaces of Silicon and Quartz

Fiber laser of 1064 nm wavelength was employed for micro/nano machining process of silicon and quartz substrates. The experimental data reveal formation of silicon nanoparticles by pulse laser ablation in liquid. Various characterization techniques were used such as UV-Visible absorption, SEM morphology to examine silicon nanoparticles. Moreover, generation of microbeams from micro lens array was created by direct writing of fiber laser on quartz. Theoretical calculations using COMSOL software were adopted to estimate the surface temperature distribution at silicon and quartz surface and underneath. It is found that maximum temperature of about (4600 K) and (2400 K) for silicon and quartz respectively when 15 W laser power, 127 ns pulse duration, 30 KHz frequency and 100 mm/sec laser speed was used. Potential applications of silicon nanoparticles and microbeams array in optoelectronics and biological imaging can be conducted due to the controllable laser micro/nano machining process.

Novel fabrication and designs for hybrid optical elements with wider angle field of view by using integrated direct laser lithographic system

Hybrid optical elements, which are diffraction pattern arrays fabricated on curved refractive optical elements, have the ability to widen the field of view angle, and improve optical performance, by combining refraction and diffraction. As such, they have high potential in next-generation optical devices. However, manufacturing a high resolution diffraction pattern array that fully covers the curve of the refracted optical surface, so that the normal vectors of every pattern are perpendicular to the tangent plane of the refractive lens surface, is challenging. Furthermore, the lack of diffractive pattern designs corresponding to the curvature makes it difficult to replace curved microlens arrays with hybrid optics. In this study, a direct laser lithographic system combined with an auto-focus system and high accuracy rotational system was built to fabricate the diffractive patterns array on a cylindrical lens. This approach provides a method to manufacture hybrid optical elements with wider field of view. In addition, we proposed novel designs of a linear zone plate (LZP) and elliptical zone plate (EZP) on a cylindrical lens that can be used for focusing light beam into lines and points, respectively. These hybrid optics exhibit superior performance in both diffraction efficiency and resolution, 25% better than traditional diffractive optical elements. An array of two types of zone plates were fabricated fully along the curve of the cylindrical lens using the proposed system, giving a 20° angle field of view, which acts like a curved cylindrical lens array and 1D curved microlens array. The performance of these hybrid optical elements were evaluated by optical verification system and simulation.

Integral imaging three-dimensional display system with anisotropic backlight for the elimination of voxel aliasing and separation.

Compared with conventional scattered backlight systems, integral imaging (InIm) display system with collimated backlight can reduce the voxel size, but apparent voxel separation and severe graininess still exist in reconstructed 3D images. In this paper, an InIm 3D display system with anisotropic backlight control of sub-pixels was proposed to resolve both voxel aliasing and voxel separation simultaneously. It consists of an anisotropic backlight unit (ABU), a transmissive liquid crystal panel (LCP), and a lens array. The ABU with specific horizontal and vertical divergence angles was proposed and designed. Within the depth of field, the light rays emitted from sub-pixels are controlled precisely by the ABU to minimize the voxel size as well as stitch adjacent voxels seamlessly, thus improving the 3D image quality effectively. In the experiment, the prototype of our proposed ABU-type InIm system was developed, and the spatial frequency was nearly two times of conventional scattered backlight InIm system. Additionally, the proposed system eliminated the voxel separation which usually occurs in collimated backlight InIm system. As a result, voxels reconstructed by our proposed system were stitched in space without aliasing and separation, thereby greatly enhancing the 3D resolution and image quality.

Injection‐compression molding process on optical quality optimization of plastic lens array

AbstractPlastic lens arrays (PLAs) have the advantages of a light weight and a compact size. However, their optical performance is often degraded by warpage, caused by the accumulation of residual stress during the injection molding process. Accordingly, the present study employs mold flow analysis simulations and a Taguchi‐Gray relational analysis (GRA) framework to optimize the processing parameters of the injection compression molding (ICM) process. The analyses focus specifically on the effects of the mold temperature, melt temperature, injection velocity, packing pressure, packing time, and compression gap on the optical path difference (OPD) and lens center displacement (LCD) of the fabricated lens array. The results confirm that the optimized processing parameters significantly improve the OPD, LCD, birefringence, and imaging properties of the PLA compared to those of a PLA fabricated using standard molding conditions.

Facile and flexible fabrication of structured array surfaces on binderless tungsten carbide by using electrical discharge machining with a novel self‐assembly ball electrode

AbstractElectrical discharge machining (EDM) method is an innovative method for the fabrication of structured array surfaces on binderless tungsten carbide (WC) which is a typical embossing mold material, compared to traditional machining methods. To improve the convenience of electrode replacement and the fabrication efficiency of the structured array, a novel self‐assembly ball electrode is innovatively developed. The feasibility of machining binderless WC with a self‐assembly ball electrode was studied and its effect on profile deviation analyzed. Furthermore, the discharge condition's effect on surface roughness, material removal rate (MRR), and tool wear ratio (TWR) was investigated. The microstructure, phase structure, and element distribution of binderless WC caused by EDM were characterized by Raman spectroscopy, scanning electron microscopy, and energy dispersive x‐ray spectroscopy. The results indicated that the maximum profile deviation of the different random structured arrays was about 3.7 μm. The surface roughness of all structured arrays was below 1 μm. The maximum TWR was about 0.008 mm3/min. Besides, the binderless WC surface after EDM presented strong D and G carbon peaks, which means the precipitation and transformation of the WC phase during the discharge process. Finally, different kinds of self‐assembly ball electrodes are developed and used to fabricate the lens array structures on binderless WC. The fast fabrication of the micro‐lens array surfaces in different arrangements sheds some light on the design and manufacturing of other functional structured surfaces.

Acoustic Forceps Based on Focused Acoustic Vortices with Different Topological Charges.

For enhanced energy concentration with improved flexibility for object manipulation, a focused acoustic vortex (FAV) is designed using a sector planar piston transducer array and acoustic lens that can produce the effective concentration of the acoustic field to perform the focusing function. Compared to the Gaussian beam, which tends to cause the object to deviate from the axis of acoustic propagation, FAVs can form a central valley region to firmly bind the objects, thus preventing off-target effects. The heat energy in the paraxial region is transferred to the vortex center in the form of heat transfer so that the temperature-sensitive liposomes captured can quickly release drugs, which has a good effect on targeted drug administration. The focused acoustic wave stopped acting on the tissue (gel) for 2 s, the temperature of the vortex center continued to rise, reaching 41.5 °C at the moment of 3.7 s, at which point the liposomes began to release the drug. The FAVs capture the drug and use its thermal effect to achieve accurate and rapid treatment. The simulation results show that the drug release temperature of temperature-sensitive liposomes can be achieved by controlling the action time of the vortices. This study provides a reliable theoretical basis for the clinical application of targeted drugs.

Étendue Expansion in Holographic Near Eye Displays through Sparse Eye-box Generation Using Lens Array Eyepiece

In this paper, we present a novel method the étendue expansion of near-eye holographic displays through the generation of a sparse eye-box. Conventional holographic near-eye displays have suffered from narrow field of view or narrow eye-box due to the limited étendue supported by a spatial light modulator. We focus on the fact that these displays typically form a dense eye-box, which could be an excessive investment of the limited étendue. By rearranging the eye-box in a sparse manner, the practical étendue can be extended. With a properly designed sparse eye-box shape, it can provide the 3D holographic images and ensure continuous light entrance to the pupil. To create a sparse eye-box, we utilize a lens array as an eyepiece lens. We optimize the spatial light modulator's phase profile for the proposed system and analyze the impact of the use of the lens array eyepiece on the holographic image quality. In particular, we focus on the lens array specification of the lenslet pitch and the focal length, deriving feasible specifications based on our analysis. We experimentally demonstrate a near eye see-through display using the proposed system and verify the étendue expansion.

Directional and Eye-Tracking Light Field Display with Efficient Rendering and Illumination.

Current efforts with light field displays are mainly concentrated on the widest possible viewing angle, while a single viewer only needs to view the display in a specific viewing direction. To make the light field display a practical practice, a super multi-view light field display is proposed to compress the information in the viewing zone of a single user by reducing the redundant viewpoints. A quasi-directional backlight is proposed, and a lenticular lens array is applied to achieve the restricted viewing zone. The eye-tracking technique is applied to extend the viewing area. Experimental results show that the proposed scheme can present a vivid 3D scene with smooth motion parallax. Only 16.7% conventional light field display data are required to achieve 3D display. Furthermore, an illumination power of 3.5 watt is sufficient to lighten a 31.5-inch light field display, which takes up 1.5% of the illumination power required for planar display of similar configuration.

Microlens array device for laser light shaping in laser scanning smart headlights.

We present, what we believe to be, a novel microlens array (MLA) scheme for laser light shaping in laser scanning smart headlight. The laser spot has a Gaussian distribution that may reach a high peak power density in the central part, which is called hot spot. When the laser beam is applied to a phosphor plate for luminous conversion, the hot spot of Gaussian beam causes thermal quench and decreases luminous efficacy. To avoid this effect, an MLA is used, so as to achieve a uniform energy distribution. In this study, we propose a laser scanning smart headlight fabricated by a new MLA structure, with an arrangement providing both light uniformity and shaping. The novel MLA is designed by two-dimensional micro-concave lens array yielding a flat-top beam. The flexible fabrication process employs laser drilling to shape the micro-hole array on the glass substrate surface and then etch it to form MLA without requiring any mask lithography process. The full-width half maximum (FWHM) of light output distribution can be adjusted by the glass etching parameters, and the light distribution could be controlled by the arranged layout of the array. Thus, beams with FWHM divergence ranging from 5° to 34° has been fabricated and characterized. The typical pixel shape is a rectangle with two different FWHMs in two orthogonal directions, and the fabrication method achieves this goal as well. This novel design and unique maskless process of the MLAs is a promising tool for development the next generation laser scanning smart headlight.

Comprehensive High-Quality Three-Dimensional Display System Based on a Simplified Light-Field Image Acquisition Method and a Full-Connected Deep Neural Network.

We propose a high-quality, three-dimensional display system based on a simplified light field image acquisition method, and a custom-trained full-connected deep neural network is proposed. The ultimate goal of the proposed system is to acquire and reconstruct the light field images with possibly the most elevated quality from the real-world objects in a general environment. A simplified light field image acquisition method acquires the three-dimensional information of natural objects in a simple way, with high-resolution/high-quality like multicamera-based methods. We trained a full-connected deep neural network model to output desired viewpoints of the object with the same quality. The custom-trained instant neural graphics primitives model with hash encoding output the overall desired viewpoints of the object within the acquired viewing angle in the same quality, based on the input perspectives, according to the pixel density of a display device and lens array specifications within the significantly short processing time. Finally, the elemental image array was rendered through the pixel re-arrangement from the entire viewpoints to visualize the entire field-of-view and re-constructed as a high-quality three-dimensional visualization on the integral imaging display. The system was implemented successfully, and the displayed visualizations and corresponding evaluated results confirmed that the proposed system offers a simple and effective way to acquire light field images from real objects with high-resolution and present high-quality three-dimensional visualization on the integral imaging display system.

Newton ring interferometry application for 2D lens array alignment with micrometer accuracy.

The dense packing of two-dimensional (2D) lens arrays with high tilt and decentration accuracies is a technological challenge in coherent beam combining, as the collimator lens parameters and 2D lens array alignment must satisfy stringent requirements. A method for 2D lens array alignment based on Newton ring interferometry (NRI) is proposed. The analytical model and the algorithm presented in this study enabled the estimation of alignment sensitivity. An optical setup for alignment tests using NRI was developed and experimentally verified, and micrometer sensitivity was demonstrated. Analytical and experimental results showed that micrometer accuracy was achieved. Its limitations and prospects for improvement are also discussed.

Designing Freeform Micro Lens Array With Prescribed Luminous Intensity for LCD Backlight Units

Designing Freeform Micro Lens Array With Prescribed Luminous Intensity for LCD Backlight Units

P‐52: Higher Brightness Mini‐LED Displays: Optimizing Collimation and Uniformity in a Thinner Form Factor

We propose a novel method for improving brightness and efficiency of BEF‐less mini‐LED displays in a thinner form factor. In place of BEFs an array of Fresnel lenses positioned over each LED followed by micro lens array diffusion films create a uniform light output. Best practices and backlight design recommendations will be discussed.

LensFD: Using Lenses for Improved Sub-6 GHz Massive MIMO Full-Duplex

Massive MIMO has emerged as a key-enabler to deliver the high data-rates in current and next-generation systems. Many massive MIMO deployments use time-division duplex (TDD), thereby opening the door for the potential use of full-duplex at base-stations. In this paper, we present LensFD, a scalable method to enable cost-effective massive MIMO full-duplex operation in sub-6 GHz frequencies with a focus on the CBRS band of 3.5 GHz. LensFD uses a low-cost lens array combined with transmit precoding to reshape the effective beam pattern of antennas in massive MIMO arrays to reduce self-interference. We tested three lens configurations in LensFD experimentally with a software-defined 40-antenna base-station and demonstrate a significant improvement in self-interference reduction and hence overall increased system capacity to 1.6× over the TDD counterpart. As an important contribution, we will open-source the large measurement dataset from our experiments.

True-color light-field display system with large depth-of-field based on joint modulation for size and arrangement of halftone dots.

A true-color light-field display system with a large depth-of-field (DOF) is demonstrated. Reducing crosstalk between viewpoints and increasing viewpoint density are the key points to realize light-field display system with large DOF. The aliasing and crosstalk of light beams in the light control unit (LCU) are reduced by adopting collimated backlight and reversely placing the aspheric cylindrical lens array (ACLA). The one-dimensional (1D) light-field encoding of halftone images increases the number of controllable beams within the LCU and improves viewpoint density. The use of 1D light-field encoding leads to a decrease in the color-depth of the light-field display system. The joint modulation for size and arrangement of halftone dots (JMSAHD) is used to increase color-depth. In the experiment, a three-dimensional (3D) model was constructed using halftone images generated by JMSAHD, and a light-field display system with a viewpoint density of 1.45 (i.e. 1.45 viewpoints per degree of view) and a DOF of 50 cm was achieved at a 100 ° viewing angle.

68‐1: Invited Paper: A Waveguide‐type Retinal Scan AR Display with Pupil Expansion System

We have developed a full‐color retinal scan AR display presenting a focus‐free image with a novel pupil switching system featuring a holographic lens array on multiple waveguide optics. The display demonstrated a stereoscopic image with 50° diagonal field of view and 5.0‐mm eyebox.

Compact lensless convolution processor for an optoelectronic convolutional neural network

To our knowledge, optical 4f systems have been widely used as a convolutional layer to perform convolutional computation in free-space optical neural networks (ONNs), which makes ONNs too bulky to be easily applied to miniaturized smart systems. Hence, we propose a compact lensless optoelectronic convolutional neural network (LOE-CNN) architecture in which a single optimized diffractive phase mask acts as an analog convolution processor to perform convolutional operation without a Fourier lens or lenslet array. We demonstrate that this LOE-CNN can be functionally comparable to existing electronic counterparts in classification performance, achieving a classification accuracy of 98.07% and 95% over the Modified National Institute of Standards and Technology dataset in simulation and experiment, respectively, which not only opens new application prospects for free-space ONNs based on a compact single-chip convolution processor, but also facilitates the development of ONN-based smart devices.