Optical Lens Research Articles

METU-DBL: a cost effective proton irradiation facility

The Middle East Technical University Defocusing Beamline (METU-DBL) is designed to deliver protons with selectable kinetic energies between 15–30 MeV, and proton flux between 106–1010 protons/cm2/s, on a maximum 21.55 to 15.40 cm target region with a beam uniformity within ±6%, in accordance with the ESA ESCC No. 25100 specification for single event effects (SEEs) tests in the low energy range. The achieved high proton fluences, allow users to test space-grade materials; electronic circuits, ASICs, FPGAs, optical lenses, structural elements, and coating layers for LEO, GEO, and interplanetary missions.The total received dose on the Device-Under-Test (DUT) from secondary particles created during proton-material interactions at the first beam collimator and the beam dump never exceed 0.1% of the dose from primary protons. The METU-DBL is equiped with several measurement stations and services to the user teams. A secondary measurement station in a rotating drum that can hold multiple samples has been constructed next to the first collimator which provides neutrons for transmission experiments. At the target region, a robotic table is located, which provides mechanical and electrical mounting points to the samples and allows multiple samples to be tested in a row. A modular vacuum box can also be attached on the robotic table for any test that may require a vacuum environment. Power rails on the robotic table provide various outputs for the DUT. For the data acquisition, high-speed networking and a modular industrial PC are available at the target station. The design of the METU-DBL control software enables test users to integrate and optimize the data acquisition and controlling of the DUT.The beam properties at the target region are measured with the diamond, Timepix3, and fiber scintillator detectors mounted on the robotic table. With diamond and Timepix3 detectors, measurements are taken from the five different points (center and the four corners) of the test area to measure the proton flux and ensure that it is uniform across the full test area. Fiber scintillators on both axes (X and Y) scan the target area to cross-check the beam profile's uniformity. Secondary doses during the irradiation are measured by a Geiger-Müller tube sensitive to electrons and gammas above 0.1 MeV and by a neutron detector located at the entrance of the R&D room. The room cools down relatively fast after any irradiation (<1 hour).Accurate linear energy deposition rates and absorbed doses on the samples are calculated using MCNP6, FLUKA and Geant4 Monte Carlo simulations. Alanine dosimetry measurements that are calibrated against these simulations are also used to estimate the absorbed dose on the sample.

시각의 구조적, 기능적 특징을 모사한 생체모사 카메라

Conventional imaging and data processing devices may not be ideal for mobile machine vision applications, such as drones and robots, due to the bulky and heavy multi-lens optics used in conventional cameras. Additionally, physical isolation of camera and processors necessitates the capture, transfer, and processing of redundant data, resulting in large power consumption and data latency. Here, we review on bio-inspired cameras inspired by the structural and functional features of biological eyes. We first summarize recent strategies to fabricate curved image sensor (CurvIS) arrays mimicking the curved retina of biological eyes. These CurvIS arrays enable aberration-free imaging with a single lens optics, leading to a miniaturization of camera module. Other optical advantages, such as wide field-of-view and deep depth-of-field, could be also offered by the integrated camera module. Next, we discuss bio-inspired cameras capable of performing in-sensor processing as well as image acquisition. As notable examples, we introduce synaptic optoelectronic devices that can efficiently enhance image contrast and reduce the noise using photon-triggered synaptic plasticity.

Continuous Vat Photopolymerization for Optical Lens Fabrication

Optical lenses require feature resolution and surface roughness that are beyond most (3D) printing methods. A new continuous projection-based vat photopolymerization process is reported that can directly shape polymer materials into optical lenses with microscale dimensional accuracy (< 14.7µm) and nanoscale surface roughness (< 20nm) without post-processing. The main idea is to utilize frustum layer stacking, instead of the conventional 2.5D layer stacking, to eliminate staircase aliasing. A continuous change of mask images is achieved using a zooming-focused projection system to generate the desired frustum layer stacking with controlled slant angles. The dynamic control of image size, objective and imaging distances, and light intensity involved in the zooming-focused continuous vat photopolymerization are systematically investigated. The experimental results reveal the effectiveness of the proposed process. The 3D-printed optical lenses with various designs, including parabolic lenses, fisheye lenses, and a laser beam expander, are fabricated with a surface roughness of 3.4nm without post-processing. The dimensional accuracy and optical performance of the 3D-printed compound parabolic concentrators and fisheye lenses within a few millimeters are investiagted. These results highlight the rapid and precise nature of this novel manufacturing process, demonstrating a promising avenue for future optical component and device fabrication.

Ophthalmic glass lens waste as an alternative soluble silica source for alkali-activation reactions

This research study was aimed at assessing the potential use of glass powder (GW), from the production of optical lenses, as a substitute of commercial sodium silicate (SS), to produce fly ash-based alkaline cements. The dissolution of the GW and the subsequent activation were achieved either with a cleaning solution (CS) from the aluminium casting industry, and a commercial sodium hydroxide solution (SH) so as to. Firstly, GW dissolution with CS and SH was evaluated at different time and temperatures, i.e.,16 h, 3, 7 and 28 days at 20 °C and 16 h at 20, 40, 60 and 80 °C, to find the best dissolution rate, which an optimum point was observed when CS was the dissolving agent. Then, several pastes were synthesized and cured for 7 days at 50 °C to assess their mechanical behaviour and alkaline-activated gel formation by compressive strength test. Furthermore, reaction products were characterized by X-ray diffraction (XRD) and electron microscopy (SEM/EDX). The observations reveal that although SH solution acted well to dissolve GW, so that the compressive strength was close to that of SS, CS also showed reasonable potential to be used as a dissolving agent for GW, rendering a cheap and environmentally friendly alternative activator. Microstructural analysis also illustrated the rise in the crystallinity of the reaction products obtained from industrial by-products, i.e., GW and CS.

A miniaturized and low-energy subcutaneous optical telemetry module for neurotechnology

Objective. This study presents a proof-of-concept optical telemetry module that leverages a single light-emitting diode (LED) to transmit data at a high bit rate while consuming low power and occupying a small area. Our experiments showed that we could achieve 108 Mbit s−1 and 54 Mbit s−1 back telemetry data rates for tissue thicknesses of 3 mm and 8 mm, respectively. Approach. The proposed module is designed to be powered by near-field coupling and achieve bidirectional communication by low-speed downlink from near-field communication. It aims to minimize the size of the implant while providing reliable transmission that meets the requirements of high-speed wireless communication from a multi-electrode array neurotechnology implant outside the body. Results. The power consumption of the module is 1.57 mW, including the power consumption of related circuits, resulting in an efficiency of 14.5 pJ bit−1, at a tissue thickness of 3 mm and a data rate of 108 Mbit. The use of an optical lens, combined with tissue scattering effect and optimized emission angle, makes the module robust to misalignments of up to ±5 mm and ±15° between the implantable and external units. The LED in the implantable unit is only 0.98 × 0.98 × 0.6 mm3, and the testing module is composed of discrete components and laboratory instruments. Significance. This work aims to show how it is possible to strike a balance between a small, reliable, and high-bit-rate data uplink between a neural implant and its proximal, wirelessly connected external unit. This optical telemetry module has the potential to be integrated into a significantly miniaturized system through an application-specific integrated circuit and can support up to 1000 channels of neural recordings, each sampled at 9 kSps with a 12-bit readout resolution.

Axisymmetrical resonance modes in an electrowetting optical lens.

Electrowetting-based adaptive optics are of great interest for applications ranging from confocal microscopy to LIDAR, but the impact of low-frequency mechanical vibration on these devices remains to be studied. We present a simple theoretical model for predicting the resonance modes induced on the liquid interface in conjunction with a numerical simulation. We experimentally confirm the resonance frequencies by contact angle modulation. They are found to be in excellent agreement with the roots of the zero-order Bessel functions of the first kind. Next, we experimentally verify that external axial vibration of an electrowetting lens filled with density mismatched liquids ( = 250 kg/m3) will exhibit observable Bessel modes on the liquid-liquid interface. An electrowetting lens filled with density matched liquids ( = 4 kg/m3) is robust to external axial vibration and is shown to be useful in mitigating the effect of vibrations in an optical system.

Beam shaping-based design for optical imaging lens

In this paper, a beam shaping-based method for design of optical imaging lens is proposed. The optical imaging lens is designed with Fresnel diffraction theory to focus light, and the focusing parameters of the lens, such as the number of the foci, the focal length, the size and the shape of the focal spot, and so on, can be set with great freedom. Therefore, the lens has great flexibility in optical imaging, and the imaging resolution can also be varied with the design. The optical imaging lenses possess advantages such as simple structure, compact size, customized imaging effect, and high performance. The proposed method can be extensively applied to the design of flat optical elements and the customized optical imaging.

511-CAM mission: a pointed 511 keV gamma-ray telescope with a focal plane detector made of stacked transition edge sensor microcalorimeter arrays

The 511 keV γ-ray emission from the galactic center region may fully or partially originate from the annihilation of positrons from dark matter particles with electrons from the interstellar medium. Alternatively, the positrons could be created by astrophysical sources, involving exclusively standard model physics. We describe here a new concept for a 511 keV mission called 511-CAM (511 keV gamma-ray camera using microcalorimeters) that combines focusing γ-ray optics with a stack of transition edge sensor microcalorimeter arrays in the focal plane. The 511-CAM detector assembly has a projected 511 keV energy resolution of 390 eV full width half maximum or better, and improves by a factor of at least 11 on the performance of state-of-the-art Ge-based Compton telescopes. Combining this unprecedented energy resolution with sub-arcmin angular resolutions afforded by Laue lens or channeling optics could make substantial contributions toward identifying the origin of the 511 keV emission through discovering and characterizing point sources and measuring line-of-sight velocities of the emitting plasmas.

Micro milling of fused silica using picosecond laser shaped single crystal diamond tools

Fused silica is widely used as a material for optical lenses owing to its excellent optical properties and low thermal expansion coefficient. However, as a hard and brittle material, there is very limited option of processing technologies to machining fused silica with surface structures. In this paper, a picosecond laser based single crystal diamond tool fabrication technology is proposed to generate micro milling tools with different geometrical designs, and the tool cutting performance is experimentally tested through micro-milling of fused silica under different cutting conditions. An optimal picosecond laser processing path is proposed to inhibit the graphitization of diamond tool and improve the concentricity of tool blades, and a multi-edge milling tool with a minimum rotary diameter of 0.4 mm can be obtained. The effects of rake angle on cutting force and the degree of brittle damage on the subsurface of fused silica are studied by micro milling tests of fused silica using the laser-shaped tools. The results show that the fused silica machined by diamond milling tool with a rake angle of −30° has the best surface finish (Ra = 41.2 nm). Using this laser-machined milling tool, a plurality of micro Fresnel lenses with aperture of 1.6 mm were successfully machined on a fused silica sheet.

Optical Imaging Deformation Inspection and Quality Level Determination of Multifocal Glasses.

Multifocal glasses are a new type of lens that can fit both nearsighted and farsighted vision on the same lens. This property allows the glass to have various curvatures in distinct regions within the glass during the grinding process. However, when the curvature varies irregularly, the glass is prone to optical deformation during imaging. Most of the previous studies on imaging deformation focus on the deformation correction of optical lenses. Consequently, this research uses an automatic deformation defect detection system for multifocal glasses to replace professional assessors. To quantify the grade of deformation of curved multifocal glasses, we first digitally imaged a pattern of concentric circles through a test glass to generate an imaged image of the glass. Second, we preprocess the image to enhance the clarity of the concentric circles' appearance. A centroid-radius model is used to represent the form variation properties of every circle in the processed image. Third, the deviation of the centroid radius for detecting deformation defects is found by a slight deviation control scheme, and we gain a difference image indicating the detected deformed regions after comparing it with the norm pattern. Fourth, based on the deformation measure and occurrence location of multifocal glasses, we build fuzzy membership functions and inference regulations to quantify the deformation's severity. Finally, a mixed model incorporating a network-based fuzzy inference and a genetic algorithm is applied to determine a quality grade for the deformation severity of detected defects. Testing outcomes show that the proposed methods attain a 94% accuracy rate of the quality levels for deformation severity, an 81% recall rate of deformation defects, and an 11% false positive rate for multifocal glass detection. This research contributes solutions to the problems of imaging deformation inspection and provides computer-aided systems for determining quality levels that meet the demands of inspection and quality control.

Cardiac resynchronization therapy device implantation using suspended personal radiation protection system: Examination of radiation protection effectiveness by dosimetry at 51 exposure sites.

Cardiologists often use fluoroscopic equipment for treatment such as cardiac implantable electronic device implantation, catheter ablation, percutaneous coronary intervention, and other procedures. Difficulties arise in protecting the head and optical lens from the exposure of radiation, which is a significant concern among physicians1,2. Currently available radiation protective clothing consists of a collar for the thyroid gland and a sleeveless apron. Although higher radiation protection can be expected by increasing the lead content of the protective clothing, there is a limit to additional lead content due to the increased weight.

Large size optical glass lens polishing based on ultrasonic vibration

Large size optical glass lens polishing based on ultrasonic vibration

Transparent organic upconversion devices displaying high-resolution, single-pixel, low-power infrared images perceived by human vision.

Crystalline photodiodes remain the most viable infrared sensing technology of choice, yet the opacity and the limitation in pixel size reduction per se restrict their development for supporting high-resolution in situ infrared images. In this work, we propose an all-organic non-fullerene-based upconversion device that brings invisible infrared signal into human vision via exciplex cohost light-emissive system. The device reaches an infrared-to-visible upconversion efficiency of 12.56% by resolving the 940-nm infrared signal (power density of 103.8 μW cm-2). We tailor a semitransparent (AVT, ~60%), large-area (10.35 cm2), lightweight (22.91 g), single-pixel upconversion panel to visualize the infrared power density down to 0.75 μW cm2, inferring a bias-switching linear dynamic range approaching 80 dB. We also demonstrate the possibility of visualizing low-intensity infrared signals from the Face ID and LiDAR, which should fill the gap in the existing technology based on pixelated complementary metal-oxide semiconductors with optical lenses.

Surface profile prediction modeling of spiral toolpath for axial ultrasonic vibration-assisted polishing

Hard and brittle materials are widely used in many frontier fields because of their better properties, and their efficient precision polishing methods are attracting much attention. The research on surface quality of optical lenses with surface finishing requirement not only involves surface roughness, but also surface form accuracy. The generated surface profile is a key factor affecting the surface form accuracy and overall smoothness. From experience, both processing mechanism of adopted method and toolpath have effects on the generated surface profile. For this, the paper presents a theoretical and experimental study of the generated surface profile of spiral toolpath in axial ultrasonic vibration-assisted polishing (UVAP). Based on classical Preston equation, Hertzian contact theory and the axial vibration-assisted processing principle, a prediction calculation model for generated surface profile of spiral toolpath is proposed. The model can specifically analyze the dwell-time distribution characteristics of periodically varying contact pressure and sliding velocity in the areas near/far-from the curvature center of curve toolpath, accurately predict the surface profile shape and material removal rate (MRR), and scientifically reveal the assisted processing principle. Accordingly, a series of experiments are conducted to verify the rationality of the proposed model and the polishing performance of axial UVAP. Compared to conventional methods, the predictions can more reasonably and accurately present the real surface profile characteristics, both high MRR and superior surface quality are obtained. This study would aid in achieving a deterministic processing technology of higher efficiency and better surface quality, laying a crucial theoretical basis for the global polishing of optical lens.

The multifunctional neutron imaging system at GPPD: Design, principles and applications

A multifunctional neutron imaging system (MNIS) has been built recently on the day-one instrument general purpose powder diffractometer (GPPD) at the China Spallation Neutron Source (CSNS). The sample position of MNIS is located three meters downstream of the diffraction sample position to maintain good imaging performance without changing the existing layout. MNIS can accommodate several significant neutron imaging technologies, including two-dimensional neutron radiation, three-dimensional computer tomography, neutron Talbot–Lau grating interferometer, and Bragg edge neutron imaging. The system has a largest field of view (FOV) of 6 × 6 cm2 and a best spatial resolution of 25μm by changing the magnification of the optical lens. The wavelength resolution is better than 0.2%. Additionally, MNIS serves as an initial validation for Energy-Resolved Neutron Imaging instrument (ERNI), a dedicated neutron imaging instrument currently under construction at CSNS.

Highly Transparent and Zirconia-Enhanced Sol-Gel Hybrid Coating on Polycarbonate Substrates for Self-Cleaning Applications.

To improve the efficacy of polymer-based substrate hybrid coatings, it is essential to simultaneously optimize mechanical strength and preserve the optical properties. In this study, a mixture of zirconium oxide (ZrO2) sol and methyltriethoxysilane modified silica (SiO2) sol-gel was dip-coated onto polycarbonate (PC) substrates to form zirconia-enhanced SiO2 hybrid coatings. Additionally, a solution containing 1H, 1H, 2H, and 2H-perfluorooctyl trichlorosilane (PFTS) was employed for surface modification. The results show that the ZrO2-SiO2 hybrid coating enhanced the mechanical strength and transmittance. The average transmittance of the coated PC reached up to 93.9% (400-800 nm), while the peak transmittance reached up to 95.1% at 700 nm. SEM images and AFM morphologies demonstrate that the ZrO2 and SiO2 nanoparticles were evenly distributed, and a flat coating was observed on the PC substrate. The PFTS-modified ZrO2-SiO2 hybrid coating also exhibited good hydrophobicity (WCA, 113°). As an antireflective coating on PC, with self-cleaning capability, the proposed coating has application prospects in optical lenses and automotive windows.

Measurement of Fine/Ultrafine Dust Using Lenticular Fiber-Based Particulate Measurement Devices

Measurement of particulate matter (PM), i.e., fine/ultrafine dust, is important for monitoring our surrounding environment. We demonstrate the fabrication of lenticular fiber-based fine/ultrafine dust measurement devices for monitoring the density and size of dust. The plano-convex lenticular fibers were fabricated by the CO2 laser polishing technique. The optical lens, used in the conventional light scattering-based fine/ultrafine dust measurement devices, was replaced by a plano-convex lenticular optical fiber to reduce the size and complexity of the dust measurement device. We utilized a light-emitting diode as the light source of the fine/ultrafine dust density measurement device. The fabricated device could indicate the dust density level (good, normal, bad, and very bad) according to the Korean standard. To estimate the size of the dust particulates, we fabricated a dust size measurement device that consists of a compact laser diode, a lenticular fiber, and a photodetector. We are successful in estimating the size of both fine and ultrafine PMs by detecting the power of the scattered light coming from the dust particulates. The dust size down to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.9 \mu \text{m}$ </tex-math></inline-formula> was detected using our dust measurement device. Our proposed dust measurement devices are simple, small, and cost-effective and can be considered as a candidate for portable applications.

On-chip generation of Bessel–Gaussian beam via concentrically distributed grating arrays for long-range sensing

Bessel beam featured with self-healing is essential to the optical sensing applications in the obstacle scattering environment. Integrated on-chip generation of the Bessel beam outperforms the conventional structure by small size, robustness, and alignment-free scheme. However, the maximum propagation distance (Zmax) provided by the existing approaches cannot support long-range sensing, and thus, it restricts its potential applications. In this work, we propose an integrated silicon photonic chip with unique structures featured with concentrically distributed grating arrays to generate the Bessel–Gaussian beam with a long propagation distance. The spot with the Bessel function profile is measured at 10.24 m without optical lenses, and the photonic chip’s operation wavelength can be continuously performed from 1500 to 1630 nm. To demonstrate the functionality of the generated Bessel–Gaussian beam, we also experimentally measure the rotation speeds of a spinning object via the rotational Doppler Effect and the distance through the phase laser ranging principle. The maximum error of the rotation speed in this experiment is measured to be 0.05%, indicating the minimum error in the current reports. By the compact size, low cost, and mass production potential of the integrated process, our approach is promising to readily enable the Bessel–Gaussian beam in widespread optical communication and micro-manipulation applications.

Effect of process parameters on surface roughness of NiCu alloy in fluid jet polishing

Fluid jet polishing is a non-contact and flexible type of polishing process for generating high-quality surface finish in optical dies manufactured from ductile materials like Monel-400 (NiCu alloy). This article presents an investigation of fluid jet polishing of Monel-400 die material with a 3D printed Ti64 tool and silicon carbide abrasive slurry with an effect of pressure, stand-off distance and polishing time on the surface finish. The response surface methodology method was used to develop the experimental plan and Analysis of Variance analysis was carried out to identify the optimized values of the control parameters to maximize the percentage change in surface roughness. The validation of the developed regression model was done by polishing the plate of Monel-400 using the optimized parameters: the pressure of 9.6 bar, stand-off distance of 32.2 mm and polishing time of 170 s. The optimized fluid jet polishing parameters successfully generated a surface roughness of 90 nm in one of the experimental tests. The predicted results were in close agreement with the experimental results. Further improving the polishing efficiency, the optimal feed rate of 20 mm/min was used to polish the 40 mm × 50 mm Monel-400 plate, the surface roughness was reduced from 300 to 80 nm in 10 multiple passes showing the reduction in peaks and valleys with the surface improvement of 73.33%. The result shows that the fluid jet polishing process tends to improve the life span of Monel-400 die steel workpieces which is beneficial for the application of various industrial components such as optical lenses, marine applications, automotive components and defence applications.

Causes of Childhood Blindness in the United States Using the IRIS® Registry (Intelligent Research in Sight)

To investigate causes of childhood blindness in the United States using the IRIS® Registry (Intelligent Research in Sight). Cross-sectional study. Patients ≤ 18 years of age with visual acuity (VA) 20/200 or worse in their better-seeing eye in the IRIS Registry during2018. Causes of blindness were classified by anatomic site and specific diagnoses. Percentages of causes of blindness. Of 81 164 children with 2018 VA data in the IRIS Registry, 961 (1.18%) had VA 20/200 or worse in their better-seeing eye. Leading causes of blindness were retinopathy of prematurity (ROP) in 301 patients (31.3%), nystagmus in 78 patients (8.1%), and cataract in 64 patients (6.7%). The retina was the leading anatomic site (47.7%) followed by optic nerve (11.6%) and lens (10.0%). A total of 52.4% of patients had treatable causes of blindness. This analysis offers a unique cross-sectional view of childhood blindness in the United States using a clinical data registry. More than one-half of blind patients had a treatable cause of blindness. Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.