Optical Lens Research Articles

Who made the noise? Systematic approach for the assessment of neutron imaging scintillators

We propose a method to analyze the characteristics of scintillator screens for neutron imaging applications. Using calculations based on the theory of cascaded linear steps as well as experimental measurements, we compared the characteristics of different lithium- and gadolinium-based scintillator screens. Our results show that, despite their much lower light output, gadolinium-based scintillators outperform lithium-based scintillators in terms of noise characteristics for a variety of imaging setups. However, the relative performance of scintillator screens is highly dependent on the other setup characteristics such as the beam spectrum, field of view, used optical lens and size of the camera sensor. Consequently, the selection of the best scintillator screen – as well as the scintillator characteristics assessment in new developments – requires a systematic consideration of all these elements, as enabled by the framework presented here.

Generation of array of square microcavity on quartz by ultrasonic micromachining process utilizing developed micro tool

Quartz possesses distinct characteristics such as exceptional hardness, high brittleness, non-conductivity, remarkable corrosion resistance, efficient transmission within specific wavelengths, strong electrical insulation properties, and the ability to withstand high temperatures and thermal shocks. These extraordinary attributes have led to its component in a wide range of applications, including the fabrication of microelectronic chips, biochips, biological channels, microfluidics, optical lenses, beam-splitting lenses, etc. Ultrasonic micromachining (USMM) is a highly promising technique within the realm of micromachining to create micro features on quartz surfaces. In the present research, array of square micro tools has been designed and developed by the wire-electrical discharge machining (EDM) process. By utilizing the developed array of square micro tools, microcavity arrays have been generated by the USMM process. The influences of process parameters on material removal rate (MRR), width deviation (WD), angular deviation, and taper of square microcavities have been investigated in the present research work. The higher MRR is obtained as 1.427 mm3/min at higher abrasive slurry concentration and lower WD of micro cavities is obtained as 37 µm and lower taper angle is 1.109° at 5% abrasive slurry concentration. The lower value of angular deviation is obtained as 0.836° at a lower power rating during the generation of an array of square microcavity on quartz by the USMM process. By employing array of micro tools, the accuracy of micro features can be improved, and also productivity can be increased.

Osmosis as nature’s method for establishing optical alignment

For eyes to maintain optimal focus, precise coordination is required between lens optics and retina position, a mechanism that in vertebrates is governed by genetics, visual feedback, and possibly intraocular pressure (IOP).1 While the underlying processes have been intensely studied in vertebrates, they remain elusive in arthropods,though visual feedback may be unimportant.2 How do arthropod eyes remain functional while undergoing substantial growth? Here, we test whether a common physiological process, osmoregulation,3 could regulate growth in the sophisticated camera-type eyes of the predatory larvae of Thermonectus marmoratus diving beetles. Upon molting, their eye tubes elongate in less than an hour, and osmotic pressure measurements reveal that this growth is preceded by a transient increase in hemolymph osmotic pressure. Histological evaluation of support cells that determine the lens-to-retina spacing reveals swelling rather than the addition of new cells. In addition, as expected, treating larvae with hyperosmotic media post-molt leads to far-sighted (hyperopic) eyes due to a failure of proper lengthening of the eye tube and results in impaired hunting success. This study suggests that osmoregulation could be of ubiquitous importance for properly focused eyes.

Three Prenatal Developments in the Retina Allow for Cortico-Retinal Image Processing in Situ in the Eye

Image processing in the retina of the eye has thus far been mainly dealt with analogous to photographic ray optics i. e., imaging lens optics and photodiode arrays. However, it does not offer an answer to the questions that are crucial to human vision: WHAT a visible object invariantly represents conceptually (a house, a tree, etc.), WHERE it is located in relation to other objects in space or which RGB-colors and/or luminosities collaborate locally. For this purpose, ray optics needs to be supplemented by diffractive wave optics, which can be described as Fresnel near-field interference in cellular or spatial gratings. The fact that interference optics plays a decisive role in vision has already been proven by the fact that in binocular vision the image brightness is preserved when closing one eye. However, with the introduction of interference-wave-optics and especially with Fresnel Nearfield interference optics the cortico-retinal image processing now becomes possible in the eye, i.e. in the retina of the peripheral visual organ. Fresnel Nearfield interference optics especially allows multilayer proceeding and a better understanding of hierarchical imaging systems. It clearly becomes apparent in the di- and trichromatic proceeding and by the separation of color proceeding from invariant object form proceeding. Color - as an example - is not produced at the visual objects and also not in the cortex, but in the Fresnel space of the retina.

Wide Field of View Under-Panel Optical Lens Design for Fingerprint Recognition of Smartphone.

Fingerprint recognition is a widely used biometric authentication method in LED-backlight smartphones. Due to the increasing demand for full-screen smartphones, under-display fingerprint recognition has become a popular trend. In this paper, we propose a design of an optical fingerprint recognition lens for under-display smartphones. The lens is composed of three plastic aspheric lenses, with an effective focal length (EFL) of 0.61 mm, a field of view (FOV) of 126°, and a total track length (TTL) of 2.54 mm. The image quality of the lens meets the target specifications, with MTF over 80% in the center FOV and over 70% in the 0.7 FOV, distortion less than 8% at an image height of 1.0 mm, and relative illumination (RI) greater than 25% at an image height of 1.0 mm. The lens also meets the current industry standards in terms of tolerance sensitivity and Monte Carlo analysis.

Evaluation of surface quality and error compensation for optical aspherical surface grinding

Optical aspherical lenses are widely used in the aerospace, electronics, and optical communication industries. Grinding is the primary processing method used to ensure their precision. It is difficult for traditional evaluation indexes to fully reflect the optical properties of optical surfaces after grinding. This paper presents a novel method for characterizing surface quality of optical aspherical surface oriented to the application of optical properties. The proposed evaluation indicators include the profile error, surface roughness, slope error, and projection-area scale-deviation value, which can be used to comprehensively evaluate the surface quality. Subsequently, a novel grinding compensation method for the optical aspherical surface is proposed, and its compensation precision is evaluated using the abovementioned evaluation indicators. The results show that the maximum surface-shape error decreases to less than 150 nm; additionally, the central cusp point is restrained. The precision and efficiency of error compensation for the optical aspherical surface are significantly better than those of the conventional method. The proposed evaluation indicators can be applied to reflect the features of optical aspheric surface directly. The high efficiency and precision compensation of optical aspherical surface can be achieved with the proposed evaluation method and modified error compensation algorithm.

Scintillator-based Timepix3 detector for neutron spin-echo techniques using intensity modulation.

A scintillator-based Timepix3 (TPX3) detector was developed to resolve the high-frequency modulation of a neutron beam in both spatial and temporal domains, as required for neutron spin-echo experiments. In this system, light from a scintillator is manipulated with an optical lens and is intensified using an image intensifier, making it detectable with the TPX3 chip. Two different scintillators, namely, 6LiF:ZnS(Ag) and 6LiI:Eu, were investigated to achieve the high resolution needed for spin-echo modulated small-angle neutron scattering (SEMSANS) and modulation of intensity with zero effort (MIEZE). The methodology for conducting event-mode analysis is described, including the optimization of clustering parameters for both scintillators. The detector with both scintillators was characterized with respect to detection efficiency, spatial resolution, count rate, uniformity, and γ-sensitivity. The 6LiF:ZnS(Ag) scintillator-based detector achieved a spatial resolution of 200μm and a count rate capability of 1.1 × 105 cps, while the 6LiI:Eu scintillator-based detector demonstrated a spatial resolution of 250μm and a count rate capability exceeding 2.9 × 105 cps. Furthermore, high-frequency intensity modulations in both spatial and temporal domains were successfully observed, confirming the suitability of this detector for SEMSANS and MIEZE techniques, respectively.

Optical lens optimization design and tolerance analysis for a depth camera

This paper describes a depth camera lens design composed of eight glass lenses, where the field of view is 100°, the focal length is 1.88 mm, and the F/# is 2. The lens design requires the lens to be fixed and the object distance to be fixed at −745.964 mm. The depth of focus ranges from −0.0047 mm to 0.0096 mm and can be obtained by selecting a spatial frequency of 60 lp/mm for the Through-focus MTF optimization design. The object distance ranges from negative infinity (-∞) to −250 mm (for the depth of field), the MTF is greater than 0.73 at 60 lp/mm, the lateral color difference is less than 1.58 μm, the optical distortion is less than 1%, and the relative illumination is greater than 64%. When conducting tolerance analysis, we select a spatial frequency requirement of tolerance MTF>0.3. At an object distance of −745.964 mm, the lens resolution can reach 80 lp/mm. The object distance is -∞, and the lens resolution is above 59 lp/mm. The object distance is −250 mm, and the lens resolution can reach over 43 lp/mm. In this work, the depth camera lens is designed to have an object distance shooting range of −6 m to −0.25 m. When the object distance is −6 m, the object depth resolution is 61 mm; while at the object distance of −0.25 m, the object depth resolution is 0.1045 mm.

Highly sensitive refractometric sensing system based on the combination of lensing and laser speckle correlation

A simple optical sensing system based on laser speckle and lensing for monitoring refractive index variations of fluids is proposed and demonstrated. The fluid of interest is contained in a cylindrical glass vessel, which acts as an optical lens whose focal length depends on the refractive index of the fluid. Focal length variations imply optical wavefront alterations that are revealed through laser speckle pattern correlation. The device exhibits a refractive index resolution on the order of 10−6, which is comparable to those of more complex and costly refractometric sensors and demonstrates the benefits of combining these two optical techniques. The simplicity and high sensitivity of the presented configuration make it greatly suitable for a variety of applications ranging from chemical sensing to specimen detection.

Amphiphilic ionic liquids as catalysts for efficient synthesis of novel isosorbide-based optical polymers with good biocompatibility and tunable properties

Accurate design and green synthesis of sustainable optical materials from renewable biomass has become vital in polymer science, especially in field of corneal contact lenses or intraocular lens (IOLs). Here we demonstrate the structure design of monomers and efficient synthesis of novel optical poly(isosorbide thioethers) (PITEs) with methyl, alicyclic or aromatic side-groups for high-performance biomedical optical materials. To regulate and control the polymerization process accurately, ionic liquids (ILs) were selected as catalysts and evaluated systematically. Since the presence of hydroxyl in anion improved proton-accepting ability combined with cations functionalized with dual activation sites, the IL tetraethylammonium lactate [TEA][Lac] in trace amount was discovered to show outstanding catalytic performance, better than the reported catalysts. According to experimental results, NMR analysis and DFT calculations, the anion-cation synergistic catalytic mechanism for nucleophilic hydrothiolation was proposed at molecular level. The activation barriers of transition structures decreased significantly from 211.1 to 16.7 kJ·mol−1 after using IL catalyst. The novel PITEs exhibited excellent biocompatibility for L929 cells, good optical transparency (>90 %) and higher refractive index (nD = 1.57 ∼ 1.61) than commercial IOLs (nD = 1.46 ∼ 1.55). Meanwhile, the PITEs possessed not only tunable mechanical properties (strain at break of 1.6 %∼367 %, storage modulus of 2.5 ∼ 4.3 GPa), but also suitable glass-transition temperature (Tg = 41.6 ∼ 92.9 °C) and good thermal stability for polymer melting or moulding process. This work provides a versatile approach for convenient fabrication of novel isosorbide-based polymers with adjustable properties for biomedical optical lenses, which are promising to achieve scale-up and application in future.

Dynamic projection mapping for non-planar objects with a variable focus lens and visual feedback.

Dynamic projection mapping for moving objects has attracted much attention in recent years. However, conventional approaches have faced some issues, such as the target objects being limited to the moving speed of the objects, the limitation of the narrow depth-of-field optics, and the planar shape objects. This work proposed an adaptive three-dimensional projection prototype, and it could project an always in-focus image on a non-planar object based on liquid lens optics. The location of the non-planar object could be detected, and the mapped projection contents calculated; as a result, a stable "printed" projection mapping should be viewed on a moving object.

Improvement in the photothermal conversion performance of a solar cavity receiver with concave spherical windows

Photothermal conversion parameters are key indicators for measuring the operational performance of solar cavity receivers. By utilizing the redistributive ability of a functional surface in an optical concave lens to transmit solar radiation, previous studies have shown that installing a concave spherical quartz window at the front end of a solar cavity receiver can homogenize the flux distribution on the receiver wall. On this basis, research has been conducted on the impact of solar cavity receivers with concave spherical windows on their photothermal conversion performance. Based on the finite volume method, a coupling model for photothermal conversion in the receiver is established to calculate the heat transfer efficiency and temperature distribution of the receiver for different windows. The results indicate that, compared with a receiver with a flat quartz window, a receiver with a concave spherical quartz window can significantly reduce the peak temperature and peak temperature gradient of the spiral tube in the receiver, effectively improving the temperature distribution of the tube. When DNI = 1000 W/m2, the flow velocity at the inlet is 2.5 m/s, and the temperature at the inlet is 650 K. The receiver with a concave spherical quartz window has a reduced temperature peak from 868.09 K to 834.23 K and a temperature gradient from 2.46 K/mm to 1.27 K/mm relative to the receiver with a flat quartz window. This study provides ideas for the design of cavity receivers and improves their photothermal conversion performance.

One-step fabricating a PDMS optical lens based on surface charging and edge pining effects of a PDMS droplet

This paper presents a one-step method for fabricating a PDMS optical lens based on the surface charging and edge pining effects of a PDMS droplet. This method works by electrically lifting the air-liquid PDMS interface initially stabilized by the edge pining effect of a PDMS droplet on a polymethyl methacrylate (PMMA) substrate. The electrical lifting was achieved under the force interaction between the negative surface charges of the PDMS droplet and the non-uniform electric field generated by a needle-plate electrode pair. Experimental results show that the electrical lifting was achieved in about 10 seconds. With the increase of the applied electric field, the magnification of the fabricated lens increases. Fabricating a lens with a resolution of 32 lp/mm and a magnification of 23.92 times was obtained under an averaged electric field of 12500 V/cm. Chlorophyll-fluorescence-based living algae detection with the PDMS lens and a smartphone imaging system was successfully achieved.

Deep Learning for Polarization Optical System Automated Design

Aiming at the problem that traditional design methods make it difficult to control the polarization aberration distribution of optical systems quickly and accurately, this study proposes an automatic optimization design method for polarization optical systems based on deep learning. The unsupervised training model based on ray tracing and polarized ray tracing was constructed by learning the reference lens structural feature data from the optical lens library, and the generalization ability of the deep neural network model was improved to achieve the automatic optimization design of the polarized optical system. The design results show that the optical system structure optimized by the network model is close to the reference lens in the full field of view and the full spectrum and that the optical system structure can be designed for different focal length requirements. The success rate of 1 million groups of initial structures designed is better than 96.403%, and the polarization effect of the optical system is effectively controlled. The proposed deep learning approach to optical design provides a new solution for future complex optical systems and also provides an effective way to improve the design accuracy of special optical systems such as polarization optical systems.

Stress analysis of a large diameter aspheric plastic lens in the variable temperature assisted injection molding process.

The technology known as precision injection molding (PIM) has shown great promise in the large-scale manufacturing of optical plastic lenses. The primary challenge with the PIM process is accurately predicting and reducing residual stress in optical plastic lenses. In this work, the finite element method (FEM) was used to analyze the residual stress distribution in plastic lenses. A three-dimensional model was created using COMSOL software to investigate how residual stress and temperature varied in optical plastic lenses during the packing and cooling stages. Based on the results, variable temperature assisted injection molding experiments were conducted. The results show that the average residual stress in the optical plastic lenses has decreased by 56%, while the minimum and maximum residual stress levels have decreased by 60% and 61%, respectively. Since this method does not require the extra heat treatment of the optical lenses, it offers considerable cost and efficiency benefits.

Integrated Deep Ultraviolet Doublet Metalens for Projection Imaging

Metalenses, with their unique modulation of light, are in great demand for many potential applications. As a proof-of-principle demonstration, we focus on designing SiO2 metalenses that operate in the deep ultraviolet region, specifically around 193 nm. Based on the deep ultraviolet metalens proposed in this paper, an integrated deep ultraviolet doublet metalens is further offered. When the incident light is a plane wave with a wavelength of 193 nm, the integrated doublet metalens can reduce the beam size by a factor of 4:1, and the emitted light is flat. The integrated doublet metalens can project the reticle image proportionally, making the projection image clear. The integrated doublet metalens has the best imaging effect at the propagation distance of 2 μm and can tolerate ±3 degrees of incident angle deviation. Our findings establish general and systematic strategies to guide the design of traditional optical lens arrays with excellent integrated doublet metalenses and pave the way for enhanced optical performance in the application of large-relative-aperture deep ultraviolet detection, deep ultraviolet microscope systems, laser beam combining systems, deep ultraviolet lithography systems, etc.

Wide heart-shaped mini-LEDs without a second lens as a large area, ultra-high luminance, and flat light source.

In recent years, the demand for outdoor advertising and industrial display applications has been steadily increasing. Outdoor environments require higher brightness levels, thus requiring a reduction in the thermal resistance of the light source package. However, using secondary optical lenses to decrease the number of light sources is not a suitable solution because it may lead to the issue of lens detachment. Therefore, this paper proposes a packaging structure for wide heart-shaped angular light distribution mini-light emitting diodes (WHS mini-LEDs) with a primary optical design to enhance the light-emitting angle. The chips are directly bonded to an aluminum substrate using the metal eutectic process to minimize thermal resistance in the packaging. The experimental results indicated that the WHS mini-LED package had a total thermal resistance of 6.7 K/W. In a 55-inch backlight module (BLM), only 448 WHS mini-LEDs coupled with a quantum dot (QD) film and a brightness enhancement film (BEF) were required. Each lamp board was operated at 20.5 V and 5.5 A. The average luminance of the liquid crystal module (LCM) can reach 2234.2 cd/m2 with a uniformity of 90% and an NTSC value of 119.3%. This design offers a competitive advantage for outdoor advertising displays and industrial displays that require large areas, high brightness, and high color saturation.

A 6-DOF camera motion correction method using IMU sensors for photogrammetry and optical measurements

Environmental conditions such as wind and ground traffic introduce motion in camera measurement systems and affect measurement accuracy. Conventional camera motion correction methods track static reference points with one or multiple cameras, reducing applicability. This study proposes a novel 6-degree-of-freedom (DOF) camera motion correction method using only an inertial measurement unit (IMU) sensor. A Kalman filter is adopted as a data fusion method to estimate the camera orientation and translation using IMU data. Six pinhole camera models are built to evaluate and correct 6-DOF camera motions. The motion correction efficiency and robustness are tested for different object distances and focal lengths of optical lenses. The motion correction ratio is statistically analysed and reaches approximately 80%. The object distance has little effect on the motion correction ratio. The rotation-induced pixel movement is independent of the object distance. More than 90% of the pixel movement noise is caused by camera rotation. The translation-induced pixel movement is inversely correlated with the object distance.

An error compensation method for single point oblique axis grinding considering the grinding wheel wear

With the increasing amount of high quality optical products, the manufacturing requirement for the high-precision optical glass lenses is on the rise. Grinding is typically the main manufacturing process for the optical mold. The degree of wheel wear has a direct impact on the precision of the grinding process. In this paper, the wear rule of grinding wheel in the grinding process of optical aspheric surface is studied with the in-site wear measurement system. A new image processing method and a wear degree evaluation method are proposed. The wear prediction model for the grinding wheel is established. Then a modified compensation method of optical aspheric surface considering grinding wheel wear is proposed. The optical aspheric surface is then compensated using a modified multinomial equation considering grinding wheel wear. The results demonstrate that the profile error of optical aspheric surface can be reduced to less than 150 nm. The proposed compensation method that takes into account the grinding wheel wear can highly improve the grinding precision and efficiency of optical aspheric surface as compared with the conventional compensation method.

Using clinical optical coherence tomography to characterise contact lens edge shape and base curve radius

ABSTRACT Clinical relevance Clinical optical coherence tomography devices are widely used in optometry and ophthalmology and may be used to measure contact lens base curvature radius and visualise contact lens edge shape. Background Knowledge of contact lens geometry facilitates fitting, while optical coherence tomography provides a powerful means of measuring geometrical form. This study evaluates the performance of a clinical optical coherence tomography device (3D OCT-1000) in characterising contact lens edge shape and measuring the back optic zone radius of rigid gas-permeable contact lenses in vitro. Methods First, an opto-mechanical optical coherence tomography contact lens adaptor was designed and 3D-printed to facilitate a contact lens being imaged using a commercial optical coherence tomography device. Second, several image-processing algorithms and a simple calibration method were developed to measure the back optic zone radius in optical coherence tomography B-scans. Finally, based on the findings of two experiments, B-scan performance was evaluated in terms of 1) capacity to differentiate between contact lens edge geometries, and 2) capacity to obtain accurate and repeatable back optic zone radius measurements. Statistical and graphical analyses were performed to characterise reliability and reproducibility. Results The 3D OCT-1000 and adaptor combination was capable of acquiring images of sufficient quality to discriminate between soft and rigid contact lens edge geometries. Additionally, statistical analysis of the rigid contact lens measurements demonstrated satisfactory back optic zone radius measurement accuracy and reproducibility. Conclusion This study demonstrates that a 3D OCT-1000 fitted with an opto-mechanical adaptor combination can be used to assess contact lens edges in vitro and that this clinical optical coherence tomography device, combined with image processing and linear calibration of the B-scans, is capable of obtaining back optic zone radius measurements of rigid gas-permeable contact lenses that are close to the ISO 18,369-2:2018 manufacturing tolerance range (±0.05 mm).