Lens Structures Research Articles

A Silicon-Based LED Packaging Substrate With an Island Structure for Phosphor Encapsulation Shaping

This paper proposes an encapsulation shaping method for white light-emitting diode packaging, using a silicon substrate with an island structure and using a simple yttrium aluminum garnet phosphor dispensing process. The technology utilizes the interaction of the interfacial tension between silicon island structure and silicone phosphor material for encapsulation shaping at an appropriate curing temperature. Various encapsulation structures, such as hemispherical and shell-type lenses, are fabricated using different encapsulation doses, which allow specific optical requirements to be fulfilled. The experimental results show that a hemispherical encapsulation lens with a radius of curvature of 0.9 mm is formed, when the diameter of the island structure is 1.8 mm and the dispensing dose is 1.5 mL. When the dispensing doses are 2.5 and 4.0 mL, shell-type lens structures with short and long cylinders, respectively, are fabricated. In terms of optical characteristics of the shell-type structure, there is a large measured variation in chromaticity at different view angles, but for the short encapsulation cylinder the uniformity of the lighting is significantly improved. The simulation result for the luminance profile is in agreement with the experimental results.

A novel method for wave focusing investigation in metamaterial half‐space and slab lens structures

SummaryApproximate image currents for the Sommerfeld half‐space problem with vertical electric and magnetic current sources above double negative half‐space is found using the discrete image theory and Laplace transform. This method would found its applications in investigation of dipole radiation above metamaterial half‐space and in describing the focusing mechanism of metamaterial lenses. In order to efficiently consider the effects of metamaterial half‐space, discrete image dipoles are defined by proposing an exponential series for reflection coefficient. Unknown constants (the loci of images) in the argument of the exponential function are determined by equating the coefficients of the Taylor series for exact reflection coefficient with those of the proposed approximate series. Thus, the calculation of integral with oscillating integrand reduces to the solution of polynomial equation for the zeros of polynomials. As an application for the proposed approach, the field focusing in double negative is investigated. Thanks to the fast and accurate methods for finding the zeros of polynomials, it is shown that in addition to its good accuracy, this method decreases the computational time for field calculations in comparison with the exact methods. It is seen that for the negative refractive index beside −1, the complex images approach to infinity and have negligible effect on the scattering field of dipole. For the other negative indexes the complex image blurs the real image. Copyright © 2015 John Wiley & Sons, Ltd.

Optimization of structure parameters of concentric plasmonic lens for 355 nm radially polarized illumination

We propose and optimize two designs of plasmonic lens structures, concentric grooves with a central hole (CGH) and concentric grooves with a central pillar (CGP), based on a traditional structure of concentric grooves (CG). The numerical investigation based on COMSOL Multiphysics is performed to optimize the three kinds of structures by a 355 nm radially polarized laser illumination. It is found that full-width at half maximum (FWHM) is closely related to the size of the center-position, and the field enhancement effect depends on the resonant wavelength of surface plasmon polaritons, permittivity, film thickness, and groove number. Compared to a FWHM of λ∕3 (λ is the wavelength of the laser beam) with the conventional CG type, the combination of localized and extended surface plasmons results in CGP and CGH parameters achieving their optimal value with a much smaller spot size of λ∕8 and higher intensity enhancement for a variety of the aspect ratios of central pillar and hole. A focused ion beam was used to fabricate the three type nanostructures with high accuracy. The CGH type with a central hole 20.88 nm in diameter and the CGP type with a central pillar 55.45 nm in diameter have been successfully fabricated approximately to their optimization results. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JNP.9

Ultra-precision machining of radial Fresnel lens on roller moulds

In Roll-to-Roll manufacturing of optical films, direct diamond turning of radial Fresnel lens structures on a roller mould was considered infeasible, due to the incapability to cut steep circular grooves on the outer cylindrical surface using conventional approach. This paper presents a novel solution to this problem. A four-axis interactive tool–workpiece motion is designed to precisely fabricate the complex microstructures. The tool path is generated from geometrical calculations considering the lens design, tool geometries and roller parameters. This process is experimentally verified with qualified profile quality and surface finish, thus making direct machining of radial Fresnel lens possible.

Aberration design of zoom lens systems using thick lens modules.

A systematic approach for the aberration design of a zoom lens system using a thick lens module is presented. Each component is treated as a thick lens module at the beginning of the design. A thick lens module refers to a thick lens component with a real lens structure, like lens materials, lens curvatures, lens thicknesses, and lens interval distances. All nine third-order aberrations of a thick lens component are considered during the design. The relationship of component aberrations in different zoom positions can be approximated from the aberration shift. After minimizing the aberrations of the zoom lens system, the nine third-order aberrations of every lens component can be determined. Then the thick lens structure of every lens component can be determined after optimization according to their first-order properties and third-order aberration targets. After a third optimization for minimum practical third-order aberrations of a zoom lens system, the aberration design using the thick lens module is complete, which provides a practical zoom lens system with thick lens structures. A double-sided telecentric zoom lens system is designed using the thick lens module in this paper, which shows that this method is practical for zoom lens design.

Single-photon emitters based on NIR color centers in diamond coupled with solid immersion lenses

Single-photon sources represent a key enabling technology in quantum optics, and single color centers in diamond are a promising platform to serve this purpose, due to their high quantum efficiency and photostability at room temperature. The widely studied nitrogen-vacancy (NV) centers are characterized by several limitations, thus other defects have recently been considered, with a specific focus of centers emitting in the near-infra red (NIR). In the present work, we report on the coupling of native NIR-emitting centers in high-quality single-crystal diamond with solid immersion lens (SIL) structures fabricated by focused ion beam (FIB) lithography. The reported improvements in terms of light collection efficiency make the proposed system an ideal platform for the development of single-photon emitters with appealing photophysical and spectral properties.

Sfrp1 and Sfrp2 are not involved in Wnt/β-catenin signal silencing during lens induction but are required for maintenance of Wnt/β-catenin signaling in lens epithelial cells

During eye lens development, regulation of Wnt/β-catenin signaling is critical for two major processes: initially it must be silent in the lens placode for lens development to proceed, but subsequently it is required for maintenance of the lens epithelium. It is not known how these different phases of Wnt/β-catenin activity/inactivity are regulated. Secreted frizzled related protein-2 (Sfrp2), a putative Wnt-Fz antagonist, is expressed in lens placode and in lens epithelial cells and has been put forward as a candidate for regional Wnt/β-catenin pathway regulation. Here we show its closely-related isoform, Sfrp1, has a complimentary pattern of expression in the lens, being absent from the placode and epithelium but expressed in the fibers. As mice with single knockouts of Sfrp1 or Sfrp2 had no defects in lens formation, we examined lenses of Sfrp1 and Sfrp2 double knockout (DKO) mice and showed that they formed lens placode and subsequent lens structures. Consistent with this we did not observe ectopic TCF/Lef activity in lens placode of DKOs. This indicates that Sfrp1 and Sfrp2 individually, or together, do not constitute the putative negative regulator that blocks Wnt/β-catenin signaling during lens induction. In contrast, Sfrp1 and Sfrp2 appear to have a positive regulatory function because Wnt/β-catenin signaling in lens epithelial cells was reduced in Sfrp1 and Sfrp2 DKO mice. Lenses that formed in DKO mice were smaller than controls and exhibited a deficient epithelium. Thus Sfrps play a role in lens development, at least in part, by regulating aspects of Wnt/β-catenin signaling in lens epithelial cells.

Can the Lens Model Provide a Biomarker for Alzheimer's Disease?

With great interest, we read the work of Ho CY et al published online on 29 May 2013 in Brain Pathology (“Beta-amyloid, Phospho-tau and Alpha-synuclein Deposits Similar to Those in The Brain Are Not Identified in The Eyes of Alzheimer’s and Parkinson’s Disease Patients”). The authors showed the absence of abnormal beta-amyloid (Aβ) deposits in the lens, retina or other structures in the eyes of Alzheimer’s disease (AD) patients. The protein aggregation characteristic of AD was not detected in the lenses to the same degree as the brains of affected patients (4). Similar findings were also reported by Michael and colleagues recently (6). This is a severe blow to the promising notion that the eye would be an attractive site for early diagnosis and monitoring of neurodegenerative disease. In previously published work of Goldstein et al and Moncaster et al, Aβ peptides were identified in the lenses of patients with AD, and Down syndrome patients with early onset AD (3, 7). AD is one of the most common conformational disorders characterized by protein accumulation in the brain (1). In addition to the brain, the aggregation of the disease-causing proteins also takes place in many other organs and tissues, especially the lens (8). Aβ was detected in lenses of both rat and monkey (2). Moreover, it has been reported that the cataracts significantly increased in lenses of an Aβ-transgenic mouse model for AD and the lens opacity was rescued by antioxidant treatment (5). Given such evidence, it is reasonable to speculate that Aβ plaques can induce the cataract formation and Aβ deposition in lens may reflect its level in brain of patients with AD. However, the relationship between Aβ accumulation in the eyes and brains of AD is uncertain and controversial. These studies with contradictory results might be explained by the use of different assays, frozen tissues and whole mount preparations, as analyzed by Ho CY et al. Importantly, the cataract is also affected by many other complex factors, and the mechanism by which Aβ accumulates in this compartment is unclear. Further large-scale, well-designed randomized controlled ophthalmological studies in subjects with AD are urgently needed.

Focusing surface plasmon polariton wave packets in space and time

AbstractThe spatiotemporal focusing of surface plasmon polariton (SPP) wave packets (WPs) by planar plasmonic‐lens coupling structures is described using combined femtosecond interferometric time‐resolved photoemission electron microscopy (ITR‐PEEM) imaging and model simulations. The focusing properties of lens structures inscribed lithographically into Ag films depend on the angle of incidence of the excitation field. Severe aberrations are introduced by the phase delay in the interaction of obliquely incident plane waves with the commonly employed circular arc‐shaped lens structures. It is shown that the aberration can be corrected by accounting for propagation delays caused by the incidence angle‐dependent retardation of the optical field‐lens structure interaction. The focusing of SPP‐WPs in both space and time is demonstrated with aberration corrected lens structures.

Improvement of the probe current in a microcolumn by introducing a subsidiary electrode in a source lens

An improved source lens structure for a microcolumn including a subsidiary control electrode is designed, and its current characteristics are analyzed. The effect of the control electrode, which was inserted between the extractor and the anode, shows improved characteristics, such as a higher probe beam current, compared to a microcolumn with a conventional source lens structures. The field enhancement factor extracted through current measurement and simulation was 3.95, and this value was applied to all column structures investigated in this work. The column with the newlydesigned source lens structure showed a drastic increase in the probe beam current according to the driving voltage applied to the control electrode. The design parameters of the newly-developed source lens structure are provided with a simulation analysis.

COB형 LED 보안등을 위한 렌즈 구조 설계

The study carried out in this dissertation focuses on the lens structure design and the light distribution for LED safety luminaires using COB type LED module. Lens structures for LED lights has been designed 1) to induce light diffusion by dual process of internal reflection and refraction, 2) to minimize the inherent LED lights" glittering, and 3) to have uniform brightness. The lens designed with the proposed structures function as diffusers for the divergence of the LED lights so that they form a wide angle of view and adjust the light distribution. We designed of lens with stable uniformity factor and average roughness using aspheric optics property. Finally we made the analysis data of the simulated data.

Stabilization of pupils in a zoom lens with two independent movements

A procedure for thin lens structural design of a new class of pupil stabilized zoom systems is presented. This is facilitated by an implementation of evolutionary programming that searches a multivariate hyperspace formed by design variables, namely, powers of individual components and intercomponent separations. Two coupled components in the lens system act as the variator for the zoom system, and another component in the system acts as the compensator. A fixed axial location of the image plane is achieved by moving the coupled variator and the compensator nonlinearly, while the entrance and the exit pupils are allowed small shifts in their axial locations over the zooming range. The latter relaxation opens up the possibility for effective two-conjugate zoom systems with only two independent component movements. Illustrative examples for thin lens structures of two-conjugate zoom systems are presented.

Beta-amyloid, phospho-tau and alpha-synuclein deposits similar to those in the brain are not identified in the eyes of Alzheimer's and Parkinson's disease patients.

Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most common neurodegenerative disorders, and are characterized by deposition of specific proteins in the brain. If similar abnormal protein deposits are present in the eye, it would facilitate noninvasive diagnosis and monitoring of disease progression. We therefore evaluated expression of proteins associated with AD and PD pathology in postmortem eyes and brains in a case-control study. Eyes from 11 cases of AD, 6 cases of PD or PD with dementia, and 6 age-matched controls were retrieved from the autopsy archives of The Johns Hopkins Hospital. Immunostains for β-amyloid, phospho-tau and α-synuclein and Congo red stains were performed in the same laboratory in both brains and eyes. No amyloid deposits or abnormal tau accumulations were detected in the lens, retina or other structures in the eyes of AD patients. Eyes also lacked definite Lewy bodies or Lewy neurites in either PD or AD cases. Patchy cytoplasmic α-synuclein positivity was seen in the retina of AD, PD and control cases, but did not correlate with the presence or extent of Lewy body pathology in the brain. Abnormal protein aggregations characteristic of AD and PD are thus not commonly present in the retinas or lens of affected patients when assayed using the same protocols as in the brain. This suggests that β-amyloid, phospho-tau and α-synuclein either do not deposit in the eye in a manner analogous to brain, or are present at lower levels or in different forms.

Design and Chromatic Aberration Analysis of Plasmonic Lenses Using the Finite Element Method

We designed plasmonic lenses and analyzed their chromatic aberration using the finite element method (FEM) in frequency domain with perfectly matched layers (PML). Plasmonic lenses permit subwavelength focusing of light in the visible and in the near infrared. The focal distance of these devices depends on the wavelength operation due to the dispersive characteristics of the lens structures and the refractive index of their constituent materials. With a uniform incident wave normal to the lens surface, focusing of light by surface plasmon polariton (SPPs) through a plasmonic lens is obtained in the axial direction. The design of three plasmonic lenses in Silver (Ag), Gold (Au) and Copper (Cu) films at two central operation wavelengths of 650 nm and 810 nm, in both, cylindrical and rectangular geometries were considered and the chromatic aberration of the lenses were analyzed by monitoring the peak position of the electromagnetic (EM) field when the wavelength changes from 625 nm to 675 nm and from 785 nm to 835 nm..

The flow of an axisymmetric stratified gravity current into a stratified ambient in a rotating system

The effect of rotation on the behaviour of an inviscid axisymmetric stratified gravity current released from a lock and propagating into a stratified ambient fluid is considered. It is assumed that both the ambient and the current are linearly stratified. We develop a one-layer shallow-water model and show that the flow is governed by four dimensionless parameters which represent the stratifications in the current and ambient, the ratio of Coriolis to inertia effects, and the height ratio of the ambient to the lock. The solution, obtained by a finite-difference method, provides the shape of the interface, radial and azimuthal speeds, and radius of propagation, as functions of time. The propagation reaches a maximum radius, dependent on the input parameters; the increase of the internal stratification reduces the radius. The system admits steady-state lens structures for which simple approximate solutions are also presented. In general, the internal stratification of the current reduces the velocity of propagation, and enhances the Coriolis effects in a rotating system.

Direct imaging of single cells and tissue at sub‐cellular spatial resolution using transmission geometry MALDI MS

The need of cellular and sub-cellular spatial resolution in laser desorption ionization (LDI)/matrix-assisted LDI (MALDI) imaging mass spectrometry (IMS) necessitates micron and sub-micron laser spot sizes at biologically relevant sensitivities, introducing significant challenges for MS technology. To this end, we have developed a transmission geometry vacuum ion source that allows the laser beam to irradiate the back side of the sample. This arrangement obviates the mechanical/ion optic complications in the source by completely separating the optical lens and ion optic structures. We have experimentally demonstrated the viability of transmission geometry MALDI MS for imaging biological tissues and cells with sub-cellular spatial resolution. Furthermore, we demonstrate that in conjunction with new sample preparation protocols, the sensitivity of this instrument is sufficient to obtain molecular images at sub-micron spatial resolution.

Broadband aperiodic air coupled ultrasonic lens

This paper demonstrates the possibility of subwavelength, defined as less than the incident wavelength, broadband focusing in an aperiodic air coupled ultrasonic lens. A near field probe is used to detect well defined resonances from 75 to 125 kHz. The spatial resolution at each of the resonant frequencies is determined and demonstrated to be smaller than the wavelength of the ultrasonic waves. The strongest resonance is observed at 82.9 kHz with a focal spot size of 3.12 mm. The subwavelength spatial resolution of the lens structures at the resonances is attributed to the near field scattering of the acoustic waves.

A novel randomly textured phosphor structure for highly efficient white light-emitting diodes

We have successfully demonstrated the enhanced luminous flux and lumen efficiency in white light-emitting diodes by the randomly textured phosphor structure. The textured phosphor structure was fabricated by a simple imprinting technique, which does not need an expensive dry-etching machine or a complex patterned definition. The textured phosphor structure increases luminous flux by 5.4% and 2.5% at a driving current of 120 mA, compared with the flat phosphor and half-spherical lens structures, respectively. The increment was due to the scattering of textured surface and also the phosphor particles, leading to the enhancement of utilization efficiency of blue light. Furthermore, the textured phosphor structure has a larger view angle at the full width at half maximum (87°) than the reference LEDs.

Scale-Invariant Features and Polar Descriptors in Omnidirectional Imaging

We propose a method to compute scale-invariant features in omnidirectional images. We present a formulation based on the Riemannian geometry for the definition of differential operators on non-Euclidian manifolds that adapt to the mirror and lens structures in omnidirectional imaging. These operators lead to a scale-space analysis that preserves the geometry of the visual information in omnidirectional images. We then build a novel scale-invariant feature detection framework for omnidirectional images that can be mapped on the sphere. We further present a new descriptor and feature matching solution for these omnidirectional images. The descriptor builds on the log-polar planar descriptors and adapts the descriptor computation to the specific geometry and the nonuniform sampling density of omnidirectional images. We also propose a rotation-invariant matching method that eliminates the orientation computation during the feature detection phase and thus decreases the computational complexity. Experimental results demonstrate that the new feature computation method combined with the adapted descriptors offers promising detection and matching performance, i.e., it improves on the common scale-invariant feature transform (SIFT) features computed on the unwrapped omnidirectional images, as well as spherical SIFT features. Finally, we show that the proposed framework also permits to match features between images with different native geometry.

Malignant glaucoma: a review of the modern literature.

Malignant glaucoma is a rare form of glaucoma that typically follows surgery in patients with primary angle closure and primary angle-closure glaucoma. In this paper, the clinical features, classification, pathogenesis, and principles of management are discussed. Despite a high prevalence of primary angle closure glaucoma in South-East Asia, the vast majority of cases of malignant glaucoma are reported in White populations. This may reflect differing mechanisms of angle closure in White and Asian patients, which somehow reduces the likelihood of an aberrant relationship developing between the lens, ciliary body, anterior hyaloid, and vitreous structures within the eye. Although the exact underlying pathogenic mechanism remains unclear, the prognosis is good with modern medical, laser, and surgical treatment modalities.