Lens Profile Research Articles

Effect of ageing and cataract formation on the Raman spectroscopic profile of human lens: An observational study.

To observe the spectroscopic profile of human lens in different age groups and varying grades of cataract and to use the data to arrive at differentiating molecular biology. An observational cross-sectional study. The study enrolled 30 patients (30 eyes) with a mean age of 59.6 years diagnosed with immature senile cataracts. The patients underwent small incision cataract surgery, and the harvested lens nuclei were examined under a Raman spectroscope for studying their molecular composition. The relative intensities of the peaks in the Raman spectra were evaluated and compared among different age groups and grades of cataract. A correlation of tyrosine doublet ratio with grade of cataract and age of the subject was calculated. Several Raman spectral peaks were observed in the range of 600 cm-1 to 1800 cm-1 with correspondence to tyrosine, phenylalanine, tryptophan, and amides I and III. A strong negative correlation between the grade of cataract and the ratio of tyrosine doublet was seen (r = -0.805). Also, a negative correlation between age and tyrosine ratio was seen (r = -0.62). The wavenumber/spectral peak of tryptophan was observed only in one sample, and amides I and III were identified, but the intensity of the peak for amide II was very small or absent. It was observed that the buried conformation of tyrosine was predominant in cases with a higher age or grade of cataract. The buried conformation of tryptophan became less in the higher grades of cataract.

Machine learning for aspherical lens form accuracy improvement in precision molding of infrared chalcogenide glass

Precision glass molding (PGM) is an effective approach to manufacturing infrared chalcogenide glass (ChG) aspherical lens with complex shapes. However, infrared ChG aspherical lens often experiences form error in the designed profile and the final profile obtained by PGM. To reduce the form error of infrared ChG aspherical lens in the PGM process, a form error compensation model based on the random forest (RF) algorithm is proposed. The infrared ChG aspherical lens profile was first machined on an electroless nickel-phosphorus (Ni–P) plating to serve as the mold for PGM. After molding, the profile data of the lens was extracted, and a compensation model based on RF was constructed to optimize the model parameters using the evaluation parameters such as root mean square error (RMSE), coefficient of determination (R2), and out-of-bag (OOB). Finally, the generated compensated profile based on the compensation model was used for the compensation machining of the mold. Through this compensation approach, we have demonstrated a substantial 63.5 % reduction in the form error of the fabricated infrared ChG aspherical lens, decreasing the Peak-to-Valley (PV) value from 1.04 μm to 0.38 μm.

Ultrasonic aperture-tunable gel lens

Conventional camera modules require mechanical moving parts to move their lenses and to adjust their focal points. This paper examines optically tunable lenses with a focal length and lens aperture that can be controlled using ultrasound vibration and a transparent gel. The lens uses the acoustic radiation force, which induces changes in the lens profile; varifocal convex and concave lenses can be fabricated by adjusting the input signals. The optical characteristics of the lenses were evaluated using ray tracing simulations. The aperture can be controlled with the driving frequency, with higher frequencies leading to a wider range of focal length changes with a lower input voltage.

Optimization of Grayscale Lithography for the Fabrication of Flat Diffractive Infrared Lenses on Silicon Wafers.

Grayscale lithography (GSL) is an alternative approach to the standard binary lithography in MEMS fabrication, enabling the fabrication of complicated, arbitrary 3D structures on a wafer without the need for multiple masks and exposure steps. Despite its advantages, GSL's effectiveness is highly dependent on controlled lab conditions, equipment consistency, and finely tuned photoresist (PR) exposure and etching processes. This works presents a thorough investigation of the challenges of GSL for silicon (Si) wafers and presents a detailed approach on how to minimize fabrication inaccuracies, aiming to replicate the intended design as closely as possible. Utilizing a maskless laser writer, all aspects of the GSL are analyzed, from photoresist exposure parameters to Si etching conditions. A practical application of GSL is demonstrated in the fabrication of 4-μm-deep f#/1 Si Fresnel lenses for long-wave infrared (LWIR) imaging (8-12 μm). The surface topography of a Fresnel lens is a good case to apply GSL, as it has varying shapes and size features that need to be preserved. The final fabricated lens profiles show a good match with the initial design, and demonstrate successful etching of coarse and fine features, and demonstrative images taken with an LWIR camera.

Wide-viewing-angle panoramic inhomogeneous free-shape lens

This paper presents a design of an inhomogeneous lens with an arbitrary curvature supporting a high field of view without distortion and aberration. The lens profile is designed based on the ray-inserting method (RIM). The advantage of this proposed structure is matching the input and output of the rays. No approximation or optimization has been considered in the innovation of the lens. Unlike most previous works, the present design can be implemented with isotropic and above unity refractive index materials. The Finite Difference Time Domain (FDTD) scheme and multi-physics simulations are employed to validate the design lens.

Monolithic silicon microlens arrays for far-infrared astrophysics.

Future far-infrared astrophysics observatories will require focal plane arrays containing thousands of ultrasensitive, superconducting detectors, each of which require efficient optical coupling to the telescope fore-optics. At longer wavelengths, many approaches have been developed, including feedhorn arrays and macroscopic arrays of lenslets. However, with wavelengths as short as 25µm, optical coupling in the far infrared remains challenging. In this paper, we present an approach to fabricate far-infrared monolithic silicon microlens arrays using grayscale lithography and deep reactive ion etching. The fabricated microlens arrays presented here are designed for two different wavebands: 25-40µm and 135-240µm. The microlens arrays have sags as deep as 150µm, are hexagonally packed with a pixel pitch of 900µm, and have an overall size as large as 80 by 15mm. We compare an as-fabricated lens profile to the design profile and calculate that the fabricated lenses would achieve 84% encircled power for the designed detector, which is only 3% less than the designed performance. We also present methods developed for antireflection coating microlens arrays and for a silicon-to-silicon die bonding process to hybridize microlens arrays with detector arrays.

3-D printed high-gain elliptic flat Luneburg lens

The antennas on remote sensing satellites play a crucial role in receiving and transmitting wireless signals, affecting data acquisition quality. Among them, Luneburg lens antennas have been successfully applied in satellite tracking due to their high-gain property. However, reducing the flat Luneburg lens(FLL) profile while maintaining performance and addressing manufacturing challenges remains a limitation. This paper first utilizes transformation optics theory to derive the permittivity distribution of the FLL. Moreover, an innovative approach is introduced by multiplying the distribution with a coefficient “g” to achieve the desired lower permittivity required for fabrication. Then, a layered implementation is used to design a circular FLL and improve its performance by compressing its horizontal profile. Therefore, a unique elliptic FLL is proposed by making a trade-off between the gain, beamwidth, and focal length of the lens antenna. The antenna achieves a 22.9 dB maximum gain with beamwidths of 9.5°(E-plane) and 7.4°(H-plane). The elliptic FLL was fabricated using 3D printing technology, and the measured results showed a small deviation from the simulated results within an acceptable range of error. The elliptic FLL possesses design flexibility and holds immense potential in applications such as remote sensing satellite communication.

Exotic image formation in strong gravitational lensing by clusters of galaxies – IV. Elliptical NFW lenses and hyperbolic umbilics

ABSTRACT A source lying near a hyperbolic umbilic (HU) singularity leads to a ring-like image formation, constituting four images with high magnification factors and lying in a small region of the lens plane. Since (based on our earlier work) the observed number of HU image formations in cluster lenses is expected to increase in the future, it is timely to investigate them in more detail. Like fold and cusp singularities, HU also satisfies the magnification relation, i.e. the signed magnification sum of the four images equals zero. This work presents a detailed study of the HU magnification relation (Rhu) considering the elliptical Navarro–Frenk–White (eNFW) lens profile suitable for cluster scale dark matter haloes. Our results show that for an isolated eNFW lens, Rhu is more sensitive to ellipticity than its mass or concentration parameter. An ellipticity greater than 0.3 results in Rhu lying close to zero with a small scatter around it. A substructure near the HU image formation causes the average Rhu value to deviate from zero and increases the scatter, with the amount of deviation depending on the image type near which the substructure lies. However, a population of substructures in the lens plane (equivalent to the galaxies inside the cluster) does not significantly shift the average Rhu value from zero but increases the scatter around it. We find that Rhu ≃ 0 for HU image formation in the Abell 1703 cluster. Repeating this test in other clusters with HU formations can be a useful indicator of substructure in cluster haloes.

Photo-induced flexible semiconductor CdSe/CdS quantum rods alignment

The anisotropic absorption and emission from semiconductor CdSe/CdS quantum rods (QRs) provide extra benefits among other photoluminescence nanocrystals. Using photo-induced alignment technique, the QRs can be oriented in liquid crystal polymer matrix at a large scale. In this article, a 2D Dammann grating pattern, within “SKL” characters domains aligned QRs in composite film, was fabricated by multi-step photo exposure using several photo masks, and a continuous geometric lens profile pattern aligned QRs was realized by the single step polarization converting holographic irradiation method. Both polarized optical microscope and fluorescence microscope are employed to determine the liquid crystal director profiles and QRs anisotropic excitation properties. We have been able to orient the QRs in fine binary and continuous patterns that confirms the strong quantum rod aligning ability of the proposed method. Thus, the proposed approach paves a way for photo-induced flexible QRs alignments to provide a highly specific and difficult-to-replicate security application at a large scale.

Influence of Instrumental Factors in the Measurement of Power Profiles of Intraocular Lenses with a Commercial Deflectometer

Deflectometry is an optical technique for determining properties such as power distribution, wavefront, etc., and measurement of the optical properties of an intraocular lens can provide relevant information for clinicians. The aim of the current study was to establish a protocol for measuring lens power maps and profiles of various optical designs of intraocular lenses with a deflectometer based on the phase-shifting Schlieren principle (NIMO TR1504, Lambda-X, Nivelles, Belgium). The results are discussed with respect to accuracy and repeatability, the influence of the use of filters, and whether to consider the intraocular lens as a thin or thick lens.

Scleral flaps, pars plana vitrectomy and gore-tex sutured posterior chamber intraocular lens placement: a case series and review of literature.

Cataract surgery is one of the most common surgical procedures performed worldwide. Intraocular lens (IOL) implants are placed routinely in the capsular bag after successful cataract extraction. However, in the absence of adequate capsular support, IOL may be placed in the anterior chamber, fixated to the iris or fixated to the sclera. The purpose of this study is to report the clinical outcomes and safety profile of a trans-scleral sutured intraocular lens (IOL) technique using scleral flaps, vitrectomy, and Gore-Tex suture to place posterior chamber IOL. Retrospective, interventional case series of eyes undergoing scleral fixation of an IOL using Gore-Tex suture with concurrent vitrectomy. Ocular examination with the logarithm of the minimum angle of resolution visual acuity (logMAR BCVA), tonometry, and slit-lamp biomicroscopy was performed on all patients at 1, 3, 6, and 12 months after the operation. All post-operative complications were recorded. Twenty-five eyes of 25 patients were included. Mean logMAR BCVA improved from 0.43 ± 0.36 (20\40 Snellen equivalent) preoperatively to 0.13 ± 0.18 (20\25 Snellen equivalent) postoperatively at 12 months (p<0.01). Indications included surgical aphakia (16) and dislocated lens implant (9). No cases of IOL opacification, suprachoroidal haemorrhage, post-operative endophthalmitis, IOL dislocation, Gore-Tex exposure, or retinal detachment were observed during the follow-up period. Ab externo scleral fixation of IOLs with Gore-Tex suture plus scleral flap is well tolerated and associated with a very low rate of suture exposition. Moreover, our study confirms excellent refractive outcomes after surgery.

Ideal micro-lenticular lens based on phase modulation of optically isotropic liquid crystal-polymer composite with three terminals

Optical phase modulation in a transparent polymer film composed of nano-sized liquid crystal (LC) droplets embedded within a polymer matrix exhibits a micro-lenticular lensing effect under controlled in-plane field switching (IPS) with interdigitated electrodes. Despite of the lensing effect, the lens profile does not match ideal one and its effective phase modulation is relatively small owing to the weak field strength over the electrodes, which causes an invariant refractive index in these regions. To achieve ideal lens profile and high phase modulation, a vertical electric field is applied between top plane and bottom interdigitated electrodes, while maintaining the in-plane fields between the bottom interdigitated electrodes. The combined effect, referred to as the vertical and in-plane switching (VIS) mode, can achieve larger phase modulation (Δδ) than the IPS mode. Consequently, the proposed micro-lenticular lens has a shorter focal length and a significantly better lens profile, similar to the ideal one. Furthermore, the diffraction efficiency (Df) is effectively improved by ∼ 6.7%, 4%, and 2% for the zeroth (0th), ±1st, and ± 2nd orders, respectively, compared to those in the IPS mode. The improved phase profile with the proposed micro-lenticular device can be used in a switchable lens from 2-dimensions (2D) to 3-dimension (3D) and tunable diffractors.

A beam-steering antenna with low deflecting-loss enabled by a miniaturized flexible lens

A miniaturized flexible lens is proposed for beam control of broadband antenna with low deflection loss. Different from traditional approaches to phase modulation, the three-segment principle presented in this article significantly lowers the maximum necessary phase difference generated by modulated waves, thus reducing the height of the lens and antenna profile. The phase modulation performance of the lens is reconfigured by adjusting the layout of the phase modulation units PMUs according to distribution requirements. Then, a Vivaldi antenna utilizing the miniaturized lens is designed, fabricated, and tested to demonstrate the system’s beam deflecting characteristics. The experimental results demonstrate the capability of the antenna to cover a deflecting range wider than [−20°, 19°] with deflecting loss below 1.4 dB throughout the entire 8–10 GHz working band. Over the operating band, the deflecting gain is greater than 8.7 dBi.

Design of a Low-Reflection Flat Lens Antenna Based on Conformal Transformation Optics

In this paper, a wideband flat lens antenna with low reflection and good performance is presented based on conformal transformation optics (CTO). Physical space optimization is applied to eliminate singular refractive index values. Furthermore, we employ the optical path rescaling method to enhance the sub-unity refractive indices and to reduce reflection. Therefore, an implementable all-dielectric isotropic medium is obtained. The final flat lens profile comprises six layers with a constant permittivity value in each layer. Simulation results of the three-dimensional structure indicate that the designed flat lens operates in a wide frequency bandwidth. The flat lens antenna has an S11 value of less than -15 dB in the frequency range of 13 to 30 GHz. The proposed lens was designed and simulated using COMSOL Multiphysics, and radiation performance results were validated using the CST Studio Suite. The simulated radiation pattern shows that the side lobe level is less than -16.5 dB in two simulation software programs, and the half-power beam width varies from 5.6° to 2.7° with increasing frequency. Moreover, the simulated antenna gain is about 28.3-35.5 dBi in the 13-30 GHz frequency range.

Large-Area and Rapid Fabrication of a Microlens Array on a Flexible Substrate for an Integral Imaging 3D Display.

A curved integral imaging three-dimensional (3D) display attracts a lot of interest due to its enhanced 3D sense of immersion and wider viewing angle. In this paper, a microlens array (MLA) based on a flexible poly(ethylene terephthalate) (PET) substrate was achieved by a straightforward, rapid, and low-cost technique. The reactive ion etching (RIE) process treated PET/CYTOP covered with a flexible mask to generate a hydrophilic-hydrophobic patterned surface. The well-designed arrays of confined adhesive droplets with a controlled geometry on a hydrophilic-hydrophobic patterned surface were formed using the blade-coating method. A flexible MLA with a diameter of 820 μm, a size of 5.3 cm × 5.1 cm, and a radius of curvature of 25 cm was fabricated and combined with a curved two-dimensional (2D) monitor to realize a lateral viewing range of 6.4 cm at a viewing distance of 25 cm, which is 4 times larger than with flat integral imaging 3D display system. The flexible MLA has the advantages of a controllable lens profile and large pitch, and it can be manufactured on a large scale. In addition, it provides a large viewing angle for the reconstructed 3D image.

On minimal focal distance of a focused ultrasound probe for neuromodulation.

Focal distance is a key parameter for a focused ultrasound probe, especially in mouse brain stimulation where targets are right below the skull. A closed-form solution for the minimal focal distance with a given transducer size was derived in this study to facilitate precise focal spot alignment with targets in the mouse brain. The spherical profile corresponding to the minimal focal distance does not produce accurate focusing. An iterative algorithm based on Snell's law was introduced for lens profile calculation. With a suitable step size, an accurate lens profile can be obtained for the minimal focal distance.

Axicon lenses with chiral-focusing properties modeling by means of analytical functions

Axicon lenses exhibit a large focal depth that generates an energy distribution, resulting in non-diffracting beams’ generation. These light structures are called Bessel beams and show numerous important applications in optical signal processing, imaging, transparent material processing, and even in metal drilling/cutting manufacturers. Asymmetrical and twisted axicon-lenses are boundary conditions on the Maxwell equation able to generate complex-structured light fields with specially designed intensity, phase, and polarization distributions. This paper presents a set of analytical functions that allows the definition of such surfaces with absolute freedom in relation to the lens profile. Obviously, before manufacturing any lens, it is necessary to compute its electromagnetic output in order to save resources. In this sense, we have studied some of these lenses by simulation using the well-known finite difference method in the time domain. Some necessary verification related to conservative magnitudes, such as the Poynting vector, have been done analytically and numerically. The numerical results show the distribution of iso-values corresponding to the electric field and 3D-vectorial representation of the chirality flux and the Poynting vector. Finally, by means of discrete fast Fourier transform, it is shown the field distributions as well as the power before and after the lens per frequency.

A Graded Index All-Dielectric Lens for Field Decorrelation and Decoupling of a Wideband MIMO Antenna

In this paper a broadband graded index all-dielectric (GID) lens that enables field decorrelation and decoupling of closely spaced wideband multiple-input-multiple-output (MIMO) antenna elements, is presented. Reduction in correlation coefficient ρ for field decorrelation and port decoupling is realized by tilting the individual antenna element radiation patterns away from each other and by suppressing the surface wave propagation inside the antenna substrate through judicious control of the permittivity profile of the GID lens using the concept of transformation electromagnetics (TE). The permittivity profile of the GID lens is designed using air-hole technology and is fabricated by additive manufacturing. To validate the proposed concept, six different examples of lens loaded wideband patch-based MIMO antenna elements arranged in two different orientations are investigated. Simulated and measured results verify the effectiveness of the proposed technique, which constitutes the reduction in ρ for both isotropic and non-isotropic propagation environments along with port-isolation enhancement without reducing the fractional bandwidth (FBW) in all of the six tested cases. Further results indicate a wide FBW having a minimum of 8.5% and a maximum of 33%, while radiation patterns with no extra backward radiation are obtained.

A Wideband High-Gain Circularly-Polarized Dielectric Horn Antenna Equipped With Lamé-Axicon Stacked-Disk Lens for Remote Sensing, Air Traffic Control and Satellite Communications

A wideband high-gain circularly polarized (CP) shaped dielectric horn-lens antenna (SDHLA) operating in the frequency band between 6.7 and 18.2 GHz [fractional impedance bandwidth (FIBW) of 92.4%] with a 3-dB axial-ratio in the frequency range from 8.1 to 16.3 GHz [fractional axial-ratio bandwidth (FARBW) of 67.2%], is presented. The antenna, composed of a suitably shaped dielectric horn, integrated with a super-ellipsoidal-axicon dielectric lens made out of stacked thin dielectric disks, is mounted on a printed circuit board (PCB) where a broadband microstrip line terminated with a radial stub is used to excite a S-shaped slot through which the circular polarization is achieved. Parameterized 3D Lamé curves describe the optimal geometries of horn and lens profiles. The antenna features a peak realized gain exceeding 13.1 dBi that is beneficial in a variety of applications, such as digital video broadcasting (DVB), remote sensing, weather monitoring, satellite communications, and air traffic control. The full-wave electromagnetic solver CST Studio Suite™, based on a locally conformal finite integration technique (FIT), was employed to design and characterize the antenna. The antenna characteristics estimated by FIT were found to be in good agreement with the experimental measurements performed on an antenna prototype.

Statistical inference for strong gravitational lensing observations in the presence of dark matter

AbstractWe study the properties of strong lenses generated by dark matter galaxy halos in the Universe and the statistical inference process to understand the density profile of the lens. For that, we used mock data of strong gravitational lenses using the publicly available software paltas, which is a pipeline based on the well‐known package lenstronomy and written in Python. The deflectors are modeled according to the so‐called elliptical power law lens profile, and the background cosmology is assumed to be that of the standard cosmological model ΛCDM. The generated lensing observations include the contribution of dark matter substructure in the form of either subhalos or halos along the line of sight. In both cases, the underlying profile is the Navarro‐Frenk‐White one, which corresponds to the cold dark matter model. Performing a statistical inference process on these mock observations, our final objective is to identify the influence of the substructure on the inferred parameters that describe the lens profile.