Lens Configuration Research Articles

Generation of pseudo-nondiffracting symmetrical Layer beams using cylindrical lenses

The pseudo-nondiffracting behavior of optical caustic beams makes them potentially useful in precise component alignment at CERN. This paper introduces an innovative method for generating one and two-dimensional symmetrical Airy-like beams, known as Layer beams, utilizing a specific configuration of plano-convex cylindrical lenses. Simulations and experimental results have validated this method, demonstrating its potential for scalable and cost-effective beam production with tunable properties, making it practical for a wide range of scientific applications.

Spatial resolution limit for a solid immersion lens

The solid immersion (SI) effect is widely used to increase the spatial resolution of optical focusing systems and even overcome the Abbe diffraction limit. Resolution enhancement offered by a SI lens is mostly a function of its geometry and refractive index nSI. While SI lenses are relatively well understood, the scaling of the resolution enhancement by such lenses is still a subject of debate, with some works reporting ≃nSI and ≃nSI2 dependencies for the hemispherical and hyperhemispherical SI lens configurations, respectively. In this paper, we offer a general argument for a resolution limit for SI optics and, then, verify it via the numerical analysis of the hemispherical and hyperhemispherical silicon SI lenses designed for the terahertz (THz) range. In fact, we find that there is no contradiction in the reported resolution enhancements ≃nSI and ≃nSI2; however, they happen in different operation regimes. We then demonstrate that the resolution values reported for the different SI lens arrangements in the visible (VIS), near-, and middle-infrared (NIR and MIR), as well as THz bands obey the derived limit. Our findings will be useful for the further design and applications of SI optics.

Hybrid meta/refractive lens design with an inverse design using physical optics

Hybrid lenses are created by combining metasurface optics with refractive optics, where refractive elements contribute optical power, while metasurfaces correct optical aberrations. We present an algorithm for optimizing metasurface nanostructures within a hybrid lens, allowing flexible interleaving of metasurface and refractive optics in the optical train. To efficiently optimize metasurface nanostructures, we develop a scalar field, ray-wave hybrid propagation method. This method facilitates the propagation of incident and derived adjoint fields through optical elements, enabling effective metasurface optimization within the framework of adjoint gradient optimization. Numerical examples of various lens configurations are presented to illustrate the versatility of the algorithm and showcase the benefits offered by the proposed approach, allowing metasurfaces to be positioned beyond the image space of a lens. Taking a F/2, 40° field-of-view, midwave infrared lens as an example, the lens exhibits an average focusing efficiency of 38% before the integration of metasurfaces. Utilizing the new algorithm to design two metasurfaces—one in the object space and one in the image space—results in significant enhancement of the average focusing efficiency to over 90%. In contrast, a counterpart design with both metasurfaces limited to the image space yields a lower average focusing efficiency of 73%.

Low-cost reversible tandem lens mesoscope for brain imaging in rodents.

The development of imaging systems that are cost-efficient and modular is essential for modern neuroscience research. In the current study, we designed, developed, and characterized a low-cost reversible tandem lens mesoscope for brain imaging in rodents. Using readily available components, we assembled a robust imaging system that is highly efficient and cost-effective. We developed a mesoscope that offers high-resolution structural and functional imaging with cost-effective lenses and CMOS camera. The reversible tandem lens configuration of the mesoscope offers two fields of view (FOVs), which can be achieved by swapping the objective and imaging lenses. The large FOV configuration of provides a spatial resolution up to , and the small FOV configuration of provides a resolution of up to . We demonstrate the efficiency of our system for imaging neuronal calcium activity in both rat and mouse brains in vivo. The careful selection of the mesoscope components ensured its compactness, portability, and versatility, meaning that different types of samples and sample holders can be easily accommodated, enabling a range of different experiments both in vivo and in vitro. The custom-built reversible FOV mesoscope is cost-effective and was developed for under US$10,000 with excellent performance.

RIS-assisted near-field localization using practical phase shift model

Our research focuses on examining the problem of localizing user equipment (UE) in the uplink scenario using reconfigurable intelligent surfaces (RIS) based lens. We carry out a thorough analysis of the Fisher information matrix (FIM) and assess the influence of various RIS-based lens configurations using an actual RIS phase-dependent amplitude variations model. Furthermore, to reduce the complexity of the maximum likelihood (ML) estimator, a simple localization algorithm-based angular expansion is presented. Simulation results show superior localization performance when prior location information is available for directional and positional channel configurations. The position error bound (PEB) and the root mean square error (RMSE) are studied to evaluate the localization accuracy of the user utilizing the realistic RIS phase-dependent amplitude model in the near-field region. Furthermore, the achievable data rate is obtained in the same region using the realistic RIS phase-dependent amplitude model. It is noticed that adopting the actual RIS phase-dependent amplitude model under the near-field channel increases the localization error and degrades the data rate performance for amplitude value less than one so, the unity assumption of the RIS phase shift model used widely in the literature is inaccurate.

Research on Off-axis Aberration Optimization Model for Bifocal Glass Lens

Presbyopia entails the gradual deterioration of the eye’s ability to focus, and bifocal lenses have become a common remedy to alleviate blurred near vision and counteract eye strain induced by prolonged usage. The refractive index and Abbe number of these lenses play a crucial role in precisely correcting focal points within the near vision range. Nevertheless, when light rays approach the lens at off-axis angles or with tilts, aberrations occur, often with uneven distribution across real glass materials. The amalgamation of bifocal lenses further compounds the complexity of these aberrations. To enhance the correction of aberrations in bifocal glass lenses, distortion and astigmatism aberration serve as input parameters to calculate the optical quality assessment of the lenses. This study introduces a novel approach to optimize the pairing of bifocal glass lenses through the Taguchi method and fuzzy inference. The experimental design involves the application of the LS9 orthogonal array, streamlining the number of experiments while upholding the reliability of experimental data. The objective is to refine the selection of glass lenses and successfully devise an optimized design model that can be effectively applied to the configuration of bifocal glass lenses.

Miniaturized fluorescence pH sensor with assembly free ball lens on a tapered multimode optical fiber.

In biochemistry, the absence of a compact, assembly-free pH sensor with high sensitivity and signal-to-noise ratio has been a persistent hurdle in achieving accurate pH measurements in real time, particularly in complex liquid environments. This manuscript introduces what we believe to be a novel solution in the form of a miniaturized pH sensor utilizing an assembly-free ball lens on a tapered multimode optical fiber (TMMF), offering the potential to revolutionize pH sensing in biochemical applications. A multimode optical fiber (MMF) was subjected to tapering processes, leading to the creation of an ultra-thin needle-like structure with a cross-sectional diameter of about 12.5 µm and a taper length of 3 mm. Subsequently, a ball lens possessing a diameter of 20 µm was fabricated at the apex of the taper. The resultant structure was coated utilizing the dip-coating technique, involving a composite mixture of epoxy and pH-sensitive dye, 2',7'-bis(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF), thereby ensconcing the tapered ball lens with dye molecules for pH sensing. This study encompassed the fabrication and evaluation of six distinct fiber structures, incorporating the cleaved endface, the convex lens, and the ball lens structures to compare light focal lengths and propagation intensities. Computational simulations and numerical analyses were conducted to elucidate the encompassing light focal distances across the full array of lens configurations. The efficacy of the proposed pH sensor was subsequently assessed through its deployment within a complex liquid medium spanning a pH spectrum ranging from 6 to 8. Real-time data acquisition was performed with a fast response time of 0.5 seconds. A comparative analysis with a pH sensor predicated upon a single TMMF embedded with the fluorescent dye underscored the substantial signal enhancement achieved by the proposed system twice the fluorescence signal magnitude. The proposed assembly-free miniaturized pH sensor not only substantiates enhanced signal collection efficiency but also decisively addresses the persistent challenges of poor signal-to-noise ratio encountered within contemporary miniaturized pH probes.

On nonparaxial single-pixel imaging of semitransparent objects using flat diffractive optics

High numerical apertures can result in distortions appearing in a single-shot image, rendering the acquisition of usable images challenging, if not outright impossible. However, in the realm of single-pixel imaging, various strategies can be employed to effectively inspect objects with an excellent resolution, contrast and brightness. Recent advancements in flat photonic components have facilitated the development of compact nonparaxial imaging systems, which show great promise, particularly in the THz range of wavelengths. These innovations hold the potential to advance fields such as communication, material inspection and spectroscopy. In this study, we delve into the imaging of semi-transparent objects with varying levels of detail. Furthermore, we introduce a nonparaxial design for a flat hyperbolical lens and evaluate its performance in these imaging scenarios, comparing it to structured illumination techniques involving Airy, Bessel, and common thin lens configurations. We present findings regarding potential improvements in imaging attributable to the nonparaxial hyperbolical lens.

TEMGYM Basic: transmission electron microscopy simulation software for teaching and training of microscope operation.

An interactive simulation of a transmission electron microscope (TEM) called TEMGYM Basic is developed here, which enables users to understand how to operate and control an electron beam without the need to access an instrument. TEMGYM Basic allows users to familiarize themselves with alignment procedures offline, reducing the time and money required to become a proficient TEM operator. In addition to teaching the basics of electron beam alignments, the software enables users to create bespoke microscope configurations and develop an understanding of how to operate the configurations without sitting at a microscope. TEMGYM Basic also creates static ray diagram figures for a given lens configuration. The available components include apertures, lenses, quadrupoles, deflectors and biprisms. The software design uses first-order ray transfer matrices to calculate ray paths through each electron microscope component, and the program is developed entirely in Python to facilitate compatibility with machine-learning packages for future exploration of automated control.

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

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

Exploring the hidden Universe: a novel phenomenological approach for recovering arbitrary gravitational-wave millilensing configurations

ABSTRACT Since the first detection of gravitational waves in 2015, gravitational-wave astronomy has emerged as a rapidly advancing field that holds great potential for studying the cosmos, from probing the properties of black holes to testing the limits of our current understanding of gravity. One important aspect of gravitational-wave astronomy is the phenomenon of gravitational lensing, where massive intervening objects can bend and magnify gravitational waves, providing a unique way to probe the distribution of matter in the Universe, as well as finding applications to fundamental physics, astrophysics, and cosmology. However, current models for gravitational-wave millilensing—a specific form of lensing where small-scale astrophysical objects can split a gravitational wave signal into multiple copies—are often limited to simple isolated lenses, which is not realistic for complex lensing scenarios. In this paper, we present a novel phenomenological approach to incorporate millilensing in data analysis in a model-independent fashion. Our approach enables the recovery of arbitrary lens configurations without the need for extensive computational lens modelling, making it a more accurate and computationally efficient tool for studying the distribution of matter in the Universe using gravitational-wave signals. When gravitational-wave lensing observations become possible, our method could provide a powerful tool for studying complex lens configurations in the future.

Cylindrical lens configuration for optimizing light delivery in a curvilinear endocavity photoacoustic imaging system.

Curvilinear endocavity ultrasound images capture a wide field of view with a miniature probe. In adapting photoacoustic imaging (PAI) to work with such ultrasound systems, light delivery is challenged by the trade-off between image quality and laser safety concerns. Here, we present two novel, to the best of our knowledge, designs based on cylindrical lenses that are optimized for transvaginal PAI B-scan imaging. Our simulation and experimental results demonstrate that, compared to conventional light delivery methods for PAI imaging, the proposed designs are safer for higher pulse energies and provide deeper imaging and a wider lateral field of view. The proposed designs could also improve the performance of endoscopic co-registered ultrasound/photoacoustic imaging in other clinical applications.

Gravitational lensing by using the 0th order of affine perturbation series of the deflection angle of a ray near a photon sphere

The 0th order of affine perturbation series of the deflection angle of a ray near a photon sphere is more accurate than a deflection angle in a strong deflection limit, which is used often, because the later has hidden error terms. We investigate gravitational lensing by using 0th order affine perturbation series of the deflection angle in a general asymptotically-flat, static, and spherical symmetric spacetime with the photon sphere. We apply our formula to Schwarzschild black hole, Reissner–Nordström black hole, and Ellis–Bronnikov wormhole spacetimes as examples. By comparing observables by using the deflection angles, we show that we can ignore the effect of the hidden error terms in the the deflection angle in the strong deflection limit on the observables in a usual lens configuration with the photon sphere since the hidden error terms are tiny. On the other hand, in a retro lensing configuration, the deflection angle in the strong-deflection-limit analysis have error of several percent and the 0th order of affine perturbation series of the deflection angle has almost half of the error. Thus, in the retro lensing configuration, we should use the 0th order of affine perturbation series of the deflection angle rather than the deflection angle in the strong-deflection-limit analysis. The 0th order of affine perturbation series of the deflection angle can give a brighter magnification by a dozen percent than the one by using the deflection angle in the strong-deflection-limit analysis.

Evaluating clinical near-infrared surgical camera systems with a view to optimizing operator and computational signal analysis.

As clinical evidence on the colorectal application of indocyanine green (ICG) perfusion angiography accrues, there is also interest in computerizing decision support. However, user interpretation and software development may be impacted by system factors affecting the displayed near-infrared (NIR) signal. We aim to assess the impact of camera positioning on the displayed NIR signal across different open and laparoscopic camera systems. The effects of distance, movement, and target location (center versus periphery) on the displayed fluorescence signal of different systems were measured under electromagnetic stereotactic guidance from an ICG-albumin model and in vivo during surgery. Systems displayed distinct fluorescence performances with variance apparent with scope optical lens configuration (0deg versus 30deg), movement, target positioning, and distance. Laparoscopic system readings fitted inverse square function distance-intensity curves with one device and demonstrated a direction dependent sigmoid curve. Laparoscopic cameras presented central targets as brighter than peripheral ones, and laparoscopes with angled optical lens configurations had a diminished field of view. One handheld open system also showed a distance-intensity relationship, whereas the other maintained a consistent signal despite distance, but both presented peripheral targets brighter than central ones. Optimal clinical use and signal computational development requires detailed appreciation of system behaviors.

RXJ0437+00: constraining dark matter with exotic gravitational lenses

ABSTRACT We present the first strong-gravitational-lensing analysis of the galaxy cluster RX J0437.1+0043 (RXJ0437; z = 0.285). Newly obtained, deep MUSE observations, Keck/MOSFIRE near-infrared spectroscopy, and Hubble Space Telescope SNAPshot imaging reveal 13 multiply imaged background galaxies, three of them (at z = 1.98, 2.97, and 6.02, respectively) in hyperbolic umbilic (H–U) lensing configurations. The H–U images are located only 20–50 kpc from the cluster centre, i.e. at distances well inside the Einstein radius where images from other lens configurations are demagnified and often unobservable. Extremely rare (only one H–U lens was known previously) these systems are able to constrain the inner slope of the mass distribution – and unlike radial arcs, the presence of H–U configurations is not biased towards shallow cores. The galaxies lensed by RXJ0437 are magnified by factors ranging from 30 to 300 and (in the case of H–U systems) stretched nearly isotropically. Taking advantage of this extreme magnification, we demonstrate how the source galaxies in H–U systems can be used to probe for small-scale (∼109 M⊙) substructures, providing additional insight into the nature of dark matter.

Monitoring presbyopia treatment with ultrasonic cavitation using shear wave elastography (SWE): Experiments and simulations

This numerical study aims at evaluating quantitative monitoring of elasticity changes induced by ultrasonic cavitation using shear waves elastography (SWE). SWE is a good method to safely evaluate the lens stiffness. Yet, the absence of backscattered signal inside the lens (regardless of the imaging technique) forbids elastography inside. Experimentally, we, thus, tracked surfaces waves on multiple models (gelatin beads, porcine lens) and evaluated dispersion curves of this waves. Finite difference time domain simulations are performed in order to evaluate elasticity with access to a few surface point, starting with a simple homogeneous inclusion towards complex inclusion closer to the lens configuration. In homogeneous inclusion, we noticed Scholte wave behavior on the dispersion. Complexifying the configuration by adding layers induced a gradient in the dispersion curves, the higher the frequency is the less the surface wave depends on the deepest layers. A similar behavior was observed experimentally: low frequencies with mostly resonances then a plateau matching Scholte wave expectation. Numerical studies indicate that the surface waves is sensitive to the shear elasticity inside the inclusion, yet this behavior is highly frequency dependent. This leads the way to investigate the frequency behavior of guided wave in experiments in lens in our team.

Sub-50 nm optical imaging in ambient air with 10× objective lens enabled by hyper-hemi-microsphere

Optical microsphere nanoscope has great potential in the inspection of integrated circuit chips for semiconductor industry and morphological characterization in biology due to its superior resolving power and label-free characteristics. However, its resolution in ambient air is restricted by the magnification and numerical aperture (NA) of microsphere. High magnification objective lens is required to be coupled with microsphere for nano-imaging beyond the diffraction limit. To overcome these challenges, in this work, high refractive index hyper-hemi-microspheres with tunable magnification up to 10× are proposed and realized by accurately tailoring their thickness with focused ion beam (FIB) milling. The effective refractive index is put forward to guide the design of hyper-hemi-microspheres. Experiments demonstrate that the imaging resolution and contrast of a hyper-hemi-microsphere with a higher magnification and larger NA excel those of a microsphere in air. Besides, the hyper-hemi-microsphere could resolve ~50 nm feature with higher image fidelity and contrast compared with liquid immersed high refractive index microspheres. With a hyper-hemi-microsphere composed microscale compound lens configuration, sub-50 nm optical imaging in ambient air is realized by only coupling with a 10× objective lens (NA = 0.3), which enhances a conventional microscope imaging power about an order of magnitude.

Generation of higher-order Laguerre–Gaussian modes from a diode-pumped Pr3+:LiYF4 laser with an intra-cavity spherical aberration

We demonstrate, for the first time to the best of our knowledge, the direct generation of higher-order Laguerre–Gaussian (LG) petal modes, formed of the coherent superposition of positive and negative LG modes with the topological charge of ± ℓ as an eigen mode, from a compact diode end-pumped P r 3 + : L i Y F 4 (YLF) laser with an intra-cavity lens configuration. The on-axis displacement of the intra-cavity lens with spherical aberration allows the selective operation of the desired higher-order LG modes with | ℓ | ≤ 31 from the laser cavity at 640 nm and 607 nm. Such visible higher-order LG modes will offer new applications in optical manipulation, quantum/optical underwater telecommunication, and microfabrication.

Ion microscopy with evolutionary-algorithm-based autofocusing

Ion microscopy is an established technique for laser focus diagnostics and the accurate, intensity-resolved measurement of laser ionization processes. In the present feasibility study, we discuss a new ion microscope design, which improves its resolution across a large range of magnifications and simplifies its operation. Instead of the common two einzel lens configuration, which is usually optimized for a fixed magnification, we propose a generic design consisting of an array of equally spaced ring electrodes, whose individually adjustable voltages are controlled by an evolutionary algorithm. In this way, we can realize aberration minimized magnifications between 25 and 100. Moreover, the algorithm can adjust the voltage settings under changing experimental conditions and facilitates autofocusing for user-defined magnification.

Design of Highly Directive GRIN MS Lens Integrated DFHA for Deep Tissue Biomedical Imaging

A novel highly directive gradient refractive index (GRIN) metasurface (MS) lens integrated dielectric-filled horn antenna (DFHA), with an enhanced signal penetration and spatial focusing, is developed for the effective monitoring and detection of tumors deep inside the body. For this purpose, two novel GRIN MS lens topologies are proposed, where an optimized refractive index distribution along with the lens aperture is generated using an improved analytical formulation. In the first lens configuration, the core layer (CL) is sandwiched between two similar impedance matching layers (IMLs) on each side. In the second configuration, the CL is still surrounded by two IMLs on both sides, but one of the IMLs, in this case, is improved to avoid the requirement of an additional dielectric layer between the lens and the biological tissue. All the layers of the MS lens are based on an array of especially designed square ring-shaped unit cells. The proposed MS lens-based DFHA enhances the signal penetration by a maximum of 12 dB at 100 mm penetration inside the torso compared to the case without a lens. It also facilitates better spatial resolution due to the presence of an MS lens, which shrinks threefold the 3 dB beamwidth at 100 mm inside the torso than that of the DFHA without an MS lens. The proposed GRIN MS lens integrated DFHA is fabricated and tested on a realistic torso phantom to evaluate the tumor detection capability deep inside the torso. The simulation and experimental results show that the proposed GRIN MS lens-based DFHA can effectively be employed for tumor detection with high resolution deep inside the body.