Showing papers on "Lens (optics) published in 2019"

Contact Lens Materials: A Materials Science Perspective

Abstract: More is demanded from ophthalmic treatments using contact lenses, which are currently used by over 125 million people around the world. Improving the material of contact lenses (CLs) is a now rapidly evolving discipline. These materials are developing alongside the advances made in related biomaterials for applications such as drug delivery. Contact lens materials are typically based on polymer- or silicone-hydrogel, with additional manufacturing technologies employed to produce the final lens. These processes are simply not enough to meet the increasing demands from CLs and the ever-increasing number of contact lens (CL) users. This review provides an advanced perspective on contact lens materials, with an emphasis on materials science employed in developing new CLs. The future trends for CL materials are to graft, incapsulate, or modify the classic CL material structure to provide new or improved functionality. In this paper, we discuss some of the fundamental material properties, present an outlook from related emerging biomaterials, and provide viewpoints of precision manufacturing in CL development.

Multibeam 3-D-Printed Luneburg Lens Fed by Magnetoelectric Dipole Antennas for Millimeter-Wave MIMO Applications

Abstract: A 3-D-printed Luneburg lens with a novel simplified geometry is presented. The rod-type structures are employed as the unit cell of the gradient-index material to realize the required permittivity distribution in the lens. A prototype designed in the Ka -band is manufactured successfully by using a commercial 3-D printing facility. The substrate-integrated waveguide fed magnetoelectric (ME)-dipole antenna with endfire radiation is introduced as the feed for the Luneburg lens due to its wideband performance and compact configuration. By combining the lens with a set of the ME-dipoles, a millimeter-wave (mm-wave) multibeam Luneburg lens antenna is designed, fabricated, and measured. An overlapped impedance bandwidth of wider than 40% that can cover the entire Ka -band and mutual coupling below −17 dB are verified by the fabricated prototype. Nine stable radiation beams with a scanning range between ±61°, gain up to 21.2 dBi with a variation of 2.6 dB, and radiation efficiency of around 75% are achieved as well. With the advantages of good operating features, low fabrication costs, and ease of integration, the proposed multibeam Luneburg lens antenna would be a promising candidate for the fifth-generation (5G) mm-wave multiple-input multiple-output (MIMO) applications in 28 and 38 GHz bands.

Printing of wirelessly rechargeable solid-state supercapacitors for soft, smart contact lenses with continuous operations

Abstract: Recent advances in smart contact lenses are essential to the realization of medical applications and vision imaging for augmented reality through wireless communication systems. However, previous research on smart contact lenses has been driven by a wired system or wireless power transfer with temporal and spatial restrictions, which can limit their continuous use and require energy storage devices. Also, the rigidity, heat, and large sizes of conventional batteries are not suitable for the soft, smart contact lens. Here, we describe a human pilot trial of a soft, smart contact lens with a wirelessly rechargeable, solid-state supercapacitor for continuous operation. After printing the supercapacitor, all device components (antenna, rectifier, and light-emitting diode) are fully integrated with stretchable structures for this soft lens without obstructing vision. The good reliability against thermal and electromagnetic radiations and the results of the in vivo tests provide the substantial promise of future smart contact lenses.

Spectral tomographic imaging with aplanatic metalens.

Abstract: Tomography is an informative imaging modality that is usually implemented by mechanical scanning, owing to the limited depth-of-field (DOF) in conventional systems. However, recent imaging systems are working towards more compact and stable architectures; therefore, developing nonmotion tomography is highly desirable. Here, we propose a metalens-based spectral imaging system with an aplanatic GaN metalens (NA = 0.78), in which large chromatic dispersion is used to access spectral focus tuning and optical zooming in the visible spectrum. After the function of wavelength-switched tomography was confirmed on cascaded samples, this aplanatic metalens is utilized to image microscopic frog egg cells and shows excellent tomographic images with distinct DOF features of the cell membrane and nucleus. Our approach makes good use of the large diffractive dispersion of the metalens and develops a new imaging technique that advances recent informative optical devices. An ultrathin “metalens” that uses semiconductor nanostructures to focus light can help microscopes resolve detailed images of live cells without complex mechanical components. In conventional tomographic imaging, a scanning instrument passes over the sample and takes multiple cross-sectional images, which are then reconstructed into a 3D picture. Tao Li from Nanjing University in China and colleagues have now simplified this technique by fabricating lenses patterned with concentric rings of gallium nitride nanopillars. The lens made of nanopillars has wavelength-dependent properties that enable focusing on different regions of a target simply by sweeping through the visible light spectrum. Experiments with frog egg cells demonstrated this approach could zoom in and obtain detailed, high quality images of the inner membrane and nucleus without harming the sample or moving the metalens.

Colour compound lenses for a portable fluorescence microscope.

Abstract: In this article, we demonstrated a handheld smartphone fluorescence microscope (HSFM) that integrates dual-functional polymer lenses with a smartphone. The HSFM consists of a smartphone, a field-portable illumination source, and a dual-functional polymer lens that performs both optical imaging and filtering. Therefore, compared with the existing smartphone fluorescence microscope, the HSFM does not need any additional optical filters. Although fluorescence imaging has traditionally played an indispensable role in biomedical and clinical applications due to its high specificity and sensitivity for detecting cells, proteins, DNAs/RNAs, etc., the bulky elements of conventional fluorescence microscopes make them inconvenient for use in point-of-care diagnosis. The HSFM demonstrated in this article solves this problem by providing a multifunctional, miniature, small-form-factor fluorescence module. This multifunctional fluorescence module can be seamlessly attached to any smartphone camera for both bright-field and fluorescence imaging at cellular-scale resolutions without the use of additional bulky lenses/filters; in fact, the HSFM achieves magnification and light filtration using a single lens. Cell and tissue observation, cell counting, plasmid transfection evaluation, and superoxide production analysis were performed using this device. Notably, this lens system has the unique capability of functioning with numerous smartphones, irrespective of the smartphone model and the camera technology housed within each device. As such, this HSFM has the potential to pave the way for real-time point-of-care diagnosis and opens up countless possibilities for personalized medicine.

Learned large field-of-view imaging with thin-plate optics

Abstract: Typical camera optics consist of a system of individual elements that are designed to compensate for the aberrations of a single lens. Recent computational cameras shift some of this correction task from the optics to post-capture processing, reducing the imaging optics to only a few optical elements. However, these systems only achieve reasonable image quality by limiting the field of view (FOV) to a few degrees - effectively ignoring severe off-axis aberrations with blur sizes of multiple hundred pixels. In this paper, we propose a lens design and learned reconstruction architecture that lift this limitation and provide an order of magnitude increase in field of view using only a single thin-plate lens element. Specifically, we design a lens to produce spatially shift-invariant point spread functions, over the full FOV, that are tailored to the proposed reconstruction architecture. We achieve this with a mixture PSF, consisting of a peak and and a low-pass component, which provides residual contrast instead of a small spot size as in traditional lens designs. To perform the reconstruction, we train a deep network on captured data from a display lab setup, eliminating the need for manual acquisition of training data in the field. We assess the proposed method in simulation and experimentally with a prototype camera system. We compare our system against existing single-element designs, including an aspherical lens and a pinhole, and we compare against a complex multielement lens, validating high-quality large field-of-view (i.e. 53°) imaging performance using only a single thin-plate element.

The strong gravitational lens finding challenge

Abstract: Large-scale imaging surveys will increase the number of galaxy-scale strong lensing candidates by maybe three orders of magnitudes beyond the number known today. Finding these rare objects will require picking them out of at least tens of millions of images, and deriving scientific results from them will require quantifying the efficiency and bias of any search method. To achieve these objectives automated methods must be developed. Because gravitational lenses are rare objects, reducing false positives will be particularly important. We present a description and results of an open gravitational lens finding challenge. Participants were asked to classify 100 000 candidate objects as to whether they were gravitational lenses or not with the goal of developing better automated methods for finding lenses in large data sets. A variety of methods were used including visual inspection, arc and ring finders, support vector machines (SVM) and convolutional neural networks (CNN). We find that many of the methods will be easily fast enough to analyse the anticipated data flow. In test data, several methods are able to identify upwards of half the lenses after applying some thresholds on the lens characteristics such as lensed image brightness, size or contrast with the lens galaxy without making a single false-positive identification. This is significantly better than direct inspection by humans was able to do. Having multi-band, ground based data is found to be better for this purpose than single-band space based data with lower noise and higher resolution, suggesting that multi-colour data is crucial. Multi-band space based data will be superior to ground based data. The most difficult challenge for a lens finder is differentiating between rare, irregular and ring-like face-on galaxies and true gravitational lenses. The degree to which the efficiency and biases of lens finders can be quantified largely depends on the realism of the simulated data on which the finders are trained.

Design of a Broadband Metasurface Luneburg Lens for Full-Angle Operation

Abstract: We present a broadband metasurface Luneburg lens for full-angle operation. The design of the Luneburg lens is based on an inverted substrate parallel-plate-waveguide structure with nonuniform circular holes etched on the upper metallic plate. We show that this structure is superior to existing designs as it allows significant simplification of the fabrication process. To achieve a smooth variation of the effective refractive index profile as well as circular symmetry for the Luneburg lens, size-variable meta-atoms are used for synthesizing the metasurface. The effective refractive index profile can be tuned by varying just the hole diameters. By introducing tapered microstrip ports that are evenly distributed on the circumference of the Luneburg lens, full-angle operation of the lens can be achieved. A prototype with a diameter of 400 mm is fabricated and experimentally evaluated at operating frequencies ranging from 6 to 9 GHz. We show good conceptual agreement between the simulated and experimental results.

Structured illumination microscopy using a photonic chip

Abstract: Structured illumination microscopy (SIM) enables live cell, super-resolution imaging at high speeds. SIM uses sophisticated optical systems to generate pre-determined excitation light patterns, and reconstruction algorithms to enhance the resolution by up to a factor of two. The optical set-up of SIM relies on delicate free-space optics to generate the light patterns, and a high numerical aperture objective lens to project the pattern on the sample. These arrangements are prone to miss-alignment, often with high costs, and with the final resolution-enhancement being limited by the numerical aperture of the collection optics. Here, we present a photonic-chip based total internal reflection fluorescence (TIRF)-SIM that greatly reduces the complexity of the optical setup needed to acquire TIRF-SIM images. This is achieved by taking out the light delivery from the microscope and transferring it to a photonic-chip. The conventional glass slide is replaced by the planar photonic chip, that both holds and illuminates the specimen. The chip is used to create a standing wave interference pattern, which illuminates the sample via evanescent fields. The phase of the interference pattern is controlled by the use of thermo-optical modulation, leaving the footprint of the light illumination path for the SIM system to around 4 by 4 cm$^2$. Furthermore, we show that by the use of the photonic-chip technology, the resolution enhancement of SIM can be increased above that of the conventional approach. In addition, by the separation of excitation and collection light paths the technology opens the possibility to use low numerical objective lenses, without sacrificing on the SIM resolution. Chip-based SIM represents a simple, stable and affordable approach, which could enable widespread penetration of the technique and might also open avenues for high throughput optical super-resolution microscopy.

Depth from a Light Field Image with Learning-Based Matching Costs

Abstract: One of the core applications of light field imaging is depth estimation. To acquire a depth map, existing approaches apply a single photo-consistency measure to an entire light field. However, this is not an optimal choice because of the non-uniform light field degradations produced by limitations in the hardware design. In this paper, we introduce a pipeline that automatically determines the best configuration for photo-consistency measure, which leads to the most reliable depth label from the light field. We analyzed the practical factors affecting degradation in lenslet light field cameras, and designed a learning based framework that can retrieve the best cost measure and optimal depth label. To enhance the reliability of our method, we augmented an existing light field benchmark to simulate realistic source dependent noise, aberrations, and vignetting artifacts. The augmented dataset was used for the training and validation of the proposed approach. Our method was competitive with several state-of-the-art methods for the benchmark and real-world light field datasets.

Recent Advances in Adaptive Liquid Crystal Lenses

Abstract: An adaptive-focus lens is a device that is capable of tuning its focal length by means of an external stimulus. Numerous techniques for the demonstration of such devices have been reported thus far. Moving beyond traditional solutions, several new approaches have been proposed in recent years based on the use of liquid crystals, which can have a great impact in emerging applications. This work focuses on the recent advances in liquid crystal lenses with diameters larger than 1 mm. Recent demonstrations and their performance characteristics are reviewed, discussing the advantages and disadvantages of the reported technologies and identifying the challenges and future prospects in the active research field of adaptive-focus liquid crystal (LC) lenses.

High-throughput synapse-resolving two-photon fluorescence microendoscopy for deep-brain volumetric imaging in vivo.

Abstract: Optical imaging has become a powerful tool for studying brains in vivo. The opacity of adult brains makes microendoscopy, with an optical probe such as a gradient index (GRIN) lens embedded into brain tissue to provide optical relay, the method of choice for imaging neurons and neural activity in deeply buried brain structures. Incorporating a Bessel focus scanning module into two-photon fluorescence microendoscopy, we extended the excitation focus axially and improved its lateral resolution. Scanning the Bessel focus in 2D, we imaged volumes of neurons at high-throughput while resolving fine structures such as synaptic terminals. We applied this approach to the volumetric anatomical imaging of dendritic spines and axonal boutons in the mouse hippocampus, and functional imaging of GABAergic neurons in the mouse lateral hypothalamus in vivo.

LinKS: Discovering galaxy-scale strong lenses in the Kilo-Degree Survey using Convolutional Neural Networks

Abstract: We present a new sample of galaxy-scale strong gravitational lens candidates, selected from 904 deg2 of Data Release 4 of the Kilo-Degree Survey, i.e. the ‘Lenses in the Kilo-Degree Survey’ (LinKS) sample. We apply two convolutional neural networks (ConvNets) to ∼88000 colour–magnitude-selected luminous red galaxies yielding a list of 3500 strong lens candidates. This list is further downselected via human inspection. The resulting LinKS sample is composed of 1983 rank-ordered targets classified as ‘potential lens candidates’ by at least one inspector. Of these, a high-grade subsample of 89 targets is identified with potential strong lenses by all inspectors. Additionally, we present a collection of another 200 strong lens candidates discovered serendipitously from various previous ConvNet runs. A straightforward application of our procedure to future Euclid or Large Synoptic Survey Telescope data can select a sample of ∼3000 lens candidates with less than 10 per cent expected false positives and requiring minimal human intervention.

Broadband lightweight flat lenses for long-wave infrared imaging

Abstract: We experimentally demonstrate imaging in the long-wave infrared (LWIR) spectral band (8 μm to 12 μm) using a single polymer flat lens based upon multilevel diffractive optics. The device thickness is only 10 μm, and chromatic aberrations are corrected over the entire LWIR band with one surface. Due to the drastic reduction in device thickness, we are able to utilize polymers with absorption in the LWIR, allowing for inexpensive manufacturing via imprint lithography. The weight of our lens is less than 100 times those of comparable refractive lenses. We fabricated and characterized 2 different flat lenses. Even with about 25% absorption losses, experiments show that our flat polymer lenses obtain good imaging with field of view of 35° and angular resolution less than 0.013°. The flat lenses were characterized with 2 different commercial LWIR image sensors. Finally, we show that, by using lossless, higher-refractive-index materials like silicon, focusing efficiencies in excess of 70% can be achieved over the entire LWIR band. Our results firmly establish the potential for lightweight, ultrathin, broadband lenses for high-quality imaging in the LWIR band.

Design and Experimental Verification of a Passive Huygens’ Metasurface Lens for Gain Enhancement of Frequency-Scanning Slotted-Waveguide Antennas

Abstract: Huygens’ metasurfaces have demonstrated their versatility in numerous applications, such as wide-angle refraction and antenna beamforming. These electrically thin structures allow the enhancement of antenna systems with passive designs. Such enhancements include improving the gain and scanning capability of feed antennas. In this paper, the design, simulation results, and measurements of a metasurface lens for gain enhancement of frequency-scanning slotted-waveguide antennas are shown. Both transverse-electric (TE) and transverse-magnetic (TM) metasurface designs are verified with full-wave simulations, which demonstrate upward of 13 dB of directivity enhancement. Additionally, a fabricated $40\lambda $ long by $15\lambda $ wide TM metasurface lens centered at 34.3 GHz was experimentally verified in conjunction with a TM frequency-scanning slotted-waveguide antenna. The waveguide antenna radiates through a 1-D slot array operating between 33.5 and 35.3 GHz and produces a 16 dB fan beam which scans in the H-plane between −26° and broadside within its operational bandwidth. The realized metasurface lens, placed at $3.05\lambda $ at 34.3 GHz away from the waveguide antenna, was able to increase its realized gain by upward of 10 dB while maintaining its scanning capabilities. With the design verified in both simulation and measurements, the proposed metasurface serves as an easy-to-fabricate, efficient, low-profile, and lightweight alternative to standard microwave lenses.

An extended catalog of galaxy-galaxy strong gravitational lenses discovered in DES using convolutional neural networks

Abstract: We search Dark Energy Survey (DES) Year 3 imaging for galaxy-galaxy strong gravitational lenses using convolutional neural networks, extending previous work with new training sets and covering a wider range of redshifts and colors. We train two neural networks using images of simulated lenses, then use them to score postage stamp images of 7.9 million sources from the Dark Energy Survey chosen to have plausible lens colors based on simulations. We examine 1175 of the highest-scored candidates and identify 152 probable or definite lenses. Examining an additional 20,000 images with lower scores, we identify a further 247 probable or definite candidates. After including 86 candidates discovered in earlier searches using neural networks and 26 candidates discovered through visual inspection of blue-near-red objects in the DES catalog, we present a catalog of 511 lens candidates.

Photonic jet lens

Abstract: Microsphere-assisted microscopy currently benefits from a considerable interest in the microscope-research community. Indeed, this new imaging technique enables the lateral resolution of optical microscopes to reach around λ/5 through a full-field and a far-field acquisition while being label-free. Despite the photonic jet clearly not being a relevant concept to justify the super-resolution phenomenon, we show here how it can be used to predict imaging formation and performance such as the image position and the microsphere magnification. This study allows a better understanding of the experimental measurements that have been observed over the last decade and that will be observed in coming years, through numerical simulations using different optical and geometrical parameters.

Wide Angle Beam Steerable High Gain Flat Top Beam Antenna Using Graded Index Metasurface Lens

Abstract: This paper presents a beam steerable low-profile lens antenna with a flat top wide beam and a high gain operating at 10.10 GHz. It consists of a graded index metasurface (GIMS) lens placed on the top of a microstrip patch antenna (MPA) radiator. An ultrathin linear graded index metasurface (LGIMS) and a radial graded index metasurface (RGIMS) lens were designed for the magnitude and phase transformation of the radiated beam from the microwave radiator. First, an LGIMS lens antenna was designed by placing an LGIMS on the top of an MPA radiator at an optimum height. A maximum measured gain of 16.37 dBi indicating a maximum gain enhancement of 11.50 dB with beam steering in a conical plane with a vertex angle of 84° was observed. Next, a flat top beam (FTB) antenna with a stable gain band was designed by placing an RGIMS on top of an LGIMS lens antenna. The measured peak gain of 14.82 dBi with an FTB pattern having a 1 dB gain variation range of about 96° is observed. Furthermore, the movement of the LGIMS and the RGIMS on top of the radiator results in continuous beam scanning with a maximum gain variation of 1 dB in a conical plane with a vertex angle of about 100°. A maximum gain of 14.82 dBi with a maximum gain enhancement of 10.30 dB at 10.15 GHz was obtained due to the linear and angular movement of the LGIMS and the RGIMS in the FTB antenna. The simulated and measured results are in good agreement.

Understanding the microstructure and mechanical properties of Ti-6Al-4V and Inconel 718 alloys manufactured by Laser Engineered Net Shaping

Abstract: Laser Engineered Net Shaping (LENS®) is a metal Additive Manufacturing (AM) technique that carries great potential for the fabrication and repair of high-integrity structural and engine components. Confident application of the LENS technique requires a fundamental understanding of the microstructure and properties of the fabricated materials, as well as their correlations to processing conditions. In this study, two alloys fabricated by LENS, Ti-6Al-4V and Inconel 718, were examined and compared to their wrought counterparts. The differences between low and high laser power fabrications, as well as the effects of various post-LENS heat treatments were systematically investigated and discussed. The interfacial bond strength between LENS depositions and substrates were also evaluated for repair purposes.

3-D Printed Circularly Polarized Modified Fresnel Lens Operating at Terahertz Frequencies

Abstract: In this paper, a novel 3-D printed circularly polarized (CP) modified Fresnel lens antenna operating at 300 GHz is introduced By virtue of the superior geometric flexibility of the 3-D printing technique, a modified Fresnel lens consisting of subwavelength discrete dielectric posts in the odd-numbered Fresnel zones is proposed It is further demonstrated that by integrating dielectric anisotropic metamaterial, the modified Fresnel lens can realize CP radiation fed by a simple linearly polarized (LP) open-ended waveguide (OEWG) The 3-D printing approach is also investigated to push the performance envelops of the 3-D printer for realization of the terahertz CP lens The measured results show that the axial ratios (ARs) of the fabricated antenna prototype are smaller than 3 dB from 265 to 320 GHz Moreover, the modified Fresnel lens has a maximum gain of 274 dBic, which is 09 dB larger than that of the conventional Fresnel zone plane antenna (FZPA) These validate the concept, the design, and the fabricated prototype

Compact High-Performance Lens Antenna Based on Impedance-Matching Gradient-Index Metamaterials

Abstract: A planar wavefront transformation lens based on gradient-index metamaterials is proposed. The designed lens is composed of isotropic and inhomogeneous metamaterials and can reach impedance matching with free space. Based on the impedance-matching metamaterial lens, we present a compact high-gain and high-aperture-efficiency horn-based lens antenna working from 8 to 12 GHz. At the center working frequency of 10 GHz, the performance of the antenna is significantly improved and the measured gain increases to 17.7 dBi, which is 6.5 dBi higher than that of the original H-plane horn antenna. The half-power beamwidth and sidelobe level in the H-plane reduces to 6.2° and 15.3 dB, respectively, and the aperture efficiency reaches 94%. Such performance is much better than that of the conventional optimal H-plane horn antenna.

Broadband Achromatic Metalens in the Midinfrared Range

Abstract: A broadband metamaterial lens that does not suffer from chromatic aberration is of particular interest for optical applications at midinfrared frequencies. Due to the intrinsic dispersion of the building blocks, though, such a broadband achromatic metalens has remained elusive. The authors use the Pancharatnam-Berry phase and propagation phase to control the wave front of light, from which the chromatic aberration can be eliminated effectively. This result points the way to practical midinfrared devices, $e.g.$ for communication technology.

Compact Air-Filled Luneburg Lens Antennas Based on Almost-Parallel Plate Waveguide Loaded With Equal-Sized Metallic Posts

Abstract: This paper presents a Luneburg lens and a Luneburg reflector lens along with the corresponding compact and cost-effective multibeam antennas in the Ka -band. The Luneburg lens is composed of an air-filled parallel plate waveguide (PPW) loaded with equal-sized metallic posts. The upper plate of the PPW is designed to a curved surface to meet the requirement of the equivalent refractive index profile, meanwhile providing a transition between the lens and the feed waveguide. Also, based on the law of reflection, a reflecting wall is introduced to the Luneburg lens to achieve a Luneburg reflector lens. By employing the WR28 rectangular waveguides as the feeders, the Luneburg lens/reflector lens antennas with single beam and multiple beams are designed and experimentally verified in the whole Ka -band. The multibeam Luneburg lens antenna show the beam scanning from −45° to +45° with 0.6 dB scan loss. The multibeam Luneburg reflector lens antenna show the beam scanning from 30° to 60° with 0.7 dB scan loss. Besides, the acceptable performances of aperture efficiency, impedance matching and multiport isolation are achieved. The results indicate that the works in this paper have application potential in the millimeter-wave (mmW) wireless communications.

Optical imaging lens

Abstract: The invention discloses an optical imaging lens. The optical imaging lens sequentially comprises a first lens with negative focal power, a second lens with positive focal power, a third lens with positive focal power, a fourth lens with positive focal power, a fifth lens with negative focal power, a sixth lens with positive focal power, a diaphragm and an optical filter from the object side to theimaging side along the optical axis, wherein the object side face of the first lens is a concave face; the image side face of the second lens is a convex face, the object side face of the third lensis a convex face; the object side face and the image side face of the fourth lens are both convex faces; the object side face and the image side face of the fifth lens are both concave faces; the object side face and the image side face of the sixth lens are both convex faces; the object side face and the image side face of the diaphragm are both concave faces; the diaphragm is arranged between the first lens and the fourth lens; the optical filter is arranged between the sixth lens and the imaging side; and the fourth lens and the fifth lens form a cemented lens. The optical imaging lens canhave a good imaging effect on monochromatic light within a wide waveband within the visible light range, and the resolving power of the lens to an object emitting or reflecting monochromatic light canbe improved.

Thermal Lens Microscope and Microchip Chemistry

Abstract: Thermal lens spectrometry was realized under an optical microscope by controlling the chromatic aberration of the objective lens system. This thermal lens microscope (TLM) is ultrasensitive to non-...

Progresses in the practical metasurface for holography and lens

Abstract: Abstract Metasurfaces have received enormous attention thanks to their unique ability to modulate electromagnetic properties of light in various frequency regimes. Recently, exploiting its fabrication ease and modulation strength, unprecedented and unique controlling of light that surpasses conventional optical devices has been suggested and studied a lot. Here, in this paper, we discuss some parts of this trend including holography, imaging application, dispersion control, and multiplexing, mostly operating for optical frequency regime. Finally, we will outlook the future of the devices with recent applications of these metasurfaces.

Lens-based integrated 2D beam-steering device with defocusing approach and broadband pulse operation for Lidar application.

Abstract: We propose an integrated two-dimensional beam-steering device based on an on-chip silicon-nitride switch/emitter structure and off-chip lens for light detection and ranging (Lidar) application at 1550 nm. In this device, light is guided by a 1 × 16 switch to one grating emitter in a 4 × 4 grating-emitter array. The beam from the grating emitter is collimated and steered by a fixed lens. By changing the grating emitter that emits light, different beam-steering angle can be achieved. A divergence angle of 0.06° and a field of view of 2.07° × 4.12° in the far field are achieved. The device has O(log2N) power consumption for N emitters, allows digital control and achieves 18 dB background suppression. Blind-zone elimination and broadband operation are also achieved in our lens-based beam-steering device. Therefore, it is suitable for broadband solid-state Lidar application.

3D-printed phononic crystal lens for elastic wave focusing and energy harvesting

Abstract: We explore elastic wave focusing and enhanced energy harvesting by means of a 3D-printed Gradient-Index Phononic Crystal Lens (GRIN-PCL) bonded on a metallic host structure. The lens layer is fabricated by 3D printing a rectangular array of cylindrical nylon stubs with varying heights. The stub heights are designed to obtain a hyperbolic secant distribution of the refractive index to achieve the required phase velocity variation in space, hence the gradient-index lens behavior. Finite element simulations are performed on composite unit cells with various stub heights to obtain the lowest antisymmetric mode Lamb wave band diagrams, yielding a correlation between the stub height and refractive index. The elastic wave focusing performance of lenses with different design parameters (gradient coefficient and aperture size) is simulated numerically under plane wave excitation. It is observed that the focal points of the wider aperture lens designs have better consistency with the analytical beam trajectory results. Experiments are conducted using a PA2200 nylon lens bonded to an aluminum plate to demonstrate wave focusing and enhanced energy harvesting within the 3D-printed GRIN-PCL domain. The piezoelectric energy harvester at the focal region of the GRIN-PCL produces 3 times more power output than the baseline harvester at the same distance in the flat plate region. The results show that 3D printing can provide a simple and practical method for implementing phononic crystal concepts with minimal modification of the host structure.