Flat Lens Research Articles

Design of a square-horn hybrid plasmonic nano-antenna array using a flat lens for optical wireless applications with beam-steering capabilities

This paper introduces a Hybrid Plasmonic Nano-Antenna (HPNA) with a gradient-index dielectric flat lens modeled with different materials to enhance and steer the radiation in a particular direction based on a phase shift array. Firstly, the design of hybrid plasmonic Nano-Antenna (NA) is introduced and analyzed considering different horn-shapes such as diamond, hexagonal, circular, rectangular, and square shapes. The commercial software Computer Simulation Technology-Microwave Studio (CST-MWS) is used to analyze the radiation characteristics of the plasmonic NAs at the standard telecommunication wavelength of 1,550 nm. The produced horn-shaped nano-antenna made up from gold cladding with low- and high-index dielectric materials of SiO2 and InGaAs, respectively. The gain of the Square Horn shape Hybrid Plasmonic Nano-Antenna (SHHPNA) achieves the greatest gain with a value of 10.7 dBi at the desired frequency and the return loss reached -18.09 dB due to the wide aperture area for SHHPNA, which results in a narrower beam-width and higher gain. Moreover, by using two different shapes of dielectric flat lens to enhance the antenna’s performance by improving directivity while correspondingly reducing beam-width, the gain is enhanced and reaches 16.7 for SHHPNA with a circular lens and 16.9 for SHHPNA with a rectangular lens compared with the traditional NA that equal to 9.03 dBi. The main lobe for SHHPNA with each lens is more directed, with Side Lobe Level (SLL) and Half Power Beam-Width (HPBW) of -13.1 dB and 16.5° for SHHPNA with a circular lens and -15.1 dB and 15.4° for SHHPNA with a rectangular lens, respectively. In addition, the array configuration was investigated, and the gain was found to be 21 dBi for the single row array of 4×1 and 23.2 dB for the array of 3×3. Moreover, the array of 4×1 and 3×3 with +90° showed gains of 18.6 dBi and 20.7 dBi, respectively, compared to traditional paper with gains of 11.20 dBi and 13.1 dBi.

Shape optimized acoustic metagratings for anomalous refraction under strong thermoviscous effects

The recent development of microacoustic metagratings opens up promising possibilities for manipulating acoustic wavefronts passively, particularly in applications such as flat acoustic lenses and ultra-high frequency ultrasound imaging. The emergence of two-photon polymerization has made it feasible to precisely manufacture microscopic structures, as required when metagratings are scaled to MHz frequencies in airborne ultrasound. Nevertheless, the downsizing process presents another hurdle as the increased thermoviscous effects result in substantial losses that must be considered during the design phase. In this study, we propose two designs for microacoustic metagratings that refract a normally incident wave towards –35 ° at 2 MHz, consisting of single-body and two-body meta-atoms. The designs are created by employing shape optimization techniques that incorporate the linearized Navier–Stokes equations in every iteration starting from a neutral geometry. This ensures that the evolution of geometric key features responsible for anomalous refraction fully accounts for thermoviscous effects, as would be the case during evolution in nature where the full set of physics is always active. Subsequently, we experimentally evaluate the effectiveness of these metagratings by employing a capacitive micromachined ultrasonic transducer as the sound source and an optical microphone as the detector, covering a frequency range from 1.8 to 2.2 MHz. Our findings confirm the single-body geometry reported in the literature and show an alternative geometry for two-body design, showcasing the successful utilization of two-photon polymerization for manufacturing microscopic acoustic metamaterials.

Antenna Optimization Using Metamaterials

Abstract Metamaterials are artificial structures engineered to exhibit electromagnetic properties not found in natural materials. These materials offer a diverse range of characteristics, including negative refractive index, reverse radiation, and electromagnetic cloaking. These unique properties find applications in microwave and optical domains, enabling improvements in antenna performance, the design of microwave filters, and the creation of flat optical lenses, among others. This study focuses on utilizing metamaterials to enhance antenna performance by boosting gain, reducing mutual coupling between MIMO antennas, converting polarization, and decreasing radar cross-section (RCS). The primary performance metric considered in this investigation is gain enhancement.

Generating optical vortex needle beams with a flat diffractive lens

We present a novel method for generating optical vortex needle beams (focused optical vortices with extended depth-of-focus) using a compact flat multilevel diffractive lens (MDL). Our experiments demonstrate that the MDL can produce focused optical vortices (FOVs) with topological charges l=1−4 (extendable to other l values), maintaining focus over distances significantly longer than conventional optical vortices. Specifically, FOVs exhibit non-diffracting behavior with a depth-of-focus (DOF) extended beyond 5 cm, compared to conventional optical vortices, which show continuous size increase due to diffraction. When the MDL is illuminated by an optical vortex of 3 mm diameter, it achieves a transmission efficiency of approximately 90% and extends the DOF several times beyond that of traditional lenses. Increasing the size of the input optical vortex further extends the DOF but introduces additional rings, with their number increasing proportionally to the value of l. Our approach, validated by both experimental results and numerical simulations, proves effective for beams such as optical vortex and Hermite-Gaussian modes and holds potential applications in high-resolution imaging, material processing, optical coherence tomography, and three-dimensional optical tweezers, offering a simple and efficient solution for generating non-diffracting beams.

Imaging with an inverse-designed 50 mm-diameter f/1 MWIR flat lens with enhanced field of view and depth of focus.

We utilize inverse design and grayscale optical lithography to create a flat lens with a diameter and focal length of 50 mm, operating in the mid-wavelength infrared (MWIR) band. This lens demonstrates an extended depth of focus (DOF ≥±100μm), a field of view (FOV ≥20°), and an angular resolution of 300μrad. We characterize the lens's performance and use it as the primary optic in a hybrid refractive-diffractive telescope, which increases the angular resolution to 160μrad. Using this telescope, we perform video imaging of aircraft and vehicles. Our experiments were constrained by the higher f-number of the focal plane array. Nonetheless, through rigorous simulations, we demonstrate that the inverse-designed flat lens surpasses the performance of a conventional Fresnel zone plate (FZP) in DOF and in FOV, even under these limitations. The flat lens, weighing approximately 20g, is significantly lighter than its refractive counterparts, confirming the feasibility of high-resolution, lightweight MWIR imaging systems.

Flat lens–based subwavelength focusing and scanning enabled by Fourier translation

Abstract We demonstrate a technique for flexibly controlling subwavelength focusing and scanning, by using the Fourier translation property of a topology-preserved flat lens. The Fourier transform property of the flat lens enables converting an initial phase shift of light into a spatial displacement of its focus. The flat lens used in the technique exhibits a numerical aperture of 0.7, leading to focusing the incident light to a subwavelength scale. Based on the technique, we realize flexible control of the focal positions with arbitrary incident light, including higher-order structured light. Particularly, the presented platform can generate multifocal spots carrying optical angular momentum, with each focal spot independently controlled by the incident phase shift. This technique results in a scanning area of 10 μm × 10 μm, allowing to realize optical scanning imaging with spatial resolution up to 700 nm. This idea is able to achieve even smaller spatial resolution when using higher-numerical-aperture flat lens and can be extended to integrated scenarios with smaller dimension. The presented technique benefits potential applications such as in scanning imaging, optical manipulation, and laser lithography.

Ultra-high NA graphene oxide flat lens on a fiber facet with near diffraction-limited focusing

The realization of a high numerical aperture (NA) fiber lens is critical for achieving high imaging resolution in endoscopes, enabling subwavelength operation in optical tweezers and high efficiency coupling between optical fibers and photonic chips. However, it remains challenging with conventional design and fabrication. Here we propose an ultrathin (400 nm) graphene oxide (GO) film lens fabricated in situ on a standard single-mode fiber facet using the femtosecond laser direct writing technique. An extremely high NA of 0.89 is achieved with a near diffraction-limited focal spot (FWHM=0.68λ), which is verified theoretically and experimentally. The diameter of the fabricated fiber GO lens is as small as 12 μm with no beam expansion structure. The proposed fiber GO lens is promising for applications such as super-resolution imaging, compact optical tweezers, medical endoscopes, and on-chip integration.

Microfluidic Metasurfaces: A New Frontier in Electromagnetic Wave Engineering

AbstractMetasurfaces, as 2D artificial electromagnetic materials, play a pivotal role in manipulating electromagnetic waves by controlling their amplitude, phase, and polarization. Achieving this control involves designing subwavelength meta‐molecules with specific geometries and periodicities. In the context of microfluidic metasurfaces, optical properties can be dynamically modulated by altering either the geometric structure of liquid meta‐molecules or the refractive index of the liquid medium. Leveraging the fluidity of liquid materials, microfluidic metasurfaces exhibit remarkable performance in terms of reconfigurability and flexibility. These properties not only establish a cutting‐edge research area but also broaden the scope of applications for active metasurface devices. Additionally, the integration of metasurfaces within microfluidic systems has led to novel functionalities, including enhanced particle manipulation and sensor technologies. Compared to conventional solid‐material‐based metasurfaces, microfluidic metasurfaces offer greater design freedom, making them advantageous for diverse fields such as electromagnetic absorption, optical sensing, holographic displays, and tunable optical meta‐devices like flat lenses and polarizers. This review provides insights into the characteristics, modulation techniques, and potential applications of microfluidic metasurfaces, illuminating both the current research landscape and promising avenues for further explorations.

Graded flat lens with negative index for silicon photonics

We have realized a graded flat lens with negative effective index operating at telecom wavelength for Silicon Photonics. We report on its design, fabrication, and experimental characterization. This photonic device behaves as a convergent lens; it has been designed so as to be fabricated on a Silicon on Insulator platform and to operate at 1.55 μm. It consists of a graded photonic crystal whose filling factor has been varied so as to fit the profile of index of the graded index lens. Since it operates in the second band of Photonic Crystals, the effective index is negative. It has been characterized in two steps: (i) first, the output beam has been scanned by a set of waveguides and a CCD camera. (ii) Second, the focusing has been investigated by Scanning Near-field Optical Microscopy. This characterization validates the design: the focal length is about 5 μm (≃ 3λ), while the width of the focal spot is 0.87 μm (0.53 λ). This compact photonic device is at the wavelength scale (thickness = 4.4λ). Our design, based on Graded Index Optics, may be adapted to design new devices perfectly suited for Photonics applications, such as a short taper or a mode converter.

Retinal Image Quality Through an Operating Microscope With Wavefront Shaping Extended Depth of Focus Intraocular Lens in Model Eye

To compare the quality of images of gratings placed in a model eye viewed through an extended depth of focus (EDoF) intraocular lens (IOL) to that of diffractive bifocal IOL or monofocal IOL. Experimental laboratory investigation. Nondiffractive wavefront shaping EDoF (CNAET0, Alcon Laboratories), echelette-designed EDoF (ZXR00V, Johnson & Johnson Vision), diffractive bifocal IOL with low power addition (SV25T, Alcon Laboratories), or monofocal IOL (CNA0T0, Alcon Laboratories) was placed in a fluid-filled model eye. A United States Air Force Resolution Grating Target was glued to the posterior surface of the model eye and viewed through a flat or a wide-angle contact lens. The contrast of the gratings viewed through the EDoF or multifocal IOLs was compared to that through the monofocal IOL. A wavefront analyzer was used to measure the spherical power of the central 4.5 mm optics of the EDoF, multifocal, and monofocal IOLs. The distribution of the dioptric power and the dioptric power map were compared. The gratings observed through the flat contact lens with CNAET0, ZXR00V, or SV25T were slightly blurred when viewed through the multifocal optics. The blurred area was in the circumferential area of CNAET0, the central area of SV25T, and the peripheral area of ZXR00V. The mean contrast was 0.258 ± 0.020 for CNAET0, 0.227 ± 0.025 for ZXR00V, and 0.221 ± 0.020 for SV25T for the 16.0 cyc/mm grating. The contrast was significantly lower for ZXR00V (P = .004) and SV25T (P = .004) than 0.303 ± 0.015 for CNA0T0 but the differences were not significant for CNAET0. For the wide-angle contact lens, the contrast for CNAET0 was 0.182 ± 0.009, for ZXR00V was 0.162 ± 0.011, and for SV25T was 0.163 ± 0.007 for the 16.0 cyc/mm grating, and none was significantly different from 0.188 ± 0.012 for CNA0T0. The dioptric variations of CNAET0 indicated a ring-shaped area of higher power corresponding to the circumferential blurred zone observed through the flat contact lens. The wavefront shaping and echelette-designed EDoF-IOLs reduce the contrast of the grating more than the monofocal IOL when viewed through the flat contact lens. The degree of reduction depended on the design of the extended-focus optics. The difference was less through the wide-angle contact lens.

Adhesion of Acanthamoeba on Scleral Contact Lenses According to Lens Shape.

To investigate the adhesion of Acanthamoeba to scleral contact lens (ScCL) surface according to lens shape. Two strains of A. polyphaga (CDC:V062 and ATCC 30461) and one clinical Acanthamoeba isolate, were inoculated onto five contact lens (CL): one first-generation silicone hydrogel (SHCL; lotrafilcon B; adhesion control) containing plasma surface treatment; two ScCL (fluorosilicone acrylate) one containing surface treatment composed of plasma and the other containing plasma with Hydra-PEG, and two CL designed with a flat shape having the same material and surface treatments of the ScCL. Trophozoites that adhered to the lens's surfaces were counted by inverted optical light microscopy. Possible alterations of the lens surface that could predispose amoeba adhesion and Acanthamoeba attached to these lens surfaces were evaluated by scanning electron microscopy (SEM). All strains revealed greater adhesion to the ScCL when compared with the flat lenses (P < 0.001). The clinical isolate and the ATCC 30461 had a higher adhesion (P < 0.001) when compared with the CDC:V062. A rough texture was observed on the surface of the lenses that have been examined by SEM. Also, SEM revealed that the isolates had a rounded appearance on the surface of the ScCL in contrast with an elongated appearance on the surface of the silicone hydrogel. The findings revealed that the curved shape of the ScCL favors amoeba adhesion.

Data-driven modeling and fast adjustment for digital coded metasurfaces database: Application in adaptive electromagnetic energy harvesting

Metasurfaces (MSs) show great promise in efficient electromagnetic energy harvesting (EMEH) due to their compactness, high efficiency, and long-distance transmission capabilities. Nonetheless, the conventional iterative and time-consuming solving process of MSs significantly escalates computational demands. Furthermore, once processed, the MS shape remains fixed and cannot be adapted to changing requirements. Accordingly, a critical challenge is the development of a new efficient solver for MS real-time tuning. Here, we introduce a class of digital coded MS databases including multiple pre-defined resonant frequency MS. The combination of multiple MS base functions from the database enables swift resonance frequency adjustments to adapt to changing environmental conditions. A topology optimization method based on data-driven modeling is employed to rapidly acquire the optimal digital coding for the corresponding MS at various operating frequencies, facilitating the construction of a database. This approach integrates a convolutional neural network and genetic algorithm (CNNGA). It not only enables more accurate and expedited forward prediction of MSs' electromagnetic (EM) response but also facilitates inverse design based on specified requirements. We employ this method to design a MS that achieves perfect energy harvesting (EH) over a broad range of incident angles and polarization directions. In addition, a data-driven modeling is used to establish an EH efficiency predictive model corresponding to MS combination. This model serves as a guide for real-time MS adjustments as per changing requirements. Compared to previously designed MSs, this model achieves rapid design and adaptive adjustment capabilities. Through the incorporation of various functional MS base functions into the database, this method can be universally applied to MS combinations tailored to specific functions, including EM cloaking, ultra-thin flat lenses, and computational MSs.

Optical trapping and manipulating with a transmissive and polarization-insensitive metalens

Abstract Trapping and manipulating micro-objects and achieving high-precision measurements of tiny forces and displacements are of paramount importance in both physical and biological research. While conventional optical tweezers rely on tightly focused beams generated by bulky microscope systems, the emergence of flat lenses, particularly metalenses, has revolutionized miniature optical tweezers applications. In contrast to traditional objectives, the metalenses can be seamlessly integrated into sample chambers, facilitating flat-optics-based light manipulation. In this study, we propose an experimentally realized transmissive and polarization-insensitive water-immersion metalens, constructed using adaptive nano-antennas. This metalens boasts an ultra-high numerical aperture of 1.28 and achieves a remarkable focusing efficiency of approximately 50 % at a wavelength of 532 nm. Employing this metalens, we successfully demonstrate stable optical trapping, achieving lateral trapping stiffness exceeding 500 pN/(μm W). This stiffness magnitude aligns with that of conventional objectives and surpasses the performance of previously reported flat lenses. Furthermore, our bead steering experiment showcases a lateral manipulation range exceeding 2 μm, including a region of around 0.5 μm exhibiting minimal changes in stiffness for smoothly optical manipulation. We believe that this metalens paves the way for flat-optics-based optical tweezers, simplifying and enhancing optical trapping and manipulation processes, attributing ease of use, reliability, high performance, and compatibility with prevalent optical tweezers applications, including single-molecule and single-cell experiments.

Nanoscale precision brings experimental metalens efficiencies on par with theoretical promises

Metalenses are flat lenses, where sub-wavelength, so-called meta-atoms manipulate the electric field to perform a given lens function. Compared to traditional lenses, the two main drawbacks of metalenses are their achromatic limitations and low efficiencies. While an abundance of simulations show that efficiencies above 90% are attainable for low numerical apertures (NA), experimental reports showing such high efficiencies are limited. Here, we use electron-beam lithography (EBL) to realize a set of lenses with varying NA from 0.08 to 0.93. The low NAs were expected to fit the model, and the higher NAs determine the validity range of the model. We find that measured efficiencies above 92% for NA = 0.24 are achievable, and that a slight modification of the simulation model extends its validility to NA = 0.6. Based on our results, we discuss that the lower efficiencies reported in the literature are caused by low-fidelity manufacturing, closing the efficiency gap between measurements and simulation in metalens fabrication.

Intensity-tunable achromatic cascade liquid crystal Pancharatnam-Berry lens

In the current solution for multiwavelength achromatic flat lenses, a one-to-one correspondence exists between the number of writing phase distributions and the number of achromatic wavelengths. Breaking this correspondence requires a complex phase design and parameter optimization. Here, we show that a dual-layer cascade liquid crystal Pancharatnam-Berry lens (CLCPBL) with two writing phase distributions and a specific coupled phase distribution between the layers can achieve three wavelength achromaticity without any parameter optimization process. Similarly, in a three-layer cascade, the number of achromatic wavelengths increases to seven through the permutations of the layers, with adjustable amplitude factors. We fabricate a three-layer CLCPBL with the design wavelengths of 396.8 nm, 1064 nm, and 1550 nm, which theoretically allows the light at 632.8, 532.8, 3383 and 450 nm to form a common focus, and test such structure. Our CLCPBL enables a wider range of applications than conventional achromatic flat lenses.

Focal length switchable metalens based on vanadium dioxide.

A metalens is a flat lens that can control the phase of light so that dispersed light can be reconcentrated. This study devised a tunable metalens with a switchable focal length based on the phase transition properties of vanadium dioxide (V O 2). The unit structure comprises three layers from bottom to top: gold, polyimide, and two square resonant rings. The metalens can not only transform incident x-polarized waves into y-polarized waves but also achieve beam focusing simultaneously. The designed metalens achieves polarization conversion efficiency at an operating frequency of 0.8THz. In the insulating state of V O 2, the beam focal point is at L=1914µm; in the metallic state, the wave converges at L=982µm, closely aligning with the predetermined focal length. By controlling external temperature, focal point switching can be achieved, making it highly versatile in practical applications.

Laser Technology for Perovskite: Fabrication and Applications

AbstractPerovskite has attracted considerable attention in the electronic and optical fields in recent years, fulfilling the requirements of the ever‐growing demand in energy, environment, security, and big data storage. Laser direct writing technology is a flexible and mask‐free approach for fabricating, structuring, modifying, and patterning perovskites. Laser irradiation can directly induce perovskites from precursors due to the photothermal and photochemical effects of laser. Therefore, various laser‐induced perovskites, such as perovskite quantum dots, nanowires, nanocrystals, and films, are summarized. In particular, the laser‐induced perovskites in glass are intensively investigated for their high stability and flexibility in 3D printing. The second part of this review examines various applications of perovskites based on laser technology, such as solar cells, flat lenses, microlasers, photoluminescence, lithography, sensors, optical encryption, and data storage. Diverse laser treatments employed for modulating and patterning perovskite devices, such as laser annealing, laser ablation, and laser‐induced defects, are discussed. Prospective challenges and future trends in this research field are also concluded.

A tunable flat terahertz lens using Dirac semimetals: a simulation study

We propose and design a flat and tunable terahertz lens achieved through a two-dimensional photonic crystal composed of an array of rods made of a Dirac semimetal placed in air as the background medium. The structure of interest is a graded index photonic crystal, made possible by the slight variations in the rods’ radii in a direction perpendicular to the direction of the light propagation. Dirac semimetals' ability to respond to variations in their Fermi energy level manifested as a change in the refractive index provides the tunability of our proposed lens. The interaction of electromagnetic waves with the designed structure is investigated for both transverse magnetic and transverse electric polarizations using two-dimensional finite-difference time-domain method.

Switchable visible and near-infrared light bifocal lens based on hybrid graphene-metasurface structures

We propose a wideband visible (VIS) and near infrared (NIR) light reflective flat lens with switching capability base on hybrid graphene-metasurface structure. This tunable flat lens structure consists of a slotted gold reflector substrate, a graphene monolayer and TiO2 nanofins that provide excellent focusing performance and tunability in the VIS and NIR range. In order to achieve the switching feature, a bi-functional device capable of switching reflection/absorption modes is required. To this end, the gold substrate with two cross slots has been used to create absorption properties and a graphene layer has been used to change the intensity of absorption and reflection. The switching property for incident light with circular polarization arises from uniformly changing the chemical potential of the graphene layer. By setting the chemical potential of graphene, μc, equal to 1.1 eV, we obtained the reflection property. The reflection mode exhibits a broadband (715–800 nm) optical response with high polarization conversion efficiency (more than 70 %). On the other hand, by choosing μc = 0.75 eV, the absorption feature is created at the wavelength of 700–780 nm. The reflected light can be focused on an arbitrary position above the structure by rotating the TiO2 nanofins with the help of Pancharatnam-Berry (PB) phase theory. In addition to obtaining the single and dual focus tunable flat lenses, we have also presented a multifunction configuration that can switch between different modes, such as non-focus, single and dual focus modes. Such switchable flat lenses can have various applications in imaging and sensing systems.

Designer graphene oxide ultrathin flat lens with versatile focusing property.

Graphene oxide (GO) flat lens has a thickness in nanoscale. They modulates the light field via both phase and amplitude modulation and hence possess excellent focusing property. In this paper, we develop a systematic design method to realize the ultrathin GO flat lens with various focusing properties. By using the Rayleigh-Sommerfield theory, the focusing property of ultrathin GO lenses is accurately calculated, then the genetic algorithm (GA) is employed to design the GO lenses. The lens works at visible frequency can have a large radius and long working distance. By setting different optimization objectives, extraordinary focusing property including sub-diffraction limit focusing with FWHM (∼1.96λ) and achromatic focusing with the wavelengths (450 nm, 550 nm, 650 nm) can be achieved. These innovative designs are fabricated and tested.