Search Results (16)

Trilobites, as typical euarthropods, possess compound eyes. In 1901, Lindström was the first to describe them in detail; on the one hand, we reconsider his descriptions of the different modes of trilobite eyes; on the other hand, we expand this by compiling the observations that have been possible in recent years. There are two, perhaps three kinds of trilobite compound eyes. The first are the primordial holochroal eyes, which are actually apposition compound eyes, similar to those of many modern diurnal crustaceans and insects. The abathochroal eyes, often referred to as the second form, are probably a subtype of the holochroal eyes. Consequently, the second is the schizochroal eye of phacopid trilobites, which are hyper-compound eyes composed of numerous small compound eyes below each of the big lenses, which appear from outside as one big lateral eye each. Thirdly, one may call the maculae light-sensitive organs, but this is still uncertain. Comparing what are probably the oldest trilobite eyes described so far with other forms, it is possible to conclude that the sensory apparatus is much older than the fossil record of trilobite eyes and probably developed in Precambrian times. The refractive apparatus, however, was developed later and separately within the systematic groups. This explains why, for example, the mandibulates have a lens and a crystalline cone. Still, the chelicerate xiphosurans, such as horseshoe crabs or eurypterids, possess a lens cylinder with an index gradient but no crystalline cone. Furthermore, this can explain why the calcite character of trilobites is unique in the arthropod kingdom. An important discovery is the probably epidermal, lens-building cells encompassing a prospective lens of Schmidtiellus reetae Bergström 1973 from the early Lower Cambrian of Estonia. We reconsider the morphology of hypostome maculae and interpret them as a potential phylogenetic relict and a potential predecessor of all arthropod ommatidial compound eyes. It will be of great relevance for future research to understand the evolution of compound eyes and vision because we witness the emergence of the first lenses in the trilobite, if not the arthropod kingdom. Full article

Gradient refractive index (GRIN) lenses have been widely used for many applications. However, the traditional manufacturing methods of GRIN lenses are very time-consuming and only suitable for macro-scale operations. In addition, those methods do not have the ability to produce other GRIN optical components with complex refractive index profiles like aspheric or freeform components. We report here an approach to produce GRIN micro-optical components in chalcogenide glass based on a direct laser writing technique. Using this approach, we are able to locally modulate the refractive index of the glass subtrates and create an arbitrary refractive index profile. To prove the flexibility of the method for the production of GRIN micro-optics, we fabricated GRIN micro-lenses and a micro-Fresnel axicon (Fraxicon). The optical properties of micro-lenses can be controlled by varying the writing parameters or the substrate thickness. As a result, the working distance of the micro-lenses can extend from 0 to more than 1000 $\mathsf{\mu }$m. Also, the micro-Fraxicon exhibits the ability to convert a Gaussian beam to a Bessel-like beam which concentrates the mid-infrared light into an approximately 1200 $\mathsf{\mu }$m long confinement zone. Full article

This study introduces a groundbreaking antenna system, the directive Metasurface Half-Maxwell Fish-Eye (MHMF) lens antenna, tailored specifically for Internet-of-Things (IoT) networks. Designed to operate at 60 GHz, this antenna ingeniously integrates a dipole antenna within a parallel-plate waveguide to illuminate a Half-Maxwell Fish-Eye (HMFE) lens. The HMFE lens serves as a focal point, enabling a crucial high gain for IoT operations. The integration of metasurface structures facilitates the attainment of the gradient refractive index essential for the lens surface. By employing commercial Ansys HFSS software, extensive numerical simulations were conducted to meticulously refine the design, focusing particularly on optimizing the dimensions of unit cells, notably the modified H-shaped cells within the parallel waveguides housing the beam launchers. A functional prototype of the antenna was constructed using a standard PCB manufacturing process. Rigorous testing in an anechoic chamber confirmed the functionality of these manufactured devices, with the experimental results closely aligning with the simulated findings. Far-field measurements have further confirmed the effectiveness of the antenna, establishing it as a high-gain antenna solution suitable for IoT applications. Specifically, it operates effectively within the 60 GHz range of the electromagnetic spectrum, which is crucial for ensuring reliable communication in IoT devices. The directive HMFE lens antenna represents a significant advancement in enhancing IoT connectivity and capabilities. Leveraging innovative design concepts and metasurface technology, it heralds a new era of adaptable and efficient IoT systems. Full article

This paper introduces an innovative antenna design utilizing a cylindrical dielectric Luneburg lens tailored for 60 GHz Internet of Things (IoT) applications. To optimize V-band communications, the permittivity of the dielectric medium is strategically adjusted by precisely manipulating the physical porosity. In IoT scenarios, employing a microstrip dipole antenna with an emission pattern resembling cos¹⁰ enhances beam illumination within the waveguide, thereby improving communication and sensing capabilities. The refractive index gradient of the Luneburg lens is modified by manipulating the material’s porosity using air holes, prioritizing signal accuracy and reliability. Fabricated with polyimide using 3D printing, the proposed antenna features a slim profile ideal for IoT applications with space constraints, such as smart homes and unmanned aerial vehicles. Its innovative design is underscored by selective laser sintering (SLS), offering scalable and cost-effective production. Measured results demonstrate the antenna’s exceptional performance, surpassing IoT deployment standards. This pioneering approach to designing multibeam Luneburg lens antennas, leveraging 3D printing’s porosity control for millimeter-wave applications, represents a significant advancement in antenna technology with scanning ability between −67 and 67 degrees. It paves the way for enhanced IoT infrastructure characterized by advanced sensing capabilities and improved connectivity. Full article

Infrared gradient refractive index (GRIN) material lenses have attracted much attention due to their continuously varying refractive index as a function of spatial coordinates in the medium. Herein, a glass accumulation thermal diffusion method was used to fabricate a high refractive index GRIN lens. Six Ge_17.2As_17.2Se_xTe_(65−x) (x = 10.5–16) glasses with good thermal stability and high refractive index (n_{@10 μm} > 3.1) were selected for thermal diffusion. The refractive index span (∆n) of 0.12 was achieved in this GRIN lens. After thermal diffusion, the lens still had good transmittance (45%) in the range of 8–12 μm. Thermal imaging confirmed that this lens can be molded into the designed shape. The refractive index profile was indirectly characterized by the structure and composition changes. The structure and composition variation became linear with the increase in temperature from 260 °C to 270 °C for 12 h, indicating that the refractive index changed linearly along the axis. The GRIN lens with a high refractive index could find applications in infrared optical systems and infrared lenses for thermal imaging. Full article

A simultaneous steady-state and transient photothermal-lens modality was used for both the thermal and optical parameters of aqueous dispersed systems (carbon and silica nanoparticles, metal iodides, surfactants, heme proteins, albumin, and their complexes). Heat-transfer parameters (thermal diffusivity and thermal effusivity), the temperature gradient of the refractive index, light absorption, and concentration parameters were assessed. To simultaneously measure thermal and optical parameters, the time scale of thermal lensing (characteristic time, $t_c$) should correspond to an excitation beam size of 60–300 µm, and the relative time intervals $\left(0.5÷5\right)t_c$ and (5$÷20)t_c$ should be selected for transient and steady-state measurements, respectively. Dual-beam thermal-lens spectrometers in a mode-mismatched optical schematic at various excitation wavelengths were built. The spectrometers implement back-synchronized detection, providing different measurement conditions for the heating and cooling parts of the thermal-lens cycle. By varying the measurement parameters depending on the dispersed system, the conditions providing the suitable precision (replicability, repeatability, and reproducibility) of thermal-lens measurements were found; setups with a broad excitation beam (waist size, 150 and 300 μm) provide longer times to attain a thermal equilibrium and, thus, the better precision of measurements of thermal diffusivity. Full article

The manipulation of refracted wavefronts is eye-catching for owning attractive applications. In this article, an airborne acoustic flat lens for broadband focusing via cross-shape structure was proposed and demonstrated, introducing the broadband manipulation of wavefronts. The designed metasurface employs gradient refractive index cells to redirect the sound wave. Based on our theory, the effective refractive indexes of our unit cells can be easily calculated. The shackle of narrowband metasurfaces is conquered, and applications in medical ultrasound imaging are just around the corner. Full article

This paper presents the design, simulation and experimental validation of a gradient-index (GRIN) metasurface lens operating at 8 GHz for microwave imaging applications. The unit cell of the metasurface consists of an electric-LC (ELC) resonator. The effective refractive index of the metasurface is controlled by varying the capacitive gap at the center of the unit cell. This allows the design of a gradient index surface. A one-dimensional gradient index lens is designed and tested at first to describe the operational principle of such lenses. The design methodology is extended to a 2D gradient index lens for its potential application as a microwave imaging device. The metasurface lenses are designed and analyzed using full-wave finite element (FEM) solver. The proposed 2D lens has an aperture of size 119 mm (3.17λ) × 119 mm (3.17λ) and thickness of only 0.6 mm (0.016λ). Horn antenna is used as source of plane waves incident on the lens to evaluate the focusing performance. Field distributions of the theoretical designs and fabricated lenses are analyzed and are shown to be in good agreement. A microwave nondestructive evaluation (NDE) experiment is performed with the 2D prototype lens to image a machined groove in a Teflon sample placed at the focal plane of the lens. Full article

Chalcogenide glasses have attracted growing interest for their potential to meet the demands of photonic applications in the Mid-Wavelength InfraRed (MWIR) and Long-Wavelength InfraRed (LWIR) transmission windows. In this work, we investigated the photosensitivity to femtosecond laser irradiation of a dedicated chalcogenide glass, along with its possible applications in micro-optics. In order to address the SWaP problem (Size, Weight and Power), this work took advantage of recent techniques in femtosecond laser direct writing to imprint flat and integrated optical systems. Here, we wanted to simplify an infrared multispectral imaging system which combines a lens array and a filter array. Each channel has a focal length of 7 mm and an f-number of 4. We show in this paper that the chosen GeS₂-based chalcogenide glass is very promising for the fabrication of graded index optics by fs-laser writing, and particularly for the fabrication of Fresnel lenses. We note a very important phase variation capacity in this infrared material corresponding to refractive index variations up to +0.055. A prototype of Fresnel GRIN lens with a refractive index gradient was fabricated and optically characterized in the Vis range. Full article

This paper proposes a dielectric slabs-based lens for millimeter-wave beamforming systems. The proposed lens is based on the graded steps of the effective refractive index of the semi-spherical lens. It consists of multiple dielectric slabs that match the selected gradient effective refractive index. These slabs have the same thicknesses and different radii. The slab thickness in this lens should not exceed a quarter of the operating wavelength to keep on a similar effective refractive index of the original semi-spherical lens. A horn antenna is used to examine the performance of the designed lens at 28 GHz frequency in terms of the maximum gain, sidelobe level, and 3 dB beamwidth. Sixteen switchable horn antennas are used to demonstrate lens capability for millimeter-wave beamforming. Every single antenna element is selected individually, thus the dielectric lens steers and enhances the corresponding radiation of the selected element in the desired direction. Full article

In the field of vehicle lighting, due to the diode laser, its small size and high energy conversion efficiency, it can be effectively used as the headlight source of high beam. In recent years, it was adopted by European advanced car manufacturers as a new generation of automotive headlight lighting products. The current mature technology on the market is to extend the laser beam by means of reflection and to use a single high-power laser as the light source to meet the needs of surface lighting. In this research, we propose a new integrated optical design for an automotive headlight system with the rod lens, gradient-index lens (GRIN lens) and freeform lens to expand the laser beam. With regard to the diffusion of the beam by reflection and refraction, the liquid lens is used as a switch for the high beam and low beam lights to meet the needs of vehicle lighting functions and to use low-power diode lasers to synthesize the array light source. Compared with the 24-W LED headlight module available in the current market, the energy saved by this proposed optical design can increase efficiency by an average of 33%. The maximum illuminance is 56.6 lux in the high-beam mode, which is 18% higher than the standard value. Let the laser light meet the lighting requirements of regulatory standard values even beyond. Full article

We improved the three-dimensional (3D) crosstalk level of multi-view 3D displays using a lens array with small f-number, thereby facilitating a wide 3D viewing window. In particular, we designed a polarization-dependent-switching liquid crystal (LC)-based gradient refractive index (GRIN) lens array that could be switched between 2D and 3D viewing modes. For the GRIN lens with a small f-number (1.08), we studied the effect of the interfacial curvature between the plano-concave isotropic polymer layer and the plano-convex birefringent LC layer on the aberration properties. We examined the conventional spherical, quadratic polynomial aspherical, and a high-order (fourth-order) polynomial aspherical curvature. For the high-order polynomial aspherical curvature, the achievable transverse spherical aberration (TSA = 10.2 µm) was considerably lower than that with the spherical (TSA = 100.3 µm) and quadratic polynomial aspherical (TSA = 30.4 µm) curvatures. Consequently, the angular luminance distributions for each view were sharper for the high-order polynomial interfacial curvature. We designed multi-view (43-view) 3D displays using the arrays of switchable LC lenses with different curvatures, and the average adjacent crosstalk levels within the entire viewing window (50°) were 68.5%, 73.3%, and 60.0% for the spherical, quadratic polynomial aspherical, and high-order polynomial aspherical curvatures, respectively. Full article

This paper proposes an effective approach to fabricate a blue phase liquid crystal (BPLC) microlens array based on a photoconductive film. Owing to the characteristics of photo-induced conducting polymer polyvinylcarbazole (PVK), in which conductivity depends on the irradiation of UV light, a progressive mask resulting in the variation of conductivity is adopted to produce the gradient distribution of the electric field. The reorientations of liquid crystals according to the gradient distribution of the electric field induce the variation of the refractive index. Thus, the incident light experiences the gradient distribution of the refractive index and results in the focusing phenomenon. The study investigates the dependence of lens performance on UV exposure time, the focal length of the lens, and focusing intensities with various incident polarizations. The BPLC microlens array exhibits advantages such as electrically tunability, polarization independence, and fast response time. Full article

An electrically tunable-focusing liquid crystal (LC) microlens array exhibiting a wide-range tunable focal length is proposed. The lower substrate has strip indium tin oxide (ITO) electrodes, the upper substrate has periodic ITO electrodes with a certain gap coated on the inner surface., and an LC microlens is generated between the two strip electrodes. For each LC microlens, the gap between the top planar electrodes is directly above the center of the microlens. Unlike the conventional LC lens, the individual LC microlens is not coated with ITO electrodes on the central part of its upper and lower substrates, which helps to maintain the LC’s horizontal orientation. In the voltage-off state, the focal length of the microlens array is infinity because of the homogeneous LC alignment. At a given operating voltage, an ideal gradient refractive index distribution is induced over the homogeneous LC layer, which leads to the focusing effect. The simulation result shows that the focal length of the LC microlens could be gradually drawn to 0.381 mm with a change of voltage. Full article

An in-plane liquid gradient index (L-GRIN) microlens is designed for dynamically adjusting the beam focusing. The ethylene glycol solution (core liquid) withde-ionized (DI) water (cladding liquid) is co-injected into the lens chamber to form a gradient refractive index profile. The influences of the diffusion coefficient, mass fraction of ethylene glycol and flow rate of liquids on the refractive index profile of L-GRIN microlens are analyzed, and the finite element method and ray tracing method are used to simulate the convection-diffusion process and beam focusing process, which is helpful for the prediction of focusing effects and manipulation of the device. It is found that not only the focal length but the focal spot of the output beam can be adjusted by the diffusion coefficient, mass fraction and flow rate of liquids. The focal length of the microlens varies from 942 to 11 μm when the mass fraction of the ethylene glycol solution varies from 0.05 to 0.4, and the focal length changes from 127.1 to 8 μm by varying the flow rate of the core liquid from 0.5 × 10³ to 5 × 10³ pL/s when there is no slip between the core and cladding inlet. The multiple adjustable microlens with a simple planar microfluidic structure can be used in integrated optics and lab-on-chip systems. Full article