Prism Array Research Articles

Continuous Viewing Angle Distribution Control of Liquid Crystal Displays Using Polarization-Dependent Prism Array Film Stacked on Directional Backlight Unit

We present a polarization-dependent prism array film for controlling the viewing angle distribution of liquid crystal (LC) display panels without loss of light efficiency. On a directional backlight unit, our polarization-dependent prism array film, made into a stacked bilayer with a well-aligned liquid crystalline reactive mesogen (RM) layer on the UV-imprinted prism structure, can continuously control the light refraction function of the prism array by electrically switching incident polarization states of a polarization-controlling layer prepared by a twisted nematic LC mode. The viewing angle control properties of the polarization-dependent prism array film are analyzed under different prism angle and refractive index conditions of the RM layer. A simple analytic model is also presented to describe the intermediate viewing angle distributions with continuously varying applied voltages and incident polarization states.

An all‐dielectric band‐stop frequency‐selective surface

ABSTRACTIn this paper, an all‐dielectric band‐stop frequency‐selective surface (FSS) is proposed for X‐band applications. The unit particle of the FSS consists of a thick upper hexagonal prism part and a thin lower hexagonal prism part for monolithic construction. The proposed FSS has a planar array of hexagonal ceramic prisms with a honeycomb‐shaped structure. The proposed FSS has three resonant dips. These are combined to establish a −10 dB fractional bandwidth (FBW) with a broad stop‐band of 31.8% (center frequency of 9.75 GHz). To demonstrate the resonant characteristic modes, cylindrical cavity mode analysis based on cylindrical wave functions is used. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:56–60, 2017

Electro-optic beam deflection based on a lithium niobate waveguide with microstructured serrated electrodes.

We report on electro-optic beam deflection using an annealed proton exchange waveguide in lithium niobate (LN) with microstructured serrated array electrodes. Due to the electro-optic effect of the LN material, the experimental results show that the beam deflection and modulation of the LN waveguide can be realized with relatively low voltages. The total length of the serrated prism array electrodes structure is ∼5 mm. With 20 V applied to the electrodes of 50, 100, and 150 μm wide waveguides, ∼1.28, ∼0.96, and ∼0.64 μm beam deflections were obtained, respectively, which are in accordance with theoretical simulation. This configuration can be potentially applied in optical beam scanning, high-speed switches, and optical beam smoothing technology.

Plasmonic enhancement of amorphous silicon solar photovoltaic cells with hexagonal silver arrays made with nanosphere lithography

Nanosphere lithography (NSL) provides an opportunity for a low-cost and scalable method to optically engineer solar photovoltaic (PV) cells. For PV applications, NSL is widely used in rear contact scenarios to excite surface plasmon polariton and/or high order diffractions, however, the top contact scenarios using NSL are rare. In this paper a systematic simulation study is conducted to determine the capability of achieving efficiency enhancement in hydrogenated amorphous silicon (a-Si:H) solar cells using NSL as a top contact plasmonic optical enhancer. The study focuses on triangular prism and sphere arrays as they are the most commonly and easily acquired through direct deposition or low-temperature annealing, respectively. For optical enhancement, a characteristic absorption profile is generated and analyzed to determine the effects of size, shape and spacing of plasmonic structures compared to an un-enhanced reference cell. The factors affecting NSL-enhanced PV performance include absorption, shielding effects, diffraction, and scattering. In the triangular prism array, parasitic absorption of the silver particles proves to be problematic, and although it can be alleviated by increasing the particle spacing, no useful enhancement was observed in the triangular prism arrays that were simulated. Sphere arrays, on the other hand, have broad scattering cross-sections that create useful scattering fields at several sizes and spacing intervals. For the simulated sphere arrays the highest enhancement found was 7.4%, which was fabricated with a 250 nm radius nanosphere and a 50 nm silver thickness, followed by annealing in inert gas. These results are promising and provide a path towards the commercialization of plasmonic a-Si:H solar cells using NSL fabrication techniques.

Increasing light capture in silicon solar cells with encapsulants incorporating air prisms to reduce metallic contact losses.

Silicon solar cells are the most widely deployed modules owing to their low-cost manufacture, large market, and suitable efficiencies for residential and commercial use. Methods to increase their solar energy collection must be easily integrated into module fabrication. We perform a theoretical and experimental study on the light collection properties of an encapsulant that incorporates a periodic array of air prisms, which overlay the metallic front contacts of silicon solar cells. We show that the light collection efficiency induced by the encapsulant depends on both the shape of the prisms and angle of incidence of incoming light. We elucidate the changes in collection efficiency in terms of the ray paths and reflection mechanisms in the encapsulant. We fabricated the encapsulant from a commercial silicone and studied the change in the external quantum efficiency (EQE) on an encapsulated, standard silicon solar cell. We observe efficiency enhancements, as compared to a uniform encapsulant, over the visible to near infrared region for a range of incident angles. This work demonstrates exactly how a periodic air prism architecture increases light collection, and how it may be designed to maximize light collection over the widest range of incident angles.

Novel electron monochromator for high resolution imaging and spectroscopy

A mirror electron monochromator has been developed for reducing the energy spread of commonly used high brightness electron sources from the characteristic range of 0.3–1 eV to values below 100 meV. The monochromator utilizes mirror optics and thereby exploits the symmetry inherent in reversing the electron trajectory to monochromatize the primary beam with a knife edge instead of a conventional slit. The performance of the key electron-optical components of the monochromator has been simulated. These components include the combination of an electron mirror with a magnetic prism array. In initial testing, the monochromator has demonstrated the ability to reduce the energy spread of a 5 keV electron beam that was generated by a Schottky electron emitter from its initial value of 0.65–0.75 eV to 180 meV with an exit beam current exceeding 1 nA and to 100 meV with an exit beam current of 50 pA. Here, the attainable energy resolution was found to be limited by the noise on the power supply. The monochromator is designed to attach to scanning and transmission electron microscopes thus making them suitable for enhancing the study of the structure, composition, and bonding states of new materials at the nanoscale. For scanning electron microscopy, the monochromator will increase the spatial resolution of the acquired images of specimens, in particular, at low landing energies where the chromatic aberrations become dominant. For transmission electron microscopy, the monochromator will refine the spectra extracted from electron spectrometers, where the energy spread of the electron source limits the achievable energy resolution.

Probing the Plasmonic Properties of Heterometallic Nanoprisms with Near-Field Fluorescence Microscopy

In an effort to optimize both the optical properties and chemical stability of plasmonic platforms for surface-enhanced fluorescence spectroscopy, a series of multilayered heterometallic structures were prepared. Gold–silver multilayered array of prisms were designed, where the gold layers acts as protective layers for the silver and extends the spectral range of the resulting localized surface plasmon resonances. Herein, we report an experimental study of the enhanced near-field fluorescence from quantum dots deposited at the surface of these platforms. This was performed using near-field scanning optical microscopy yielding simultaneous measurements of topographical features and near-field fluorescence of the prismatic arrays. Hence, the individual localized fluorescent hot-spots could be imaged and spatially correlated with the geometry of the nanostructures for distinct polarization configuration of the excitation light with respect to the orientation of the structures. Furthermore, the fluorescence enhancement was evaluated spatially and temporally for the series of the nanoprism platforms. In particular, the quenching of the near-field fluorescence due to the metal structures was carefully evaluated for the metal–fluorophore hybrid systems.

Separation of multiple images via directional guidance using structured prism and pyramid arrays.

We propose a new concept of separating images through a directional guide of multi-visuals by using structured prism or pyramid arrays. By placing prism arrays onto two different image arrays, the two collective images below the facets are guided to different directions. Using optical calculations, we identify a condition for successful image separation. Transparent pyramid arrays are used to separate four images into four directions. The direction of refracted rays can be controlled by the refractive index of prisms and liquid filled into the voids. In addition, the images can be switched by stretching and releasing an elastomeric prism array.

An optofluidic tunable Fresnel lens for spatial focal control based on electrowetting-on-dielectric (EWOD)

A Fresnel lens is an optical device that approximates the performance of a conventional bulk lens while using far less lens material for both cost and space effectiveness. However, the use of current solid-type materials fixes the lens optical performance. In this paper, we propose a linear array of liquid prisms to function as a tunable Fresnel lens where each prism is individually controlled by electrowetting-on-dielectric (EWOD) to replace the subsections of a conventional Fresnel lens. Symmetric and asymmetric control of each prism in our Fresnel lens allows spatial focal tuning along the longitudinal (i.e. z-axis) as well as lateral (i.e. x-axis) directions. Analytical studies were conducted to understand the effect of beam steering angle β on the lens performance, particularly for spatial focal control. A 3×1 liquid prism array was fabricated to demonstrate the viability of our proposed configuration for a tunable Fresnel lens. By individually controlling each prism using EWOD, we have achieved spatial focal control along the longitudinal (263mm≤flong≤∞) and the lateral (0≤flat≤30mm) directions. The optofluidic tunable Fresnel lens presented here would show the lens capability for spatial focal control which can be used for potential optical applications such as tracking eye movement for smart displays, or following the motion of the sun for use in compact concentrated photovoltaic (CPV) systems.

Large-aperture prism-array lens for high-energy X-ray focusing.

A new prism-array lens for high-energy X-ray focusing has been constructed using an array of different prisms obtained from different parabolic structures by removal of passive parts of material leading to a multiple of 2π phase variation. Under the thin-lens approximation the phase changes caused by this lens for a plane wave are exactly the same as those caused by a parabolic lens without any additional corrections when they have the same focal length, which will provide good focusing; at the same time, the total transmission and effective aperture of this lens are both larger than those of a compound kinoform lens with the same focal length, geometrical aperture and feature size. This geometry can have a large aperture that is not limited by the feature size of the lens. Prototype nickel lenses with an aperture of 1.77 mm and focal length of 3 m were fabricated by LIGA technology, and were tested using CCD camera and knife-edge scan method at the X-ray Imaging and Biomedical Application Beamline BL13W1 at Shanghai Synchrotron Radiation Facility, and provided a focal width of 7.7 µm and a photon flux gain of 14 at an X-ray energy of 50 keV.

Estimating the magnetization distribution within rectangular rock samples

AbstractOver the last decades, scanning magnetic microscopy techniques have been increasingly used in paleomagnetism and rock magnetism. Different from standard paleomagnetic magnetometers, scanning magnetic microscopes produce high‐resolution maps of the vertical component of the magnetic induction field (flux density) on a plane located over the sample. These high‐resolution magnetic maps can be used for estimating the magnetization distribution within a rock sample by inversion. Previous studies have estimated the magnetization distribution within rock samples by inverting the magnetic data measured on a single plane above the sample. Here we present a new spatial domain method for inverting the magnetic induction measured on four planes around the sample in order to retrieve its internal magnetization distribution. We have presumed that the internal magnetization distribution of the sample varies along one of its axes. Our method approximates the sample geometry by an interpretation model composed of a one‐dimensional array of juxtaposed rectangular prisms with uniform magnetization. The Cartesian components of the magnetization vector within each rectangular prism are the parameters to be estimated by solving a linear inverse problem. Our method automatically deals with the averaging of the measured magnetic data due to the finite size of the magnetic sensor, preventing the application of a deconvolution before the inversion. Tests with synthetic data show the performance of our method in retrieving complex magnetization distributions even in the presence of magnetization heterogeneities. Moreover, they show the advantage of inverting the magnetic data on four planes around the sample and how this new acquisition scheme improves the estimated magnetization distribution within the rock sample. We have also applied our method to invert experimentally measured magnetic data produced by a highly magnetized synthetic sample that was manufactured in the laboratory. The results show that even in the presence of apparent position noise, our method was able to retrieve the magnetization distribution consistent with the isothermal remanent magnetization induced in the sample.

Effects of Dipole and Quadrupole Modes on the Switchable Total Transmission and Reflection in an Array of Rectangular Silver Prisms

Using an array of rectangular silver prisms, we numerically demonstrated that close to 100% transmission and reflection of the electromagnetic wave can be switched by slightly changing the incident wavelengths of less than 10 nm. The calculations showed that the resonance wavelengths are associated with the coherent dipole coupling among nanoparticles, and similar phenomena can also be achieved when the quadrupole mode of the metal nanoparticles is excited. While the change from total transmission to total reflection can be obtained relatively easier when the dipole mode is excited, the difference of the resonance wavelengths between the total transmission and reflection is larger. At the resonance wavelength of quadrupole excitation, the change between the total transmission and the reflection is very sharp and shows a Fano-shaped spectral profile; however, achieving close to 100% transmission and reflection is challenging. We studied the effects of prism width, height, and interparticle distance on the ...

Multi-aperture foveated imaging.

Foveated imaging, such as that evolved by biological systems to provide high angular resolution with a reduced space-bandwidth product, also offers advantages for man-made task-specific imaging. Foveated imaging systems using exclusively optical distortion are complex, bulky, and high cost, however. We demonstrate foveated imaging using a planar array of identical cameras combined with a prism array and superresolution reconstruction of a mosaicked image with a foveal variation in angular resolution of 5.9:1 and a quadrupling of the field of view. The combination of low-cost, mass-produced cameras and optics with computational image recovery offers enhanced capability of achieving large foveal ratios from compact, low-cost imaging systems.

Polarization and sizes variation immune optical absorbers

In this paper, a novel optical absorber that is flexible in size for fabrication and unique properties is studied numerically by aid of finite difference in time domain (FDTD) algorithm. The structure consists of three layers based on the metal–dielectric–metal design scheme. The middle layer is a dielectric in which the electronic and magnetic resonance energy dissipates. The bottom side is a metallic plane and the top layer is a hexagonal prism array. We also investigate the influence of the structure parameters on the absorbance and the absorption wavelength. The results show that a perfect absorber can be designed, and the number of the absorption peaks varies from two to three for the different radius of circumcircle of the hexagonal prism ranging from 280 nm to 400 nm. Meanwhile, position of the first absorption peak is nearly unchanged. This unique feature may be a significant advantage and possesses great potential applications such as biosensing and photovoltaic. Additionally, position and amplitude of the first absorption peak is constant for broad incident angles. The absorption is insensitive to the polarization of the incident beam due to the highly symmetric structure.

Cylindrical chains of water drops condensing on microstructured lubricant-infused surfaces.

We studied the condensation of water drops on a micro-structured lubricant-infused surfaces. Hierarchical micro-prism surfaces were fabricated by soft imprinting with wet TiO2 nanoparticle paste. After hydrophobization, the patterned surfaces were infused with silicone oil as a lubricant. When cooling at high humidity (over 80%), water drops nucleate and start growing on the surface. Once they have reached a certain size, the drops at neighboring channels of the micro-prisms attract each other and spontaneously form cylindrical chains. These chains of drops align perpendicular to the prism array. The morphology and the length-to-width ratio of the chains of drops depend on the thickness of the lubricant layer. This new concept of water drop alignment on lubricant-infused surfaces offers a new route for pattern formation with condensed drops.

One step fabrication of polymeric ratchet structures of diverse tilting angles

A novel method to fabricate asymmetric ratchet-like micro structures with various tilting angles is presented by controlling the light transmission pathway with double-layered Lucius prism arrays.

Approach to change optimal viewing distance of autostereoscopic display based on parallax barrier

Abstract An approach to change the optimal viewing distance of autostereoscopic is proposed. The optimal viewing distance can be changed by setting up a prism array instead of changing the parameters of the display. The theoretical formula to determine the optimal viewing distances are deduced and prism array structure is designed. The parameters of the prism array are optimised. The simulation results by optical analysis software ASAP show that this approach is correct and feasible.

Demonstration of a snapshot full-Stokes division-of-aperture imaging polarimeter using Wollaston prism array

A snapshot full-Stokes division-of-aperture imaging polarimeter using a Wollaston prism array (WPA) is theoretically described and experimentally demonstrated. Two-dimensional spatial distributions of six polarization eigenstates, linear (0°, 90°, 45°, 135°), and left and right circular polarization states, are identified and separated by the WPA simultaneously and projected onto the six portions of a single focal-plane array by a lens array. The conditions of the measurement matrix formed by the six polarization modulation channels are naturally superior for immunity to Gaussian and Poisson noise. The unique properties of the WPA, such as its high extinction ratio, optical efficiency and transmittance, can further ensure the achievement of immunity. The snapshot principle and the conditions of the measurement matrix are discussed. A proof-of-concept system using a complementary metal oxide semiconductor (CMOS) sensor for visible light is built and validated using laboratory and outdoor measurements.

Design and optical analyses of an arrayed microfluidic tunable prism panel for enhancing solar energy collection

We present the design and optical analyses of an arrayed microfluidic tunable prism panel that enables wide solar tracking and high solar concentration while minimizing energy loss. Each of the liquid prism modules is implemented by a microfluidic (i.e. non-mechanical) technology based on electrowetting for adaptive solar beam steering. Therefore the proposed platform offers a low-cost, lightweight and precise solar tracking system while obviating the need for bulky and heavy mechanical moving parts essentially required for a conventional motor-driven solar tracker. In this paper, various liquid prism configurations in terms of design (single, double, triple and quad-stacked prism arrays) as well as optical materials are considered and their impact on optical performance aspects such as solar beam steering, reflection losses and beam concentration is studied. Our system is able to achieve a wide solar tracking covering the whole-day movement of the Sun and a reflection loss below 4.4% with a Rayleigh’s film for a quad-stacked prism configuration. Furthermore, an arrayed prism panel is proposed to increase the aperture area and thus allows for the collection of large amounts of sunlight. Our simulation study based on the optical design software, ZEMAX, indicates that the prism panel is capable of high solar concentration up to 2032× factor even without conventional solar tracking devices. We also deal with dispersion characteristics of the materials and their corresponding effect on concentration factor. The proposed microfluidic platform has a potential for high solar energy harvesting and is not only economically viable, but also reliable and practical for various solar power applications.

Insights Into the Solution Crystallization of Oriented Alq3 and Znq2 Microprisms and Nanorods.

Optimized solution-based methods to grow high quality micro- and nanocrystals of organic semi-conductors with defined size, shape and orientation are important to a variety of optoelectronic applications. In this context, we report the growth of single crystal micro- and nanostructures of the organic semiconductors Tris(8-hydroxyquinoline)aluminum (Alq3) and bis(8-hydroxyquinoline)zinc (Znq2) terminating in flat crystal planes using a combination of evaporative and antisolvent crystallization. By controlling substrate-specific nucleation and optimizing the conditions of growth, we generate vertically-oriented hexagonal prism arrays of Alq3, and vertical half-disks and sharp-edged rectangular prisms of Znq2. The effect of process variables such as ambient vapour pressure, choice of anti-solvent and temperature on the morphology and crystal habit of the nanostructures were studied and the results of varying them catalogued to gain a better understanding of the mechanism of growth.