Liquid crystals are of technological interest as they allow for optical effects which can be electrically controlled. In this paper we present an electro-optical device consisting of nematic liquid crystals addressed by an electrode structure consisting of thin films of polymer wrapped single walled carbon nanotubes (nanohybrids). Thin films of nanohybrids display excellent optical transmission and electrical conduction properties. Due to the randomly organised nanohybrids these composite films produce interesting director profile arrangements within the liquid crystal layers. As a result, enhanced scattering of laser and white light was observed from these liquid crystal cells which bend themselves as electrically controllable optical diffusers and beam shapers.
A novel imaging technique that produces accurate amplitude and phase images of an optical fiber facet using only a phase-only liquid-crystal on silicon (LCOS) spatial light modulator (SLM) and a single-pixel detector is presented. The system can take images in two orthogonal polarizations and so provides a powerful tool for modal characterization of multimode fibers, which is of increasing importance due to their burgeoning use in telecommunications and medical applications. This technique first uses a simulated annealing algorithm to compute a hologram that collects light from a small region of the fiber facet. Next, the fiber facet is automatically brought into focus using adaptive aberration correction on the SLM. Finally, a common-path interferometer is created using the SLM, and the phase of the optical field at each pixel is determined. Finally, high-definition amplitude and phase images of a ring-core refractive index fiber are presented as a proof-of-principle demonstration of the technique.
Liquid crystal over silicon (LCoS) spatial light modulator technology has become dominant in industries such as pico-projection, which require high-quality reflective microdisplays for intensity modulation of light. They are, however, restricted from being used in wider optical applications, such as computer-generated holography, adaptive optics, and optical correlation, due to their phase modulation ability. The main drawback of these devices is that their modulation is based on simple planar or twisted nematic liquid crystals, which are inherently slow mechanisms due to their viscoelastic properties. Their use is also limited due to fact that the phase modulation is dependent on the state of polarization of the illumination. In this paper, we demonstrate that a polymer-stabilized blue-phase liquid crystal can offer both phase modulation and high speed switching in a silicon backplane device which is independent of the input polarization state. The LCoS device shows continuous phase modulation of light with a submillisecond switching time and insensitivity to the input light polarization direction. This type of phase modulation opens up a whole new class of applications for LCoS technology.
This work presents an original approach to create holograms based on the optical scattering of plasmonic nanoparticles. By analogy to the diffraction produced by the scattering of atoms in X-ray crystallography, we show that plasmonic nanoparticles can produce a wave-front reconstruction when they are sampled on a diffractive plane. By applying this method, all of the scattering characteristics of the nanoparticles are transferred to the reconstructed field. Hence, we demonstrate that a narrow-band reconstruction can be achieved for direct white light illumination on an array of plasmonic nanoparticles. Furthermore, multicolor capabilities are shown with minimal cross-talk by multiplexing different plasmonic nanoparticles at subwavelength distances. The holograms were fabricated from a single subwavelength thin film of silver and demonstrate that the total amount of binary information stored in the plane can exceed the limits of diffraction and that this wavelength modulation can be detected optically in the far field.
Developing noninvasive and accurate diagnostics that are easily manufactured, robust, and reusable will provide monitoring of high-risk individuals in any clinical or point-of-care environment. We have developed a clinically relevant optical glucose nanosensor that can be reused at least 400 times without a compromise in accuracy. The use of a single 6 ns laser (? = 532 nm, 200 mJ) pulse rapidly produced off-axis Bragg diffraction gratings consisting of ordered silver nanoparticles embedded within a phenylboronic acid-functionalized hydrogel. This sensor exhibited reversible large wavelength shifts and diffracted the spectrum of narrow-band light over the wavelength range ?peak ? 510-1100 nm. The experimental sensitivity of the sensor permits diagnosis of glucosuria in the urine samples of diabetic patients with an improved performance compared to commercial high-throughput urinalysis devices. The sensor response was achieved within 5 min, reset to baseline in ?10 s. It is anticipated that this sensing platform will have implications for the development of reusable, equipment-free colorimetric point-of-care diagnostic devices for diabetes screening.
This article continues a debate with Gareth Jones about the ethics of anatomy. The article discusses the distinction between direct and indirect reasons to require the deceased's consent prior to anatomical use. Getting this distinction wrong has potentially radical and unwelcome implications for the ethics of many uses of dead bodies. The article then exposes an ambiguity in asking what anatomical uses are ethical: we must distinguish between, on the one hand, who ought to have the power to make decisions and, on the other, how those with power ought to exercise it. It then applies this distinction to the ethics of the public display of bodies for entertainment.
Devitrite is a novel material produced by heat treatment of commercial soda-lime-silica glass. It consists of fans of needle-like crystals which can extend up to several millimeters and have interspacings of up to a few hundred nanometers. To date, only the material properties of devitrite have been reported, and there has been a distinct lack of research on using it for optical applications. In this study, we demonstrate that randomly oriented fans of devitrite crystals can act as highly efficient diffusers for visible light. Devitrite crystals produce phase modulation of light because of their relatively high anisotropy. The nanoscale spacings between these needles enable light to be diffused to large scattering angles. Experimentally measured results suggest that light diffusion patterns with beam widths of up to 120° are produced. Since devitrite is an inexpensive material to produce, it has the potential to be used in a variety of commercial applications.
We prove theoretically and experimentally the concept of polarization holography by producing visible diffraction through radiation emitted by plasmonic nanoantennas. We show a methodology to selectively activate the nanoantenna emission by controlling the orientation of the electric field of a beam. Additionally, we demonstrate that it is possible to superpose two independent transverse nanoantennas in the same plane without producing interference in their radiated field. Hence, we introduce an alternative view to the traditional concept of holography where fringes (or diffractive units) are band-limited to half the wavelength.
In this Letter, we use a reconfigurable hologram to dynamically control the position of incidence of the pump beam onto a liquid-crystal dye-based laser. The results show that there is an increase in the stability of the laser output with time and the average power when compared with the output of the same laser when it is optically excited using a static pump beam. This technique also provides additional functionality, such as wavelength tuning and spatial shaping of the pump beam, both of which are demonstrated here.
Multiwalled carbon nanotubes are highly diffractive structures in the optical regime. Their metallic character and large scattering cross-section allow their usage as diffractive elements in Fraunhofer holograms. This work elaborates some important features of the far field diffraction patterns produced from periodic arrays of nanotubes. A theoretical approach for the interaction of arrays of nanotubes with light is presented and a computer generated hologram is calculated by means of periodical patterns. Based on the results, fabrication of carbon nanotube arrays (in holographic patterns) was performed. Experimentally measured diffraction patterns were in good agreement with the calculations.
Highly dense periodic arrays of multiwalled carbon nanotubes behave like low-density plasma of very heavy charged particles, acting as metamaterials. These arrays with nanoscale lattice constants can be designed to display extended plasmonic band gaps within the optical regime, encompassing the crucial optical windows (850 and 1550 nm) simultaneously. We demonstrate an interesting metamaterial waveguide effect displayed by these nanotube arrays containing line defects. The nanotube arrays with lattice constants of 400 nm and radius of 50 nm were studied. Reflection experiments conducted on the nanoscale structures were in agreement with numerical calculations.
Three-dimensional (3D) optical microscopy based on integral imaging techniques is limited mainly by diffraction effects and the pitch of the microlens array used to sample the specimen. We integrate nanotechnology to the integral imaging technique and demonstrate a nanophotonic 3D microscope, where a nanophotonic lens array is used to finely sample the specimen. The resolution limitation due to diffraction is reduced by capturing images before the diffraction effects predominate and hence overcomes the bottleneck of achieving high resolution in an integral imaging 3D microscope.
Spatial light modulators based around liquid crystal on silicon have found use in a variety of telecommunications applications, including the optimization of multimode fibers, free-space communications, and wavelength selective switching. Ferroelectric liquid crystals are attractive in these areas due to their fast switching times and high phase stability, but the necessity for the liquid crystal to spend equal time in each of its two possible states is an issue of practical concern. Using the highly parallel nature of a graphics processing unit architecture, it is possible to calculate DC balancing schemes of exceptional quality and stability.
In this paper we demonstrate photonic band-edge laser emission from emulsion-based polymer dispersed liquid crystals. The lasing medium consists of dye-doped chiral nematic droplets dispersed within a polymer matrix that spontaneously align as the film dries. Such lasers can be easily formed on single substrates with no alignment layers. The system combines the self-organizing periodic structure of chiral nematic liquid crystals with the simplicity of the emulsion procedure so as to produce a material that retains the emission characteristics of band-edge lasers yet can be readily coated. Sequential and stacked layers demonstrate the possibility of achieving simultaneous multi-wavelength laser output from glass, metallic, and flexible substrates.
A novel transparent liquid-crystal-based microlens array has been fabricated using an array of vertically aligned multi-wall carbon nanofibers (MWCNFs) on a quartz substrate and its optical characteristics investigated. Electron beam lithography was used for the catalyst patterning on a quartz substrate to grow the MWCNF array of electrodes. The structure of the electrode array was determined through simulation to achieve the best optical performance. Both the patterned catalyst and growth parameters were optimized for optimal MWCNF properties. We report an in-depth optical characterization of these reconfigurable hybrid liquid crystal and nanofiber microlens arrays.
Reconfigurable liquid crystal microlenses employing arrays of multiwalled carbon nanotubes (MWNTs) have been designed and fabricated. The cells consist of arrays of 2 microm high MWNTs grown by plasma-enhanced chemical vapor deposition on silicon with a top electrode of indium tin oxide coated glass positioned 20 microm above the silicon and the gap filled with the nematic liquid crystal BLO48. Simulations have found that, while its nematic liquid crystal aligns with MWNTs within a distance of 10nm, this distance is greatly enhanced by the application of an external electric field. Polarized light experiments show that light is focused with focal lengths ranging from approximately 7 microm to 12 microm.
We present electro-optic characteristics of a transparent nanophotonic device fabricated on quartz substrate based on multiwall carbon nanotubes and nematic liquid crystals (LCs). The nanotube electrodes spawn a Gaussian electric field to three dimensionally address the LC molecules. The electro-optic characteristics of the device were investigated to optimize the device performance and it was found that lower driving voltages were suitable for microlens array and phase modulation applications, while higher driving voltages with a holding voltage can be used for display-related applications.
Hepatocellular ballooning is a key finding in nonalcoholic steatohepatitis (NASH). It is conventionally defined by hemotoxylin and eosin (H&E) staining showing enlarged cells with rarefied cytoplasm and recently by changes in the cytoskeleton. Fat droplets are emerging as important organelles in cell metabolism. To address a possible relation between fat droplets and ballooning, we studied fat staining, H&E, and keratin 18 staining in human NASH.
Computer generated holography is an extremely demanding and complex task when it comes to providing realistic reconstructions with full parallax, occlusion, and shadowing. We present an algorithm designed for data-parallel computing on modern graphics processing units to alleviate the computational burden. We apply Gaussian interpolation to create a continuous surface representation from discrete input object points. The algorithm maintains a potential occluder list for each individual hologram plane sample to keep the number of visibility tests to a minimum. We experimented with two approximations that simplify and accelerate occlusion computation. It is observed that letting several neighboring hologram plane samples share visibility information on object points leads to significantly faster computation without causing noticeable artifacts in the reconstructed images. Computing a reduced sample set via nonuniform sampling is also found to be an effective acceleration technique.
How are we supposed to decide the rights and wrongs of banning smoking in bars, restricting adverts for junk food, nagging people into being screened for cancers, or banning the sale of party pills? The aim of this paper is to think through the political ethics of trying to make people healthier through influencing or restricting their choices. This paper covers: (1) Paternalism. What it is, what it assumes. (2) The place of health in well-being, and how this makes paternalism problematic. (3) The mistakes people make in acting in their own interests, and the implications for pro-health paternalism. (4) Autonomy objections to paternalism. The paper (5) finishes on a note of hope, by commending the currently fashionable libertarian paternalism: trying to have ones carrot cake and eat it too. A persistent theme is that thinking sensibly about making people healthier needs subtlety, not broad, ringing declarations.
We present a method of rapidly producing computer-generated holograms that exhibit geometric occlusion in the reconstructed image. Conceptually, a bundle of rays is shot from every hologram sample into the object volume. We use z buffering to find the nearest intersecting object point for every ray and add its complex field contribution to the corresponding hologram sample. Each hologram sample belongs to an independent operation, allowing us to exploit the parallel computing capability of modern programmable graphics processing units (GPUs). Unlike algorithms that use points or planar segments as the basis for constructing the hologram, our algorithms complexity is dependent on fixed system parameters, such as the number of ray-casting operations, and can therefore handle complicated models more efficiently. The finite number of hologram pixels is, in effect, a windowing function, and from analyzing the Wigner distribution function of windowed free-space transfer function we find an upper limit on the cone angle of the ray bundle. Experimentally, we found that an angular sampling distance of 0.01 degrees for a 2.66 degrees cone angle produces acceptable reconstruction quality.
One of the key technologies to evolve in the displays market in recent years is liquid crystal over silicon (LCOS) microdisplays. Traditional LCOS devices and applications such as rear projection televisions, have been based on intensity modulation electro-optical effects, however, recent developments have shown that multi-level phase modulation from these devices is extremely sought after for applications such as holographic projectors, optical correlators and adaptive optics. Here, we propose alternative device geometry based on the flexoelectric-optic effect in a chiral nematic liquid crystal. This device is capable of delivering a multilevel phase shift at response times less than 100 microsec which has been verified by phase shift interferometry using an LCOS test device. The flexoelectric on silicon device, due to its remarkable characteristics, enables the next generation of holographic devices to be realized.
The carbon nanotube-liquid-crystal (CNT-LC) nanophotonic device is a class of device based on the hybrid combination of a sparse array of multiwall carbon nanotube electrodes grown on a silicon surface in a liquid-crystal cell. The multiwall carbon nanotubes act as individual electrode sites that spawn an electric-field profile, dictating the refractive index profile within the liquid crystal and hence creating a series of graded index profiles, which form various optical elements such as a simple microlens array. We present the refractive index and therefore phase modulation capabilities of a CNT-LC nanophotonic device with experimental results as well as computer modeling and potential applications.
Carbon nanotubes are used as the smallest possible scattering element for diffracting light in a highly controlled manner to produce a 2D image. An array of carbon nanotubes is elegantly patterned to produce a high resolution hologram. In response to incident light on the hologram, a high contrast and wide field of view CAMBRIDGE image is produced.
An ultrasmall tunable microlens with a diameter of 1.5 ?m is fabricated using nematic liquid crystals (electrically tunable medium) and vertically aligned carbon nanofibers (CNFs, electrodes). Individual CNFs are grown at the center of circular dielectric regions. This allows the CNFs to produce a more Gaussian electric field profile and hence more uniformity in lens array switching.
This paper presents experimental optimization of number and geometry of nanotube electrodes in a liquid crystal media from wavefront aberrations for realizing nanophotonic devices. The refractive-index gradient profiles from different nanotube geometries--arrays of one, three, four, and five--were studied along with wavefront aberrations using Zernike polynomials. The optimizations help the device to make application in the areas of voltage reconfigurable microlens arrays, high-resolution displays, wavefront sensors, holograms, and phase modulators.
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