Search

Electrically polarizable micro- and nanoparticles and droplets can be trapped using the gradient electric field of electrodes. But the spatial profile of the resultant dielectrophoretic force is fixed once the electrode structure is defined. To change the force profile, entire complex lab-on-a-chip systems must be re-fabricated with modified electrode structures. To overcome this problem, we propose an approach for the dynamic control of the spatial profile of the dielectrophoretic force by interfacing the trap electrodes with a resistor and an inductor to form a resonant resistor–inductor–capacitor (RLC) circuit. Using a dielectrophoretically trapped water droplet suspended in silicone oil, we show that the resonator amplitude, detuning, and linewidth can be continuously varied by changing the supply voltage, supply frequency, and the circuit resistance to obtain the desired trap depth, range, and stiffness. We show that by proper tuning of the resonator, the trap range can be extended without increasing the supply voltage, thus preventing sensitive samples from exposure to high electric fields at the stable trapping position. Such unprecedented dynamic control of dielectrophoretic forces opens avenues for the tunable active manipulation of sensitive biological and biochemical specimen in droplet microfluidic devices used for single-cell and biochemical reaction analysis.

Lab-on-a-chip (LOC) devices capable of manipulating micro/nano-sized samples have spurred advances in biotechnology and chemistry. Designing and analyzing new and more advanced LOCs require accurate modeling and simulation of sample/particle dynamics inside such devices. In this work, we present a generalized computational physics model to simulate particle/sample trajectories under the influence of dielectrophoretic or optical forces inside LOC devices. The model takes into account time varying applied forces, Brownian motion, fluid flow, collision mechanics, and hindered diffusion caused by hydrodynamic interactions. We develop a numerical solver incorporating the aforementioned physics and use it to simulate two example cases: first, an optical trapping experiment, and second, a dielectrophoretic cell sorter device. In both cases, the numerical results are found to be consistent with experimental observations, thus proving the generality of the model. The numerical solver can simulate time evolution of the positions and velocities of an arbitrarily large number of particles simultaneously. This allows us to characterize and optimize a wide range of LOCs. The developed numerical solver is made freely available through a GitHub repository so that researchers can use it to develop and simulate new designs.

Trapping and manipulation of micro and nanoparticles are essential functional elements of lab-on-a-chip and micro total analysis systems with applications ranging from single cell analysis, diagnostics, drug discovery, and chemical synthesis. Reliable optical trapping of subwavelength particles is difficult due to the diffraction limited gradient of the optical intensity. Near-field traps have emerged as excellent systems to overcome this bottleneck. Using a periodic arrangement of C-shaped apertures we demonstrate the on-chip manipulation of single sub-wavelength polystyrene beads. The wavelength and polarization sensitivity of these resonant nanostructures is exploited to expose the trapped bead to a time varying near-field force using wavelength and polarization multiplexing schemes. While optical trapping has the advantage of being contactless, dielectrophoresis provides higher forces due to the flexibility of applying larger voltages and field gradients. The RF/Microwave frequency regime where dielectrophoresis operates allows increased polarizability of certain samples due to contribution from orientational, molecular and atomic polarizations as well as particle’s electrical conductivity. Combining the above advantages of both the techniques we discuss photoinduced dielectrophoretic trapping and manipulation of nanoparticles. Using dielectrophoretic trapping we discuss the simultaneous manipulation of beads and droplets as a route for on chip chemical synthesis.

X-ray imaging by means of a grating-based Talbot-Lau interferometer has become an important tool for a wide variety of application areas such as security, medical and materials analysis. Imaging modalities include attenuation, differential phase contrast, and visibility contrast (or so-called dark field). We have developed a novel modeling approach based on ray tracing with commercially available software (Zemax OpticStudio) that yields image projections for all three modalities. The results compare favorably with experimental findings. Our polychromatic ray-based model accommodates realistic 3-D CAD objects with tailored materials properties and also allows for both surface and bulk scattering. As such, the model can simulate imaging of complicated objects as well as assist in a physical understanding of experimental projection details.

Typical x-ray detectors have a fundamental trade-off between resolution and quantum efficiency (QE). High quantum efficiency x-ray detection requires a thick conversion medium, but decreases the resolution due to limited pixel aspect ratios for both direct and indirect x-ray detection. We present a method for x-ray detection, holographic x-ray detection, which uses photorefractive materials to create a high resolution and high efficiency detector. The x-ray image is recorded in the volume of the photorefractive material, bypassing the aspect ratio issue of typical x-ray detectors. Holographic x-ray detection operates in three stages: recording an x-ray hologram in a photorefractive crystal, reading the hologram with visible light, and then erasing the hologram using ultraviolet light. We have experimentally demonstrated holographic x-ray detection with a resolution of 208 lp/mm (80% QE at 40 keV), an order of magnitude resolution improvement over commercially available x-ray detectors while maintaining > 80% QE.

This Letter covers the design and implementation of a generalizable system for the precise alignment of X-ray gratings. Next-generation high-energy grating-based Differential Phase Contrast (gDPC) X-ray imaging systems require precise alignment of the X-ray gratings as low as 1 mrad in rotation and 0.5 mm in translation. In this work, we designed holographic fiducial marks, consisting of four reflective Fresnel zone plates, each placed in a separate quadrant of the mark. When illuminated with a collimated laser beam, each mark creates a predefined pattern of four points, which changes quantitatively for any misalignment in each of the three translational and three rotational degrees of freedom. We fabricated the designed fiducial marks using photolithography and etching processes. The experimental system is implemented using a HeNe laser and an optical imaging system, which includes a beam expander, a plate beam splitter, and a CMOS camera, suitable for aligning practical gratings in gDPC X-ray imaging systems. Our experimental results demonstrate the rotational precision capabilities of the reported alignment system down to 0.42 mrad around the optical axis and 0.03 mrad around the axes perpendicular to the optical axis. The translational precision of 83.64 μ m along the optical axis and 1.22 μ m along the axes perpendicular to the optical axis is also demonstrated.This Letter covers the design and implementation of a generalizable system for the precise alignment of X-ray gratings. Next-generation high-energy grating-based Differential Phase Contrast (gDPC) X-ray imaging systems require precise alignment of the X-ray gratings as low as 1 mrad in rotation and 0.5 mm in translation. In this work, we designed holographic fiducial marks, consisting of four reflective Fresnel zone plates, each placed in a separate quadrant of the mark. When illuminated with a collimated laser beam, each mark creates a predefined pattern of four points, which changes quantitatively for any misalignment in each of the three translational and three rotational degrees of freedom. We fabricated the designed fiducial marks using photolithography and etching processes. The experimental system is implemented using a HeNe laser and an optical imaging system, which includes a beam expander, a plate beam splitter, and a CMOS camera, suitable for aligning practical gratings in gDPC X-ray ...

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological and physical sciences over the past few decades. The progress made in this field invites further study of even smaller systems and at a larger scale, with tools that could be distributed more easily and made more widely available. Unfortunately, the fundamental laws of diffraction limit the minimum size of the focal spot of a laser beam, which makes particles smaller than a half-wavelength in diameter hard to trap and generally prevents an operator from discriminating between particles which are closer together than one half-wavelength. This precludes the optical manipulation of many closely-spaced nanoparticles and limits the resolution of optical-mechanical systems. Furthermore, manipulation using focused beams requires beam-forming or steering optics, which can be very bulky and expensive. To address these limitations in the system scalability of conventional optical trapping our lab has devised an alternative technique which utilizes near-field optics to move particles across a chip. Instead of focusing laser beams in the far-field, the optical near field of plasmonic resonators produces the necessary local optical intensity enhancement to overcome the restrictions of diffraction and manipulate particles at higher resolution. Closely-spaced resonators produce strong optical traps which can be addressed to mediate the hand-off of particles from one to the next in a conveyor-belt-like fashion. Here, we describe how to design and produce a conveyor belt using a gold surface patterned with plasmonic C-shaped resonators and how to operate it with polarized laser light to achieve super-resolution nanoparticle manipulation and transport. The nano-optical conveyor belt chip can be produced using lithography techniques and easily packaged and distributed.

In the implementation of most resolution enhancement techniques for optical lithography, full 3D simulation of effects such as topography imbalance in phase masks can be successfully modeled. However, these simulators do not appear to capture the full range of effects that impact the transmission of light through conducting (or partially conducting) films. In particular, certain resonant sub-wavelength geometric shapes, such as the C-aperture in a metallic conducting film, have been shown to have transmission values that are factors of 10^3-10^5 higher than simple geometric projections would predict. Using a new finite difference time domain solver that explicitly includes internal currents and analyzes the Poynting vector behavior of the EM fields, we can better understand the complex behavior of these resonant apertures. The currents are highly dependent on the polarization of the incoming EM excitation, as is the extraordinary transmission. We have also applied this in a limited fashion to geometries such as those expected to appear on photomasks in the 45nm node, when not extraordinary transmission but extraordinary opacity is predicted. These effects are also highly polarization dependent.

In this paper, we discuss fundamental issues underlying holographic data storage: grating formation, recording and readout of thick and thin holograms, multiplexing techniques, signal-to-noise ratio considerations, and readout techniques suitable for conventional, phase conjugate, and associative search data retrieval. Next, we consider holographic materials characteristics for digital data storage, followed by a discussion on photorefractive media, fixing techniques, and noise in photovoltaic and other media with a local response. Subsequently, we discuss photopolymer materials, followed by a discussion on system tradeoffs and a section on signal processing and en/decoding techniques, succeeded by a discussion on electronic implementations for control, signal encoding, and recovery. We proceed further by presenting significant demonstrations of digital holographic systems. We close by discussing the outlook for future holographic data storage systems and potential applications for which holographic data storage systems would be particularly suited.

variable-area resonator with the hot and ambient heat-exchangers (HHX, AHX) and the regenerator (REG) located at one end enclosed in a coaxial annular tube. Heat-transfer in the heat-exchangers is modeled via source terms which drive the local gas temperature towards the imposed temperature. Turning on the sources terms generates a finite-amplitude perturbation that is amplified until a limit cycle is reached. Simulations have been carried out for HHX temperatures in the range 460K ‐ 500K and an AHX temperature of 300K. Acoustic nonlinearities are detectable from the early stages of operation in the form of streaming. Complex system-wide streaming flow patterns rapidly develop and control the operation of the device in the nonlinear stages. A solution decomposition based on sharp-spectral filtering is adopted to extract the wave-induced Reynolds stresses and energy fluxes at the limit cycle. The key processes involved are traveling-wave streaming in the feedback inertance, periodic vortex roll-up around the edges of the annular tube and near-wall acoustic shear-stresses in the variable-area sections of the resonator. The first drives the mean advection of hot fluid away from the HX/REG (Gedeon streaming), causing heat leakage. The latter is contained by introducing an AHX2 (creating a thermal buffer tube, or TBT) resulting in the saturation of acoustic energy growth in the system. A simplified numerical model is adopted todirectly simulate acoustic streaming as an axially symmetric incompressible flow driven by the acoustic wave-induced stresses. Key features such as the intensity of Gedeon streaming are correctly predicted. The evaluation of the nonlinear energy fluxes reveals that the efficiency of the device deteriorates with the drive ratio and that the acoustic power in the TBT is balanced primarily by the mean advection and thermoacoustic heat transport. Thermoacoustic Stirling heat engines (TASHE) are devices that can convert heat into acoustic power with very high efficiencies. This potential is due to the absence of moving parts and relative simplicity of the components. This results in low manufacturing and maintenance costs making these systems an attractive alternative for clean and effective energy generation. The core energy conversion process occurs in the regenerator ‐ a porous metallic block, placed between a hot and a cold heat-exchanger, sustaining a mean temperature gradient in the axial direction. Acoustic waves propagating through it (with the right phase) can be amplified via a thermodynamic process resembling a Stirling cycle. Most designs explored up to the mid 1980’s were based on acoustic standing waves and had efficiencies typically less than 5%. A significant breakthrough was made by Ceperley (1979) 5 who showed that traveling-waves can extract acoustic energy more efficiently, leading to the concept of traveling-wave TASHE, currently used today 2 . In this configuration the generated acoustic power is in part resupplied to the regenerator via some form of feedback loop and in part directed towards a resonator for energy extraction. This design is the focus of the present study. Improving the technology behind TASHEs is still of particular interest in the last decade with research efforts being made worldwide (see Garrett (2004) 6 for a review). A recent breakthrough, for example, has been made by Tijiani and co-workers 16 who designed a traveling-wave TASHE achieving a remarkable overall efficiency equal to 49% of the Carnot limit. Current design choices for TASHEs, however, are not informed by an accurate description of the underlying fluid mechanics. In particular state-of-the-art prediction capabilities and technological design can significantly benefit from a direct modeling of the nonlinear, system-wide, three-dimensional processes limiting the efficiencies of such devices.

We develop a plasmonic trapping and conveyor system based on resonant C-shaped engravings driven by polarization rotation and wavelength switching.

New multicomponent InF 3 -based bulk glasses have been investigated. The molar composition of the base glass is 28% InF 3 –20% ZnF 2 –16.5% BaF 2 –12% GaF 3 –9% PbF 2 –6% NaCl–5% SrF 2 –3% CaF 2 –0.5% PrF 3 . A number of variations of the base glass were prepared and their refractive indices and densities measured. Resistance to crystallization allowed the preparation of large pieces of the base glass. The infrared and Raman spectra show that the base composition has a longer wavelength multiphonon edge at 10 μm and a phonon energy of 509 cm −1 , in comparison with 8 μm and 574 cm −1 for ZBLAN, which reveals that the present glasses have a lower phonon energy and a greater transparency in the infrared than ZBLAN. Reduction of PbF 2 concentration in the base composition provided glasses with smaller refractive indices than the base glass.

A transient, two-dimensional drift-diffusion model is developed for optically addressed spatial light modulators made with quantum-well materials. The transport of free and well-confined carriers is considered along with nonlinear transport effects such as velocity saturation, field-dependent carrier escape from quantum wells, and resonant absorption. In addition to full numerical solutions to the transport equations, analytical and simplified numerical solutions are developed to describe basic screening behavior and to give estimates of speed and resolution performance. In particular, a self-consistent small signal model is developed to justify the surface-charge picture often used to describe device operation. This model is also used to simulate grating formation and decay. It is found that the maximum screening rate and peak grating amplitude are achieved using vertical drift lengths much longer than the device length. A detailed analysis of resolution performance is also given in which the effects of ...

We have carried out the first three-dimensional numerical simulation of a thermoacoustic Stirling heatengine (TASHE). The goal is to lay the groundwork for full-scale, time-resolved Navier-Stokes simulations that allow for the direct description of the non-linear processes limiting the overall efficiency of such devices. The TASHE model adopted for the present study is a double-Helmholtz resonator with the engine module at one end. The latter is composed of an infinitely thin annular tube holding the heat-exchanger/regenerator (HX/REG) unit – the only component not directly resolved. All walls are modeled as adiabatic, no-slip boundaries with a local wall-normal resolution resolving the boundary layer thickness. An imposed temperature difference across the regenerator of ∆T = 200K is sufficient to initiate the thermoacoustic instability leading to the generation of acoustic energy in the system. After the application of the heat source, the acoustic fluctuations in the engine rapidly settle towards an exponentially amplified pure tone at 59.8 Hz. By tracking a fluid parcel in the regenerator it is shown how the thermoacoustic instability intensifies exclusively plane waves traveling in the direction of the imposed temperature gradient. The Lagrangian thermodynamic history of the fluid parcel resembles a Stirling heat-engine cycle, unveiling the conversion mechanisms of heat into mechanical work central to any TASHE. A well-defined acoustic network of traveling waves looping around the HX/REG unit is established and analyzed with the aid of the time-resolved data. A simple lumped-parameter model is used to investigate the linear stability properties of the initial acoustic perturbation revealing, in particular, that the acoustic energy growth is maximized at the lowest resonant frequencies of the system. Non-linear effects are detectable from the very beginning and become dynamically important only after the first two seconds of operation. It is shown that intense acoustic fluctuations in the feedback loop component drive complex system-wide streaming flow patterns responsible, in particular, for the mean advection of hot fluid away from the HX/REG (thermal leakage) in the direction of the imposed temperature gradient and around the annular tube. This unwanted effect is contained by the introduction of a second ambient heat-exchanger, commonly found in the design of real TASHEs, allowing for the establishment of a dynamical thermal equilibrium in the system. A limit cycle in fully non-linear conditions is finally obtained for an acoustic amplitude of 178 dB.

A three-color, solid-state, volumetric display based on two-step, two-frequency upconversion in rare earth-doped heavy metal fluoride glass is described. The device uses infrared laser beams that intersect inside a transparent volume of active optical material to address red, green, and blue voxels by sequential two-step resonant absorption. Three-dimensional wire-frame images, surface areas, and solids are drawn by scanning the point of intersection of the lasers around inside of the material. The prototype device is driven with laser diodes, uses conventional focusing optics and mechanical scanners, and is bright enough to be seen in ambient room lighting conditions. QuickTime movie of the three-dimensional display.

Fluoride-based glasses are potential host materials for fiber lasers, amplifiers and solid state three-dimensional (3D) displays. Fluorozirconate (ZrF 4 -BaF 2 -LaF 3 -AlF 3 -NaF), fluoride phosphate (AlF 3 -SrF 2 -CaF 2 - MgF 2 -P 2 O 5) and fluoroin­ date (InF 3 -ZnF 2 -BaF 2 - GaF 3 -PbF 2 -REF 3 -S rF 2 -NaF-CaF 2) glasses were investigated in terms of their absorption and crystallization properties to compare their potential to be used as optical devices. Phonon sideband (PSB) measurements were employed to determine the local vibration behavior of the rare earth (RE) ion sites. A modified Judd-Ofelt treatment allows the description of transition probabilities between Pr 3+ energy levels, including error estimates for the fitted parameters Ω,. In the investigated fluoroindate glasses melted in vitreous carbon crucibles using a reactive atmosphere, processing fanlike crystals composed of Sr and RE fluorides caused manufacturing problems.

A zoom objective lens for a multi-layer optical rec ording has been designed. A newly proposed optical power arrangement enables varying back focal length while focal length invariant by a linear movement of sin gle zooming component. The zoom lens is implemented into multi- layer and multi-bit holographic recording system em ploying 405 nm blue lasers. 1. INTRODUCTION Recently, multilayer micro holographic optical disc systems have been investigated to attain high capa city and high data transfer rate [1,2]. In the multilayer recordi ng, micro-holograms are recorded throughout the vol ume of recording material by changing the recording depth. For such multilayer recording systems, objective l ens accesses to multiple recording layers. The design of objecti ve lens needs to satisfy couple of constraints. Fir st, working distance, air spacing between objective lens and re cording disc, is unchanged while changing the recor ding layer. Numerical aperture (NA) must be an invariant for th e range of recording depth to equalize transverse s ize and modulation of index of refraction of the micro holo grams. Ideally, the number of moving elements shoul d be a minimum. Also, a linear relation between zooming of the element and recording depth is preferable. Typical way to design such optics is depicted in Fi g. 1. First, an intermediate image, a virtual or re al one, is formed by a movable zooming optics. Then, the inter mediate image is relayed to a final focal point ins ide a recording medium by a secondary optics consisting o f high NA objective elements. Moving the first opti cs along optical axis alters conjugate ratio between the int ermediate image and final image, therefore, the fin al image position also moves, which ends up with selection of writing depth. The approach is rather a simple one however we immediately notice several drawbacks of the approac h if we recall the design requirement for optical d ata storage applications. First, the system focal length varies as the writing depth changes. Consequently, NA va ries as selection of recording layers. As a result, a varia ble aperture and tuning of laser power is needed to equalize the transverse size and modulation of index of refracti on of the micro holograms. Second, the location of the final image nonlinearly moves with respect to the movement of t he zooming element. This would impose an additional requirement on actuators for selection of writing d epth. To overcome such issues, we propose an optica l power arrangement having constant focal length as well as linear movement of zooming element. Note that, eve n being able to implement such additional features, the pro posed optical power arrangement requires only one m oving component. Thus, our approach inherits the simple i mplementation of the conventional approach. Importa ntly, such a minimum optical power arrangement is possible onl y if specific combination of power is adopted for t he zooming optical component. In this paper, first analysis of the proposed power arrangement is described. Based on the power arrangement, we discuss design of all off-the-shelf write/read optics having a constant numerical aper ture (NA) of 0.4 for a range of writing depth of 0.2 mm. Design and implementation of multi-layer and multi-bit mic ro holographic recording system employing blue lasers will be addressed.

Plasmonic Near-Field Transducers (NFTs) find use in Energy-Assisted Magnetic Recording (EAMR) schemes, where a high-anisotropy recording medium is locally heated to the Curie temperature, allowing conventional magnetic recording heads to overcome the high coercivity of the medium. However, coupling efficiency is low, and the conditions for excitation and resonance are poorly understood. In this work, we explore the behavior of a canonical EAMR setup including rectangular dielectric waveguide, elliptic cylinder gold NFT, and conductive planar recording medium. We systematically examine the effects of polarization and angle; spacing between NFT, waveguide, and recording medium; and variations in NFT size and incident wavelength.

A novel optical system architecture employing local holographic recording with a pico-second pulsed fiber laser and a small page size SLM has the potential towards realizing compact, high capacity and high data transfer rate optical storage.

A zoom objective lens has been designed and implemented based on a newly proposed power arrangement having a constant focal length and a linear movement of single zooming component for selection of recording layers.

We consider holographic optical data storage systems implemented with photorefractive media. Our viewpoint emphasizes the close interaction between materials and device issues. First we discuss our current understanding of photorefractive physics as it pertains to the holographic data storage problem. Then we consider architecture issues, including angular, phase-encoded, and wavelength-multiplexing techniques, and several approaches to increasing the signal-to-noise ratio of the recordings. Finally, we discuss materials issues related to crystal growth and how crystal quality impacts the performance of data storage systems. Both bulk and fibre crystal growth techniques are reviewed.

We discuss wavelength selection for true-color holography by investigating the sampling nature of the holographic process. During holographic recording the chosen wavelengths point sample the surfacereflectance functions of the objects in a scene. To understand the effect of this sampling on color perception, we study the tristimulus values of points in the reconstructed hologram. The sampling results in the holographic process being mathematically equivalent to integral approximations for the tristimulus integrals. By selecting efficient approximations, we infer wavelengths to use in color holography. Our analysis not only suggests wavelengths for the usual three-color holography but also suggests the use of four or more wavelengths to improve color reproduction in holography.

We present a practical real-time optical pre-processor intended to enhance small defects in a smooth surface. The heart of the system is a photorefractive BSO phase conjugate mirror which reflects only the low intensity features of the object’s optical Fourier Transform. By adjusting the beam ratios so that only the low intensity, high spatial frequency image components are phase conjugated and inverse transformed, an image consisting of just the defects is produced. To our knowledge, this is the first use of this technique on opaque and non-periodic objects. We present experimental data showing enhancement of defects smaller than 0.2 μm.

The geometrical design characteristics of multiple-image holograms are evaluated. A figure of merit expressing these characteristics as a function of the hologram diameter and the distance between the hologram and the image plane is developed. This value is then used to compare two designs which are capable of forming several hundred interconnections. The results indicate that these connections can be formed between points on the substrate separated by 2-3 cm provided that the holograms are separated from the substrate plane by 0.5-1 cm. Each hologram design is experimentally demonstrated in bleached photographic emulsions.

We describe a novel method for the recall of linear combinations of stored data pages in a volume holographic memory based on phase-code multiplexing. Recall is demonstrated by use of a compound phase-and-amplitude spatial light modulator in the reference beam path.

We examine the consequences of permanent phase distortions on the replay of transmission volume holograms with a phase-conjugated reference wave. In the absence of Bragg degeneracies and significant Bragg mismatch, for negligible dispersion in the spatial frequency response and for negligible variation in obliquity, phase-conjugated reference waves compensate for the effects of phase distortions and permit cross-talk-free multiplexing by using orthogonal reference waves. Spatial frequency dispersion, however, is a source of image distortion and cross talk.

We present a defect-enhancement system capable of detecting submicrometer defects on opaque periodic structures using real-time holography in photorefractive crystals. We detect 0.5-microm defects with ~90% success rate and 0.3-microm defects with85% success rate while inspecting an area greater than 1 mm(2) in real time. To our knowledge, these defects have an area 100 times smaller than those previously detected with any real-time holographic technique.

Optical interconnects for highly parallel computer architecture require high density optical switch arrays with dimensions of 100 × 100 or larger. Previously reported integrated switch array designs have been limited to 8 × 8 waveguides.1 While achieving high switching speeds and relatively low insertion losses, these switches are limited by long interaction lengths which lead to array dimensions of as long as 60 mm. Our switch design consists of two sets of parallel waveguides which intersect at right angles. The intersections are doped with a material to locally sensitize the region to the photorefractive effect. We have fabricated arrays based on standard Ti:LiNbO3 technology, using iron as a photorefractive sensitizer. Interfering beams are used to write an index grating at the waveguide intersections. This grating can then be used to diffract a portion of a data beam into the crossing waveguide. The diffraction efficiency depends on the length of the interaction region. Thus, insertion loss is traded off against switch density. We have constructed arrays of 15 × 15 up to 50 × 50 waveguides in an active area of only 5 mm square.

We describe what are to our knowledge the first photorefractive holographic recordings in a fiber. A plane-wave reference and an image-carrying object beam are incident upon the fiber in a reflection geometry. We report results on the angular sensitivity of the recordings, the image quality, and readout efficiency as a function of the reference-wave input angle when the object wave propagates along the bore of the fiber. These experiments are carried out for two relatively short, 4- and 8-mm, multimode 1-mm-diameter fibers. The results suggest that an array of fibers might favorably replace bulk materials for certain computer and signal-processing applications.

We report high-intensity nano-aperture Vertical-Cavity Surface- Emitting Lasers (VCSELs) with sub-100nm near-field spots using ridge apertures. Power transmission efficiency through different ridge apertures, including bowtie, C, H and I-shaped apertures on VCSELs were studied. Significantly higher transmission efficiencies were obtained from the ridge apertures than those from conventional square apertures. Mechanisms for high transmission through the ridge apertures are explained through simulation and waveguide theory. A new quadruple-ridge aperture is proposed and designed via simulation. With the high-intensity and small spot size, VCSELs using these ridge nano-apertures are very promising means to realize applications such as ultrahigh-density near-field optical data storage and ultrahigh-resolution near-field imaging etc.

A novel joint application of holography and photochromic materials to the experimental measurement of velocity gradients in a fluid flow is presented. A short study of some photochromic materials of interest is presented from the point of view of their applicability to experimental fluid mechanics. This includes a spatiotemporal model for the photoinduced conversion reaction which allows for optimization of the experimental conditions. The forced Rayleigh scattering method for measuring velocity gradients using photochromic materials is then briefly described and applied to the measurement of the velocity gradient in a boundary layer. Spatial resolution of 100 μm and gradient resolution of 3 sec−1 are obtained using these techniques.

We have conducted measurements of the linear electro‐optic coefficient (r41) and electrogyratory coefficient (η41) in Bi12TiO20 at 633 nm. A precise knowledge of these coefficients is important for evaluating the holographic recording properties of this photorefractive material. We have employed both transverse and longitudinal electric field geometries. For each geometry, we present the results of dc as well as ac techniques. Based on these results we find r41=5.75±0.10 pm/V and ‖η41‖≤0.30±0.05 pm/V. We critically examine our measurements and discuss their relative accuracy. Our findings are compared to those previously reported by other investigators.

Hologram recording in photorefractive media is classically performed in the blue-green spectral range and suffers from optical erasure under continuous readout, unless a thermal fixing technique is applied. Gated optical holographic recording allows us to obtain high-diffraction efficiencies in the near InfraRed (IR) jointly with long-term storage. In particular, the roles of stoichiometry and dopant reduction state in LiNbO3 in the optimization of sensitivity is analyzed, in order to perform digital information storage in such materials via the two-photon technique.

We report a high-intensity nano-aperture vertical-cavity surface-emitting laser (VCSEL) utilizing a bowtie-shaped aperture. A maximum power of 188 microW is achieved from a 180 nm bowtie aperture at a wavelength of 970 nm. The near-field full width at half-maximum intensity spot size 20 nm away from the bowtie aperture is 64 nm x 66 nm from simulation, and the peak near-field intensity is estimated to be as high as 47 mW/microm(2). This intensity is high enough to realize near-field optical recording, and the small spot size corresponds to storage densities up to 150 Gbits/in(2). The bowtie-aperture VCSEL also enables other applications, such as compact high-intensity probes for ultrahigh-resolution near-field imaging and single molecule fluorescence and spectroscopy.

We demonstrated a record-high-intensity bowtie nano-aperture vertical-cavity surface-emitting laser (VCSEL) with near-field spot size of 65 nm. The bowtie aperture VCSEL is very promising to realize ultradense near-field optical data storage.

We demonstrated a record-high-intensity bowtie nano-aperture vertical-cavity surfaceemitting laser (VCSEL) with near-field spot size of 65 nm. The bowtie aperture VCSEL is very promising to realize near-field applications such as ultradense optical data storage.

The Fourier transform lens consisting of an aspherical element is analyzed in terms of the supportable number of pixels by formalizing an en-squared-power ratio as a function of the Nyquist aperture ratio and aberrations.

An aspherical-meniscus and air-spaced-spherics are identified as minimum aberration configurations for page-based holographic recordings. Air-spaced-apsherics attain imaging NA’s of 0.7 for holographic recording only, and of 0.45 for a combination of holographic and surface recording.

A unique C-aperture metallic waveguide with a 90° bend and tapered region having applications to HAMR is presented. The structure has a small footprint and yet shows high throughput and a small spot size.

High NA (0.7 ~ 0.8) objective lens in which both object and pupil aberrations are compensated for are designed in two-element configurations, and are usable for a combination of holographic and surface recordings.

For 45nm lithography and beyond, polarization and other electromagnetic effects such as surface plasmons may begin to affect the transmission through a photomask. Such phenomena are highly polarization sensitive, and may amplify the effects of line-edge roughness (LER) and variations in mask composition. A reduction in the mask material conductivity can mitigate the impact of these effects, but more accurate simulation is required to predict these effects well.

Tilt tolerance of media is compared for bit-based and page-based holographic storage systems having an equal diffraction efficiency per bit detector, dynamic range of the medium, and surface recording density. We have formalized the diffraction efficiency degradation caused by aberrations of a reconstructing reference beam induced by tilt of the medium, using a coupled wave theory in the Fourier domain. The bit-based holographic storage system has a larger media tilt tolerance compared with a page-based system with relatively large page size.

We designed and demonstrated a unique C-shaped nanoaperture (C-aperture) Vertical-Cavity Surface-Emitting Laser with an estimated maximum net power of 113 μW coming from a 70nm C-aperture. Simulation shows the near-field FWHM spot size at 30nm away from the C-aperture is 94nm and 108nm in X and Y direction. We estimate the peak near-field intensity from the C-aperture VCSEL to be as high as 13.7mW/μm 2 . This high intensity and small spot size is promising to realize high-density near-field optical data storage.

This paper discusses recent advances in the understanding of holographic data storage in photorefractive SBN. The implications of electrical fixing procedures on the storage architecture will be treated by using a systems approach.

We demonstrate 12-layer storage of 5.84 Gbits per square inch via micro-holograms written and read at 0.532 nm from a 125 micron photopolymer disk continuously rotating at 3600 RPM. Scaling predicts a potential TByte capacity.

We propose and demonstrate multi-layer storage in holographic photopolymer by locally altering the reflectivity of a factory-written reflection hologram at the focus of a single objective lens. Linear, two-photon and thermal writing mechanisms are demonstrated.

A new holographic data storage material is currently being developed at General Electric. This material is based on a thermoplastic host doped with dyes with narrowband absorption resonances. The dye is photosensitive and irreversibly bleaches under exposure to light. The reduction in concentration of the dye in the host after exposure induces refractive index variations at wavelengths away from the dye absorption peak according to the well-known Kramers-Kronig relationship. The approach proposed here requires different recording and readout wavelengths to prevent data erasure during readout. Samples were produced using different dyes and various concentrations in a polycarbonate host. The extensive experience developed in th e past with polycarbonate for optical media promises to make the proposed material very inexpensive. These samples were characterized using holographic techniques as well as using spectroscopic transmission and ellipsometry. The results of the characterizations indicate that this material approach can offer very large dynamic range, but have thus far shown very low sensitivity. Further work is required to demonstrate materials having both sufficient dynamic range and sensitivity for holographic storage applications. We believe that if this condition can be satisfied, this new material approach will be an excellent candidate for high-density holographic media for content distribution. Keywords: holographic data storage, narrow-band material, dye-doped polycarbonate

We present theoretical calculations and experimental measurements of silicon micromachining rates, efficiency of laser pulse utilization, and morphology changes under UV nanosecond pulses with intensities ranging from 0.5 GW/cm2 to 150 GW/cm2. Three distinct irradiance regimes are identified based on laser intensity. At low intensity, proper gas dynamics and ablation vapor plume kinetics are taken into account in our theoretical modeling. At medium high intensity, we incorporate the proper plasma dynamics, and predict the effects of the laser generated vapor plasma and the electron hole plasma on the laser-matter interaction. At even higher intensity, we attribute the observed increased ablation rate to energy re-radiation from the laser heated hot plasma, the strong shock wave, and the accompanied strong shock wave heating effects. Experimentally measured data in these regimes agree well with our calculations, without changing parameters in the calculations used for the three regimes. Our results can be applied toward quantitatively characterize the behavior of ablation results under different laser parameters to achieve optimal results for micromachining of slots and vias on silicon wafers.

In this article, we propose and demonstrate a novel holographic optical disk storage system based on polarization-collinear holography. This method will enable us to construct a small volumetric optical disk storage system with CD and DVD upper compatibility.