bluuebunny/crossref_metadata_2025 huggingface dataset:
Exact determination of complex refractive indices of multiple quantum-well slab waveguides
Authors: Molter L. A. , Dutta M.
Published: February 2023

Optical waveguides and waveguide devices formed by incorporating multiple-quantum-well (MQW) layers into the guiding or adjacent nonguiding regions are of particular interest for switching and other signal-processing applications because of their nonlinear properties. In this work, slab waveguides and waveguide couplers are analyzed exactly to determine the propagation constants, indices of refraction, and shapes of the modes supported by structures formed by an arbitrary number of MQW layers of differing composition. A complex index of refraction represents the dielectric and absorptive properties of each layer composing the MQW region; these values are then used in computer simulations that form matrix representations of the field variables to match the boundary conditions between each pair of layers. Thus, the complex propagation constants of each mode of a guiding structure formed by any number of layers are computed without explicitly writing and matching expressions for the fields at each boundary. Values obtained for propagation constants and effective indices of the modes of isolated waveguides and waveguide couplers will be compared with those obtained by means of a variety of approximations that substitute weighted averages of the indicesof the individual layers for the index of the MQW region.
Refractive-index change of LiNbO3 by H+–Li+ exchange
Authors: Ito Kenchi , Hada Masahiko , Kawamoto Kazumi
Published: February 2023

The H+–Li+ exchange technique in LiNbO3 is useful for the preparation of optical waveguides because it creates a large increase in the extraordinary refractive index. We have considered the reason for this increase both experimentally and theoretically. The exchange rate x of H+ and Li+ is about 0.7, as measured by nuclear-reaction analysis with a high-energy 15N ion beam. Electron diffraction shows that the space group does not change, and x-ray diffraction shows that the lattice constant hardly changes. Measurements of the infrared-absorption spectrum suggest that H+ is located in the plane where oxygen atoms are packed most closely. Two optimized positions of H+ in the plane have been decided by calculating the total energy of clusters that include hydrogen and oxygen atoms by the coupled Hartree–Fock method. The calculated first-order polarizability of clusters that include hydrogen and oxygen atoms is much larger than that of clusters including lithium and oxygen atoms. As a result of the decomposition contributions of molecule orbitals, this seems to arise from the s orbital, which is the lowest unoccupied orbital in all of the clusters. It suggests that the small atomic radius of H+ is the reason for the refractive-index change.
Fundamental physical and technological constraints on optical information processing and computing
Authors: Kyriakakis C. , Asthana P. , Karim Z. , Nordin G. , Rilum J. , Tanguay A. R.
Published: February 2023

The design constraints and resultant performance boundaries applicable to the developemnt of optical information processing and computing systems derive directly from certain fundamental limitations imposed by physical laws, as well as from specific algorithmic (and associated architectural) choices implemented within a given device or component technology base.1 In general, a given processing or computation function can be partitioned into the cost (in energy or otherwise) of representation, the cost of computation, and the cost of detection and utilization of the desired computational result. For operation at the quantum limits, for example, analog representations are favored for architectures and algorithms that implement a high degree of computational complexity (irreducible number of equivalent binary operations) per unit detected output resolution element, whereas binary representations favor operations with a somewhat lower degree of complexity. The relevant performance tradeoffs among the various possible computational paradigms, however, are often strongly influenced by the current and projected technological status of the requisite photonic components, including both coherent and dynamically reconfigurable volume holographic optical interconnection elements and both one- and two-dimensional array detectors. In this presentation, we examine a broad range of interrelated—and at times conflicting—device requirements from three complementary perspectives: the fundamental physical limitations that affect the performance of any photonic component function; the current status of component development with respect to such fundamental limits; and the technological considerations that impact present and future device design and development. The implications of these considerations on the evolution of practically implementable algorithms and architectures that exhibit significant computational advantages will be addressed.
Static and dynamic global stereo acuity: effects of age
Authors: Chao Gung-mei , Hanna Florence , Linberg John V. , Odom J. Vernon
Published: February 2023

Several investigations have observed that local and global stereo acuity decrease as age increases. However, in these studies the monocular visual acuity of the older population was impaired, and this might explain the observed stereo deficits. In this study we asked, "Does the stereo acuity decrease as age increases for people who have normal monocular visual acuity?" We measured the global static and dynamic stereo thresholds in 58 subjects aged 20–79 years. All subjects were emmetropic and/or had corrected visual acuity of 20/20 or better. None had a history of strabismus, glaucoma, or diabetes mellitus. The stimuli were static or disparity-reversing horizontal gratings-in-depth generated by dynamic anaglyphic random-element stereograms. The visual field was 5.4° × 7.6° and the cyclopean spatial-frequency was 0.63 cycles/deg at a viewing distance of 2 m. The mean luminance through chromatic filters (W ratten 29 and 65) was 3.7 cd/m2. A 0.5 diopter lens was placed in front of chromatic filters to correct for the viewing distance. Disparity was reversed at 1.9 Hz in the dynamic-stimulus condition. A method of adjustments was used to determine the stereo threshold. Five ascending and five descending thresholds were obtained for each subject. The average of 10 thresholds was defined as the subject's stereo threshold. We found that static stereo threshold did not increase with age but that dynamic stereo threshold did significantly increase with age (r = 0.344, df = 56, p < 0.01). We interpret these results as indicating that there is no unique global stereo acuity deficit in the aging population and that the significant decrease in dynamic stereo acuity occurs because of the attenuation of temporal processing in the elderly.
Diffraction properties of photorefractive gratings with polarization asymmetry between the write-read beams
Authors: Saxena R. , Yeh P.
Published: February 2023

A dynamic hologram can always be updated to allow for any movement of the optical components (e.g., alignment drift over time). This makes the dynamic hologram useful in optical signal processing. We have studied the diffraction efficiency η of dynamic photorefractive gratings as a function of the polarization asymmetry between simultaneous write-read beams of comparable intensity. Photorefractive two-beam coupling effects are present both between the writing-beam pair and between the read beam and its diffracted beam. The nonlinear and nonreciprocal nature of diffraction efficiency1,2 as a function of read-beam intensity is examined for various ratios of ΓW/ΓR, where ΓW (ΓR) is the two-beam coupling constant during writing (reading). The diffraction efficienty η is also expected to show oscillatory behavior as a function of beam ratio during writing,3 when the write beams are ordinary-polarized and the read beam is extraordinary-polarized.
Reflectance-difference spectroscopy: application to semiconductor crystal growth by OMCVD and MBE
Authors: Aspnes D. E.
Published: February 2023

New insights into the physics and chemistry of semiconductor surfaces are being provided by reflectance-difference spectroscopy (RDS), a noninvasive normal-incidence optical probe that takes advantage of the intrinsic symmetry of cubic materials to enhance the ordinarily weak surface contribution to the overall optical signal. A recently developed double-modulation version has yielded the first direct optical measurements of surface dielectric responses under steady-state conditions, thereby realizing a 20-year goal of surface spectroscopy and opening up new possibilities in the study of interfaces and of surfaces under either UHV or non-UHV conditions.
Wiener-filtering approach to phase retrieval from modulus data
Authors: Frieden B. Roy , Oh C.
Published: February 2023

Consider the problem of estimating the phase of a complex image spectrum from knowledge of its modulus. Current algorithms are computation-intensive, requiring either a large execution time, owing to iterative convergence to a solution, or a large central memory requirement, owing to the necessity of storing four-dimensional tensors.
Diffraction of atoms from a two-frequency standing wave
Authors: Martin Peter J. , Hall John L.
Published: February 2023

We investigate the diffraction of a three-level atom from a "walking" light wave composed of counterpropagating traveling waves of different frequencies. The coupling of the two nondegenerate internal ground states by means of an off-resonant Raman transition resonantly couples the initial external momentum state to only one other momentum state. This happens even in the Raman-Nath regime, where the interaction time is short enough that momentum transfer is not constrained by phase-matching conditions. The final momentum state depends on the initial internal state of the atom and the relative directions of the two traveling waves. By using multiple diffraction regions, this process can be used to coherently split a beam of atoms into two beams that are widely separated in momentum space. This type of beam splitter would be useful in the building an atom interferometer.
High-speed compact correlator using VLSI liquid-crystal spatial light modulators
Authors: Turner Richard , Jared David A. , Johnson Kristina M. , Crossland Bill , Birch Martin , Vass David , Underwood Ian
Published: February 2023

The design and operation of a high-speed compact correlator that uses 176 × 176 very-large-scale integration/ferroelectric liquid-crystal (VLSI/FLC) spatial light modulators is presented. The VLSI/FLC devices1 have pixels on 30 μm centers and are used as the input and filter planes of a Van der Lugt correlator. The small pixel size of the spatial light modulators and the folded optical design, which uses telephoto transform lenses, allow the system to be compacted to roughly a 10 cm cube, while maintaining proper scaling between the input and filter planes. The use of ferroelectric liquid-crystal materials, which can switch in less than 25 μs at room temperature, allows for potential system throughput speeds greater than 40000 correlations per second. However, operation at such high speeds is beyond the capacity of current correlation-plane detection methods. For correlation rates of 500-1000 Hz, three detection methods employing standard charge-coupled devices, custom VLSI, and grey-coded photodiodes are investigated.2 The influence of VLSI device parameters, such as resolution, speed, and contrast ratio, on correlator performance are modelled, and experimental results are presented.
Optical characterization of ferroelectric liquid-crystal/silicon VLSI spatial light modulator
Authors: Hartman Nile F. , Drabik Timothy J. , Gaylord Thomas K. , Handschy Mark A.
Published: February 2023

Two-dimensional spatial light modulators (SLMs) are critically important in optical computing systems. A particularly promising type of SLM consists of a ferroelectric liquid-crystal (FLC) light-modulating layer on top of a silicon complementary metal-oxide semiconductor (CMOS) very-large-scale integrated (VLSI) circuit.1
Temperature measurements for turbomachinery applications using O2LIF/O2 Raman scattering
Authors: Annen K. D. , Epstein A. H. , Kolczak F.
Published: February 2023

Proof-of-principle experiments have been performed with O2 laser-induced fluorescence (LIF) and O2 Raman scattering to determine temperature for turbomachinery applications. A broadband ArF excimer laser was used in the experiments, and both sidescatter and backscatter configurations were investigated. The O2 LIF signal was collected broadband by means of glass filters and was ratioed to the O2 Raman signal to produce a quantity that was dependent only on temperature in the sidescatter configuration. Experiments in the backscatter configuration showed that spectrally resolved O2 LIF data must be collected to avoid interference from window fluorescence. The experimental results agreed with published computational results on the dependence of the O2LIF emission with temperature. Potential problems and solutions associated with the application of this technique to turbomachinery measurements are discussed.
Silicon VLSI/ferroelectric liquid-crystal micropower optoelectronic computing devices
Authors: Drabik Timothy J. , Handschy Mark A.
Published: February 2023

We have elsewhere reported high-performance electrically addressed1 and thresholding, optically addressed spatial light modulators (SLMs) based on silicon complementary-metal-oxide-semicon ductor (CMOS) integrated circuitry that employ a ferroelectric liquid-crystal (FLC) light-modulating layer in direct contact with the silicon chip. We now report progress toward a silicon retina device similar to that of Mead2 for detection of edges and motion but augmented with optical outputs for direct readout of the processed image. The higher speed of optical readout permits the silicon retina to detect motion that occurs on time scales that are short compared to the limit set by the slower electronic readout. Furthermore, the image is output in a form that is directly suitable for subsequent optical processing. We also report refinements of the electrically addressed device that are intended to approach the limits imposed by speed–power constraints, and we discuss the design issues that accompany this performance regime.
Analysis of depolarization associated with light scattering
Authors: Azzam R. M. A. , Gray J. F.
Published: February 2023

Elastic light scattering is described by the linear transformation S' = MS, where S and S' are the Stokes vectors before and after scattering and M = (mij) is the Mueller matrix that succinctly describes the light-sample interaction. In this study we examine the degree of polarization of the scattered light r' = f(r, θ, ε; mij) as a function of the degree of polarization r, and the azimuth and ellipticity angles θ and ε of the totally polarized component of the incident light. For a given Mueller matrix mij, the following properties of the function f(r, θ, ε) are considered: (1) Surfaces or loci of input polarizations (r, θ, ε) in the Stokes-Poincaré space that lead to r' = constant. These have been proved to be a family of ellipsoids. Sections of those ellipsoids with the θ = constant equi-azimuth planes are shown. Also, the intersection of those ellipsoids with the Poincaré sphere (r = 1) are represented by a family of contours in the θ–ε plane. (2) Over the surface of a sphere r = constant (0 < r < 1) the values of θ and ε that produce the extrema (maxima and minima) of r‘ are found. (3) Over the surface of a sphere r = constant, , the average value of r', is determined as a function of r. Several light scattering matrices from the published literature are tested as examples. A Mueller matrix that leads to r' > 1 for any input state is obviously in error and nonphysical.
Glass waveguide fabrication technology: a review
Authors: Albert Jacques
Published: February 2023

After 20 years of research, glass optical waveguides are finally reaching a mature stage in which mass-produced, quality passive devices are commercially available. There has recently been a surge of interest in these waveguides owing to the widespread use of optical fibers in densely interconnected networks.
Grafted GaAs photodetectors embedded in a glass waveguide
Authors: Yi-Yan A. , Chan W. K. , Gmitter T. J. , Florez L. T. , Andreadakis N. , Nguyen C. K.
Published: February 2023

We have previously demonstrated waveguide-detector devices made by grafting a thin GaAs film directly onto the surface of glass-channel waveguides.1 Coupling efficiency of light from the waveguide to the detector has been, in general, low because of the presence of an inherent ~10 nm thick, low-index layer at the semiconductor/waveguide bonding interface.2
Calculation of light scattering from particles and structures on surfaces by using the coupled-dipole method
Authors: Taubenblatt M. A. , Tran T. K.
Published: February 2023

Understanding the interaction of light with particles or other three-dimensional structures on surfaces is of interest in the semiconductor industry for both contamination inspection and lithography. Light scattering from a particle in free space can be calculated by means of the coupled-dipole method.1 In this method the object, which may be irregularly shaped, is modeled as a collection of dipoles that interact with one another and with the incident electromagnetic field. We have extended this method for use in the presence of a surface by modifying the interaction matrix to include both the direct contribution of a dipole and its reflection from the surface. The reflected dipole fields must be computed by means of the Sommerfeld integral expressions. The method permits full three-dimensional calculations of light scattering from dielectric structures on a surface. The calculation is efficient for structures as large as a wavelength. We have calculated light scattering from several objects, including polystyrene spheres on silicon with diameters as great as 0.85 λ, with varying angles of incidence. In addition, the method maybe applied to lithography structures and layered substrates.
Buildup of steady-state femtosecond pulses in a colliding-pulse mode-locked dye laser
Authors: Pan Ci-Ling , Chang C. S. , Kuo Jahn-Chung
Published: February 2023

We have studied the evolution of the pulse widths and the corresponding spectra of femtosecond optical pulses generated by a colliding-pulse mode-locked (CPM) dye laser (λ = 620 nm) with (case I) and without (case II) compensating prisms. The build-up time to steady state took ~10 µs for case I. The peak wavelength of the corresponding spectra shifted slightly to the red as the pulses evolved. Otherwise, the spectra did not exhibit distinct features. In case II, the pulse width exhibited an oscillatory behavior and approached the steady state after a delay of ~50 µs. A dramatically changed spectrum was also observed at the first minimum of oscillation. These results were in good agreement with our proposed physical mechanisms.
Pulse narrowing in mode-locked lasers through polarization and transverse effects
Authors: Piché Michel , McCarthy Nathalie , Salin Francis
Published: February 2023

It has recently been reported1,2 that Ti:sapphire lasers can generate subpicosecond pulses, even without the help of a nonlinear coupled cavity or of a saturable absorber. In the first case,1 a loss modulator was used to initiate mode-locking; however, the pulse duration was too short to be consistent with pure active mode-locking.
Ultrafast nonradiative relaxation of Nd3+
Authors: Lee H. W. H. , Hughes R. S.
Published: February 2023

We have observed extremely fast nonradiative relaxation (picosecond to femtosecond) between closely spaced crystal field states derived from the 4G5/2,2G7/2 Stark manifold of Nd3+ in glassy media. The relaxation is significantly faster than that predicted by an indiscriminate application of the energy-gap law, and it is highly wavelength-dependent. Femtosecond accumulated-photon-echo techniques were used at 13 K, revealing single and nonexponential echo decays. Relaxation was found to involve single phonon processes. Generally, the dephasing rate increased as higher-lying crystal field states were excited, reflecting the larger number of available terminal levels for the relaxation and the phonon density of states. However, a detailed plot of the dephasing rate versus wavelength revealed considerable unexpected structure. As higher-lying states were excited, the relaxation rate did not increase in the expected monotonic fashion. Surprisingly, the relaxation rate decreased in various spectral regions as the excitation energy was increased. By using T2-selective dynamic-excitation spectroscopy, we assigned these regions to the spectral locations of the inhomogeneously broadened crystal field states in the Stark manifold. Site-dependent electron-phonon interaction and a strong correlation between the inhomogeneous broadening of the crystal field states are deduced from the data.
Sub-shot-noise measurements with pulsed twin beams of light
Authors: Huang Jianming , Aytür Orhan , Kumar Prem
Published: February 2023

Recently, we have observed as much as 7 dB of quantum-noise reduction in the direct difference detection of twin-beam signal and idler outputs from a traveling-wave optical parametric amplifier (OPA).1 The OPA, which consists of a type-II phase-matched KTiOPO4 crystal, is pumped by the second harmonic of a mode-locked and Q-switched Nd:YAG laser. Here we describe an experiment in which we used these twin-beam pulses to improve on the optimal (shot-noise-limited) direct-detection signal-to-noise ratio (SNR) that can be achieved with coherent-state pulses of light of the same peak power.
Optimized designs of Er3+-doped silica fiber lasers at 1.56 µm pumped with 980-nm diode lasers
Authors: Bastien Steven P. , Sunak Harish R. D.
Published: February 2023

A simple theoretical model is presented and shown to be useful for modeling single-mode pumping at 980 nm of Er3+-doped silica fiber lasers. We show the benefits of using large refractive index differences and small doping radii. The obtained designs presented exhibit slope efficiencies close to the theoretical limitand threshold powers around 1 mW.
Noninvasive measurement of ocular pigments by reflectometry and fluorophotometry
Authors: Delori François C.
Published: February 2023

Optical methods for diagnosing and treating ocular disease are affected both by the scattering characteristics of tissues in the stratified layers of the fundus (retina, choroid, and sclera) and by the absorption of light by ocular pigments. Both reflectance and fluorescence methods for studying these pigments (melanin, hemoglobin, lipofuscin, macular, and visual pigments) have relied on numerous optical simplifications. Optical models1,2 have been introduced to aid understanding of the overall optical characteristics of the fundus layers and to characterize the amount of melanin and hemoglobin in the choroid.
Elements of early vision
Authors: Adelson Edward H.
Published: February 2023

Early vision is generally considered to involve modules that extract a discrete set of elementary properties, such as motion, color, and disparity. These properties might be called the elements of vision. But from where do these elements come? Is it possible to derive a catalog of visual elements from first principles?
Shape modeling through parametric descriptions
Authors: Bajcsy Ruzena , Solina Franc , Gupta Alok , Leonardis Ales
Published: February 2023

Our approach to shape modeling is based on parametric description of all aspects of shape: volume, surface, and contour. We advocate this description as an immediate step applied directly to range data. The rationale behind this approach is the following: (1) The representation is compact, i.e., it has a large expressive power with a small set of parameters; (2) the parameters have natural interpretations: position of the object in three-dimensional space, orientation, size, curvature, shape, etc.; (3) the models are recovered from data by using numerical fitting procedures that provide a measure of goodness of fit, which in turn can be used in a feedback loop to improve the description according to the task; (4) the representation provides a predictable segmentation of a scene into its parts.
Curvature is an independent feature in visual search
Authors: Wolfe Jeremy M. , Yee Alice , Friedman Stacia
Published: February 2023

Some searches for targets among distractors are performed with reaction times (RT’s) independent of set size. Such parallel searches are made possible by modules that process features across the visual field. If parallel processes cannot perform the task, the search is serial, with RT increasing linearly with set size and with blank trial slopes twice the target trial slopes. Few features support a parallel search (e.g., color, orientation). Is curvature such a feature?
Evolving scene descriptions
Authors: Bobick Aaron F.
Published: February 2023

Research is presented concerning the dynamic construction of a model of the environment by a vision system by using multiple representations to describe objects.
Patterns from aspherical rain and dew
Authors: Fraser Alistair B.
Published: February 2023

Spherical water drops have long been evoked to explain familiar natural optical phenomena, such as the rainbow, corona, glory, and heiligenschein, but there is little in the literature to suggest that any such phenomena are caused by aspherical water drops. Two examples of readily observable patterns will be presented: the supernumerary bows and the sylvanshine.
IR extinction by mixed particles
Authors: Volz Frederic E.
Published: February 2023

Most aerosol particles are of mixed composition. This raises the question of shifts and distortion of the IR bands of their constituents. Shifts of as much as −40 cm-1 have been found in wide-spaced bands of dry submicrometer particles consisting of internal mixes of alkali salts that were obtained by spraying solutions. Furthermore, overlapping bands merged. This was not observed with weaker and broader bands of ammonia salts. Comparison of these observations with theory is difficult because observed bands of small particles, especially if they are spheres, are much wider than is predicted by theory. Because most of the particles are "roundish," it has been assumed that the anisotropic internal structures (crystallites, dendrites, and voids from solution evaporation) might permit averaging of the theoretical results. This explains the experimental observations much better than recently promoted continuous distribution of ellipsoids, especially if one also considers reflectance of powders pressed to bulk density. Spectra of particles containing insoluble compounds showed little distortion. In conclusion, band shifts in atmospheric aerosols might be negligible.
Holographic animation
Authors: Andrews John R.
Published: February 2023

Animation adds a new dimension to the information content and appeal of a hologram. Animation has been previously incorporated in holographic stereograms by creating a vertical array of exit pupils that both have the spatial viewpoint and vary simultaneously in time. Although this can create an effective visual display, the superposition of time and viewpoint on the same axis creates perceptual distortions. The holographic animation that we demonstrate eliminates this problem by creating a spatially multiplexed hologram in which the exit pupil is parallel to the line between the two eyes (horizontal) with an array of different exit pupils perpendicular to this direction (vertical). In addition to animation in the vertical direction, horizontal parallax can be incorporated, as with normal holographic stereograms. To reduce the effects of chromatic dispersion in blurring the vertical time sequence, reflection holograms are most convenient for viewing under white-light illumination. The small remaining chromatic dispersion can be eliminated by using an auxiliary dispersive element between the hologram and the light source. A generalization of the animation concept permits parameters other than time to vary in the image sequence along the vertical direction.
Wave-front propagation from exact algebraic equations
Authors: Farouki Rida T. , Chastang Jean-Claude A.
Published: February 2023

Wave fronts in isotropic media can, by Huygens’ principle, be described as envelopes of circles. By using this fact and the appropriate elimination method, the exact algebraic expression for the anticaustics of all the usual optical surfaces in reflection and refraction are derived for a finite distance source. An anticaustic is a wave front of zero optical-path difference. Once the equation of the anticaustic is known, the equation of the parallel wave front corresponding to any optical path difference can be formally found by the same process, although this time the computations are considerably more difficult. By means of this new equation the wave front can be mapped at various instants during its propagation. What happens as the wave front contracts and approaches the focal region is of particular interest. That the cusps of the wave front map the caustic is thus beautifully illustrated. Intriguing conclusions can also be deduced from these algebraic wave-front equations.
Visibility-dependent depth of focus for incoherent sources
Authors: Raj K. , Pieper R. J. , Poon T.-C.
Published: February 2023

The criterion for depth of focus is expressed solely in terms of the f/number of the lens and the wavelength of light. Perceived image quality can generally be expected to depend not only on these parameters but also on the spectral content of the object. Assuming that the optical designer knows in advance the highest frequency to be resolved in the image, with a minimum allowed visibility, a more precise criterion can be formulated. The performance of an incoherent imaging system can be specified in terms of its optical transfer function (OTF). Pieper et al.1 studied the resolution dependence of depth of focus in an incoherent imaging system, wherein the system response to spatially periodic impulses was studied and the expression for the impulse response involving arbitrary pupils was derived. The resulting analytical expression was posed in a normalized form, obviating the need for specification of actual physical lengths. The Rayleigh criterion adopted for impulse objects is not valid when the analysis is extended to nonimpulse objects, such as sinusoidal inputs. In our presentation we study the imaging properties of circularly symmetric apertures with sinusoidal sources under defocused conditions. Visibility is used as a criterion to evaluate the imaging properties. For sinusoidal inputs, the relationship between visibility and OTF follows directly from the definition of the former. Deterioration of visibility with the deviation from focus is then related to the spatial frequency through the OTF. The deviation from focus is expressed in terms of a normalized out-of-focus parameter.
Differentiation of optical images using a Fresnel lens optical element written onto a magneto-optic spatial light modulator
Authors: Davis Jeffrey A. , Brandt Werner V. , Cottrell Don M. , Bunch Robert M.
Published: February 2023

The derivative of an object can be obtained by subtracting two linearly shifted versions of the object, and the linear shift can be obtained by shifting the optical center of a lens. In this work, we use a computer program to form an optical element by subtracting two Fresnel lenses having different optical centers. The two images that are formed subtract in areas where they overlap so that only the edges remain. This optical element is then written onto a magneto-optic spatial light modulator (MOSLM), which permits programmable differentiation of the image. The spatial direction of the image differentiation can be varied by changing the direction in which the two lenses are shifted. Results showing the differentiation operations of d/dx, d/dy, and d2/dxdy are presented.
High-speed optical image processing with rare-earth-doped fluoride glasses
Authors: de Rochemont L. Pierre
Published: February 2023

Stimulated photon echoes from optically active ions in glasses have long been used to study effects related to the molecular dynamics of the host medium in the immediate vicinity of the active site. Recently, photon echoes have been suggested for use in high speed optical circuitry and in optical memory storage. This technology offers unique systems potential because it permits analog spatial information to be processed at digital-gate intervals. Because active ions can be incorporated into the matrix of a glass in higher concentrations than they can be doped into the lattice of a crystal, amorphous solids are potentially more suitable host materials for these applications than are crystals. In this paper the Judd-Ofelt parameters and the Einstein coefficients are used to calculate the time evolution of population gratings and stimulated echo intensities at 0.8 and 1.22μm from an inverted ensemble of erbium ions in doped (2 mol. %) heavy-metal fluorozirconate glass. A simple mathematical model composed of constant-condition interaction and relaxation sequences is invoked.
Optical neural networks based on stimulated photorefractive effects
Authors: Owechko Y. , Dunning G. , Soffer B.
Published: February 2023

Photorefractive implementations of optical neural networks (ONN) can be divided into two architectures: stimulated and nonstimulated. In nonstimulated photorefractive ONN's, each connection weight is stored in the relatively well-defined grating that is formed by the interference of two plane or spherical waves. The connection weights are updated by superimposing new gratings on the old ones and by using an exposure schedule to compensate for grating erasure. Bragg ambiguity effects, in which a particular grating can be read out by beams different from the ones that wrote the grating, are a source of crosstalk in such architectures. The stimulated photorefractive optical neural network (SPONN) stores each connection weight in a continuum of spatially and angularly multiplexed gratings. The precise distribution of the gratings is determined by beam fanning, which is seeded by scattering of the incident beams by crystal inhomogeneities, and it evolves according to the dynamics of photorefractive two-and four-wave mixing. We have shown experimentally that sets of such multiplexed gratings generated in both self-and mutually-pumped photorefractive phase-conjugate mirrors can serve as global interconnection networks without the Bragg-ambiguity crosstalk characteristic of nonstimulated ONN's. A simple geometric argument shows that scattering off two or more gratings in series is sufficient to break the Bragg ambiguity. This permits us to arrange optical neurons in arbitrary patterns on spatial light modulators and to fully utilize the spatial light modulator's space-bandwidth product. We will present recent experimental results on crosstalk in SPONN and will discuss our progress towards implementing a complete optical neural network.
Optoelectronic associative memory using a parallel readout optical disk
Authors: Krishnamoorthy A. , Marchand P. , Esener S.
Published: February 2023

We evaluate Inner-product and outer-product algorithms for associative memory. We show that the page-serial, bit-parallel inner-product method has lower storage requirements and system complexity than do other algorithms, and it achieves minimum error recall. Storage capacity can be traded off for fault tolerance. The high capacity (1 Gb) and high throughputs (1.5 Gb/s) obtainable with the motionless parallel-readout optical disk make it suitable to implement an associative memory capable of fast retrieval (25 ms). The associative memory system consists of a detector array, an Si/PLZT exclusive-OR gate-array, and a variable-threshold detector (VTD) with fast local-decision circuitry. The intensity at the VTD is a measure of the mismatch between the query image and the stored image that is being read. Two modes of operation are possible. If the threshold is preset at the VTD, all disk images close to the query are retrieved in one rotation. Alternatively, all Hamming distances are calculated during the first rotation of the disk, and the closest match is retrieved during the next rotation.
Neural-net algorithms and their optical implementations
Authors: Casasent David
Published: February 2023

Neural networks (NN's) for multiple-class pattern recognition (PR) offer an organized and efficient optimization procedure to produce nonlinear-discriminant decision surfaces. These NN techniques are automated and are needed for difficult PR problems. Many NN algorithms and applications have problems, such as requiring an excessive number of neurons, not using existing PR techniques, and requiring a number of ad hoc parameters to be selected (thus, not achieving the automated advantages of NN's). This paper offers algorithms and architecture solutions to these issues. The resultant NN combines NN/PR algorithms, plus analog/digital and optical/electronic technologies. 1 consider a three-layer NN (this can produce any piecewise linear decision surface) with analog input neurons and weights (optics provides this and is needed to realize its full advantages). The large number of interconnections possible optically is its major advantage. Initial weights (not random ones, as is conventional) and an automatically selected number of hidden-layer neurons are provided by means of PR techniques. The weights are then adapted by means of NN techniques. The number of input neurons is reduced by using feature-space and symbolic input neuron representations. A hybrid optical/digital architecture is described, and various applications of it (demonstrating its multifunctional nature) are noted.
Optical unit for performing closest-vector selection for application to neural networks
Authors: Krishnamurthy A. K. , Collins S. A. , Ahalt S. C. , Stewart D.
Published: February 2023

Selecting a closest or "distinguished" vector from a set of vectors is a fundamental operation in many applications, including self-organizing neural networks. The closest-vector-selection (CVS) operation determines the exemplar vector (drawn from a set of vectors) that is closest to an arbitrary input vector presented to the system. CVS systems are useful in a number of applications, such as self-organizing neural networks for vector quantization. Applications include communication and radar target identification. We present the design of an optical system that performs the CVS operation. The design uses a gray wedge and a Hughes liquid-crystal light valve for an optical matrix-vector operation and in various logic operations.
Recent progress with leaky-mode (antiguided) arrays
Authors: Hadley G. Ronald
Published: February 2023

Although the first arrays employing anti-guiding were reported almost 10 years ago, renewed interest in leaky-mode arrays commenced only two years ago with the fabrication of arrays with considerably improved performance.1 These devices lased in the fundamental mode with a diffraction-limited on-axis far-field peak at currents as much as 2.5 times threshold. Since that time, further improvements have been made, both in our understanding of these devices and in our understanding of their emission characteristics. Theoretically, work began with the use of the effective-index method, which has provided important insights into the nature of leaky array modes.2 Newer work has employed both analytic and numerical methods that include the full two-dimensional cross-sectional structure of these devices.3,4 The two most significant achievements of this body of theoretical work have been (1) the illumination of the discrimination mechanisms present2-4 and (2) the discovery of resonance effects in device design.2 Recent experimental achievements include pulsed operation to 10 times threshold, cw operation of 250 mW per facet, and the design and fabrication of a new generation of devices. These new devices have lower internal losses than older devices and should eventually demonstrate improved efficiencies and emission quality.
Novel packaging for high-performance low-cost diode laser arrays
Authors: Karpinski A. A. , Pesarcik S. F. , Linden K. J. , Geoffroy L. M. , Mastrovito A. , Magee C. J.
Published: February 2023

High-power arrays are needed for pumping new and developing solid-state lasers. These arrays can generate peak heat loads of 1 kW/cm2, yet they require a minimum of temperature variation among lasers in the package. As an additional complication, these arrays require advances in manufacturing to reduce prices to affordable levels.
Potential performance of surface-emitting lasers
Authors: Iga Kenichi
Published: February 2023

Summary not available at press time.
Direct measurement of stimulated emission in two-photon downconversion
Authors: Wang L. J. , Zou X. Y. , Mandel L.
Published: February 2023

Measurements have been made of the rate at which signal photons are produced in a nonlinear crystal in the process of parametric downconversion, when a coherent light beam from a He:Ne laser is injected into the crystal in the direction of the conjugate-idler photons. The latter provides a stimulating field for the downconversion. When the phase matching condition inside the nonlinear medium is satisfied, the rate of downconversion is enhanced by the presence of the He–Ne laser beam by a factor of the form 1 + βIi, where li is the intensity of the He:Ne laser beam. The effect of defocusing either the pump beam or the He–Ne idler beam is investigated. Possible use of this phenomenon to study the photon amplifier with single-photon input will be discussed.
Starting a lens design
Authors: Grey David S.
Published: February 2023

The first step in selecting a starting configuration is a careful study of requirements. Vignetting, mechanical limits, unusual pupil requirements, unusual distortion specification or allowance, resolution, and method of evaluation are basic requirements. Question the client: Some specifications may be rigid, and others may be target values. The client may know a configuration you have missed. Usually one starts with a known model and plans to make modifications; otherwise, one has no reason to expect success. Useful configurations to consider as added components are field flatteners, aplanatic surfaces, surfaces with the A-stop imaged near the center of curvature, and the separated doublet for correcting high-order spherical aberration. The plan should be based on full consideration of all limiting aberrations of the model. A well-reasoned conjecture about the cause of limiting aberrations and a plan for their alleviation is always worth a hard try. Sometimes thin-lens algebraic solutions of firstorder requirements, or even third-order aberrations, can be useful—especially for relay systems. A simple interactive program, or even a programmable calculator, can be invaluable in converting to a thick-lens starting model. Finally, a starting model can be based on the conjecture "What would happen if...?"
The y-nuand y- y ¯methods for optical systems layout—choosing the right tool for the job
Authors: Seppala Lynn G. , Sweatt William
Published: February 2023

The ynu and y-

y
¯

methods are two commonly taught techniques for the paraxial layout and analysis of optical systems. These methods are based on two very different visualizations of first-order optics. In this paper we first show how these techniques are used. Then, we discuss several design problems that have been solved by using one approach or the other. We are hopeful that this presentation will give designers a clearer picture of the relative strengths of these two design tools.
Microchannel arrays and readouts for the extreme ultraviolet and soft-x-ray bands
Authors: Lampton Michael , Siegmund O. H. W.
Published: February 2023

We review recent advances in the technology of microchannel-plate photon-counting image systems, with particular emphasis given to space flight applications.
Experiments with soft-x-ray Fourier-transform holography
Authors: McNulty I. , Kirz J. , Jacobsen C. , Howells M. R. , Anderson E. H.
Published: February 2023

We report tests of a holographic microscope with submicrometer resolution. We used the microscope to record Fourier-transform holograms of gold test patterns (50 nm finest dimension) with 3.4 nm wavelength radiation from the soft-x-ray undulator at the National Synchrotron Light Source. The high-brightness undulator source enabled us to generate holograms of sufficient contrast to be numerically reconstructed from exposures of 10-30 min obtained with a chargecoupled-device (CCD) detector. The coherent x-ray flux through the 100 µ2 test objects was 9 × 105 photons/s and was 2 × 106 photons/s in the reference source. The microscope used a 90 µm diameter zone plate as a beam splitter (50 nm finest zone width) both to illuminate the object and to form a focused reference spot. A low-noise integrating CCD camera recorded the interference between the reference and object wavefields, which had a mean spatial period of ~200 µm. After making background corrections, we performed discrete Fourier-transform reconstructions of 512 × 512 pixel arrays of the hologram data, which yielded images of the test patterns having features resolved to better than 1 µm. This approach to Fourier-transform holography demonstrates high-resolution x-ray microscopy by using a relatively coarse-grained detector; this permits fast turnaround from hologram acquisition to wave-front reconstruction.
Rare-earth-doped glass waveguides
Authors: Li M. J. , Wang W. J. , Honkanen S. , Najafi S. I.
Published: February 2023

Rare-earth-doped glass waveguides are suitable for the fabrication of stable and low-threshold lasers in both the visible and infrared regions.1 We have investigated potassium, silver, and cesium ion-exchange to produce neodymium- and erbium-doped glass channel waveguides. We studied two configurations. In the first configuration, the waveguides were produced in a commercially available rare-earth-doped substrate. In the second, a waveguide was made in an undoped glass. Then, it was spin coated with a rare-earth-doped phosphate layer. Channel waveguides with different dimensions were produced, and the propagation losses as well as the absorption and emission spectra of these waveguides were determined.
Review of lithography requirements for 16-265 Mbit DRAM generations
Authors: Seidel Thomas E.
Published: February 2023

Lithography capabilities and requirements for the formation of submicrometer features are reviewed. The capabilities are related to the performance characteristics of the optical systems: wavelength and numerical aperture, which determine minimum critical-feature size and depth of focus; and the intensity (energy deposited perunittime) and speed of registration, which partially determine throughput. Commercial acceptance criteria include wafer throughput for a given cost rate and the yield and utilization that the equipment affords. Cost of entry and facility transparency are also significant issues. Current g- and i-line systems are capable of producing dimensions as small as 0.8 and 0.6μm. The ability to extend i-line systems to fabricate critical features as small as 0.5 μm with limited depth of focus is considered. Deep ultraviolet (DUV) 248 nm systems in development demonstrate feature sizes as small as 0.4 μm. Both sharp-line sources and broadband systems are in advanced states of development. Approaches for deep-submicrometer systems include extensions of DUV systems to shorter wavelengths, x rays, and even electron or ion beams. The relative advantages and limiting issues of such systems will be discussed. Many breakthroughs, such as source, resist, and registration capability, are required before a preferred path for deep-submicrometer systems can be selected and commercialized. Technical and economic requirements will be summarized.