bluuebunny/crossref_metadata_2025 huggingface dataset:
Nested Crossbar Connection Networks for Optically Interconnected Processor Arrays
Authors: Feldman Michael R. , Guest Clark C.
Published: February 2023

A new family of interconnection networks, termed the nested crossbar, has been developed. These networks are particularly well suited for processor arrays using optical interconnections due to their high bisection width and high degree of spatial invariance. While a k-ary m-dimensional hypercube has a connectivity ranging from a ring to a binary hypercube, a base-b, m-dimensional nested crossbar has a connectivity ranging from a binary hypercube to a full crossbar (fully connected network). The nested crossbar connection networks were designed to take full advantage of the benefits of optical interconnects. Their high bisection width (a measure of the global nature of a connection topology) allows them to perform efficient, communication intensive computation. Although high bisection width networks occupy a great deal of area in fully electronic implementations, optically interconnected VLSI nested crossbars have very slow area growth rates. This is due to their high degree of spatial invariance which allows holographic nested crossbar connections to be formed in a space invariant or basis set connection system. The nested crossbar networks allow use of minimum numbers of optoelectronic transmitters and detectors to solve certain problems in a given time. For example, a 2-D nested crossbar requiring O(N3/2) optoelectronic components can be used to compute a matrix-vector multiplication in O(logN) time (N is the number of elements in the vector). A base 2 nested crossbar can compute the multiplication in O(N1/2 log2N) time with only O(N) transmitters and detectors.
Fabrication approach and simulation studies for grating coupled VLSI photodetectors
Authors: Clymer Bradley D. , Gillfillan Dana
Published: February 2023

The large absorption depth for red-infrared photons propagating in silicon makes fast response times for integrated photodetectors difficult to achieve. Typical high speed photodetectors for light in this wavelength range are PIN diodes, where the intrinsic layer is used to extend the region of electric field to allow drift mechanisms to dominate diffusion mechanisms in carrier transport across a junction boundary. Since the fabrication of a large intrinsic layer is not easily incorporated in VLSI processing, an alternative approach has been developed in which the direction of light propagation in the silicon is altered by a surface-relief grating at the silicon-silicon dioxide interface. Propagation of light at an oblique angle in the silicon allows the photons to be absorbed closer to the silicon surface, within the drift region of a shallow vertical pn junction. We expect this grating structure to be made using periodic structures drawn in standard fabrication masks and the bird's beak effect that disturbs the flatness of the silicon-silicon dioxide interface during oxide growth. We present a description of layout modifications required to generate the periodic mask structures and computer simulations of diffraction efficiency for various grating modes with varying grating depth and period.
GaAs optical novelty filter
Authors: Liu Duncan T. H. , Cheng Li-Jen
Published: February 2023

Recently, much attention has been focused on the optical novelty filter1 because of its parallel processing nature. An optical novelty filter is capable of extracting the nonstationary parts of an optical image, i.e., it can simulate the motion-detecting function found in the vision systems of some animals, e.g., frogs, and is potentially useful in the target-tracking system. The optical novelty filter has been implemented using two-beam coupling or four-wave mixing in photorefractive crystals, e.g., BaTiO3. We report the basic properties of a singlepixel GaAs optical novelty filter inplemented using phase conjugate interferometry (four-wave mixing). The relations between the response times of the phase conjugate mirror and the optical novelty filter and between those of the phase modulator (piezomirror) and the optical novelty filter were experimentally investigated. The resolution of an optical novelty filter is discussed and derived. From the derived expression, a photorefractive medium can be selected to yield the maximum output resolution possible. Based on this and the short response time of GaAs, a GaAs optical novelty filter has the potential of being a high resolution device of its kind.
Lateral and wavefront aberrations of a photorefractive phase conjugator
Authors: Papen George C. , Saleh Bahaa E. A.
Published: February 2023

A beam reflected from a photorefractive phase conjugate mirror may experience a transverse displacement (lateral shift) and wavefront aberration (longitudinal shift), if a dc electric field is present or if the probe beam is frequency detuned relative to the pumps. These shifts, which can be of the order of several wavelengths for the lateral shift and tens of wavelengths for the longitudinal shift, are a result of the angular dependence of the reflectivity, an effect similar to the Goos-Hanchen effect. The angular dependence of the reflectivity is a spatially dispersive effect arising from the nonlocal nature of the wave interaction. We assume that the incident beam is paraxial and slowly varying in space and represent it as a superposition of plane waves (angular spectrum). The complex reflectivity is then expanded about the beam axis, each plane wave component is multiplied by its complex reflectivity, and added to form the conjugate beam. The linear term in this expansion generates the lateral shift whereas the quadratic term is responsible for the longitudinal shift. Pulsed beams are distorted because they contain harmonic components, each of which undergoes different shifts.
New method for reconstructing phase factor
Authors: Zhang Yue , Gu Peisheng , Zhuang Songlin
Published: February 2023

In a Fourier transform system, an object f(x) is interrelated to its Fourier spectrum F(u) by Fourier transform. Our goal is to recover the phase factor of the object from the measured intensity data. By means of the discrete Fourier transform, assuming the sampling number is N, it is shown that the intensity at one point in the Fourier plane directly connects with both the phase term and the amplitude term of N points in the object plane. Because of the large number N, the relationship as usual is somewhat complex. To simplify it, we may allow fewer sampling points into the system. A particularly successful approach to solving this problem is to let only two neighboring points, n and n+ 1, pass the system. Therefore, the corresponding formula tells us that, if three intensity measurements at three points in the Fourier plane are taken, the phase difference of the object between the two sampling points will then be mastered. Letting n change from 1 to N — 1, we now can reconstruct the phase distribution of the object function.
Two-dimensional power spectrum of microrough silver thin film surfaces
Authors: Varnier Françoise , Rasigni Georges , Mayani Nicole
Published: February 2023

The surface structure characterization our team has developed for several years (based on microdensitometer analysis of shadowed surface replicas) makes it possible to determine the statistical parameters which describe any microrough surface. In particular, it is easy to compute the power spectrum, which is a 1-D function. How the 2-D power spectrum which characterizes an isotropic rough surface can be computed from the 1-D one is shown here. Then, it is possible to compare—in the low spatial frequency range—the results given by this method with those obtained by optical methods. We present the results we obtained for the 2-D power spectra connected with a large set of microrough silver thin films, the rms height of which varies from 10 to 80 Å. (These silver films were evaporated onto fluoride underlayers.) Results are compared with those obtained by FECO, scattering studies, etc. Moreover, the study of the optical reflectance of these silver films near the surface plasmon makes it possible to compute these 2-D power spectra in another way and to compare their numerical values with the previous results.
Hafnium oxide and aluminum oxide coatings for UV applications
Authors: Starke A. , Schink H. , Ebert J. , Kolbe J. , Welling H.
Published: February 2023

Single layers of hafnia, alumina, and silica on quartz substrates were deposited by reactive ion plating and ion beam sputtering. Refractive indices and extinction coefficients were determined by spectrophotometric analysis and related to the process parameters. Water adsorption was examined with the aid of optical transmission in the range from 2 to 4 µm. Laser-induced damage testing was performed by a KrF excimer laser at 248 nm. The tested samples were quarterwave stacks of Al2O3/SiO2 and HfO2/SiO2 on silica substrates. All the results are compared and related to the properties of conventional evaported coatings.
Spectroscopic studies of diatomic metals and semiconductors
Authors: Morse Michael D. , Fu Zhenwen , Hamrick Yoon Mi , Lemire George W. , Taylor Scott
Published: February 2023

Resonant two-photon ionization spectroscopy of diatomic metals and semiconductors is now helping us to understand the electronic structure of these interesting species in some detail. Recent results on GaAs (demonstrating an X3Σ− ground state and a 3Π state located near 23,500 cm−1, which is predissociated by a repulsive 5Σ− state), NiCu (demonstrating electronic structure which may be understood in terms of ligand field theory), and NiPd, NiPt, PdPt, and Pt2 are presented. In Ni2, NiPt, and Pt2, abrupt onset of predissociation in a very dense manifold of electronic states allows the bond strengths to be measured as 2.07, 2.80, and 3.14 eV, respectively. Compared to the coinage metal dimers CU2, CuAu, and AU2, with bond strengths of 2.01, 2.34, and 2.29 eV, respectively, these results indicate d-electron contributions to the bonding of 0.06, 0.46, and 0.85 eV in Ni2, NiPt, and Pt2, respectively. High resolution investigations of NiPd and NiPt are also presented.
Gradient index optics
Authors: Moore Duncan T.
Published: February 2023

The principal advantage of gradient index optics is the simplification of optics systems by the elimination of one or two lenses in a multilens system. This results in reduced cost, size, and weight without a sacrifice in performance. This tutorial begins with an understanding of the basics of gradient index materials, both in the optical regime and in other areas of physics. Lens design of axial, radial, and spherical gradient materials is discussed. The problems of materials measurements are described, with particular emphasis on materials and the limits of gradient index design in terms of current and future materials. Finally, the currently existing systems are required.
Athermalization using gradient index materials
Authors: Gardner Leo R. , Moore Duncan T.
Published: February 2023

The change of focal length with temperature of a radial gradient index lens is modeled using finite differences. It is found that the gradient and homogeneous contributions to the focal length change can be balanced against each other for a net change of zero. It is important to emphasize that using this method, these athermalized solutions can be found for single element lenses even when using materials with high expansion coefficients, i.e., polymers. A double graphing technique is developed which visually identifies these athermalized solutions by comparing the effect of the gradient and homogeneous contributions to the focal length change. An athermalization coefficient for the special case of a flat surfaced radial gradient index lens (Wood lens) is derived and presented in simplified form.
Monte Carlo simulation of strong acoustooptic interaction
Authors: Bridge William J. , Korpel Adrian
Published: February 2023

In the conventional approach to strong acoustooptic interaction, the usual model is that of a rectangular sound column illuminated by a plane wave of light. By considering either the coupled modes of the unperturbed medium or the eigenmodes of the perturbed medium, a solution can then be found which predicts discrete plane waves of light as the diffracted orders. This model gives results in reasonable agreement with theory for configurations that approximate it. However, the physical reality of strongly interacting, arbitrary, diffracting sound and light fields is obviously very different from the simple, plane wave-sound column model. Qualitatively, any discrete orders predicted by the latter model can be explained in terms of multiple scattering in the physics based approach.1 Quantitatively, the solution must be framed in terms of Feynman diagrams and path integrals.2 A quantum mechanical interpretation of this formalism is one of photon transitions induced by the sound field. We report here on recent successful numerical experiments that simulate this quantum mechanical model by Monte Carlo methods using a classical computer.
Optically detected x-ray absorption spectroscopy of luminescent materials
Authors: Weber Marvin J. , Wong J. , Greegor R. B. , Lytle F. W. , Sandstrom D. R.
Published: February 2023

X-ray absorption near edge and extended fine structure (EXAFS/XANES) has been observed from luminescence excitation spectra of crystals and glasses using synchrotron radiation. The luminescence may either be intrinsic (recombination radiation from alkaki halides, alkaline earth fluorides, oxides) or from activator ions (rare earths, transition metals, organic dyes) excited directly or indirectly. Core electron excitations of cations and anions in luminescent materials have been investigated in the energy range from the VUV to hard x-rays. Absorption features may appear as an increase or decrease in the luminescence intensity depending on the sample thickness with respect to the x-ray absorption length, observation geometry, and intermediate relaxation processes. For materials with multiple sites, conventional x-ray absorption spectroscopy measures some average of different site populations. Since luminescence spectra vary with the local environment, using optical detection measurements can be both atom specific via the characteristic x-ray absorption edge energy and site and valence specific via the optical wavelength.
Growth and electric field-enhanced properties of SBN
Authors: Wilde Jeff , Hesselink Lambertus
Published: February 2023

Recent development of a computer-controlled Czochralski crystal growth system at Stanford University has allowed us to produce large single-crystal Sr0.6Ba0.4Nb2O6 boules. Since this material is grown in a solid solution, striations are normally present and difficult to suppress. We discuss the nature of the striations and a simple scattering measurement that provides quantitative information about the degree of compositional variation in our samples. The results show that the effect of striations on laser beam propagation is negligible over a wide range of input angles.
Planar integration of free-space optical components: a theoretical analysis
Authors: Jahns Jurgen
Published: February 2023

In complex optical systems consisting of many optical components, alignment and stability of those components become critical issues. In a recent paper we proposed to solve these problems by integrating free-space optical components on one side of a planar substrate and propagate the light in a zigzag path between the two sides of the substrates.1 The optical components can be computer generated and fabricated by lithogrpahic techniques, for example. In this paper we address several problems connected with this approach such as aberrations, light efficiency as well as fabrication issues. For our analysis, we concentrate on diffractive optical elements which are implemented as blazed phase structures.
Integrated-optical array generator
Authors: Downs M. M. , Jahns J.
Published: February 2023

In an earlier paper we proposed to integrate optical components on single substrates using planar fabrication techniques.1 The motivation for this proposal was to alleviate the tight alignment tolerances required to build an optical computer. An integrated optical array generator was fabricated to demonstrate this idea. It consists of two components, a phase grating and a diffractive lens, incorporated on one side of a planar quartz glass substrate.
Large-area chromogenic coatings: results and challenges
Authors: Granqvist C. G.
Published: February 2023

Chromogenic materials can be used to regulate the throughput of radiant energy in response to dynamic needs. Among the potential large-area applications, we note windows in buildings and cars. Chromogenics encompasses photochromies, thermochromies electrochromics and certain liquid-crystal-based light shutters. Most chromogenic devices incorporate thin films of nonconventional materials. This paper attempts to give a survey of the worldwide R&D efforts on chromogenics, with emphasis on electrochromic and thermochromie thin films. For example, we discuss electrochromics-based laminated all-solid state devices containing LLWO3 and Li
y
NiOz films, and thermochromie VO
x
F
y
films.
Gradient-index optical filters by ion beam assisted deposition
Authors: Donovan E. P. , Carosella C. A. , Hubler G. K.
Published: February 2023

Gradient-index films up to 5-µm thickness have been produced by simultaneous deposition of electron beam evaporated silicon and of energetic nitrogen particles from a 500-eV Kaufman ion source. The relative fluxes of beam and evaporant atoms determine the ratio of nitrogen to silicon in the films and therefore control the index. The near infrared refractive index of amorphous silicon-nitrogen films decreases monotonically with composition from pure silicon to stoichiometric silicon nitride. Thin film devices were fabricated under computer control using Faraday cups to monitor the ion beam current and a quartz crystal oscillator to monitor the evaporation rate of Si. The utility of the method is demonstrated by devices including antireflection coatings, narrowband rejection filters of the rugate design, and broadband IR reflectors.
Shape-invariant representation and recognition of 3-D solids
Authors: Jankowski M. , Eichmann G.
Published: February 2023

The enclosing surface, or boundary, of a well-behaved 3-D rigid solid unambiguously specifies the object. More importantly, the boundary captures the notation of a shape, which is an intrinsic property of solid objects. There are numerous data acquisition techniques which provide geometrically explicit image information in the form of depth maps. It is of great interest to be able to extract compact, canonical shape features of an object from the geometry of the bounding surface. The so-called 3-D shape descriptors provide a viewer-independent image representation that greatly simplifies the recognition task. New 3-D shape descriptors are calculated from the differential characteristics of a solid's bounding surface. First, the bounding surface is represented by a hierarchy of bivariate functions projected on a sphere. The representation, at the top level, is an intrinsic surface function independent of the object that is embedded in its 3-D coordinate space. A subsequent Fourier transformation maps significant features for a correct classification of solids. The notation of similarity of objects, based on their shape characteristics, is simplified to a measurement of distance in a multidimensional feature space. Similar objects cluster naturally in the multidimensional descriptor space.
Brillouin resonances in the interaction of a two-level system with laser radiation
Authors: Postan A. , Rai Jagdish , Bowden C. M.
Published: February 2023

New resonances are predicted in the interaction of a two-level system (TLS) with laser radiation. These resonances are related to the nonlinear coupling between the TLS and Brillouin enhanced acoustic waves driven by the laser radiation. Resonances in phase conjugation by four-wave mixing driven by stimulated Brillouin scattering (SBS) of laser radiation in fluids have been studied elsewhere.1,2 The coupling of such resonances to the TLS interaction with laser radiation influences the spectral behavior of the TLS. Such resonances appear in addition to the Rabi sidebands. The inclusion of these resonances should have important practical implications in processes that depend on accurate spectral behavior such as in the fields of laser spectroscopy, four-wave mixing, and phase conjugation. Here the new resonances are demonstrated for two mutually detuned counterpropagating laser beams interacting with a TLS at frequencies that may be detuned from the TLS spectral line center. The nonlinear Maxwell Bloch equations coupled to the acoustic wave equation are solved numerically. Damping due to viscosity is taken into account. Wave depletion is included and no perturbation theory approximations are assumed in the numerical solution of these equations.
Modeling of nonlinear absorption in semiconductor single heterostructure Schottky barrier devices
Authors: Jokerst N. M. , Garmire Elsa M.
Published: February 2023

Large light-induced changes in absorption have been observed in single hetero structure Schottky barrier devices consisting of In(Fe)/InGaAsP(un)/Au. The Schottky barrier forms a depletion region at the metal-semiconductor interface. Excess photogenerated carriers in the epilayer (hv = Eg) are spatially separated: electrons are trapped in the epilayer and holes are removed, resulting in long carrier lifetimes and large excess electron concentrations.
Semiconductor biased superlattices as electron wave interference filter/emitters
Authors: Glytsis Elias N. , Gaylord Thomas K. , Brennan Kevin F.
Published: February 2023

Starting from fundamental principles, quantitative analogies between quantum electron waves in semiconductors and electromagnetic optical waves in dielectrics have been developed.1 Due to those analogies optical design techniques can be adapted for the design of narrowband superlattice electron filter/emitters. A voltage-biased semiconductor superlattice structure can serve simultaneously as an electron filter and as a continuously tunable emitter. The thickness of each superlattice layer is restricted to be an integer multiple of the monolayer thickness. Furthermore, for practical materials (Ga1−
x
Al
x
As), there is a usable composition range and a range of usable electron energies to avoid intervalley and phonon scattering that degrade the electron coherence. Under these constraints, an optimum design procedure has been developed that specifies the layer compositions and thicknesses for a given bias voltage and input kinetic energy. Examples of Ga1−
x
Al
x
As filter/emitters are presented. Sensitivity of the device to fabrication variations is investigated. These superlattice electron filter/emitters can exhibit very narrow electron kinetic energy passbands and can be integrated into solid state devices for potential use as monoenergetic emitters for electroluminescent devices, photodetectors, and fast ballistic transistors.
Influence of absorptive and phase gratings on two-wave mixing in saturable absorbers
Authors: Boothroyd S. A. , Chrostowski J. , O'Sullivan M. S.
Published: February 2023

The ratio of the imaginary to the real part of the complex nonlinear refractive index has been measured by two-wave mixing in acridine orange doped fluorophosphate glass, fluorescein doped boric acid glass, and ruby at argon-ion wavelengths. A new and simple two-wave mixing measurement is described in which one of the beams contributing to a stationary interference pattern in the nonlinear absorber is subject to a phase transient. This results in a variation of the energy coupling between the beams from which the phase of the nonlinear index and also the sign of its real and imaginary parts can be determined. A simple theory based on homogeneously broadened absorption agrees with the phase of the nonlinear index in acridine, but not in fluorescein where excited state absorption is determined to be greater than absorption from the ground state. These results are compared with new nondegenerate two-wave mixing measurements in which the contribution from the phase and absorption gratings can be determined independently.1 Comparison of results from the two approaches enables the contribution of excited state absorption to the two-wave mixing to be qualified.
Rank reduction and fixed point quantization for optimum approximation of projection operators
Authors: Voran Stephen D. , Scharf Louis L.
Published: February 2023

Projection operators form a basic building block for many mathematically optimal detection and estimation structures. For optical signal processing, a projector representation that is compatible with binary spatial light modulators is needed. When separating signals from significant amounts of additive noise, reduced-rank projectors outperform full-rank projectors. Thus, to attain optimal optical signal processing performance, the effects of rank reduction and quantization must be considered jointly. Rank reduction is a matter of deciding which orthogonal projector modes should be retained and which should be discarded. The quantization problem involves distributing the modes retained over a fixed number of binary spatial light modulators. We describe how the statistics of a stationary signal are used to build a projection operator that is matched to that signal. We then define a signal processing performance metric which indicates how well the projector separates that signal from additive noise. Our analysis tracks the effects of rank reduction and quantization, resulting in design equations for low-rank quantized projectors which are optimal under our metric. In effect, these design equations tell how to allocate a fixed amount of expensive hardware for best optical signal processing results.
Fisher information, disorder, and optical signal estimation
Authors: Frieden B. Roy
Published: February 2023

Optical signals may be regarded as probability laws (on photon events). The problem of optical signal recovery may therefore be viewed as a problem in estimating a probability law p(x). Maximum entropy has, in the past, been used for this purpose. Here, we discuss instead the use of minimum Fisher information

I
=

∫
d

x

[

p
′

(
x
)

]

2

/
p

(
x
)

. Consider a physical system consisting of a random aggregate of particles or pho tons. Consider the experiment of measuring one particle's coordinate y, and from this, best estimating the mean coordinate θ of the ensemble, where y = θ + x. As time passes, the particles randomly become more spread out, so that the error in the estimate should increase. But the error goes inversely as I. Therefore, I should statistically decrease with time. With no constraint on the system, as t → ∞, I → 0, defining a maximally random law p(x) = constant. However, in the presence of a physical constraint, I should approach a finite value, obeying I = minimum. When the constraint is linear in the mean kinetic energy of the system, the solution p(x) obeys the stationary differential equation for the system. In this way, the Schrodinger (energy) wave equation, Helmholtz wave equation, diffusion equation, and Maxwell-Boltzmann law may be derived from one classical principle of disorder.
Coevaporated reduced-stress gradient-index films
Authors: Targove J. D. , Murphy A. R.
Published: February 2023

The coevaporation of LaF3 and BaF2 has been investigated as a means of reducing the large intrinsic tensile stress of fluoride films deposited at ambient temperature. CeF3 and BaF2 have previously been coevaporated from a single source for stress reduction.1 We have used coevaporation from separate sources for increased composition control and to allow separate deposition rate control for the two materials as a means of depositing gradient-index films. LaF3 was chosen as a UV transmissive material with chemical properties identical to CeF3. Refractive indices of the films decreased significantly. Gradient-index films with sinusoidal index profiles were then deposited by varying the BaF2 deposition rate while maintaining the LaF3 rate constant. This method thus allows gradient-index films with reduced stress to be deposited at wavelengths from the ultraviolet to the infrared.
Multiple-pump raman compensation technique for WDM soliton-based fiber communication systems
Authors: Wang L. K. , Yang C. C.
Published: February 2023

Since stimulated Raman scattering can convert energy from the higher frequency waves to the lower frequency waves, it has been used to amplify the decaying signal transmitted along the optical fiber. In a soliton-based fiber communication system, it has been verified theoretically and experimentally that the Raman scattering can provide a means for maintaining solitons over several thousand kilometers of fiber. In such a Raman compensation technique, quasi-cw pump waves are injected periodically into the fiber so that the decaying signal pulses are amplified during propagation. However, the research in the past is mainly focused on single-channel systems. In this study, we present a Raman compensation technique for wavelength-division-multiplexed systems. When multiple channels exist in a fiber, the energy conversion due to Raman scattering from the higher frequency channels into the lower frequency channels must be considered. In this presentation, we first point out the disadvantages of using one pump frequency for the entire multiple channels. Then we describe the technique of using multiple pump waves with different frequencies. In the pump scheme, each channel signal is amplified by the composite gain provided by all pump waves. It is shown that the proposed amplification scheme is quite general. The simulation results are also presented.
Effect of intrapulse Raman scattering on soliton-effect pulse compression
Authors: Agrawal Govind P.
Published: February 2023

Optical fibers can be used for pulse compression in the wavelength region of anomalous group-velocity dispersion by exploiting the periodic evolution of the higher-order solitons which undergo an initial pulse-narrowing stage. By choosing the fiber length judiciously, the pulse is made to exit out of the fiber when it is narrowest. The optimum fiber length and the compression factor are obtained by solving the nonlinear Schrodinger equation (NSE).1 The predictions of the NSE are accurate for picosecond pulses but need modification for femtosecond input pulses as several higher-order nonlinear effects become important for such short pulses. The most important among them is intrapulse stimulated Raman scattering, a phenomenon responsible for the soliton self-frequency shift and soliton decay. In this paper, we study numerically the effect of intrapulse Raman scattering on soliton-effect pulse compression by solving the generalized NSE. Even though the pulse evolution is no longer periodic, the input pulse is compressed significantly at an optimum fiber length. The compression factor is larger than that occurring without the Raman effect. Furthermore, the compressed pulse is generally pedestal-free.
Acoustooptic interactions in the presence of diffraction for optical beams with arbitrary profiles
Authors: Banerjee Partha P. , Tarn Chen-Wen
Published: February 2023

Starting from the coupled wave equations describing acoustooptic (AO) interactions in the presence of propagational diffraction, a Fourier transform technique is used to express the interactions in the spatial frequency domain. The method used is identical to the technique for solving the paraxial wave equation to derive the transfer function of propagation and, hence, the Fresnel diffraction formula during free-space propagation of a light beam in the presence of diffraction. The coupled interaction equations in the spatial frequency domain clearly bring out the effect of propagational diffraction of the various scattered orders on the interaction process. To check the formulation, Bragg diffraction of a Gaussian light beam is considered. Results indicate, among other things, a shift in the expected centers of the zeroth-order and the first-order light beams. Detailed numerical simulations, comprising Fourier transforming the input beam profile to calculate the spectra of the scattered beams and hence, their profile in space using the inverse transform, are also presented.
Optoelectronic bypass/exchange switches
Authors: Cheng L. , Sawchuk A. A.
Published: February 2023

Multistage networks, such as the Omega/shuffle-exchange network, Clos/Benes network, etc., are widely used in telecommunications and parallel signal processing today. An optical implementation of these networks is desirable because of its high data rates, low crosstalk, and the feasibility of 2-D structures in optics. Shuffling interconnections and bypass/exchange switches are two basic building blocks in a multi stage network. The free-space optical perfect shuffle, 2-D folded perfect shuffle, and 2-D separable shuffle have been described.1-4 Stirk and Athale proposed an optical implementation for bypass/exchange switch based on latching logic5. We present several optoelectronic designs for single and multistage 2×2 bypass/exchange switch modules. One design is for a general 2×2 single stage circuit switched module which can perform bypass, exchange, and broadcasting functions. In this module, control and power are supplied at wavelength λ2, while data are passed at wavelength λ1. A second design is for a bypass/exchange switch in which both data and control are carried at λ1, while power is supplied at λ2. This design can operate in both packet or circuit switched mode. Finally, we discuss modules for use in multistage networks. In this application, signal routing information can be inserted from a controller at each stage, or the data can be self-routed by headers attached to each data packet. We also present a multistage bypass/exchange 2×2 switch capable of central control or self-routing.
Dynamic bistability of an optical ring circuit having photorefractive gain, loss, and a photorefractive feedback coupling element: experiment
Authors: Lininger Diana M. , Manns Anno Her , Anderson Dana Z.
Published: February 2023

We demonstrate the operation of an optical ring circuit having photorefractive gain, loss, and a photorefractive feedback coupling element that replaces a mirror of a conventional ring resonator. The feedback element serves two purposes: it compensates for resonator length changes thereby maintaining an injected signal on resonance and it also provides the circuit with a short-term memory. We present experimental results illustrating the bistable behavior of the circuit in the presence of an injected signal. Once the circuit is switched on by an injected signal it remains latched to that state in the absence of the signal for a memory time governed by the response time of the feedback element.
Photorefractive effect in the presence of shallow trapping sites
Authors: Tayebati P. , Mahgerefteh D.
Published: February 2023

To explain a number of anomalous photorefractive effects, we present a complete analytical solution to a band transport model of the photorefractive effect which includes a shallow trapping level in addition to the deep donor and acceptor levels of the conventional models. We assume that a single charge carrier, for example, electrons, is responsible for transport. At room temperature and in the dark, the shallow level is completely empty, while the deep donor level is partially full. Light excites charges from each level to the conduction band. In addition, the electrons in the shallow traps can be thermally excited to the conduction band. The free carriers are assumed to recombine to either level in a time which is short compared to the grating build-up time. We solve for the space charge grating in each level and the space charge field in steady state as a function of light intensity and grating spacing. We also solve for the time development of these gratings in the dark in a certain regime of parameters. The predictions of the model agree well with results of photorefractive dark decay experiments in both Bi12SiO20 and BaTiO3, as well as transient photoconductivity experiments in Bi12SiO20.
Height and gradient from shading
Authors: Horn Berthold K. P.
Published: February 2023

A special case of the shape from shading problem, applicable to surfaces with unusual reflecting properties, was solved by Rindfleisch (1966). For the special reflectance properties he considered, a profile of the solution surface can be obtained by integrating along predetermined straight lines in the image plane. The general problem was formulated and solved later (Horn, 1970 and 1975). The method of characteristic strip expansion was used originally to solve the nonlinear first-order partial differential image irradiance equation. The reflectance map makes the analysis of the shape from shading algorithm much easier, provided that both light sources and viewer are far away from the scene being viewed (Horn, 1977; Horn and Sjoberg, 1979). Several iterative schemes, mostly based on minimization of some function containing an integral of the brightness error, arose later (Woodham, 1977; Strat, 1979; Ikeuchi and Horn, 1981; Kirk, 1984; Brooks and Horn, 1985; Horn and Brooks, 1986; Kirk, 1987; Frankot and Chellappa, 1988). For a collection of papers on shape from shading, as well as a review of the subject and an extensive bibliography, see “Shape from Shading" (Horn and Brooks, 1989).
Second harmonic generation in ferroelectric liquid crystals
Authors: Robinson Michael G. , Liu Jian Y. , Johnson Kristina M. , Walba David M.
Published: February 2023

Some organic functional groups have been shown to have very large optical nonlinear coefficients. By incorporating such molecules into ferroelectric liquid crystal molecules, the difficult macroscopic alignment of such molecules becomes feasible and the resulting crystals yield large bulk optical nonlinearities which include SHG. The aim of this work is to investigate different FLC materials using SHG with results being reported at the meeting.
Neural networks applied to diffraction pattern sampling
Authors: George Nicholas , Wang Shen-Ge
Published: February 2023

While diffraction pattern sampling has been widely used in the classification of patterns, its usage has been somewhat limited by the need to devise rather sophisticated algorithms. We describe sorting or classifying a variety of patterns using the ring-wedge photodetector and commercially available neural network software. With this combination, it is no longer necessary to write specialized software, and experiments which previously might have taken 4-6 months are now completed in 4 h or less. Three separate experiments are described quantitatively. First, thumbprints are sorted for eight individuals using six prints from each person. A learning set of four prints is shown to give excellent results and both ring and wedge data are used for the input neuron signals. Second, as an experiment in particulate analysis, colloidal suspensions of polyvinyltoluene spheres have been measured over a concentration of 256-1. Finally, automatic image quality assessment is described using a variety of input imagery. Widespread new uses are predicted for this hybrid system that combines the ring-wedge photodetector and the neural network.
Superachromatic Gauss objectives
Authors: Mercado R. I.
Published: February 2023

In an earlier paper1 simple criteria for color correction were derived from the dispersion formulas of Hartmann, Cauchy, Schmidt, Conrady, and Buchdahl. These criteria were used to develop a simple method for selecting optical materials that can be used for designing lens systems with color correction for at least three wavelengths. Glass combinations found by this method have been used to design superachromatic objectives of the Gauss type that are well corrected for monochromatic aberrations and color corrected at four widely separated wavelengths in a spectral band extending from the visible to the near infrared regions of the electromagnetic spectrum. The design configurations of objectives comprising six lens elements made of two different optical glasses and design examples using three glass types are presented. The performance evaluation of these designs at relative apertures of F/4 (12° field) and F/5 (20° field) is shown.
Cw Conical Emission: First Comparison and Agreement Between Theory and Experiment
Authors: Valley J. F. , Khitrova G. , Gibbs H. M. , Grantham J. W. , Jiajin Xu
Published: February 2023

The use of a cw laser beam detuned from resonance by only a few gigahertz to observe conical emission1 makes the computational problem tractable (2 CRAY CPU hours per spectrum), leading to a simple physical model of this spatio-temporal instability. From the excellent qualitative agreement between computations and experimental observations, one understands the physics of conical emission as follows: self-trapping2 of A1, probe generation by resonance fluorescence, Raman-gain amplification3,4 of this probe which produces A3(ω3), four-wave mixing3 between A1(ω1) and A3(ω3) which generates A4(ω4 = 2ω1 - ω3) and transfers energy back and forth between A3 and A4, division of A4 into A4L and A4R by optical-Stark-shifted absorption, division of A3 into A3L and A3R by four-wave-mixing coupling, and formation of the cone from A4L (and sometimes from the low-energy shoulder of A4R) by propagation through the spatially-dependent index of refraction prepared by A1(x,y,z). We both observe and compute that light A4(ω4) of a particular frequency may appear both in the cone and in the center, ruling out phase matching as the determinant of the cone angle, unlike many other cones, e.g., two-wavelength conical emission.5
Spatially Resolved Raman Study of Self-Organized X(2) Gratings in Optical Fibers
Authors: Kamal A. , Weinberger D. A. , Weber W. H.
Published: February 2023

It is widely accepted that efficient second harmonic generation (SHG) in optical fibers results from self-organized χ(2) gratings. In this paper, we report the first direct observation of a modulation in the material properties of a conditioned fiber as measured by its spatially resolved Raman spectrum. Light from an argon laser operating at 514.5 nm was coupled through the fiber and Raman spectra of scattered light emitted perpendicular to the fiber axis were recorded with a spatial resolution of 5 µm. A single run was comprised of 24 such spectra, each sequentially displaced from the other by 2-3 µm along the axis of the fiber. Fibers previously conditioned for SHG showed a periodic modulation with position of ±3% in the strength of the entire low frequency portion of the Raman spectrum. A four parameter least squares fit to a sine wave yielded a coherence length of 27 µm when the seeding SH was in the fundamental mode. Coherence lengths of 35 µm and 50 µm were measured when the seeding green was in LP11 and LP02 modes, respectively.
Temperature-tuned Noncritically Phase-matched LiB3O5 for Doubling Nd: YAG Laser
Authors: Lin J. T. , Horner A. M. , Kato K.
Published: February 2023

We report the first demonstration of efficient frequency doubling of a Nd:YAG laser using the new nonlinear crystal of LiB3O5 operated at the noncritically phase-matched (type-1) temperature of 149°C. Acceptance width (3.9 °C-cm) and angular widths were measured.
Observation of the Fundamental Spatial Optical Soliton in a Glass Waveguide
Authors: Aitchison J.S. , Weiner A.M. , Silberberg Y. , Oliver M.K. , Jackel J.L. , Leaird D.E. , Vogel E.M. , Smith P.W.E.
Published: February 2023

We report the observation of spatial optical solitons using 75 fs pulses in a planar glass waveguide.
Temperature, Temporal Coincidence, and Intensity Effects in Seeded Second Harmonic Generation of Germanosilicate Fibers
Authors: Selker M.D. , Lawandy N.M.
Published: February 2023

Since Stolen and Tom demonstrated in 1987 that seeding germanosilicate fibers with the second harmonic results in rapid preparation(1), many fundamental questions about the physical mechanisms responsible remain unanswered. We have studied the temperature dependence, temporal correlation and intensity dependence of the preparation process for seeded fibers using an Nd: YAG laser and fibers with only Ge doping.
InGaAs/InAlAs Multiquantum Well Photodetectors in the Mid-Infrared Band
Authors: Hasnain G. , Levine B. F. , Sivco D. L. , Cho A. Y.
Published: February 2023

We demonstrate the first intersubband detectors in the 3-5 μm mid-infrared band using bound to continuum state absorption in InGaAs/InAlAs multiquantum well (MQW) structures. These detectors are background limited at temperatures below 120K with a

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for a 180° field of view. Photo-detectors with broad spectral response peaked at 4 μm showed good optical gain, low dark current and high detectivity. A MQW structure consisting of 50-periods of 30 Å In0.53Ga0.47As quantum wells (doped n = 2×1018 cm-3) and 300 Å undoped In0.52Al0.48As barriers was grown by molecular beam epitaxy on Fe-doped InP substrates. The measured absorption spectrum of this sample at room temperature is peaked at 279 meV (λ = 4.44 µm) with a full width at half maximum (FWHM) of 93 meV. We obtained the broad 33% linewidth covering the full 3-5 µm band by pushing the excited state higher up into the continuum. The noise measured in the MOW detectors is limited by the shot-noise of the dark current, which, for typical 200 µm mesa detectors, is determined by thermally assisted tunneling through the thick barriers. The peak detectivity of this 4 µm detector at 77K is thus

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.
Border visibility and cone excitation space
Authors: Boynton Robert M.
Published: February 2023

The distinctness of a border formed between two equiluminant fields has been measured by three independent procedures whose results are in good agreement. These are: (1) matching against a luminance-dependent border; (2) direct rating; (3) resistance to perceptual fading during prolonged fixation. Border visibility depends almost entirely on the ratio of excitation of L and M cones. When this ratio is unity, even large differences in S-cone excitation are largely ineffective and the two fields seem to melt together perceptually. These relations are easily visualized in a chromaticity diagram proposed by MacLeod and Boynton1 which plots S-cone excitation vs L/M excitation ratio at equal luminance. The strength of contours at equal luminance can be understood in terms of color opponent receptive fields which are critical for spatial vision and which receive input only from L and M cones. S-cones, which contribute little or nothing to luminance, appear to function mainly to provide a second dimension of chromatic vision. Their minimal contribution to border perception relates to their paucity in the receptor mosaic.
Improvement of the properties of SISAM using the theory of Hilbert and Schmidt
Authors: Shan Zijuan , Ni Zhenyu , Li Zhengzhi
Published: February 2023

The original spectrum measured in the interferometric spectrometer with selection by amplitude modulation (SISAM) has been reconstructed, we believe for the first time, by solving the integral equation associated with the irradiance distribution in the receiving plane, using the theory of Hilbert and Schmidt. The number of sampling points is reduced greatly by dividing the larger range of wavenumber into several smaller ones and choosing the appropriate parameter. The instrumental function we obtain has a very small width and does not show noticeable sidelobes. A pure rotational spectrum of 14N216O is reconstructed with a high resolution in our computer experiment. It is also shown from our calculation that the recovery is good even if the order of random noise reaches 10−2. In addition, because the kernel of the integral equation is decided by the spectrometer and is independent of the spectrum, the calculated results can be stored as memory and used for any spectrum. Therefore it is possible to finish the recovery procedure within a very short time.