bluuebunny/crossref_metadata_2025 huggingface dataset:
Photon-limited phase-gradient stellar image reconstruction
Authors: Aitken G. J. M. , Johnson R.
Published: February 2023

Atmospheric turbulence precludes the direct measurement of the spatial-spectral phase of a small stellar object; however, measurement of the gradient of the phase, followed by integration to obtain the phase function, has proved a viable procedure. Our phase-gradient (PG) algorithm is based on the Fourier differentiation theorem and requires the evaluation of the cross-correlation of the nth speckle image i
n
with each of i
n
, (xi
n
), and (yi
n
). Modulus information is obtained from conventional speckle interferometry. At very low light levels where the detector can deliver the image as a list of photon addresses, the cross-correlations are simply 2-D histograms of weighted address differences. Bias terms are eliminated by omitting all photon self-products. A photon-event version of the PG algorithm has been successfully demonstrated on computer-simulated data and on real stellar data obtained from Steward Observatory, Tucson. A detailed comparison with the well-known Knox-Thompson algorithm, operating in the photon-address mode, shows that the PG process gives lower rms errors, is less sensitive to defects in the data, and requires only half of the memory size and number of computing operations.
Symbolic substitution applied to image processing
Authors: Goodman Stephen D. , Rhodes William T.
Published: February 2023

Optical hardware for symbolic substitution is under serious consideration for optical computing applications. We show that symbolic substitution systems can be applied to image processing. Of particular importance are (1) nonlinear filtering operations applied to shapes (morphological transformations) and to level-sliced imagery and (2) linear filtering operations applied to bit-sliced images.
Method for the characterization of proton exchange in Ti:LINbO3 waveguides
Authors: Verber Carl M. , Agapiou George
Published: February 2023

The titanium-indiffused proton-exchange (TIPE) method has been shown to be very effective in the fabrication of lenses on planar Ti:LiNbO3 waveguides. It should also be useful for the fabrication of gratings and other passive components. The characteristics of these components are determined by the index indifference between the planar titanium-indiffused region and the TIPE region. It is, therefore, of interest to have a direct method for measuring this difference and thereby being able to characterize the TIPE process in terms of the fabrication parameters such as exchange time, exchange temperature, and degree of buffering of the exchange solution. The method we have developed for directly measuring the TIPE index change consists of forming an isosceles triangle by the TIPE process and directing a wide collimated guided wave into the triangle perpendicular to the base. The two halves of the beam are refracted toward the symmetry line of the triangle and intersect, forming a fringe pattern outside the waveguide. The fringe spacing and, therefore, the index difference can be measured with an accuracy of ~0.1%.
Optical waveguides in oxygen-implanted buried-oxide silicon-on-Insulator structures
Authors: Kurdi Bulent N. , Hall Dennis G.
Published: February 2023

Silicon-on-insulator (SOI) technology is currently under development by the microelectronics industry. We find these SOI structures promising for uses in the area of integrated optics. These structures comprise a single-crystal silicon layer separated from a conventional silicon substrate by a thin layer of silicon dioxide. The oxide layer is formed by oxygen ion implantation, and the implantation parameters are controllable for a desired device geometry. We analyzed these structures for their optical waveguiding properties and find that the top crystalline silicon layer can support TE modes with acceptably low losses. The mode attenuation is <1 dB/cm for a wavelength of λ = 1.3 Aim even for a silicon-diode layer thickness of only a few tenths of 1 μm, which is a fraction of the oxide thickness required in other silicon-based waveguide structures. We present results for the modes supported in these structures in terms of effective mode index, attenuation, and field profiles as a function of device parameters. We also find that the TM modes in these devices with their high losses make them ideal as integrated optics polarizers.
Squeezed state enhanced polarization Interferometry
Authors: Grangier P. , Yurke B. , Slusher Richard E.
Published: February 2023

Since the first proposal by Caves1 that squeezed light could be used to enhance the sensitivity of a gravitational wave interferometric antenna, squeezed states have been demonstrated in the laboratory but not yet used in an actual measurement system. This paper describes a polarization interferometer experiment, operated with a squeezed light source, designed to improve the interferometer sensitivity beyond the standard quantum limit. The interferometer consists of two polarization beam splitters, whose axes are oriented 45° with respect to each other. Linearly polarized incident laser light is transmitted by the first polarizer and split by the second one, which also acts as the splitter for a balanced homodyne detector. A rotation of the polarization between the two polarizers can be detected with quantum-limited sensitivity (e.g., ±1 μrad). The squeezed light entering the other port of the interferometer is produced using a χ2 crystal (KTP) in an optical cavity, pumped by a frequency-doubled cw ring Nd:YAG laser. The interferometer sensitivity can thus be increased by a factor depending on the degree of squeezing achieved and on the detector quantum efficiency. Sensitivity increases by factors between 2 and 3 are predicted, and current performance is described.
Squeezing with phase diffusion in parametric amplifiers
Authors: Drummond P. D. , Reid M. D.
Published: February 2023

We calculate the squeezing or quadrature spectrum of a nondegenerate parametric amplifier in an interferometer. Squeezing is found to occur below and above threshold. The new feature in the above threshold behavior is the existence of spontaneous phase diffusion in the transmitted signal, even with a stable pump. A novel technique is developed to calculate the quadrature fluctuations in the presence of phase diffusion. We find that squeezing occurs but is restricted to relatively high frequencies due to the phase diffusion. Another application of our theory is in the case of a subharmonic oscillator with a phase-diffusing pump. Squeezing is maintained here also, except at low frequencies. The presence of phase diffusion in quadrature phase sensitive detection can be expected to be universal. In all cases it tends to reduce or destroy the low-frequency squeezing and thereby increases low-frequency noise in a phase sensitive measurement. Our new stochastic technique, therefore, has a wide range of uses.
Nonlinear quantum-stochastic model for the parameteric oscillator
Authors: Wolinsky M. , Carmichael H. J.
Published: February 2023

The positive Prepresentation has proved a useful tool for analyzing optical systems which exhibit squeezing. The Glauber-Sudarshan phase-space representation gives a Fokker-Planck equation without positive semidefinite diffusion for systems which generate nonclassical fields. The positive Prepresentation provides a method for guaranteeing positive semidefinite diffusion and enables a quantum- dynamical model to be formulated in terms of classical stochastic differential equations. In previous work we had some success in applying this approach to describe the decay of the unstable state above threshold in a degenerate parametric oscillator.1 Below threshold a linearized analysis of fluctuations recovers the predictions of squeezing obtained by alternative methods.
Entropy content of squeezed states
Authors: Rai Jagdish , Rai Suranjana
Published: February 2023

The entropy of an ensemble of systems is defined in classical statistical mechanics by the relation where k is the Boltzmann constant and p
n
is the probability of finding the system in state n. It is possible to generalize this definition of entropy to a quantum state ψ(x) with Fourier transform ϕ(p) by defining p
n
as1 The corresponding entropies for the two quadratures

x
^

and

p
^

are defined as For the coherent state

S

(
x
)

=

S

(
p
)

and has the minimum value. For the x quadrature squeezed state,

S

(
x
)

decreases at the expense of

S

(
p
)

and vice versa. This definition of entropy has applications in information theory and optical communication using squeezed states.
Use of balanced homodyne detectors for tests of Bell’s inequality
Authors: Oliver Brian J. , Stroud C. R.
Published: February 2023

The balanced homodyne detector has made possible the detection of squeezed states of light. The essential feature of this detector is that it allows measurement of an arbitrary linear combination of the canonically conjugate observables of the electromagnetic field. We show that it is precisely this feature of the detector which provides a means for studying EPR nonlocality and Bell's inequality. A simple physical statement of this is that a homodyne detector is to its signal field as a Stern-Gerlach magnet is to a spin. Thus a pair of homodyne detectors can be used in the same manner as the magnets in Bohm’s gedanken experiment for studying the EPR question. The quantum mechanical state which demonstrates a violation of Bell's inequality in this system has correlations between the modes entering the two homodyne detectors. It should be noted that this correlation is not between the polarizations of the modes, as in all past EPR experiments using light, rather it is between the occupation numbers of the two modes.
Second harmonic generation and statistical properties of light
Authors: Rzazewski Kaźimierz , Ekert Artur
Published: February 2023

A second harmonic generation is the simplest nonlinear optical process. Together with the inverse process of parametric downconversion it often serves as a test case for various ideas in quantum optics.
Amplitude-squared squeezed states
Authors: Hillery Mark
Published: February 2023

The real and imaginary parts of the square of the field amplitude obey an uncertainty relation. If the uncertainty in either of these variables is less than it would be in a minimum uncertainty state with equal uncertainties in both variables, the state is amplitude-squared squeezed. This is a nonclassical effect which can be produced by second harmonic generation, two-photon absorption, and degenerate parametric amplification, as well as by higher-order processes. Amplitude-squared squeezing can be converted into normal squeezing by interactions in which the square of the amplitude of one field is coupled to the amplitude of another. Second harmonic generation and some forms of four-wave mixing provide examples of such processes.
Squeezing with coupled pendulums: two-level atoms in a cavity
Authors: Raizen M. G. , Orozco L. A. , Min Xiao , Brecha R. J. , Kimble H. Jeffrey
Published: February 2023

A theoretical and experimental investigation of the generation of squeezed states of light has been carried out for a system of two-level atoms inside a high-finesse cavity. The regime that we consider is such that the coupling of atoms to the cavity mode produces a splitting in the normal mode structure of the atom-field system (the so-called vacuum-field Rabi splitting). We have employed this splitting to generate squeezing with observed reductions in photocurrent noise of 30 % below the shot-noise level. A degree of squeezing of ~50% is inferred for the field state in the absence of propagation and detection losses. Squeezing has been observed in two different cavity geometries with quite different coupling coefficients. In each case, the frequency of best squeezing corresponds to that of the normal mode splitting

g

N

(g= single atom coupling coefficent and N = number of atoms) in good agreement with our theoretical predictions. Regions of parameter space with very large degrees of squeezing (>20×) are identified. Preliminary extensions of the theory into a transient regime with (cavity lifetime) ≪ (interaction time) ≪ (atomic lifetime) are described.
Weak-field transmitted and fluorescent spectra for an atom in a resonant cavity
Authors: Rice P. R. , Carmichael H. J.
Published: February 2023

There is increasing interest in the photon statistics and spectroscopic properties of the radiation from atoms confined in an optical cavity. Effects such as the cavity enhancement and inhibition of spontaneous emission, which were first observed using microwave cavities, have recently been measured at optical frequencies.1 Recent measurements of squeezing and the dynamic effects of single-quantum-level splittings also demonstrate the possibilities for quantum-statistical studies of coupled atom-cavity systems at optical frequencies.2 We study a single two-level atom confined inside an optical cavity which is driven by coherent light in resonance with both cavity and atom. For weak driving field intensities we have calculated the spectrum of the light transmitted by the cavity and fluorescence out the sides of the cavity.
Nonlinear optics near the band edge in multiple-quantum-well structures
Authors: Heritage J. P. , Von Lehmen A. , Zucker J. E. , Chemla D. S.
Published: February 2023

We have investigated the optical properties of GaAs quantum wells in the spectral region below the band edge using a two-wavelength picosecond optical pulse technique. Optical pumping in the transparent region produces modulation of the excitonic absorption which is probed with an optical pulse tuned to the excitonic absorption. We identify two distinct physical mechanisms that lead to the absorption modulation. First, a real population of carriers is produced by phonon-assisted absorption. These carriers bleach the excitonic transition by the action of the exclusion principle. The second mechanism involves virtual populations induced by the off-resonant optical excitation.
High-power optical Stark effects in multiple-quantum-well structures
Authors: Mysyrowicz A. , Hulin D. , Antonetti A. , Migus A.
Published: February 2023

Different optical phenomena occurring in GaAs multiquantum wells after irradiation with an intense femtosecond laser pulse are described. The accent is put on a discussion of the optical Stark effect at very high intensities.
Contributions to optical absorption in GaAs/AlGaAs multiple quantum wells
Authors: Kost Alan , Kawase Masatoshi , Garmire Elsa
Published: February 2023

An examination of the contribution of excitons, compared to the continuum states, to the optical properties of GaAs/AlGaAs multiple quantum wells illuminates the mechanisms underlying nonlinear absorption and nonlinear refraction and yields information which is useful for optimizing devices which incorporate these materials. We have measured the absorption as a function of intensity at three different wavelengths—above the band edge, on the excitonic resonance, and far below the band edge—to separate the effects. We find that different well thicknesses have different saturation intensities both for excitonic and continuum absorption.
Optical nonlinearities of GaAs hetero n-i-p-i structures
Authors: Chavez-Pirson Arturo , Gibbs Hyatt M. , Dohler Gottfried H. , Miller Jeffrey N.
Published: February 2023

Hetero n-i-p-i crystals are periodic arrays of n-and p-doped layers interspersed with undoped (i-) layers of a different smaller band gap semiconductor.1 We measure the frequency dependence of the nonlinear absorption changes at room temperature. We deduce the nonlinear refractive-index changes associated with the nonlinear absorption changes by a Kramers-Kronig transformation. The hetero n-i-p-i samples are grown by molecular beam epitaxy on GaAs substrates and consist of intrinsic layers of GaAs and doped layers of AIGaAs (x = 0.3). In the experiment we directly measure the nonlinear transmission changes through the sample by a pump and probe technique using an optical multichannel analyzer. The pump beam from the dye laser is tuned inside the band gap of the GaAs for efficient generation of free carriers. The broadband probe and the pump are synchronously modulated by acoustooptic modulators of varying pulse lengths (typically 1 µs) with varying repetition rates. The probe passes through the sample under different pumping intensities and is collected by the optical multichannel analyzer.
Tilt in the triangular shearing interferometer
Authors: Wenzel Robert G.
Published: February 2023

The wedged shearing plate interferometer is a very useful and simple device for the analysis of optical wavefronts. Its use is limited to sources with coherence length greater than the optical path difference between the two exiting beams. The triangular shearing interferometer, on the other hand, is an equal path device without tilt when used in the conventional way.
Surface wave interferometry and the infrared plasma frequency
Authors: Kaplan S. G. , Riffe D. M. , Sievers A. J.
Published: February 2023

Our previous high-temperature surface electromagnetic wave (SEW) studies1 using grating couplers, which led to the discovery of a cogenerated free space radiation (FSR) component to the detected signal and subsequent determination of ω
p
for tungsten at 10 µm, demonstrated the sensitivity of SEW interference spectroscopy to this parameter. However, the technique is limited by the need to use ultrahigh vacuum to maintain a clean sample at the elevated temperatures which are needed to kill off the SEWs and observe the weak FSR component scattered from the output coupler. We are now developing a room temperature technique to measure interference between SEWs and FSR. Using aperture excitation of the surface waves and letting the edge of the metal sample act as the output coupler, we have detected interference between FSR diffracting from the aperture and SEWs coupled off the sample edge using 10-µm laser radiation. By adjusting the aperture size the FSR and SEW amplitude can be made about equal, which permits observation of the interference. Preliminary results on copper yield ω
p
= 7.1 ± 0.4 eV.
Use of a real-time visibility plot as a path matching diagnostic and variable yardstick.
Authors: Tansey Richard J. , Widen K. C.
Published: February 2023

A common problem in laser systems is the requirement for path length matching of separate beam paths. A device is described which is easy to use, inexpensive, and capable of measuring equal path lengths to 0.5% of the coherence length. A mirror in one leg of an interferometer introduces a 2-μm path change at 100 Hz using a PZT and ramp generator. An rms voltmeter sends the rms voltage level from a detector placed at the output of the interferometer to an oscilloscope. If a translation stage attached to a mirror of the interferometer is moved at a known rate, the resultant oscilloscope trace represents the visibility vs optical path difference. The peak signal corresponds to the minimum path length difference. Using an argon laser with a 20-mm coherence length, the zero optical path length difference point was located to within 100 μm after an initial path difference of 50 mm. This was confirmed with a white light source. Experiments are discussed in which the coherence length of the source was gradually changed to obtain a variable yardstick.
Infrared Talbot deflection interferometry and its uses
Authors: Yu Xin , Ming Wanlin
Published: February 2023

Talbot deflection interferometry has recently been widely used for collimating light beams, measuring focal length, birefringence and phase object, determining temperature field and density field of a transparent medium, etc.
Textural segmentation using an optical scanning technique
Authors: Poon Ting-Chung , Park Jinwoo , Indebetouw Guy
Published: February 2023

Two types of filter capable of extracting the boundary between textural domains modulated by different spatial frequencies have recently been proposed.1,2 These filters are extrapolations of tonal edge detection filters: the odd-type (w-Gaussian) and the even-type (w2-Gausslan). We first review briefly the model of a textural edge In an image and the textural edge extraction filters. We then describe an optical scanning system capable of making both filters. It Is shown that the textural edge extraction filter based on the odd-type tonal edge detection filter produces an output with one single peak, whereas that based on the even-type filter produces two peaks as an output.
Continuous-order derivative for optical signals and images
Authors: Rabal H. , Zernino L. , Ojedacastaneda J.
Published: February 2023

The derivative operation plays an important role in Fourier optics. For example, it can be used for describing the propagation in free space, analyzing the influence of wave aberrations, visualizing phase structures for edge enhancement, and image deblurring. In many of these applications the order of the derivative operation is performed in an integer number and sometimes in a rational number. Here we propose the use of the derivative operation, whose order is a real number. Consequently, the derivative can be applied in a continuous manner.
Acoustooptic multichannel spectrum analyzer
Authors: Lee Hyuk
Published: February 2023

The two important parameters which characterize the function of the acoustooptic spectrum analyzer are diffraction efficiency and frequency bandwidth. However, diffraction efficiency and bandwidth cannot be increased at the same time for the conventional acoustooptic spectrum analyzer. In this case, the large transducer bandwidth cannot be used because of the smaller intrinsic bandwidth as the interaction length is increased. The concept of eliminating the trade-off between diffraction efficiency and bandwidth is based on the channelization of the device to cover the whole transducer bandwidth. The property of each channel is determined by the intrinsic bandwidth, which becomes smaller as the diffraction efficiency is increased. Therefore, we can increase the diffraction efficiency independent of the bandwidth if we increase the number of channels accordingly. The channelization can be achieved by either applying the acousto-electrooptic effect or using polychromatic lightwaves.
Using laser correlation theory to image an acoustic standing wavefront
Authors: Yi Ming , Yang Xuanmin
Published: February 2023

Imaging of phase objects can be divided into two cases: For large phase-changed objects, Topler invented a phase-to-amplitude conversion technique based on geometric optics using incoherent light—the so-called schlieren method. For small objects, Zernike invented a phase contrast method based on diffraction theory that used coherent light. However, for an acoustic standing wavefront the phase contrast method is not satisfactory; we did not pursue the reason.
Extracting 3-D egomotion information from a 2-D flow field. A biological solution?
Authors: Perrone John A.
Published: February 2023

It is well established that the human visual system can sense the speed and direction of motion in a moving retinal image. Computational techniques have recently been proposed which emulate this property of the visual system (e.g., Ref. 1). We show that by using a specific pattern of connections among directionally selective motion sensors, it is possible to construct a system for extracting 3-D egomotion parameters (heading, rotation, and environmental layout) from the 2-D retinal velocity field generated by motion through a rigid environment. A 3-D motion filter can be constructed for a particular heading direction by connecting a set of 2-D motion sensors which are directed radially outward from the filter position. Any activity in the sensors is summed. When an array of such 3-D filters is used, forward translation produces a peak of activity in the filter which coincides with the direction of heading. This peak is detectable even if the eye/camera rotates during the translation. Rotational filters are constructed in a similar fashion to detect roll, pitch, and yaw.
Spatial and temporal gradients of paired Gabor filters predict movement discrimination
Authors: Lawton Teri B.
Published: February 2023

This study found that both global and local contrast differences are used to discriminate left-right movement. Movement discrimination was examined by measuring an observer’s ability to discriminate shifts in the position of contrast differences over time for a large range of background contrasts, spatial frequencies, and exposure durations. The contrasts needed to discriminate between two test patterns separated in time by a short interval and shifted in position optimally relative to a multifrequency background were measured using two alternative forced-choice procedures. Multifrequency backgrounds determined the window of visibility used to discriminate movement. A neural network model implemented by the weighted difference and sum of the output of paired odd- and even-symmetric simple and complex cells (the spatial and temporal gradients of paired Gabor filters) pooled across the window of visibility predicts horizontal movement discrimination.
Spatiotemporal blur paths for image flow estimation
Authors: Spetsakis Minas E. , Aloimonos John (Yiannis)
Published: February 2023

We propose an alternative method for obtaining an estimation of the optical flow of a sequence of images that does not use the f
x
• u + f
y
• v + f
t
= 0 and does not depend on the assumptions of it. The method works best for image sequences with nonsmooth intensity variation. The method in brief is as follows: A sequence of k images is shifted each one by a distance a and b in the direction of x and y, respectively, with respect to its previous one and added.
Two-scale solution for atmospheric scintillation from a point source
Authors: Whitman Alan M. , Beran Mark J.
Published: February 2023

In a previous work we presented 3-D numerical solutions for the scintillation index vs range for a plane wave propagating in the atmosphere. The index-of-refraction fluctuations were represented by a modified Kolmogorov spectrum which included an inner scale. We present a numerical solution for the scintillation index vs range resulting from a point source when the inner scale is taken to be zero. The formulation is again based on the two-scale procedure. We show how the point-source solution differs from the plane wave case and discuss some general aspects of the finite-beam problem.
Cirrus cloud transmittance and backscatter measured with an infrared CO2 lidar
Authors: Hall Freeman F.
Published: February 2023

We have measured the transmittance of cirrus clouds at 10.59-μm wavelength with a CO2 lidar using two independent methods. The first method used backscatter from the calibration target El Chichon stratospheric cloud that was present over Boulder during 1982 and 1983. The second method used conical lidar scans at different zenith angles when uniform cirrus decks were present during the 1986 FIRE intensive observations in Oshkosh, WI. Extinction coefficients from both methods average 0.1 km−1 for thin cirrus, 0.5 km thick to 0.6 km−1 for cirrus several kilometers thick. There is a wide standard deviation in extinction values. Extinction to backscatter ratios vary from ~800 sr for thin clouds to 2600 sr for thick clouds.
Uses of liquid crystal TV and magnetooptic spatial light modulators in optical parallel logic
Authors: Yu Francis T. S. , Jutamulia S. , Lu T. , Gregory Don A.
Published: February 2023

New experimental implementations of optical parallel logic using commercially available inexpensive liquid crystal televisions (LCTVs) and magnetooptic spatial light modulators (MOSLMs) are discussed. Logic gates as switches are essential elements in digital computing systems. A digital computer can be described as a finite state machine, whose physical realization requires numerous Boolean logic gates. Boolean logic operations include sixteen possible functions or gates. The complete implementation of sixteen optical parallel logic gates is discussed. Different schemes are applied to the system using LCTVs and the system using MOSLMs. The experimental results and the application of xor gate to a real time binary image subtraction are presented.
Ommatidia of the human retina
Authors: Bouman Maarten A.
Published: February 2023

The frequency of the seeing curve and absolute thresholds including their relation to area show that two to four quantum absorptions in a group of one to three red cones, one to three green cones, or in a group of a variable number of rods suffices for vision. The proportionality of absolute threshold and chromatic threshold with a square root of stimulus area indicates that both rely on a twofold quantum coincidence mechanism. Luminance signals from two or more singly hit red and green cones and color signals from multifold hit red and green cones can be discriminated. Achromatic intervals and frequencies for specific color names around threshold level indicate that these signals are generated in ommatidia consisting of two red cones, two or three green cones, and one blue cone. The scotopic receptive unit at 12° nasal from the fovea then has about sixty submits in which two and more quantum absorptions in rods produce white signals. The scotopic achromatic signals originate from two or more submits which are each excited by one or more quanta. Each submit may contain a single cone with about forty satellite rods.
Depth, lightness, and brightness of ach romatic surfaces
Authors: Reeves Adam , Schirillo James , Arend Lawrence
Published: February 2023

Gilchrist’s1 subjects saw a test paper as adjacent to either a paper in a distant brightly lit room or a second paper in a closer dimly lit room (the apparent depth of the test being determined by interposition cues). The test and two other papers were always retinally adjacent. Gilchrist reported that grey-scale matches to the test were strongly influenced by the apparently coplanar paper; the other noncoplanar paper had virtually no effect. We wondered what Gilchrist's subjects had matched: brightness or lightness. We accurately simulated the rooms (excluding shadows) on a high-quality monitor. Luminance ratios (unlike Gilchrist's) under each illuminant were natural, not exceeding 30:1. Lightness matches showed Gilchrist's effect but to a lesser degree whether depth was cued by interposition alone or by stereo in addition. Brightness matches showed no effect of perceived depth. Results were replicated with a method of adjustment.
Cross-phase modulation in optical fibers
Authors: Islam Mohammed N. , Mollenauer L. F. , Stolen R. H. , Simpson J. R. , Shang H. T.
Published: February 2023

Raman or parametric optical pulse amplification in fibers involves copropagation of a pump pulse and a weaker signal pulse. The nonlinear index change induced by the pump (δn = n
2
I
p
) can phase modulate and thereby spectrally broaden the signal. The spectral features and broadening resulting from this cross-phase modulation (XPM) depend on the walk-off between the pump and signal pulses. Although these spectral features can be complicated, we show that they can be understood both qualitatively and quantitatively by concentrating on the phase change as a function of walk-off. To verify our ideas experimentally, we have used a ring cavity fiber Raman amplification soliton laser (FRASL).1 The effects of walk-off on XPM are conveniently explored in the FRASL because the pump and signal wavelengths are close to the zero dispersion wavelength λ0 in the fiber. When the fiber length is less than the walk-off length (50- and 100-m fibers), XPM dominates the spectral features. On the other hand, when there is complete walk-off between the pump and signal (400-m fiber), the effects of XPM are reduced considerably, but they are not canceled completely because the walk-off is asymmetrized by pump depletion.
Nonlinear pulse propagation in optical fibers
Authors: Blow K. J.
Published: February 2023

The nonlinear Schrodinger equation (NLS) is the central equation for understanding the propagation of pulses in optical fibers. Most problems consist of studying the effects of perturbations on the propagation of solitons. This requires an understanding of the unperturbed NLS, and inverse scattering theory is introduced through the Zakarov-Shabat (ZS) equations. We show how the ZS equations can be used to aid the interpretation of numerical results. The NLS and ZS equations can both be solved numerically, and schemes are presented for each.
Modeling of integrated optical devices
Authors: Hawkins Raymond J.
Published: February 2023

The design of optimized integrated optical devices requires a detailed understanding of the factors that affect device behavior. Numerical simulation is playing an increasingly important role in providing a complete picture of device behavior and in suggesting the design options that have the best chance of realizing optimum device performance.
Antireflection dielectric overcoated high-spatial-frequency rectangular-groove surface-relief gratings on lossy materials
Authors: Glytsis E. N. , Gaylord Thomas K.
Published: February 2023

Zero-reflectivity surfaces on lossy materials are useful for eliminating unwanted reflections. Surface-relief gratings on metal surfaces can produce unity transmissivity and thus total absorption. A rigorous impedance matching approach is used. The zero reflectivity condition and the equivalence of the homogeneous layer and the grating in the long-wavelength limit produce a system of nonlinear transcendental equations. First, the required thickness and complex refractive index for a single homogeneous lossy layer antireflection coating are calculated. Then the filling factor and groove depth of the equivalent high-spatial-frequency rectangular-groove surface-relief grating are determined. The analysis includes multiple dielectric overlayers for grating protection and for broad banding the antireflection characteristics. It is shown that multiple zero reflectivity solutions exist for both TE and TM polarizations for arbitrary angles of incidence and for any complex refractive-index substrate. Necessary and sufficient conditions in the parametric space are also computed. The inclusion of one or more dielectric overlayers gives additional design flexibility. The sensitivity of the antireflection design as a function of the angle of incidence and wavelength is presented.
Uniform asymptotic description of ultrashort optical pulses
Authors: Oughstun Kurt E.
Published: February 2023

The uniform asymptotic description of the propagation of an input rectangle-modulated harmonic signal of angular frequency ω
c
and initial pulse width T into the half-space z ᐳ 0 that is occupied by a single resonance Lorentz medium is described. The asymptotic description is developed by representing the input rectangular pulse as the difference between two Heaviside unit step-function modulated signals that are separated in time by the initial pulse width T. This representation clearly shows that the resultant pulse distortion in the dispersive medium is solely due to the Sommerfeld and Brillouin precursor fields that are associated with the leading and trailing edges of the input pulse. The dynamic evolution of the pulse with increasing propagation distance z ᐳ 0 is described for both long and very short initial pulse widths T. In both cases it is shown that the pulse distortion becomes severe when the propagation distance z is such that the precursor fields associated with the trailing edge of the pulse interfere with the precursor fields associated with the leading edge.
Erroneous explanations of the Zernike phase-contrast method
Authors: Goodman Douglas S.
Published: February 2023

Analyses of the Zernike phase-contrast method in many standard texts1,2 lead to a palpably wrong result. A common conclusion is as follows: For a phase object, whose amplitude transmittance is of the form expiϕ(x,y), the image irradiance goes as 1 + 2ϕ(x,y). Consider the case of a step phase object with amplitude transmittance 1 for x ᐸ 0 and expiα for x ᐳ 0. The standard analysis predicts a different image irradiance in the two areas. However, absolute phase is not manifested in an image, so an image is insensitive to an overall phase shift undergone by light in traversing the object. Thus the image of a broad clear area must be constant regardless of the thickness of the area. Therefore, the image of a phase step object must be identical in both regions, sufficiently far from the discontinuity. The error in the standard analysis is related to the commonly accepted notion that for a periodic object, as the period becomes large compared with the width of the lens response function, the form of each image unit is like that of a nonperiodic object. With the Zernike method, however, this is not the case.
Absorption digital refractometry
Authors: Collett Edward
Published: February 2023

This paper describes the measurement of the refractive index and the absorption coefficient of optical materials, e.g., metals and semiconductors, by a new method which we call absorption digital refractometry. This method rests on the simplification in Fresnel’s equations for reflection and the existence of high-resolution digital voltmeters. Unlike the classical methods which are optomechanical absorption digital refractometry is an optoelectronic method for determining the refractive index and absorption coefficient. We begin the paper by briefly discussing Ketteler’s equations. This is followed by describing the polarizing behavior of optical materials in terms of their Mueller reflection matrices.
Diffraction patterns in the shadows of disks and obstacles
Authors: English R. Edward , George Nicholas
Published: February 2023

We present a precise calculation of the fields behind a conducting circular disk. The only assumption inherent in the calculation is that the true aperture field is approximated by the incident field. We compare this result with the rigorous electromagnetic calculation behind a perfectly conducting metal sphere. Although these are two physically different problems, one nonetheless expects certain similarities in their diffraction patterns. The calculations show that the two cases differ only slightly in the Fresnel region (paraxial). For the near field we present a detailed discussion of the differences. A numerical example is given, and photographs of the shadow region diffraction patterns are compared.
Study of in vivo physiology using positron emission topography
Authors: Correia John
Published: February 2023

No summary was available at press time.
Optical phase conjugation-based ultrafast digital computation
Authors: Li Yao , Eichmann George , Dorsinville Roger , Alfano Robert R.
Published: February 2023

An ultrafast parallel optical phase conjugation (OPC) effect for the use of optical digital computation is described. Using spatially encoded logic values, symbols, optical binary, multiple-varied logic, symbolic, as well as interconnect operations are performed. The proposed processors are experimentally verified with a 32-ps pulse Nd3+:YAG laser. Based on these elemental processors, an OPC-based optical digital computer architecture is proposed. Using this architecture, iterative arithmetic and symbolic computation examples are presented. Some of the OPC computer performance factors, such as real-time encoding, signal amplification, etc. are also discussed.
Noise in optical matrix-vector multipliers: experiments
Authors: Batsell S. G. , Jong T. L. , Walkup John F. , Krile Thomas F.
Published: February 2023

Considerable interest has been expressed in the use of optical matrix-vector multipliers. The accuracy of these processors is limited by sources of deterministic and random error. We measure both the component and system noise levels associated with various implementations. These are compared with earlier theoretical calculations. We then use these results to determine the accuracy limits of the processors.
Programmable logic array design using polarization-encoded optical shadow-casting
Authors: Karim M. A. , Awwal A. A. S. , Dayton U.
Published: February 2023

An efficient optical computing system may involve the use of a programmable logic array (PLA) where only on outputs are stored in locations addressable by the inputs. The lensless optical shadow-casting (OSC) system1 using LEDs provides an easier and reliable means to generate logic operations. This scheme has been recently extended2,3 to include polarized sources, masks, and encoding codes, thus increasing the design flexibility. In an OSC, each LED produces a shadow of the input overlap pattern, which along with the other similarly produced shadows give an output overlap pattern which is subsequently decoded by means of decoding masks. The original1 and polarization-encoded2,3 optical shadow-casting systems explored so far are designed to generate only one output at a time. We report the design of a polarization-encoded PLA device where multiple outputs are generated simultaneously for all the input pixels without switching either LEDs or mask. The proposed algorithm is thereafter employed to design an optimal multiple-output binary multiplication unit.
Three-dimensional analysis of a nonlinear directional coupler
Authors: Feit M. D. , Fleck J. A.
Published: February 2023

The propagating beam method is used to carry out a fully 3-D analysis of a nonlinear optical waveguide and a directional coupler formed from a pair of nonlinear waveguides. It is shown that for interesting levels of the index nonlinearity a beam in a monomode waveguide can undergo self-focusing and self-phase modulation. The latter effect results in an apparent shifting of the propagation constant. Both effects make it difficult to describe the field accurately in terms of modes. In the light of this behavior it is not surprising that the propagating beam method and coupled-mode theory predict different characteristics for the nonlinear coupler. The self-focusing induced in the waveguides is interesting of itself because it occurs at powers several orders of magnitude below the threshold for self-focusing in an unguided medium.
Automated feature recognition from image data intermapping
Authors: Mitra Sunanda
Published: February 2023

Development in new image modalities for physiological systems generates a significant and vast amount of data for image reconstruction. Extraction of salient features for normal and anomalous patterns of such images necessitates data compression for reduction in computation time. Data compression based on visual system models can achieve compression that exceeds the classical saturation limit. In addition automated recognition of identifying patterns in an image requires image mapping and registration leading to accurate image matching for detection of change and classification of data. Since the new image modalities such as position emission tomography and magnetic resonance imaging have a wide dynamic range of the raw digital image, image enhancement techniques that include geometric transformations and remapping to match sequential images or to compare images from different modalities may have more promise in automated recognition of pattern changes.
Use of digital image analysis techniques in the image analysis of cataract eyes
Authors: Wu Ji-Zong , Zhang Feng-Lin , Huang Shi-Ke
Published: February 2023

The images of cataract eyes are analyzed and studied, making the assumption that the digital image is a spatial 2-D curved surface with different grey levels and utilizing the idea of a family of equal grey-level curves and a family of dissected grey-level curves which can be produced separately by cutting in horizontal planes and dissecting in vertical planes.
Matrix-matrix multiplication by modifying the Stanford optical vector-matrix multiplier
Authors: Gheen Gregory
Published: February 2023

This paper presents a modified version of the Stanford optical vector-matrix multiplier1 which is able to perform matrix-matrix multiplication. In the Stanford processor, an input row vector is multiplied by a matrix mask to give a resulting output column vector. If two row vectors are present in the input plane, the two output column vectors are spatially superimposed in the output plane. This makes it impossible to distinguish the two column vectors. However, if a linear phase mask (which varies in phase along the length of the row vector) is placed over one of the input row vectors, its output column vector is displaced to the side of the other column vector.
SERRS and surface fluorescence of laser dyes adsorbed on Ag film
Authors: Chen Ting , Liang Fang , Chen Wen-Ju , Mo Yu-Jun
Published: February 2023

Surface enhancement of resonance Raman scattering (SERRS) from a series of laser dyes (sodium fluorescein, rhodamine 6G, rhodamine 110, rhodamine B, DCM, and coumarins) adsorbed on chemically deposited silver film is presented. The observed Ag–O, Ag–N spectral lines at ~200 cm−1 confirm the chemisorbed nature of most dye molecules on the Ag surface. An assignment of the SERRS spectra of sodium fluorescein at various pH values verifies the structural and configurational changes of their cationic, neutral, and anionic forms and implies their different interaction behavior with the Ag surface. Sodium fluorescein is found to be a good surface fluorescence probe molecule owing to the sensitive change of its quantum efficiency with the pH value in solution. On Ag film, the fluorescence of sodium fluorescein becomes more intense as its quantum efficiency goes down. Comparing the fluorescence of laser dye on Ag film and a silica surface, we find that it is quenched on very low coverage Ag film and is enhanced on a moderate coverage Ag film.
Intensity distribution for an inhomogeneous medium
Authors: Haus Joseph W. , Rim Y. H. , Schroeder John
Published: February 2023

We model an inhomogeneous dielectric slab by a distribution of small dielectric boxes. A coherent scalar electromagnetic wave is incident on the dielectric slab, and it is transmitted or reflected at each interface. The contributions to first order in the index of refraction are summed, and diffraction in the material can be neglected. The light that emerges from the slab has a partially random phase distribution which increases the diffraction of the wave propagating in free space. The scattered intensity is ensemble averaged over the distribution of dielectric boxes; this distribution is taken to be Gaussian with a finite correlation length. Results are presented for the far-field intensity distribution of backward- and forward-scattered light. The contributions of the slab length, the wavelength of light, and the correlation length of the dielectric medium are explained. The consequences of these results to recent experiments are elucidated.
Sodium core-excited fluorescence enhancement by charge transfer
Authors: Holmgren D. E. , Prelewitz D. F.
Published: February 2023

We have demonstrated a technique which enhances emission lines of core-excited Na transitions occurring in a hollow-cathode discharge. The technique should apply to other alkali atoms and could help in identifying the core-excited visible spectra of heavier alkali atoms. In our experiment, stored population is produced by the discharge in the Na-ion metastable level 2p53s J = 2. A pulsed dye laser is used to transfer this population to a higher ion level of the 2p53p configuration. Core-excited neutral atoms are subsequently produced by an exothermic charge transfer from ground neutrals to the enhanced parent 2p53p ion population. We observe enhanced fluorescence (2 to 3 times above background levels) from neutral 2p53s3d, 2p53s4s, and possibly 2p53p2 configurations when the metastable ion population is transferred to higher ion levels.