bluuebunny/crossref_metadata_2025 huggingface dataset:
Determining isoluminance in naive subjects using heterochromatic modulation photometry
Authors: Nichols M. J. , Lindsey D. T. , Sanocki E.
Published: February 2023

We used HMP1 to establish isoluminance for 667-nm, R, and 550-nm, G, counterphase flickering lights in thirty-eight university males. In HMP, R and G are presented in a series of fixed luminance ratios (R/G) and modulation. M. is reduced to the flicker threshold. Plots of log 1/M vs log R/G are V-shaped. Isoluminance is determined by using a model to estimate the location of the V with respect to the log R/G axis. The model requires that M depend on the sensitivity to luminance contrast S and that S depend on the observer’s limiting Weber fraction C
w
, and the mean luminance L of each stimulus: S = 1q/(C
w
). We initially assumed linearity (q = 1.0). Goodness of fit was highly variable but improved significantly if q was allowed to vary (0.2 ≤ q ≤ 1.0). We also examined the assumption that C
w
is invariant with chromaticity by holding the mean luminance constant across R/G in two experienced observers. That assumption proved true for R/G less than the isoluminance point but not for greater values of R/G.
GaAs optoelectronic neurons
Authors: Lin Steven , Psaltis Demetri
Published: February 2023

Monolithically integrated optoelectronic circuits have emerged as a viable solution for implementing nonlinear operations and providing gain in optical neural networks. However, before they can be incorporated into a practical system, these devices must be in the form of large arrays and have sufficient optical gain to compensate for the optical losses due to the low efficiency of the interconnection medium. Furthermore, they much dissipate little electrical power so that the performance will not be limited by heat dissipation and at the same time exhibit high input sensitivity to accommodate the low input power received by the neurons. In this paper, several integration schemes utilizing GaAs light emitting diodes (LEDs), heterojunction bipolar phototransistors. metal-semiconductor field-effect transistors (MESFETs) and optical field-effect transistors (OPFETs) are presented. Typical results in optoelectronic neurons that incorporate phototransistors as the detectors show a differential optical gain of 10-40, which the neurons that incorporate OPFETs as detectors show a gain of approximately 80. The electrical power dissipations in these neurons are less than 2 mW/neuron and the switching energy is measured to be between 10 and 40 pJ. While these results generate optimism, issues like scalability, processing limitations and compatibility, device integrability, input-output isolation, and tradeoff between power dissipation and optical gain still need to be addressed before high density arrays can be practically incorporated in neural networks.
Optical signal processing based on wavelet transform
Authors: Lu X. J. , Katz A. , Kanterakis E. G. , Li Yao , Zhang Yan , Caviris N. P.
Published: February 2023

Signal decomposition and reconstruction based on wavelet transformations have promising uses in signal analysis, detection, and data compression. A real-time multichannel optical system for signal wavelet transform has been constructed. The optical processing system is comprised of an acoustooptic cell as the input transducer, an LCD panel as filter device, and another LCD as the sampling screen. A CCD camera serves as a detector for the processed signal representation. An optical wavelet transform is performed by spatial filtering the signal with a multichannel filter written on the LCD panel. The sampled output signals can then be used to identify (detect) desirable signal properties, data compression, or input to a secondary system (neural network) for further processing. Experimental results such as signal multiresolution representation, detail signal representation and signal reconstruction are presented.
Coherent optical processor for generating inverse filters
Authors: Abushagur Mustafa A. G. , Berinato Robert J. , Riasati Vahid
Published: February 2023

Restoration of blurred images has been approached by different optical and digital signal processing techniques, one of which is using inverse filters. Inverse filters require the generation of the function 1/H(x,y) where H(x,y) is the transfer function of the filter. In this paper we present a new algorithm to generate an inverse filter transfer function without performing the division operation directly. The algorithm is an iterative one. The condition for convergence of the algorithm is derived theoretically and confirmed with computer simulations. A new architecture for a coherent optical processor is introduced to realize the inverse filter algorithm. System requirements and speed of convergence are presented. Uses of the generated inverse filter in pattern recognition, image restoration, and deconvolution are discussed. This method is compared with the holographic inverse filter method.
Image restoration from a geometrical viewpoint
Authors: Haddad Jane , Stark Henry
Published: February 2023

In the classical image restoration problem by constrained least-squares, a constraint on the noise variance is combined with a smoothing operation to restore the image and reduce the effect of ill-conditioning. The smoothing operation is not always easy to justify from a physical point of view and therefore has an ad-hoc flavor. We propose an alternative approach to image restoration based on Hilbert space ideas in which the restored image must be at the intersection of sets of vectors that are physically constrained. This approach allows for the incorporation of significant prior knowledge, about both the noise and the signal to be restored. We compare the two approaches analytically and numerically.
Signal recovery from subband energy constraints
Authors: Stark Henry , Pang Jia
Published: February 2023

Prior knowledge of the frequency subband energy partition of an image is useful for its recovery from insufficient or noisy data. We consider how such knowledge can be associated with constraint sets and derive two algorithms for image recovery based on projection methods. One algorithm assumes prior knowledge of a reference image while the other assumes prior knowledge of a reference energy. The former leads to a convex projection algorithm while the latter leads to a generalized projection algorithm. The algorithms enable the integration of data from sensors operating in different frequency regions. Results from computer simulations are presented.
Weak localization of photons in biological tissue using a cw laser
Authors: Yoon G. , Roy D. N. G. , Benner R. E. , Straight R. C.
Published: February 2023

When light is scattered through a randomly in homogeneous medium, backscattering within a narrow cone is enhanced.1 This enhancement occurs because of the phase coherence between waves that travel the same paths in opposite directions. Recently, a femtosecond laser with a synchroscan streak camera was used to measure the enhanced backscattering.2 However, the technique is equipment-intensive. In our experiment, a simpler setup using the CCD array and cw lasers, such as a He-Ne, are used to measure the coherent peaks from biological tissues. Unlike from a liquid medium with scattering particles, the images from a solid surface show specklelike fluctuations. Ensemble averaging is required to reveal the coherent peak. The peak shapes are influenced by the beam polarization. With the polarization parallel to the plane of incidence, a sharper peak is observed. In addition, the relation of the peak shape to the optical properties such as transport mean free path and absorption length are discussed.
First-order layout of asymmetric systems
Authors: Stone Bryan D. , Forbes G. W.
Published: February 2023

One useful method in the design of axially symmetric optical systems is to specify the configuration of the system up to the final surface and then to choose the curvature of this surface so that the resulting system possesses any specified focal length. By surrendering the curvature of the final surface as a free parameter, the dimensionality of the design space is reduced by one. We discuss the generalization of such a procedure for asymmetric systems. The imposition of constraints on the first-order imagery of asymmetric systems can significantly reduce the dimensionality of the design space. For example, the design space associated with systems composed of three spherical mirrors is reduced from ten to four when such systems are required to possess the first-order imaging properties of some axially symmetric system.
Imaging in optical systems with reduced symmetry
Authors: Collins Stuart A. , Zabel Mark
Published: February 2023

We examine ray matrices for optical systems with reduced symmetry. Here we consider the description of a complete optical system as described by a 4 × 4 ray matrix. In general, all sixteen matrix elements will be nonzero. Imaging conditions are presented for the general case of astigmatic line objects written in terms of the input object information and the general ray matrix elements. An example showing the application to astigmatism in a simple optical system is presented. Finally, a scheme for finding the general ray matrix from computer ray tracing is indicated.
Photocount statistics for pump-noise-suppressed lasers
Authors: Zhu Chang , Caves Carlton M.
Published: February 2023

A laser with a Poissonian random pump, operated far above threshold, has Poissonian statistics both for the intracavity photon number and for extracavity photocounts. We analyze a pump-noise-suppressed laser using the positive P representation. When the pump noise is suppressed below a critical level, the intracavity photon-number distribution becomes sub-Poissonian.1,2 When the spontaneous decay of the upper lasing level is also eliminated, intracavity photon-number fluctuations can be diminished by a factor up to half. For counting times much shorter than the cavity decay time, the extracavity photocount statistics are essentially Poissonian, since cavity decay dominates. For counting times comparable with or larger than the cavity lifetime, the extracavity photocount statistics become sub-Poissonian. In the limit that intracavity photon-number fluctuations are diminished by one half, the extracavity photocount noise can be completely suppressed for counting times much longer than the cavity lifetime. The cavity mode occupies an incoherent superposition of two states 180° out of phase, both of which diffuse in phase. In the microlaser regime, quantum diffusion between these two states can result in 180° phase jumps, which are in addition to ordinary phase diffusion.
Use of quantum correlation for intensity noise reduction in semiconductor lasers
Authors: Karlsson Anders , Bjork Gunnar
Published: February 2023

The quantum correlation between junction voltage fluctuations1/frequency fluctuations2 and the intensity fluctuations of a semiconductor laser may be used to reduce the intensity noise. Here we address squeezed-state generation discussing both fundamental and practical limitations on noise reduction in conventional semiconductor lasers and microcavity lasers. In conventional semiconductor lasers, starting with intensity noise at the standard quantum limit, ideally a 3-dB amplitude squeezing is possible. This fundamental limit is set by spontaneous emission noise. Another fundamental limit is that noise reduction beyond the level set by optical losses and pump noise is not possible. It is also shown that the number-phase uncertainty in some conditions can reach the ultimate limit set by Heisenberg’s uncertainty principle. These conditions are clarified and a comparison made between junction voltage and frequency noise feedforward. Feedforward schemes realizing intensity noise reduction are discussed.
Measurement technique for the spatial coherence of x-ray sources
Authors: Nugent K. A. , Trebes J. E.
Published: February 2023

This paper proposes and analyzes a technique that will allow the spatial coherence properties of short-wavelength radiation sources to be measured. The technique is based on the analysis of the partially coherent diffraction patterns produced by a uniformly redundant array. The technique is particularly suited to short pulse sources and allows, assuming a Schell model for the mutual intensity function, a complete determination of the complex coherence factor for the radiation. Some measurements of the spatial coherence of the Se soft x-ray laser at the Lawrence Livermore National Laboratory are presented.
Resonant nonlinear interaction of x-ray laser radiation with plasma
Authors: Shkolnikov P. L. , Kaplan A. E.
Published: February 2023

Recent developments in x-ray laser (XRL) research makes possible the observation of x-ray resonant nonlinear effects (XRNEs). The first obvious choice1 of the environment for such effects is the plasma consisting of the same ions that gives rise to the laser action itself, both active (i.e., during the lasing process) and passive (at smaller densities). Perfect resonance between the XRL radiation and the corresponding plasma transition could lead to significant nonlinearities, e.g., to the change of the phase front up to 2π across the beam in the SE24+ XRL at the length 5-10 cm due to nonlinear refractive index.1 However, XRNEs in XRL or XRL-like plasmas re quire not only high temperature but also additional x-ray pumping (for passive plasma). We have found a number of resonant couples XRL line-plasma transition in which significant XRNEs can be observed in much simpler conditions attainable by discharge devices, and which cover wavelengths from 236.26 Å to 43.18 Å.
Characterization of the Hubble Space Telescope point spread function using phase retrieval
Authors: Fienup J. R.
Published: February 2023

Characteristics of the Hubble Space Telescope (HST) that affect image deblurring are described, with emphasis on the phase errors that are determined by phase retrieval algorithms. The aberrations of the HST are determined from the measured point spread functions (PSFs) by phase retrieval algorithms of two types: nonlinear least squares optimization over coefficients of Zernike polynomials and iterative transform algorithms. In either case, accurate and comprehensive optical system models are needed to satisfy stringent requirements on the retrieved phase error, both for the purpose of building appropriate correction optics and for analytic computation of space variant PSFs for image deblurring. This paper describes phase retrieval algorithms incorporating a system model that involves multiple-plane propagation through the system and weighted error metrics that allow for bad CCD pixels to be ignored. Analytic expressions of the gradient of the error metric, with respect to either polynomial coefficients or point-by-point phase maps, are derived that allow for a full gradient calculation to be performed with a small number of fast Fourier transforms (FFTs) independent of the number of parameters. Other system characteristics that hinder image deconvolution are described, including the telescope jitter, the space-variant nature of the system, finite spectral bandwidth, and image undersampling.
Noise effects on the transmission of optical solitons
Authors: Gordon James P.
Published: February 2023

I will discuss the limits imposed by noise on the long-distance transmission of information via optical solitons. Phase noise prohibits the use of phase sensitive systems. Amplitude (energy) noise and timing noise (the Gordon-Haus effect) yield limitations on the information rate. The recent idea of soliton guiding using filters in the line reduces the soliton fluctuations at the expense of increased background noise.
Nonlinear frequency chirping and compression of ultrashort pulses in high-gain laser amplifiers
Authors: Hong Meng-Yuan , Dienes Andrew
Published: February 2023

Fast self-phase modulation (FSPM) and slow self-phase modulation (SSPM) cause nonlinear chirp of ultrashort pulses. FSPM originates from the optical Kerr effect, while SSPM occurs in amplifiers of low saturation energy. Either effect or both can be present in laser amplifiers. We present a theoretical numerical study of the amplitude distortion and chirp of ultrashort pulses and of their compression by frequency-domain phase compensation. Various shapes (Gaussian, sech2 and asymmetrical pulses) are used in numerical integration of the nonlinear equations in the time domain. The distorted and chirped output pulses are Fourier transformed and the phases in the frequency domain are compensated by subtraction of combinations of various phase functions (second-order, third-order,1 V-shape, etc.). The phases in the frequency domain are sensitive to the shape and chirp of the output pulses resulting from the nonlinear time-domain effects. The shape and width of the compressed pulse depends on the input pulse shape, on the nonlinear gain medium, and on the compensator we use. The maximum amount of compression is related to the linear portion of the chirp. These results are relevant to dye laser, diode laser and other systems, and may be useful for understanding and improving mode-locking as well.
Generation of steerable electromagnetic waves from semiconductor surfaces by spatial light modulators
Authors: Zhang X.-C. , Auston D. H.
Published: February 2023

We describe a novel optoelectronic technique to steer a submillimeter wave with two degrees of freedom. The propagation direction and the center frequency of an electromagnetic radiation can be controlled by varying the optical pattern of a laser beam on the semiconductor surface. This technique provides a comprehensive method to steer submillimeter waves in a line-of-sight arrangement.
Nonlinear optical phase rectification
Authors: Biernacki Anne Marie , Khoury Jehad , Cronin-Golomb Mark , Woods Charles L.
Published: February 2023

Experimental results are presented for an optical phase rectifier using nonlinear optical processing. We show that this device can be used to convert complex amplitude multiplicative optical noise on a positive scalar image to additive optical noise. Our implementation of phase rectification uses diffusive photorefractive two-beam coupling in a thin crystal of barium titanate. A weak plane wave reference beam is amplified point by point to saturation using the noisy image as a strong pump. At saturation all the power at a given point in the noisy pump is transferred to the corresponding overlap point in the weak plane wave. The amplitude of the reference becomes that of the pump but, because the beam coupling occurs in the diffusion regime, the phase of the reference remains uniform after amplification. The converted image can be subjected to additional noise reduction using methods for dealing with additive (signal dependent) noise,1 or multiplicative positive scalar noise.2 Such treatment is possible because the Fourier transform of the converted image shows the diffraction pattern of the signal embedded in a broad and weak speckle pattern. Alternative implementations of real-time optical rectification using optically addressed spatial light modulators require that the output amplitude of the spatial light modulator be specifically adjusted to be the square root of the input intensity. Cascading an initial optical phase rectifier with a Fourier-plane phase-preserving thresholding device1 dramatically reduces multiplicative noise with good optical efficiency and provides a coherent signal output.
Photorefractive adaptive autocorrelation measurements of surface roughness
Authors: Khoury Jehad , Biernacki Anne Marie , Cronin-Golomb Mark , Woods Charles L.
Published: February 2023

We show that adaptive optical autocorrelation can be used to measure the typical grain size of a rough surface. According to second-order statistics,1 the autocorrelation of the optical image of a surface provides a measurement of its grain size. This grain size may be found from the ratio of the peak (de) intensity to the broad background intensity in the autocorrelation. A photorefractive autocorrelator may be made by modifying a four-wave mixing correlator.2 A beam bearing an image of the rough surface is presented as one input to a correlator using bismuth germanate (BGO) in the Fourier plane. After passage through the BGO, this beam is phase conjugated by a barium titanate crystal. The resulting complex conjugate of the image beam is presented automatically self-aligned as the second input. The third input is a plane wave in the Fourier plane. The output of the device is the autocorrelation of the constant amplitude, phase modulated surface image. This autocorrelation consists of a sharp (de component) surrounded by a broad low-intensity background of the cross correlation of the rough surface.3 The ratio of the de component to the cross correlation component is used to determine the surface roughness properties. Care was taken to capture all of the diffracted light from the surface to avoid finite aperture effects.4 The autocorrelator measurements agree with microscopic surface measurements.
Transient energy partitioning in a self-pumped phase conjugator
Authors: Aharoni A. , Bashaw M. C. , Hesselink Lambertus
Published: February 2023

We identify three separate regimes in the evolution of self-pumped phase conjugation in photorefractive media. These are evident from the time evolution of transmission, omnidirectional scatter, and phase-conjugate reflection intensities measured experimentally. Initially, beam fanning occurs, manifested by depletion of the transmitted light to one-third of its initial value. This is followed by a gradual increase in the omnidirectional scatter intensity caused by spreading of the light paths in the crystal, until almost all the crystal is flooded. Only much later does the phase-conjugate beam appear and grow to half of the input intensity at the expense of both the transmitted and scattered light. The three processes persist for different durations: fanning is appreciably faster than the other two processes. Each regime is characterized by different beam spread within the crystal, which is observed in top-view images. We postulate physical mechanisms to describe the observed phenomena.
Achromatic prism/grating and double-grating waveguide input/output couplers
Authors: Spaulding Kevin E. , Morris G. Michael
Published: February 2023

Input/output couplers are important components of many devices incorporating integrated-optical circuits. Prism couplers and grating couplers are two of the most common types of coupler in use; however, the sensitivity of the coupling characteristics to variations in the wavelength of the light can significantly limit their usefulness for many applications and/or placed tight constraints on other system components. Even thermal fluctuations associated with laser diodes can cause unacceptable changes in the performance of these components. In this paper, we show that the use of a compensating grating external to the waveguide can improve the usable wavelength range for the conventional couplers by several orders of magnitude. For double-grating couplers wavelength ranges of the order of 12 nm are shown to be possible for typical waveguide materials, and for prism/grating couplers the range can be as large as 40-200 nm, making broadband operation possible. Experimental results are presented which show excellent agreement with the theoretically predicted values.
Dispersion compensation and pulse compression using waveguide grating filters
Authors: Winick Kim A. , Roman Jose E.
Published: February 2023

In long distance optical communication systems, fiber chromatic dispersion degrades the system’s transmission capabilities by limiting the achievable bit rates and repeater spacings. One way to solve this problem is to perform dispersion compensation, or equivalently pulse compression, in the communications network. Recently, chromatic dispersion compensation in a 5-Gbit/s transmission system has been achieved with a fiber Fabry-Perot optical equalizer. The amount of dispersion compensated by a single Fabry-Perot equalizer is, however, limited. Linearly chirped waveguide grating filters can also be used for dispersion compensation as reported by Ouel lette.1 In this paper, we derive the grating parameters needed to obtain nearly optimum dispersion compensation. The resulting aperiodic grating filter has both a flat amplitude and a quadratic phase response over the pulse bandwidth. The response corresponds to the ideal transfer function for the compression linearly chirped pulses. The filter is analytically designed by cascading a Butterworth filter with an all-pass network. The pole placement of the all-pass network is selected to give the desired quadratic phase response. The grating parameters, corresponding to this filter, are obtained by solving the inverse problem for contradirectional waveguide coupling using the Gelfand-Levitan-Marchenko method.2
Self-induced transparency soliton propagation in an erbium-doped optical fiber waveguide
Authors: Nakazawa Masataka , Kimura Yasuo , Suzuki Kazunori , Kurokawa Kenji , Kubota Hirokazu
Published: February 2023

The recent development of the EDFA (erbium-doped fiber amplifier) offers the possibility for uses of the fibers to experiments on coherent pulse propagation such as self-induced transparency (SIT). The guiding of the radiation by the fiber structure eliminates diffraction effects and makes possible the interaction of the radiation with the fiber medium which has resonance effects over long distances. To date, however, experiments on SIT solitons have suffered from diffraction effects that were further complicated by nonlinear interactions. In the present paper, we report for the first time the observation of SIT soliton propagation in an erbium- doped resonant fiber waveguide.
Semiconductor microdisk lasers
Authors: Slusher R. E. , McCall S. L. , Stark J. B. , Levi A. F. J. , Logan R. A. , Pearton S. J.
Published: February 2023

Strong optical confinement in InGaAsP/InGaAs layered quantum-well microdisks is obtained due to the large refractive index contrast between the semiconductor (n=3.5) and the low-index air or SiO2 surrounding the semiconductor disk. The 5 and 10μ diameter microdisks are 500 to 1500Å thick, less than a half wavelength in the semiconductor. Whispering-gallery optical modes traveling around the microdisk edge have high Q values and only one of these modes is dominant within the photoluminescent spectral region for the InGaAs quantum well gain medium. Optically pumped microdisks lased at 1.3 to 1.5μm wavelengths when the substrate temperature was in the 77 to 270°K range. Thresholds as low as 50μW have been measured for CW pumping and substrate temperatures near 77°K. These microlasers have potential for thresholds near a microwatt if the pumped carriers are confined to the very small volume of the whispering-gallery mode. The disks are formed by selective etching of MOCVD-grown InGaAsP/InGaAs on InP substrates, resulting in a thin disk supported by an InP pedestal. High efficiency coupling of the laser field into thin optical waveguides should be possible by positioning the waveguide in the evanescent region surrounding the disks.
High efficiency, Ultrafast all-optical switching in a nonlinear directional couple in Al0.18Ga0.82As at 1550 nm
Authors: Stegeman George
Published: February 2023

There has been considerable interest in all-optical switching devices which utilize the nonresonant contribution to the nonlinear refractive index, n2. The nonresonant nature of the effects puts the response time in the femtosecond regime. We think that using semiconductors right below their two-photon edge allow use of the two photon enhanced n2. We present the first experimental demonstration of an all-optical switch, in a semiconductor waveguide, where the transmission of the device is not limited by linear or nonlinear absorption. The waveguides consist of a strip loaded waveguide. A 4 μm isolation layer of Al0.25Ga0.75As was grown on a n+ GaAs Substrate. The guiding layer consisted of 1.5 μm thick layer of Al0.18Ga0.82As and a cladding of 1.5 μm of Al0.25Ga0.75As. The cladding was etched 1.2 μm to produce 5 μm ridges for the guide spaced by 4 μm. The coupling region was 6.25 mm. The experiment were done using a color-center laser producing 10 psec pulses in the 1.55 μm spectral region. The particular directional coupler used was 0.63 coupling lengths long. Calculations using an instantaneous nonlinearity agreed very well with the experiments. Using our model we were able to estimate the n2 at 7.0- 9.0x10-14cm2/W.
Visible-light (657 nm) InGaP/InAlGaP strained quantum-well vertical-cavity surface-emitting laser
Authors: Bryan R.P. , Schneider R.P. , Lott J.A. , Olbright G.R.
Published: February 2023

We report the first visible-light (657 nm) operation of a vertical-cavity surface-emitting laser in a photopumped intrinsic structure. Vertical-cavity surface-emitting lasers (VCSELs) have recently attracted a great deal of interest because of their surface-normal operation, potential for extremely low-threshold currents, ease of fabrication of closely-spaced 1- and 2-dimensional arrays and integration with other devices such as transistors for photonic switching applications. To date operation of vertical-cavity surface-emitting laser has been limited to the range between 770 nm and 980 nm. We have extended this range into the visible where numerous applications exist including: ultrafast holographic memory, visible laser projection displays, and local area networks based on inexpensive, rugged plastic fibers. The structure was grown using low-pressure metalorganic vapor phase epitaxy in a single growth sequence on 6° misorientated (100) GaAs substrates. The active region consists In0.54Ga0.46P strained quantum wells and In0.48(AlyGal-y)0.52P (y=0.7-1.0) graded barriers whereas the distributed Bragg reflectors are AlAs/Al0.5Ga0.5As. Room temperature optical-pump lasing was achieved with a very low threshold power (~ 1 kW/cm2 average power, ~ 4 ps pulses, 82 MHz), comparable to our best AlGaAs/GaAs VCSELs operating at 850 nm. This work effectively demonstrates the viability of visible-VCSEL technology, and opens the door for a broad range of new materials and device physics research and visible-light optoelectronic applications. The SNL research is supported by DOE contract No. DE-ACO4-76DP00789.
377 fs Pulse Generation from a Passively Mode-Locked Erbium-Doped Fiber Ring Laser
Authors: Sun Y. , Sulhoff J. W. , Harvey G. T. , Zyskind J. L. , Zirngibl M. , Hong B. J. , Islam M. N. , Hugi J. , Stulz L. W. , Stone J. , DiGiovanni D. J. , Picirilli A. B. , Presby H.
Published: February 2023

We report the first sub-picosecond pulses using a multiple quantum well (MQW) saturable absorber in a mode-locked erbium doped fiber laser. The all-fiber bidirectional ring laser configuration includes a one percent output coupler, a polarization controller and a 1.23 meter erbium-doped fiber pumped by a 1480 nm laser diode. As a fast saturable absorber, we used a strained InGaAs/GaAs-on-GaAs MQW stack similar to that in Ref. 1, but with an indium content of 68%.
Tunable, synchronized, high energy, femtosecond laser pulses with Gaussian spatial profile
Authors: Wang J.-K. , Siegal Y. , Lü C. , Mazur E.
Published: February 2023

We use self-phase modulation in a single-mode fiber to produce broadband 200-μJ pulses of 42-fs duration with a nearly perfect Gaussian profile.
Russian optical materials
Authors: Petrovsky Gury , Amosov Arkady , Stepanchouk Victor , Saepoff Martin , Vaynerman Vladimir
Published: February 2023

Creation of a Joint Venture, the PETROSIL Corporation, between Dynasil International, Inc (subsidiary of Dynasil Corporation of America) and the Vaviliov Institute of Optics (St. Petersburg, Russia) has resulted in the ability to provide a broad range of Russian manufactured optical materials (fused silica/quartz, optical glasses and crystals) readily available for the Western market.
What’s constant in contrast constancy?
Authors: Brady Nuala , Field David J.
Published: February 2023

Previous work in contrast constancy1 has shown that at suprathreshold levels, sinusoidal gratings of equal amplitude are judged equal in contrast across a range of frequencies. If this result applies to broadband scenes whose amplitude spectra fall off as a function of frequency, it suggests that low frequency structures should appear higher in contrast relative to high frequency detail where the amplitude is considerably lower. Unfortunately, experiments using sinusoidal stimuli say little about how frequency selective units integrate across the spectrum. They therefore provide insufficient information to conclude anything about contrast constancy in broadband stimuli. To explore this issue, we had subjects match the contrast in pairs of bandpass noise patterns. The stimuli were generated by filtering white noise into octave wide bands with peak spatial frequency ranging from 0.25 to 32 c/deg of visual angle. Stimuli were judged equal in contrast when they had constant power or variance. In such patterns the amplitude of the peak spatial frequency falls in proportion to frequency. Contrast sensitivity, if defined in the traditional sense of amplitude inverse, will increase as a function of frequency out to 32 c/deg.
Effect of higher-order statistics of images on signal detection performance of human observers
Authors: Yao Jie , Barrett Harrison H. , Rolland Jannick P.
Published: February 2023

Recent work has shown that a linear discriminant model derived from the work of Harold Hotelling can account for a significant body of psychophysical data.1-3 This model utilizes only the first- and second-order statistics of the image and is insensitive to the shape of the grey level histogram. A natural question is whether the human observer is also insensitive to the shape of the histogram or whether human observer performance is sensitive to higher-order statistics in a image. To answer this question, a psychophysical study was conducted. The images viewed by human observers were simulated ones with inhomogeneous, random backgrounds, and Poisson noise. The mean, variance, and autocorrelation function of the images were controlled to be the same for all images. The grey level histograms of half of the images were designed to be distinctly non-Gaussian, while the other half had Gaussian histograms. Thus the first- and second-order statistics were constant, and only higher-orders were variable. Our results indicate that human detectability is independent of the shape of the grey level histograms, and that the Hotelling observer remains a good predictor of human performance in spite of this variability.
Contrast coding in the amblyopic visual system
Authors: Levi Dennis M. , Klein Stanley A.
Published: February 2023

Humans with amblyopia show marked deficits in positional judgments. We measured Vernier acuity for edges and lines over a wide range of contrast. Our results suggest that in both amblyopic and normal eyes, the spatial localization of abutting edges or lines improves with increasing stimulus contrast (with a slope of about -0.6 on log-log coordinates).
Laser beam diameter measurement using a periodic logarithmic grating
Authors: Awwal A. A. S. , Klemer D. , Birt T. , Vallapareddy M. , Kurek C. , Kauffman H. , Turumella S. , Flahive J.
Published: February 2023

Measurement of the laser beam diameter is essential for estimation of the beam divergence, in optical disks, and metrology application utilizing laser sensors. While the rectangular (Ronchi) ruling of a particular period (L) is capable of estimating the beam radius (ro) for ro/L ranging from between 0.2 and 1.2, triangular and sinusoid gratings1 extend the range to a much smaller radius compared to the grating period. The upper limit of the beam diameter measurement has recently been improved by formulation of an aperiodic ruling.2 However, because of the rectangular (discontinuous) nature of the grating, the lower values of the beam radius cannot be measured. In this work, we propose a novel grating with periodic logarithmic transmission characteristics that are capable of extending the range to both higher and lower values of the beam radius. Our proposed logarithmic periodic grating provides a linear variation of k for ro/L between 0 to 1.2. Using two or more gratings it is possible to extend the beam radius on a truly continuous scale. Gratings of such characteristics can be fabricated by contact screen method.
Phase shifting electron interferometry
Authors: Ru Qingxin , Endo Junji , Tanji Takayoshi
Published: February 2023

Electron interferometry is a powerful way to observe the phase variation of a coherent electron beam passed through samples such as quantized magnetic fluxons, and thin crystal films. Until now, the phase variation was measured by optically or digitally reconstructing the Leith-Upatnicks-type electron interferograms recorded in an electron photographic film. We describe an electron phase shifting method to directly measure electron phase variation. A field emission electron gun is used to achieve a coherent electron beam, and a Mollenstetd-Duker type biprism is installed in a 200 kV electron microscope to generate the interference pattern. The phase shift between the two interference electron beams is obtained by slightly varying the angle of the incident beam.
Femtosecond time-resolved absorption spectroscopy
Authors: Walkup Robert E.
Published: February 2023

Femtosecond time-resolved absorption spectroscopy is discussed in terms of a simple model in which the collision complex is regarded as a time- dependent dipole oscillator. This model is applied to recent measurements of the absorption spectra molecules in the process of dissociating. When the dissociation process yields a narrow wave packet, the dominant feature in the absorption spectra is generally a sharp feature at the transition frequency for separated atoms. The spectrum in this impact region reflects an effective phase- shift for a partial collision which begins at the time of excitation by the probe pulse. By inspection of the data, one can directly see when the atoms have reached the Weisskopf radius, the point where the partial collision provides a phase- shift of 1 radian. Moreover, by measuring the phase-shift as a function of pump-probe delay, one can recover the molecular transition frequency along the path of dissociation. For broad wave packets, there can be a large phase-shift spread, and the spectra approach a statistical limit, in which the absorption profile directly reflects the distribution of molecular transition frequencies at the time of excitation by the probe pulse. Measurements of the spectral power density of the transmitted probe pulse, are compared and contrasted with measurements based on laser-induced fluorescence.
Ballistic electron diffraction by semiconductor gratings: analysis, design, and analogies to electromagnetic diffraction
Authors: Henderson Gregory N. , Glytsis Elias N. , Gaylord Thomas K.
Published: February 2023

Due to recent advances in the growth and fabrication of nanostructure electronic devices, it has been demonstrated that ballistic electron waves can be reflected, refracted, interfered, waveguided, and diffracted in a manner analogous to electromagnetic optics.1 This has provided a surge of interest in the new field of semiconductor electron wave optics. In this paper, ballistic electron grating diffraction by a grating with an arbitrary effective mass and/or potential energy profile is analyzed using a rigorous coupled-wave analysis (RCWA). These results are related to electromagnetic diffraction by a permittivity grating. It is shown that electron diffraction by a kinetic energy grating is exactly analogous to TE electromagnetic diffraction and that electron diffraction by an effective mass grating is exactly analogous to TM electromagnetic diffraction. Approximate solutions to the RCWA equations are derived that are equivalent to Bragg regime and Raman-Nath diffraction. Using these results, sample electron wave diffractive switches and multiplexers are designed and analyzed. Both Bragg regime and Raman-Nath regime devices are designed using achievable device configurations. The angular and energy selectivity of these devices are examined.
Electron waveguiding in quantum wells, voltage- induced quantum wells, and quantum barriers
Authors: Wilson D. W. , Glytsis E. N. , Gaylord T. K.
Published: February 2023

Recent experiments have produced ballistic electron transport over micron lengths in semiconductor 2-D electron gas (2DEG) systems. This has made possible the demonstration of electron devices that exhibit impressive optical like behavior.1-3 In these devices, the quantum well at the 2DEG interface acts as a slab waveguide for ballistic electron waves. We show how finite- potential heterostructure wells, homostructure voltage-induced wells, and heterostructure barriers can act as electron slab waveguides. We find that the waveguiding in all these structures is described by a single dispersion relation and can occur at energies above all band edges. The guided-mode cutoffs, electron velocity, effective mass, density of states, and ballistic current density are determined. A multiple layer theory is developed to analyze wells and barriers with arbitrary potential energy profiles. The maximum ballistic guided current flowing in a given direction for a ten-monolayer Ga0.75Al0.25As/GaAs/- Ga0.9Al0.1. As waveguide is found to be 2.3 mA/μm of waveguide width. This relatively large value suggests that interconnecting multiple ballistic electron devices through a single slab waveguide may be feasible.
Filling-in of Fraunhofer lines in the ocean by both Raman and Brillouin scattering
Authors: Kattawar George W. , Xu Xin
Published: February 2023

One of the important areas in ocean optics still in its infancy is the effect of both Raman and Brillouin scattering on certain high resolution spectroscopic features in the apparent optical properties of the ocean. We have developed a Monte Carlo program that is capable of accurately accounting for both Raman and Brillouin scattering in the ocean. The program is capable of coupling an inhomogeneous atmosphere to an inhomogeneous ocean through a dielectric interface. We present results showing the effect of these inelastic phenomena on the filling-in of certain Fraunhofer lines in the solar spectrum. We show how the amount of fill varies with solar zenith angle, angle of view, depth in the ocean, and magnitude of the cross sections. By monitoring these effects a great deal can be learned about the relative importance of these inelastic processes in oceanic optics.
Measuring oceanic absorption with the integrating cavity absorption meter
Authors: Fry Edward S. , Kattawar George W. , Pope Robin M. , Montgomery Robbin L.
Published: February 2023

We have developed an integrating cavity absorption meter that is, in principal, rigorously independent of scattering effects. We review the theoretical basis for the instrument, describe one of the prototypes that has been constructed and tested, and present experimental results for absorption spectra of various samples. Measurement results from an August 1990 optical closure cruise for particulate and dissolved absorption of oceanic samples are presented. The particulate absorption measurements are compared to results for the same samples measured using the glass fiber filter technique. Results are also presented for absorption measurements of a laboratory phytoplankton culture as a function of time after treatment with a herbicide. Specifically, a phytoplankton culture was injected with DCMU and the absorption spectra of this culture was compared with that of a control culture over a 2-week period. Results show the effects of the herbicide on the growth of the culture.
High-gain InGaAs heterojunction phototransistor operating at 930 nm using resonant periodic absorption for surface-emitting laser logic devices
Authors: Bryan R. P. , Olbright G. R. , Brennan T. M. , Fu W. S. , Tsao J. Y.
Published: February 2023

Using a new technique called resonant periodic absorption, we have achieved high-optical gain in InGaAs/GaAs heterojunction phototransistors (HPTs) for wavelengths at which GaAs substrates are transparent(>925 nm). These devices are promising for optoelectronic interconnect, optical-logic device, neural network, and lightwave communication uses. Specifically, these InGaAs HPTs are ideally suited for integration with InGaAs vertical cavity surface-emitting laser (VCSEL) diodes to produce monolithic surface-emitting laser logic (CELL) devices.1 Resonant periodic absorption is achieved in an asymmetric microresonator consisting of a strained layer InGaAs/GaAs HPT sandwiched between distributed Bragg reflectors. By aligning the optical intensity maxima with the InGaAs quantum wells in the collector region of the phototransistor, we are able to achieve high gain(>600 at a 4.0-V bias and a 50-mA collector current) at wavelengths >900 nm from a structure in which the absorption coefficient, aL, is only ~0.1. We describe the design, growth, and fabrication of a monolithic CELL consisting of an InGaAs/GaAs HPT and VCSEL operating at 930 nm. CELL devices are cascadable optical logic devices (smart pixels) in which incident light generates photocurrent in the phototransistor that is internally amplified and then used to drive the VCSEL above threshold. These devices will operate at a wavelength that is in the passband of the GaAs substrate and therefore avoid the problems associated with the removal of the substrate in AlGaAs/GaAs CELL structures operating in transmission.
Optimization of absorption of self electrooptic effect devices: a systems perspective
Authors: Lentine A. L. , Miller D. A. B. , Chirovsky L. M. F. , D'Asaro L. A.
Published: February 2023

For self electrooptic effect devices (SEEDs)1 and for some smart pixels,2 similar devices are used for optical modulators and detectors. Maximizing the contrast ratio or the difference in optical transmissivity (or reflectivity for reflection mode devices3) of the devices in the two states does not give optimum performance because sufficient light must be absorbed in the detector. We calculate the bit rate and signal tolerances for symmetric SEEDs (S-SEEDs) as a function of the absorption coefficients of the devices using a two-state absorption model. To maximize the system bit rate, we show that the optical transmissivities (or reflectivities) for a S-SEED for the two states should be ~58 and 0%. The calculated system bit rate agrees with measured results for a photonic ring counter to within 20%. We also discuss optimum absorptions for logic-SEEDs (L-SEEDs), currently the only demonstrated quantum well smart pixel technology,4 and for SEEDs that have electronic gain.2
Spatial light modulator-based real-time multiple beam splitter
Authors: Tam Eddy C. , Zhou Shaomin , Song Qiwang
Published: February 2023

Two-dimensional multiple beam splitters (MBSs) are needed in parallel processing, optical communication, optical interconnects, and applications alike. In this paper, we demonstrate the use of a liquid crystal television spatial light modulator (in phase-only modulation mode) to implement a real-time programmable MBS. The SLM we used has a pixel size of the order of 80 µm, and is capable of phase modulation at a continuous level. The structure of the MBS is first designed with a computer based on an adaptive iterative technique. The major physical features of the SLM, i.e., the pixel gap (or the dead zone), phase and amplitude variations of the SLMs grid structure, have also been considered in designing the MBS. The computer-designed MBS is then sent to the SLM, and another iteration based on the feedback in an optical architecture is conducted. The purpose of this step is to fine tune the design of the MBS to account for the detail pixel structure of the SLM. As a result, an optimum programmable MBS with high diffraction efficiency and high diffraction-spots uniformity can be made.