bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Debye effect
Authors: Lawandy N. M. , MacDonald R.
Published: February 2023

The interaction of acoustic waves with charged colloids results in electrical signals. This phenomena, known as the Debye effect, results due to the instantaneous separation between the charged colloidal particle and its surrounding double layer. The separation results in a macroscopic polarization within the medium, which creates a voltage difference. This work demonstrates that radiation pressure forces can be used to impulsively move the colloid, resulting in a dipolar electric field. Experiments were performed using 100 ps, 1.06-µm pulses and 80 ps, 532-nm pulses incident on aqueous colloidal suspensions of charged latex spheres. Experiments were performed on random colloidal suspensions as well as high density crystals ordered in an fcc lattice. The dependence of the effect on sphere size and pulse intensity are presented. The effect exhibits the expected polarity when opposite sides of the sample are illuminated. Using electro-optic sampling, the dynamics of the double layer response can be directly probed on a picosecond time scale.
Optical matrix inversion processor
Authors: Abushagur Mustafa A. G. , Atashi Adel
Published: February 2023

Linear algebra problem solving constitutes a major part of all scientific and engineering problems. One of the basic operations in linear algebra is computing the inverse of the matrix that can be used in solving systems of linear equations among others. The proposed processor is based on a parallel optical vector-matrix multiplier. The operation is an iterative one producing an approximate matrix inverse. The computing complexity of this algorithm for computing the inverse of an N × N matrix is O(N), while the complexity using a sequential electronic computer is O(N3). Reducing complexity results in less computing time, which is very appealing for solving large systems of equations like those of computational fluid dynamics problems.
Conservation laws and inverse problems for partially coherent free fields
Authors: Kowarz Marek W. , Wolf Emil
Published: February 2023

Excellent approximations to many optical fields are provided by free fields, i.e., fields in which contributions from evanescent waves are neglected. In this paper, we show that certain conservation laws hold for fields of this kind, which in some respects resemble the usual energy conservation laws. In particular we find that the field spectrum, integrated over a cross-section perpendicular to any chosen direction, is invariant on propagation. Similar results hold for the Wigner form of the cross-spectral density. These conservation laws provide insight and simple solutions to some inverse problems for partially coherent fields. As an example, we show that they may be used to determine the normalized spectrum of a planar, secondary source from the knowledge of the field spectrum in a plane parallel to the source plane. We also show that the new conservation laws make it possible to determine the cross-spectral density of a quasihomogeneous source from the knowledge of the cross-spectral density of the field at all pairs of points in any plane parallel to the source plane.
Neural organization of binocular vision
Authors: Freeman Ralph D. , Ohzawa Izumi , DeAngelis Gregory C.
Published: February 2023

The first major stage of binocular integration in the visual pathways occurs at the level of striate cortex. Neurons here are thought to process stereoscopic depth information from incongruities in left and right eye receptive fields. This idea is hampered by serious theoretical constraints that prevent an integration of monocular form and binocular disparity encoding. We propose an alternative scheme that provides for this integration in a neurally parsimonious manner. In the alternative notion, disparity information is conveyed by differences in receptive field structure (phase) between left and right eyes. This requires that some first-order cortical neurons (simple cells) have a different receptive field structure for left and right eyes. Detailed tests of cells in the cat’s striate cortex confirm that this requirement holds. Furthermore, there is evidence of a specialization for horizontal disparities which is required for animals with laterally separated eyes. Additional tests of second-order cortical neurons (complex cells) demonstrate that a subset are specialized for the processing of disparity information provided by small groups of simple cells. Considered together, these experimental tests are consistent with the alternative notion of the neural basis of depth discrimination.
Incoherent dynamic lenslet array processor for neural networks
Authors: Wiley D. J. , Glaser I. , Jenkins B. K. , Sawchuk A. A.
Published: February 2023

Optical techniques have shown promise for massively parallel interconnection of simple processors. These techniques may offer advantages in parallel computing and neural network implementation. The lenslet array processor is an incoherent optoelectronic processor that offers matrix algebraic operations with 2-D arrays of input and output data. Inner and outer products on bipolar analog data can be performed, as well as binary interconnections of 2-D arrays. Bipolar data is accommodated by using a combination of optical and electronic processing steps. These operations form the basis for implementation of a wide variety of neural network models. Incorporation of SLMs allows implementation of adaptive networks; competitive learning and multiple parallel Perceptron network implementations are described. An experimental system using video technology and incoherent, polychromatic light is described. A frame-grabber card in a PC stores and processes images being sent to and received from the optics. Subtraction is performed electronically in the PC. A liquid crystal TV controls the input to the network, and a CRT writes the interconnection weights onto a liquid crystal light valve. A CCD camera captures the result of the weighted optical interconnection.
Cavity quantum electrodynamics
Authors: Mossberg T.
Published: February 2023

Cavities are employed to effect various changes in the electromagnetic reservoir to which specimen atoms are coupled. Reservoirs of diverse character ranging from single-modelike to strongly frequency dependent can be realized. Generally speaking, atoms coupled to perturbed electromagnetic reservoirs display novel dynamics that can be of practical as well as fundamental importance.
Experimental results for atmospheric correction using laser guide stars
Authors: Fugate Robert Q.
Published: February 2023

The Phillips Laboratory has been developing laser guide star adaptive optics since 1982 under a military research program that has only recently permitted public release of data. In 1983 we demonstrated the feasibility of the laser guide star concept in an experiment at the Starfire Optical Range (SOR). The experiment quantitatively confirmed D. L. Fried’s theory that the wavefront error incurred by using the laser guide star instead of a real guide star increases with the 5/3 power of the aperture diameter. In early 1989 we successfully operated a closed loop, continuous correction adaptive optics system on the SOR 1.5-m telescope using a copper vapor laser to generate artificial beacons by Rayleigh backscatter at 10-km range.
Uses of smart pixels in photonic switching
Authors: Hinton H. S.
Published: February 2023

This paper begins with a discussion of the advantages of smart pixels used in photonic switching systems based on free-space digital optics. This is followed with a description of the optics and optical hardware required for such systems. Finally, several smart pixel-based photonic switching architectures are reviewed.
New probe for imaging of optical phase objects
Authors: Yi Ming , Yang Xuan-Min , Fan Zi-Yu , Zhu Li , Yang Xuan-Min
Published: February 2023

The imaging of optical microphase objects is an important research area attracting much successful effort, such as the phase contrast method and the center dark field method. Generally, the application is not as simple as the theory suggests. In this paper, we have analyzed the interaction between optical phase objects and light, specifically the spatial frequency spectra. The characters for imaging phase objects and a potential way to obtain it have been studied based on this analysis. As a result, a theory to summarize those methods and a π phase plate technique have been developed. The new technique for imaging the phase grating has been utilized in these experiments. This process resulted in successful imaging of the acoustic phase grating, and provided accurate and valuable information. Compared with other methods, the π phase plate method has many advantages, for example, it is clear and easy to understand theoretically, and it has reduced the requirements for the apparatus, especially the phase compensatory plate. Therefore the π phase plate method has great potential in both future research of imaging and industrial manufacturing.
Contrast affects perceived depth
Authors: Rohaly Ann Marie , Wilson Hugh R.
Published: February 2023

It is now generally accepted that depth information is processed by a set of mechanisms, each tuned to a restricted range of disparities. The contrast dependence of stereoacuity argues that these mechanisms are also tuned for contrast. Due to the resulting confounding of contrast and disparity, it should be possible to alter the perceived depth of a test pattern simply by changing its contrast. We tested this hypothesis with a series of depth matching experiments. Over the range of 10–100% contrast, perceived depth varies as a power law function of contrast. In addition, at low contrasts the test pattern always appears to be farther away than the 50% contrast comparison pattern, regardless of whether the test disparity is crossed or uncrossed. In other words, the test appears to have more depth than the comparison in the uncrossed case and less depth (closer to the fronto-parallel plane) than the comparison in the crossed case. Although the test pattern appears to be smaller than the comparison at low contrasts, control experiments indicate that this is not the result of inferring distance from size.
Interaction of color and luminance in stereo perception
Authors: Kovacs Ilona , Papathomas Thomas V. , Julesz Bela
Published: February 2023

Although it is well known that stereo perception is seriously impaired at equiluminance,1 the role of color in stereopsis and its interaction with other visual attributes cannot be studied adequately with equiluminant stimuli alone. The interaction of color and luminance signals in the perception of depth is of particular importance. We have developed a technique, based on multiattribute random-dot stereograms,2 which allows us to study such interactions in global stereopsis (see Ref. 3 for a study on the role of color in local stereopsis). Basically, the technique enables one to render a color-defined cyclopean object simultaneously with, but independently of, a luminance-defined object. Thus, among the options, color (C) can define an object while the luminance (L) is randomized (C × L, C across L), or they can both define the same object (C + L), or C defines one object while L defines another object at a different disparity (C ⟷ L, C against L).
Resonance fluorescence with squeezed light excitation
Authors: Vyas Reeta , Singh Surendra
Published: February 2023

Resonance fluorescence from a single two-level atom driven by a beam of squeezed light is studied in the weak field limit. We consider the situation where the atom is coupled to the ordinary vacuum and only a few field modes corresponding to the driving field are squeezed. The field produced by the degenerate optical parametric oscillator is used as the driving field. This driving field can be described in terms of two real independent Gaussian processes. Heisenberg equations of motion are solved in the steady-state, and analytic expressions for the fluorescent light intensity and the spectrum of fluorescent light are derived. We also consider photon statistics of fluorescent light. In particular, squeezing, antibunching, and sub-Poissonian statistics of fluorescent photons are discussed and analytic expressions for the quadrature variance and the two-time intensity correlation function are presented. Contrary to the case of coherent excitation the second-order intensity correlation function does not factorize.
First analysis of artificial guide star focus anisoplanatism
Authors: Fried David L. , Roberts Phillip H.
Published: February 2023

The backscatter from a laser beam focused in the atmosphere can be used as an artificial guide star reference for the wavefront sensor of an adaptive optics astronomical imaging system. The wavefront information thus provided represents probing of the turbulence along a somewhat different propagation path than the path the starlight to be imaged will follow, with a resultant discrepancy in the wavefront sensor’s output. This discrepancy has become known as focus anisoplanatism. In the period Dec. 81-Jan. 82 we carried out a detailed analysis of the effect of focus anisoplanatism on image resolution (or rather on antenna gain). Our results indicated that the effective diameter, corresponding in a diffraction-limited sense to the achievable antenna gain could be interestingly large, e.g., of the order of 0.5 m for operation at a wavelength as short as 0.35 µm, if the backscatter altitude were 20 km. A copy of the original manuscript of our analysis is exhibited and the analysis reviewed. A graph of the originally obtained results is presented.
Image formation of dilute arrays for optical information processing
Authors: Lohmann Adolf W.
Published: February 2023

A typical job in 3-D optoelectronics is image formation of a regular array of point sources onto a similar array of detector elements. Most likely the array will be dilute, meaning light sources that are small compared to the distance between sources. The distance from source array to detector array will be in the order of the array size, if a bulk component such as a beam splitter has to be placed somewhere between source array and detector array. We compare three different optical setups, which employ macrolenses and/or array of micro lenses. The comparison is performed in the spirit of complexity theory. That provides us with an understanding of the scaling behavior of the three setups.
Measurement of the forward light scattering from polystyrene spheres with a barium titanate crystal
Authors: Oh Choonghoon , Padmabandu G. G. , Fry Edward S.
Published: February 2023

Measurement of forward light scattering is important for several reasons. Due to the sheer magnitude of the volume scattering function in the forward direction, it must be resolved at and near zero degrees to do high resolution imagery calculations and to predict laser beam propagation. Another fundamental reason is the direct relationship of the forwardscattering amplitude to the extinction cross section via the optical theorem. The major difficulty in measuring the forwardscattering is the presence of the intense unscattered incident field. A novelty filter based on beam fanning in a photorefractive barium titanate crystal is used to separate the scattered and unscattered beams. Because of the constant Brownian motion of the aerosol particles the scattered field has a time dependence; this is a necessary condition to take advantage of the novelty filter. In this work we present measurements of intensity of the scattered field as a function of angle at and near zero degrees for polystyrene spheres of radii ranging from 5 to 45 μm.
Photoresist exposure control using light scatter
Authors: Hickman K. C. , Gaspar S. M. , Bishop K. P. , Naqvi S. S. , McNeil J. R.
Published: February 2023

Design geometries of microelectronics devices are shrinking. Today, CDs of 0.8 μm are common, and 0.35 μm and smaller are goals of the near future. These small geometries place increasingly stringent requirements on fabrication process control, such as photoresist exposure. This is especially significant when it is realized that up to 50% of the processing time for advanced devices can be in lithography. Changes in the optical properties of a surface influence the amount of light coupled into photoresist during exposure. This, in turn, causes a change in the CD of the developed photoresist pattern, which is undesirable in light of shrinking CDs. Changes in optical properties of a surface occur, for example, from variations in optical thickness of films (including photoresist) on a wafer and from variation in optical thickness of films (including photoresist) on a wafer and from variation to metal roughness that might occur from the process variations. There is presently no direct monitor of photoresist exposure. Calibration samples (send-ahead wafers) are used to determine optimal exposure time; subsequent processing is performed open loop using this established constant exposure time. Slight changes in optical properties of wafers are not accommodated in this arrangement. We have used light scattered from latent images in photoresist as a direct monitor of exposure dose. Using this technique, we have demonstrated a 3× improvement in CD control for variations of film thickness on wafers compared to using fixed exposure time. The technique can be incorporated for real-time control of photoresist exposure.
Determination of polarization measurement precision
Authors: McElhaney Russell W.
Published: February 2023

Recent investigations in the detection and measurement of the linear polarization characteristics of a scene have suggested that polarization-sensitive sensors offer increased capability (over conventional sensors) in: (1) distinguishing targets (polarized) from a cluttered background (unpolarized), (2) discriminating between targets with different polarization signatures, and/or (3) establishing the relative orientation of a target. However, the detection/measurement of the linear polarization descriptors of a scene (degree of linear polarization, Stokes Vector, etc.) involves a nontrivial, arithmetic combination of a specific set of intensity measurements—each measurement with inherent accuracy/precision errors. The precision of the derived polarization parameters is seen to be a complex function of the precision of the individual intensity measurements and the specific measurement technique employed. This paper examines the relationship between measurement precision error [in terms of signal-to-noise ratio (SNR)] and the precision of two key derived polarization parameters (degree of linear polarization and linear polarization angle). The relationship is quantified for three widely accepted polarization measurement techniques (Pickering, modified Pickering, and Fessenkov methods). This analysis provides the system designer with a solid reference for determining the required SNR to achieve the polarization measurement precision necessary to meet system requirements.
Ultracompact waveguide optoelectronics on InP
Authors: Deri R. J.
Published: February 2023

Monolithic integration of optical waveguides with sources or detectors is of current interest for enhancing the functionality of optoelectronic circuits with on-chip optical signal processing. A major drawback to this approach has been the large size, typically many millimeters, required for optical routing structures such as directional couplers. Large chip size is incompatible with the high cost of the III-V materials needed for sources and detectors in fiber optic applications. This paper describes recent demonstrations of compact (< 1 mm long), easily integrable low-loss couplers. We show that self-imaging in over-moded couplers achieves compact lithographically defined devices, and that vertical coupling can provide extremely small (< 100 μm) devices with no critical lithographic tolerances. Both approaches result in couplers that are insensitive to the operating optical wavelength. Vertical impedance matching is shown to provide simple integration of these devices with high performance photodetectors, without epitaxial regrowth.
Computation of photonic bands
Authors: Leung K. M.
Published: February 2023

Since its introduction a few years ago, the idea of photonic bands in 3-D periodic dielectric structures has been rapidly gaining acceptance. Initial theoretical calculations of photonic bands based on the scalar wave equation have quickly been replaced by full vector wave calculations based on Maxwell’s equations. Realistic computations can now be made using the plane-wave method. A structure exhibiting a bonafide forbidden frequency gap has recently been proposed by Yablonovitch. Results computed for the bands and the attenuation length within the band gap are in excellent agreement with experimental findings. The gap size to mid-gap ratio is found to be ~19%. The gap persists for refractive-index contrast as low as 2. In a similar structure more appropriate for microfabrication, the relative gap size can be as large as 21%. The minimum threshold refractive-index contrast for a true gap, however, remains ~2.
Optical limiting at visible wavelengths using free-carrier nonlinearities in GaP
Authors: Allan G. R. , Rychnovsky S. R. , Smirl Arthur L. , Boggess Thomas F.
Published: February 2023

We report use of free-carrier absorption and refraction in GaP in optical limiting of visible radiation. Excitation of GaP at wavelengths between ~446–546 nm results in indirect transitions between the valence band and the conduction band minima near the χ-points. The resulting photogenerated electron–hole pairs provide a carrier density dependent source of absorption and refraction. On time scales short compared with recombination and diffusion times, such optical nonlinearities are strictly fluence dependent. Limiters utilizing GaP therefore can operate over a wide range of pulse durations. Furthermore, the incorporation of mid-gap impurity states in GaP may extend the operation of the limiter below the intrinsic indirect absorption edge, thereby providing a relatively broadband yet resonant response. The configuration discussed here is achieved by focusing a ~30-ps 532-nm pulse into a thin wafer of GaP, recollimating the beam with a second identical lens, and then transmitting the beam through an aperture to take advantage of the optically induced lensing in the sample. As the fluence at the sample is increased, the system transmission decreases, and the output fluence becomes clamped at ~0.6 μJ/cm2 for fluences at the sample greater than ~100 mJ/cm2. Pump-probe measurements verify that the nonlinearity depends only on the accumulated carrier density and that is recovers on a time scale long compared with a nanosecond. This result indicates that the device should function equally well for nanosecond excitation.
Multifrequency dispersive optical bistability in nonlinear ring cavities
Authors: Banerjee Partha P. , Pliszka Pawel
Published: February 2023

We analyze a simple model of dispersive optical bistability in a ring cavity filled with a Kerr medium in the presence of two and three (carrier and one sideband pair) different frequencies. The steady-state characteristics are shown and the condition for selective switching is studied. We show the phenomenon of the so-called competition for resonance between different frequencies. The characteristic phenomenon of locking of the output intensities is presented. The model of two frequencies may also be used to describe bistability in the presence of two different polarizations. For three frequencies our discussion is based on the rigorous propagation equations, which admit a real Hamiltonian description and are completely integrable. We also discuss a general numerical approach, based on a relaxation method, for finding steady-state solutions and checking their stability. The relaxation dynamics is physically related to a finite response time of the medium. The effect of this finite response time on the stability of the steady states and on the dynamics is also discussed.
Propagation of solitons in a nonlinear loop mirror
Authors: Duling I. N. , Chen C. J. , Menyuk C.
Published: February 2023

Solitonlike pulses traveling through a nonlinear loop mirror (NOLM) have shown behavior significantly different than that on nonsoliton pulses. In addition, these devices have been used to passively mode-lock fiber lasers operating in the soliton forming wavelength range. For this reason it is necessary to have a clear picture of how the NOLM responds for different input conditions and loop lengths.
Vertical cavity lasers with a metallic intracavity laser
Authors: Jewell J. L. , Scherer A. , Brennan T. , Asom M. T. , Focht M. , Tell B. , Brown-Goebeler K. , Olbright G. R. , Harbison J. P. , Florez L. T.
Published: February 2023

Efficiency and maximum power obtainable from vertical cavity lasers (VCL) are low at present due to high series resistance. It is possible to circumvent this and maintain high cavity quality by using a highly conductive, extremely thin metallic layer located in a node (null) of the standing waves just above the active layer. The fabrication was as follows: Bottom mirror and active region were essentially the same as in previous VCLs, and n-doped Al
x
Ga1-
x
As/AlAs mirror with an active region about a quarterwave thick. After ~1000 Å of p-doped AlGaAs on top of the active region the epitaxial growth stopped. An ~50-Å Au layer was evaporated on top of this and a conventional dielectric mirror (TiO2/SiO2) completed the structure. Current is injected from thicker Au contacts just to the side of the cavity into the thin layer, then directly into the p-doped layer just above (~1000 Å) the active region. Optically pumped lasing occurred at 240-pj input to such a device. The l–V response of a separate similar device, 10 μm in diameter, showed a nearly constant ~100 ohm resistance. More precise fabrication should yield better performance, both optically and electrically and electrically, in a single device.
Temperature dependence and thermal dissipation limits in operation of vertical cavity surface-emitting laser arrays
Authors: Von Lehmen A. , Banwell T. , Mahoney D. , Carrion L. , Chang-Hasnain C. , Florez L. T. , Harbison J. P.
Published: February 2023

Vertical cavity surface-emitting lasers are a potential device technology for a variety of uses ranging from optical interconnects to displays. Two related issues of crucial importance for this device technology are the temperature dependence of the performance of individual devices, and limitations imposed on operation of an N × N array by thermal dissipation considerations. Here we discuss both issues. First, we report experimental measurements of the temperature dependence of threshold current, maximum power, and differential efficiency for MBE-grown InGa-As/GaAs vertical cavity surface-emitting lasers with current confinement provided by proton implantation techniques. We observe maximum cw outputs in the temperature range ~11–85°C pf ~8 mW–100 μW for a 20-μm diameter device. Device threshold current over this temperature range varies from ≃2–22 mA. We also report a calculation that set limits on per-element power dissipation in an 8 × 8 array as a function of temperature, element spacing and thermal resistance. These results essentially delineate the range of current-voltage for each element (laser) given a fixed maximum desired temperature rise.
Deterministic neural network used in the nesting problem
Authors: Servin M. , Cuevas F. J. , Davila A. , Marroquin J. L.
Published: February 2023

A deterministic neural network, used to solve the optimizing problem of nesting (how to put as many 2-D patterns as possible in a given irregular and finite larger area), is presented. Nesting is one of the most important operations that many industries have to deal with; such industries have to cut raw material into patterns that will be the building blocks of a product. Artificial neural networks have proved to be useful in solving n-p kind of problems where the number of possible solutions grow exponentially as the problem gets bigger. It is well known that any deterministic optimizing network of this type will in general find a local minimum of the problem at hand, close enough to the global minimum to be worth considering. We propose an internal energy function E that translates into mathematical terms the goal and the constraints of the nesting problem. Afterward a free energy F expression for this system, which is valid at high temperatures, is derived. A synchronous continuous system is proposed to find a minimum of this free energy and a solution to the problem is found, continuously decreasing the absolute temperature parameter of this system until it reaches the zero temperature where the minimum of the internal energy and the minimum of the free energy coincides, having as a consequence a solution to the initial nesting problem.
The bifurcating neuron
Authors: Farhat Nabil H. , Eldefrawy Mostafa
Published: February 2023

Present neural network models ignore temporal considerations, and hence synchronicity in neural networks, by representing neuron response with a transfer function relating frequency of action potentials (firing frequency) to activation potential. Models of living neuron based on the Hudgkin-Huxley model of the excitable membrane of the squid’s axon and its Fitzhugh-Nagumo approximation, exhibit much more complex and rich behavior than that described by firing frequency-activation potential models. We describe the theory, operation, and properties of an integrate-and-fire neuron which we call the bifurcating neuron and show it has rich complex behavior capable of exhibiting synchronous firing or phase-locked operation, periodic firing, chaotic firing, bursting, and bifurcation between these modes of operation. An optoelectronic realization of the bifurcating neuron in the form of a nonlinear relaxation oscillator is described and experimental verification of its behavior is presented. The circuit shows that bifurcating neuron networks could be easier to construct than sigmoidal neuron networks. A population of bifurcating neurons, coupled through a connection matrix, represent a bifurcating neural network that is expected to exhibit properties not normally observed in networks of sigmoidal neurons. These include feature binding, cognition, quenching, and chaos, all of which play a role in higher level brain function. We expect the bifurcating neuron will lead to a new generation of neural networks more neuromorphic and hence more powerful than networks being dealt with today and that optics will play a role in the implementation of bifurcating neuron networks.
Flicker photometry as a function of retinal illuminance
Authors: Jin Qiu , Pokorny Joel , Smith Vivianne C.
Published: February 2023

We measured spectral sensitivity for wavelengths 500–700 nm by heterochromatic flicker photometry (HFP) to a 570-nm standard light. We also measured spectral sensitivity for the same wavelengths using a flickering light on a 570-nm background. The alternation rate 16 Hz for both protocols. The parameter was the retinal illuminance of the 570-nm standard in the HFP protocol and the 570-nm background in the flicker sensitivity protocol. Retinal illuminance varied over a three-log unit range from 1.6 to 500 td in half-log unit steps. We then fit the HFP spectral sensitivity data at each retinal illuminance by an additive combination of Smith-Pokorny fundamentals. The flicker sensitivity data were treated in the same way. From these functions we could derive the relative change in LWS/MWS components for HFP as a function of retinal illuminance. The HFP functions showed a decrease in LWS/MWS as retinal illuminance increased, similar to reported data. From the flicker sensitivity data, we could also derive the amount of LWS and MWS components as function of background retinal illuminance. These could be plotted as a threshold-vs-radiance function and traced out a Weber function.
Experimental study of a high-gain Ne-like Ge soft x-ray laser by double-massive target coupling
Authors: Shiji Wang , Yuan Gu , Guanlin Zhou , Songyu Yu , Sizu Fu , Yuanlong Ni , Jiang Wu , Guoqiang Han , Zhengliang Zhou , Gucping Zhang , Jiatian Sheng , Huimin Peng , Yunfeng Shao , Zunqi Lin , Shuseng Wang , Wannian Chen
Published: February 2023

By means of a novel double-massive target coupling experimental design, the adverse refraction effect of the x-ray laser beam was reduced, and significant amplification on five lasing lines was observed with wavelengths at 19.6, 23.2, 23.6, 24.7 and 28.6 nm from 3p–3s transitions in Ne-like Ge ions along an elongated plasma column. The fit gain coefficients did not decrease apparently up to 4.0 cm in total target length. Maximum gain-length product values achieved were over 14 for two of the five lasing lines at 23.2 and 23.6 nm. Temporally resolved measurements of x-ray laser spectra, which were made with a soft x-ray streak camera coupled to a flat-field grazing-incidence grating spectrograph, indicated that the duration of the gain was ~0.8 ns comparable to the Gaussian driving laser pulse width, 1 ns (FWHM) in our experiment. The measured divergence and refraction angles of the x-ray laser beam at 23.6 nm are presented. The dimension and position of the gain region were estimated.
Soft x-ray source for space astronomy studies
Authors: Sun Zhong-Yuan
Published: February 2023

A new small-sized soft x-ray source of 0.2-2-keV range is described. The soft x-ray source consists of electron gun, focusing electrode, and anticathode. The electron gun is ceramic-to-metal vacuum seal. The anticathode is made from a stainless tube and cooled by tap water. The target can be fixed onto the top of the stainless tube and can be easily exchanged. It is usually made by Cu. Al, or C for receiving the different wavelengths. The x-ray source spot can be adjusted by moving the stainless tube along its axis of operation. The diameter of the x-ray source is ~1 mm. The material of the x-ray output window is 1-μm thick polypropylene film, using Ni mesh, which transmits 80% of the radiation, to support it. Thus we get the high soft x-ray intensity. The total power is 1-2 kW. The tests we did with this source included determining the detective quantum efficiency of detectors; measuring the reflectivity of x-ray mirrors; and measuring the transmittivity of windows. These data are important in the study of space astronomical instruments.
Donor and acceptor modes in photonic band-gap materials
Authors: Mead Robert D. , Brommer Karl D. , Rappe Andrew M. , Joannopoulos J. D.
Published: February 2023

A dielectric material with a 3-D periodicity may have a photonic gap in its frequency spectrum in which propagating electromagnetic modes are forbidden.1 Recently, a number of materials that have such a gap have been discovered.2,3 Electromagnetic modes with frequencies in this forbidden region must be localized in all three dimensions. We show that lattice imperfections can introduce such exponentially localized states in the photonic band gap. We focus on the frequency spectrum of dielectric structures containing defects in an FCC lattices of nonspherical atoms,3 and compare the results of our calculations with the experiments of Yablonovitch. We consider impurities of two types: air spheres in the dielectric region and dielectric spheres in the air region. In both cases, localized photon modes are found to be introduced into the gap. Variation of the size of the impurity sphere leads to complete tunability of the frequency of this localized mode. We also discuss the localization of light at the surface of a photonic band-gap material.
Measurement of photonic band structure using coherent microwave transient spectroscopy
Authors: Robertson W. M. , Arjavalingam G.
Published: February 2023

The photonic band structure of a 2-D dielectric array has been investigated using the coherent microwave transient spectroscopy (COMITS) technique. COMITS, which is based on electromagnetic transients radiated and received by optoelectronically pulsed antennas, is capable of measuring the complex transmission function of a sample in the 15 GHz-140 GHz frequency range in a single experiment. A 2-D photonic crystal was constructed using 1.2-mm diameter alumina ceramic rods arranged in a uniform square lattice of periodicity 3 mm. The lateral extent of the sample was much larger than the diameter of the broadband microwave beam, eliminating any end effects. The frequency dependent amplitude transmission of the sample clearly indicates the fundamental and higher photonic band gaps along the symmetry directions. The position of the measured fundamental gap is in agreement with theoretical predictions for a 2-D system.1 Furthermore, the phase sensitive nature of the COMITS technique has been used to investigate propagation at frequencies above the fundamental gap. These results are presented together with the effect of polarization on these 2-D samples.
Polarization dynamics of phase grating formation in birefringent optical fibers
Authors: An Sunghyuck , Sipe J. E.
Published: February 2023

Since the discovery of the phase grating formation in optical fibers by Hill et al., there have been considerable efforts both experimentally and theoretically to understand the governing physical mechanism. The microscopic description of the formation of the photosensitive grating is still unclear. Recently, however, it was shown that a local two-photon bleaching model could explain both the experimentally observed time dependence of the reflectivity and the role of Fresnel reflection at each end of fiber.1 Parent et al. were the first to observe that the refractive index changes induced in optical fibers by grating formation were anisotropic.2 In this paper we generalize the local two-photon bleaching model to describe the anisotropic grating formation in birefringent optical fibers and, using symmetry arguments, we show that there are only two important material parameters. We show that the dynamics of the polarization grating formation exhibits a universality similar to that seen in the dynamics of Bragg gratings, and study how the dynamics of the grating development is related to the material parameters.
New format for the dispersion equation for nonlinear waveguides
Authors: Chiang H. Kenny , Kenan Richard P. , Summers Christopher J.
Published: February 2023

Nonlinear optical waveguides have been receiving increasing attention in recent years because of their potential use as all-optical switching devices. Several different forms of the dispersion equation are currently used to find the modal solutions of these waveguides.1,2 The most widely used dispersion equation is in the addition form presented by Boardman.2 This type of nonlinear dispersion equation is easy to use. However, spurious roots may appear in the calculations. In the addition form dispersion equation, there is a multiplication term of the two electric fields at the two sides of the waveguide boundaries. Because of the quadratic relationship between the two electric fields, it is difficult to determine their signs. We have found the existence of spurious roots even for a single-mode self-defocusing nonlinear waveguide, for which the two boundary fields were assumed to have the same sign. We present a new dispersion equation formed by taking the ratio of two addition form dispersion equations. Thus, the multiplication term of the electric fields is removed. The new dispersion equation is efficient to calculate, has direct physical meaning, and avoids the appearance of spurious roots.
Design and applications of active fiber devices
Authors: Laming R. I. , Payne D. N.
Published: February 2023

Excellent gain performance has been achieved from diode-pumped erbium-doped fiber amplifiers (EDFA) and they are now accepted as a basic building block of future optical fiber communications networks. Nevertheless, EDFAs are still being refined in several key areas. These include optimum pump wavelength, fiber design, and distributed amplifiers as well as techniques to tailor the gain spectrum. In addition, control aspects such as supervisory and automatic gain control as well as the associated components are under investigation.
Erbium-doped fiber amplifiers for ultrashort pulse generation and optical soliton communication
Authors: Nakazawa Masataka
Published: February 2023

In 1989 it was shown for the first time that erbium-doped fiber amplifiers1 (EDFAs) are useful for soliton amplification and transmission2; it was also shown that the lumped amplifier technique using EDFAs made it possible to move the dream of soliton communication into an actual developmental stage.3 Our technique, dynamic soliton communication, also known as the guiding center soliton or super soliton,4 has a wide range of use from L
a
≪ Zsp to L
a
~ Zsp depending on the maximum required transmission distances. Here L
a
and Zsp are the repeater spacing and the soliton period. However, when we seriously compare the cost/bit of linear high speed IM/DD or coherent systems and the present soliton system, the extension of the repeater spacing becomes crucial. We describe single-pass soliton transmission at 10 Gbit/s over 1000 km with a 50-km repeater spacing. Furthermore, 20 Gbit/s over 500 km experiment, in which a nonlinear soliton interaction occurs, is presented. With the aid of EDFAs, soliton technologies such as soliton switching using nonlinear (amplifying) loop mirrors and amplification and generation of femtosecond solitons have sufficiently matured. Applications of EDFAs to these areas are presented.
Novel optical waveguide beam steering device
Authors: Chiang H. Kenny , Summers Christopher J. , Kenan Richard P.
Published: February 2023

We present a new optical waveguide beam steering device, consisting of a pair of asynchronous waveguides. The asynchronous operation prevents coupling between the two waveguides but results in a phase delay between them. Using this effect, the output light can be steered in the far field by varying the phase delay. Analyses of the beam steering device shows that the separation between the waveguides should be small, and the light confinement in the two waveguides should be weak, but the waveguides should not be coupled. For these considerations, a device with a steering angle of up to 20°, with side lobe intensities 10 dB below the main lobe was designed. Far field analysis is valid here for distances >100 μm from the end of the device. For uses in all-optical switching, the proposed device geometry consists of AlGaAs multiple quantum well nonlinear waveguide and an AlGaAs linear waveguide. The refractive index of the nonlinear guide is modulated by an external controlling light beam. The induced phase difference between the two waveguiding modes results in the steering of the output light, which is collected by fiber waveguides in the far field.
Holographic optical processing elements for digital processing and interconnection. 2: multiprocessor computing system
Authors: Kostrzewski Andrew , Lu Taiwei , Chou Hung , Lin Freddie
Published: February 2023

We present an optical digital processor system containing an array of processing elements. Each processing element is capable of executing arithmetic, logic and interconnect operations. To provide fast execution speed, we use the lookup-table approach. Results of operations are precalculated and stored in truth tables. To record a set of lookup-tables, a modified dual-rail spatial encoding method is used. The truth-tables are recorded in a novel holographic content-addressable memory. To implement a large number of processing elements, a spatially multiplexed hologram was used.
Variability in color matching, photoreceptor alignment, and the Stiles-Crawford II effect
Authors: Burns Stephen A. , Elsner Ann C. , Gorrand J. M. , Kreitz Mark R.
Published: February 2023

Color matches depend on the optical density and extinction spectrum of the cone photopigments. In addition it has been proposed that there is a physical effect of cone orientation on color matches (the Stiles-Crawford II effect). We have investigated this in ten observers by measuring (1) the retinal reflectance as a function of position in the pupil plan (the reflectometric version of the Stiles-Crawford I effect) and (2) Rayleigh color matches as a function of retinal illuminance. From the reflectometric data we calculate the position in the pupil and the spatial spread of the reflected light. From the color-matching data we calculate the optical density of the cone photopigments and the half-bleach illuminance. Both the optical density and half-bleach illuminance were significantly correlated with the spatial spread of the reflectance in the plane of the pupil. Observers with a smaller spread had higher densities (r = 0.82) and lower half-bleach illuminances (r = 0.67). Additional measurements of color matches for various pupil entry positions in two observers showed a strong dependence of the low illuminance match on pupil entry but not of the high illuminance (bleached) match. The half-bleach illuminance varied as expected due to the Stiles-Crawford I effect. These results are consistent with an optical density model of the Stiles-Crawford II effect. No additional wavelength dependent properties are required. The data also indicate that the variation in color matches in the normal population includes variation in the physical properties of the cones (e.g., the spread of cone orientations or cone apertures), as well as the optical density of individual cones and the extinction spectrum of the cones photopigments.
Nonlinear optical coherent gating for medical imaging with lasers
Authors: Bashkansky M. , Reintjes J.
Published: February 2023

It is often desirable to form an image of the object hidden in or behind a scattering medium. For example, the whole new field of transillumination1,2 was established in medicine. Several techniques, relying on the fact that the highly scattered light is delayed in time with respect to the less scattered light, have been used. Various time gating2 techniques with very short laser pulses (<10 psec) have been employed. Recently a chrono-coherent imaging3 technique was developed with long broadband laser pulses. The interference between imaging and reference beams is recorded on the film as a holographic image. One of the disadvantages of this method is the holographic image degradation due to the scattered light. It is also not a real-time imaging technique. We developed a new nonlinear optical cross-correlation technique for hidden object imaging which can be used with long broadband laser pulses. Using nonlinear optical techniques the following advantages are attained: good discrimination against scattered radiation, real-time imaging, image amplification resulting in extremely high sensitivity, up or down conversion of image to a more convenient laser wavelength. This is a general method that can be used with many nonlinear optical processes. We discuss some of the relevant nonlinear optical effects, their advantages, and disadvantages.