bluuebunny/crossref_metadata_2025 huggingface dataset:
Light scattering from rough surfaces using the coupled-dipole method
Authors: Taubenblatt Marc A.
Published: February 2023

Light scattering from rough surfaces is of interest in many fields. In the semiconductor industry specifically, the ability to detect sub-tenth-micron contamination particles on rough surfaces such as polysilicon and metals, is becoming increasingly important. Theoretical understanding of the scattering properties of these surfaces offers insight into the design of optically based methods. The coupled-dipole method has previously been shown to be a viable calculational technique for computing light scattering from particles on surfaces. By modeling a rough surface as a distribution of dipoles, light scattering from rough surfaces may also be computed. Light scattering from polysilicon surfaces, characterized by atomic force microscopy, have been calculated and compared to experimental data.
Holographic polarizing 2×2 bypass/exchange switch
Authors: Wang J. M. , Sawchuk A. A.
Published: February 2023

2 × 2 bypass/exchange switches are useful elements for multistage interconnection networks. We present an alternative design for a 2 × 2 bypass/exchange switch using the properties of volume holograms. The switch is a sandwich structure containing a volume hologram placed between two right angle prisms. The hologram is recorded with the Bragg angle equal to 45°. According to the coupled wave equations developed by Kogelnik, this hologram has the following properties. If the incident light is polarized parallel to the plane of incidence, the light passes through the hologram without any diffraction due to the polarization selectivity of volume phase gratings. If the incident light is polarized perpendicular to the plane of incidence, the light is diffracted. By properly controlling the polarization of the incident light, these characteristics can be used to make a bypass/exchange switch.
One-copy algorithm for optical 2-D shuffles: theory and experiment
Authors: Cheng L. , Wang J. M. , Sawchuk A. A.
Published: February 2023

A light efficient algorithm is important for any optical computer or optical interconnection system. Here, we discuss a light efficient procedure called the one-copy algorithm which implements various types of shuffle on a 2-D array of channels.1 These optical 2-D shuffles can be used in parallel signal processing, computing, and telecommunication routing systems. We found that for a 2-D array having r
m
channels (where r is prime and m is even), both 2-D r
k
-folded and separable shuffles can be achieved using this algorithm in a single stage whenever 1 ≤ k ≤ m/2. The 2-D inverse folded rk shuffle using the one-copy algorithm can be built in a single stage only when k = m/2. On the other hand, the 2-D inverse separable r
k
shuffle using the one-copy algorithm can be realized in a single stage whenever 1 ≤ k ≤ m/2. Multistage implementations of the one-copy algorithm for any inverse shuffles are possible. The number of stages required in this case is dependent on k,m, and the type of inverse shuffle performed. Experimental results on the holographic implementation of 2-D perfect shuffles for sixty-four channels based on the one-copy algorithm with high light efficiency are presented.2
Theoretical studies of a coupled laser system consisting of a large number of elements
Authors: Jiang Ziping , McCall M.
Published: February 2023

In analyzing practical examples of extended coupled systems such as multistripe semiconductor laser arrays or various types of surface-emitting structures, we have established a simplified model for N nearly-identical coupled elements. A complex coupling constant has been assumed (so that both direct and evanescent coupling is included) as well as a variable coupling strength which ranges from nearest-neighbor only to all-to-all coupling. In our numerical experiments, for N = 100 elements, we have defined the parameter regimes for achieving phase-locking, partial phase-locking and phase-unlocking. These regimes have been established with respect to variations in cavity resonance frequencies, drive currents and coupling strengths. It was found that for a purely real coupling constant, the synchronization is much easier than for purely imaginary coupling.
Dyed gelatin film as a storage material for volume phase holograms
Authors: Lindvold L. R.
Published: February 2023

Dye-sensitized gelatin is a common recording material for volume holograms. The dye acts as a spectral sensitizer in light-sensitive materials such as silver halide, dichromated gelatin, and photopolymers, mostly used as volume phase recording media. The dye, however, can be used in a pure gelatin matrix also for real-time experiments, e.g., degenerate four-wave mixing facilitated by the cis-trans isomerization of the dye to record polarization-sensitive gratings. This paper describes some preliminary results concerning an observed photoinduced crosslinking effect of a dyed gelatin. The system comprises a halogenated xanthene dye, Eosin Y in a gelatin matrix, an electron donor (triethanolamine) and hydrogen-hexachloroplatinate (IV), a prehardening agent. Experiments have shown that this photochemical reaction—a photooxidation process—constitutes a system with the capability of recording volume phase holograms. As the selection of dyes with photooxidizing properties is vast in terms of spectral sensitivity such a system could in theory be tailored to any laser wavelength in the visible and possibly near-infrared.
Coupling between isotropic and birefringent fibers by VBPM
Authors: Gomelsky L. , Liu J. M.
Published: February 2023

A vectorial beam propagation method (VBPM) based on the vectorial wave equation has been developed to overcome the limitation of the existing scalar beam propagation method (SBPM). The polarizing effects of both the structural geometry, such as waveguiding boundaries, and the material properties, such as anisotropy, are included in this method. As an application of the VBPM, the circular transversely polarized (TE01) eigenmode of the isotropic fiber is propagated into the birefringent fiber of the same radius and the same index step between the core and the cladding. The effects of the birefringence, such as the loss of the circular symmetry, and the waveguiding geometry are shown. The inability of the SBPM to adequately handle this problem is demonstrated as well.
Physical bases of color vision
Authors: Maloney Laurence T.
Published: February 2023

Recent computational theories of color vision demonstrate that it is possible to achieve exact color constancy over a limited range of lights and surfaces described by linear models. First, I review this work, describing what is meant by a linear model. Second, I review evidence related to three conjectures concerning constraints on surface spectral reflectances: (1) that surface spectral reflectances fall within a linear model with a small number of parameters; (2) that surface spectral reflectances fall within a linear model composed of band-limited functions with a small number of parameters; and (3) that the broad, smooth shape of the spectral sensitivity of human photoreceptors enhance the observed constraints on surface reflectance functions.
A gallery of appearance
Authors: Shafer Steven A.
Published: February 2023

What makes things look the way they do? Humans are very good at making rapid determination of what things are made of, whether they are smooth or rough, and what color they are. In face, we are so good at this that we se things in terms of these interpretations rather than in terms of the actual optical appearance. As a result, we frequently overlook the actual physical appearance and are not aware of exactly how it reveals the properties of the surface. There is not even a good vocabulary for describing the physical appearance of surfaces, which makes it difficult to make progress in the measurement of appearance by instruments or the analysis of images by computer vision. Yet these processes are highly structured, and visual images are far from random signals.
Representing illuminants and surfaces for predicting receptor responses
Authors: Marimont David H. , Wandell Brian A.
Published: February 2023

To transfer color images between color devices, we seek a representation that efficiently encodes the color information necessary for accurate reproduction. Our representations emphasize physical properties of illuminants and surfaces: the illuminant’s spectral power density and the surface’s spectral reflectance function. Encoding these spectral functions with finite-dimensional linear models facilitates analysis and computations based on them, but discards some of the information they contain. Existing techniques for computing linear models have emphasized accuracy in approximating the spectral functions themselves. For our applications, however, accurately approximating spectral functions is far less important than accurately approximating the receptor responses of a set of color devices, for example, a camera, scanner, or the human eye, to a set of surfaces and illuminants. Here we introduce a new technique for building linear models that takes a collection of devices, surfaces, and illuminants, and builds linear models that are optimal for predicting receptor responses.
Color reflection models on materials
Authors: Tominaga Shoji
Published: February 2023

An important role of surface spectral reflectance is to supply the physical basis for object color perception and surface identification. The behavior of the reflectance function depends on the surface materials. In this paper we propose color reflection models for a variety of objects based on the analysis of the reflected light spectra from the object surfaces and their surface spectral reflectances. First, we test the adequacy of the standard dichromatic reflection model. The model assumes that the reflected light is composed of two components of specular and diffuse reflections and that the specular reflection is constant over the visible wavelength. The experimental results show that the standard model is adequate for many materials, but it is inadequate for metals composed of only specular reflection, and for some paper and cloth. Next, we analyze the surface spectral reflectances of these inadequate materials to supply a proper model. The paper and cloth can be approximated with the generalized dichromatic reflection model with chromatic specular reflection. Furthermore, metals can be approximated with the dichromatic reflection model with two specular reflection components. Thus, it is shown that color reflection for most objects is expressed in three kinds of dichromatic reflection models.
Polychromatic neural network
Authors: Yu Francis T. S. , Yang Xiang Y. , Reeser Wade , Matsushita Kenji , Gregory Don A.
Published: February 2023

We have recently proposed and demonstrated optical neural networks (ONNs) with liquid crystal televisions (LCTVs), in which usually color LCTVs are used.1,2 Since each color pixel is composed of red, green, and blue elements, the resolution is reduced. However, the color LCTVs offer the capability of storing and processing color information. A polychromatic ONN is presented in this paper. In the training phase, the color images are decomposed into three primary colors. The monochrome interconnection weight matrices (IWMs) are constructed based on three independent training sets in primary colors. The polychromatic IWM is then composed and displayed on the LCTV for the reconstruction of the stored color patterns.
The biophysical basis of laser angioplasty
Authors: Grundfest Warren S.
Published: February 2023

This lecture will discuss the patho-physiology of the arterial wall and the selection of ablation parameters, including: wavelength, pulse duration, and power density, which are required to deal with arterial obstruction. The system constraints, such as arterial tortuousity, calcifications, and lesion eccentricity will be addressed as well as results from current clinical trials.
An angiosurgery system using a tripled Nd:YAG laser
Authors: Feld Michael S. , Itzkan Irving , Kramer John R.
Published: February 2023

We describe an integrated system for laser treatment of atherosclerosis using 355-nm radiation for ablation and visible light for spectroscopic diagnosis and guidance. Both spectroscopy and ablation share the same fibers in a unique catheter design.
Implementing TQM … the hard part
Authors: Smith Fred B.
Published: February 2023

For many of us, the TQM movement is long overdue and critical for the United States to remain a world leader. We find that doing it is not easy. There are a number of reasons including the culture change required by everyone to be successful.
Apodized acoustooptic tunable filters
Authors: Chang I. C.
Published: February 2023

The acoustooptic tunable filter (AOTF) is an electronically programmable spectral filter with large optical throughput.1 The small size, low weight, and rugged construction makes it well suited to spaceborne systems. One major deficiency of current AOTFs that limits its potential for system deployment is the high side lobes in the bandpass response. In principle these side lobes can be suppressed by suitable amplitude apodization of the acoustic excitation. Previous attempts have not yet produced acceptable results because of the difficulty of implementing the apodized transducer. Several apodization techniques were studied, including tapered dielectric coupling, segmented transducer, electrode shaping, and tapered transducer. A theoretical analysis of these apodization techniques were made and the bandpass responses were calculated using various choices of weighting functions. These techniques were experimentally investigated.
Compact fingerprint sensor using an internal multireflected optical path
Authors: Shinzaki Takashi , Igaki Seigo , Kato Masayuki , Mori Masahiro
Published: February 2023

To satisfy the need for fingerprint sensors in security applications, we have developed a compact sensor only 22 mm thick. First, we studied a holographic fingerprint sensor1 consisting of a flat glass plate with a hologram. Unfortunately, the sensor needed a thermally controlled laser diode for its light source, which is relatively large. Thus, to develop a compact low-cost illuminator, we investigated a compact optics system, using four light-emitting diodes, that does not require a hologram. The focusing optics consists of a flat glass plate attached to the aperture and a short-focal-length lens that shortens the optical path. The optical aberration can be reduced by setting the aperture at the center of the lens curvature, so that only the light incident perpendicular to the lens surface is transmitted. A mirror was fabricated on an incline of the glass plate opposite the lens to internally reflect the light toward the lens. This enabled us to reduce the sensor size. We were able to produce a prototype sensor with a CCD driver and an AD converter that is no larger than a cigarette case (80 by 55 by 22 mm).
Confocal spheroids as elements of off-axis reflecting systems
Authors: Stavroudis Orestes N. , Ames Alan J.
Published: February 2023

The problem considered is the design of complicated off-axis mirror systems. The approach is to use components that consist of pairs of prolate spheroidal mirrors which share a common conic focus but not a common axis. By conic focus we mean the focus of the spheroid and not necessarily an optical focus. In this configuration a ray through one of the conic foci must pass through all the others. If pupils are located at each of the conic foci, all such rays must be chief rays. A pseudoaxis is defined as that chief ray about which all other rays are symmetric. A necessary condition for the existence of a pseudoaxis provides relationships between the eccentricities and the angles between the conic axes. Conditions assuring that such a system is afocal or forms an image result in conditions on the vertex curvatures of the spheroids.
Phase modulation formats for coherent optical receivers with photorefractive beam combiners
Authors: Davidson F. , Field C.
Published: February 2023

We discuss the effect of high speed phase modulation impressed on one of two optical beams incident on a photorefractive crystal used in a two-wave mixing configuration in a coherent optical receiver. Phase modulation on the signal beam reduces the average visibility of the fringe system inside the photorefractive material. This in turn reduces the coherent superposition properties of the refractive-index grating formed in the material. In the undepleted pump approximation, a single parameter κ=|Eejφs(
t
)|, where ϕ
s
(t) is the phase modulation carried by the signal beam, characterizes the reduction in two-wave mixing coherent superposition properties of the grating with κ = 1 yielding the usual energy transfer equations for forward two-wave mixing. This rules out the use of some phase modulation formats commonly used in microwave communication systems. We propose some alternative phase modulation formats that can be detected with photorefractive beam combiners including the phase modulation equivalent of Q = 4 pulse position modulation and a tri-state phase format that has a unity bandwidth expansion factor.
Optical homodyne 220-Mbps communication system using photorefractive beam combining
Authors: Davidson F. , Field F. , Sun X.
Published: February 2023

Coherent optical communication systems that contain conventional optical beam splitters require complicated subsystems to maintain precise angular alignment and spatial-mode matching between signal and local oscillator laser light prior to photodetection. It has been shown that the volume index of refraction gratings formed inside photorefractive materials may also be used to coherently combine signal and local oscillator light.1 Systems that contain photorefractive beam combiners are much simpler to implement as the refractive index grating forms wherever the two optical beams overlap and adjusts its position automatically, on a time scale given by the grating formation time, to changes in spatial-mode profile or angle of arrival of either beam. The experimental performance is reported of an optical homodyne communication system that used a Nd:YAG unidirectional ring oscillator laser at 1064 nm, a phase modulation format equivalent to quaternary pulse position modulation at a source data rate of 220 Mbps, and an InP:Fe photorefractive beam combiner.
Trans-reflective blazed echelon grating for wavelength division demultiplexing
Authors: Helaly Anwar , Abushagur Mustafa A. G.
Published: February 2023

Blazed diffraction gratings are important devices in wavelength division multiplexing optical communication systems. Echelon gratings are used to obtain higher linear dispersion and correspondingly higher resolution. We propose a transreflective blazed grating to achieve further increase in the resolving power. The proposed grating has the same structure as the reflection-type echelon grating except that the angle between the two edges of the groove (blazed angle) is 45° where the horizontal edge is transmissive while the other edge is reflective. For a horizontal illuminating light beam, the light reflected by one (reflective) edge is normally incident on the other (transmissive) edge and passes vertically through the medium of the grating. The optical path difference per step is d = H + nW, where H is the horizontal step size, W is the vertical step size, and n is the refractive index of the grating material. The proposed grating acts as a combination of reflection and transmission type echelon gratings with optical path difference per step of ~H + W or (n – 1)W larger than that of a reflection-or a transmission-type grating of the same size, respectively. Thus, the interference order and the linear dispersion are larger than those of the echelon grating, which results in a much higher channel capacity, arranged side-by-side symmetrically.
Photon scanning tunneling microscope using diode lasers
Authors: Jiang S. , Ohsawa H. , Tomita N. , Ohtsu M.
Published: February 2023

A novel superresolution photon scanning tunneling microscope (PSTM) using diode lasers and optical fibers has measured a submicron structure sample in a noncontact and nondestructive manner. Diode lasers, which can be directly high speed modulated, are used to make the system more compact (25 × 20 × 12 cm3) and the measuring time shorter. The principle of the operation is that the evanescent flied (tunneling photon) depending on the topography of the sample is picked up by a fiber probe on which the subwavelength aperture is fabricated. The top of the fiber probe was sharpened by HF selective etching to achieve 80-nm radius of curvature. A stepped SiO2 thin film 9 nm high optical disk with submicron sized pits similar to a moth-eye structure was observed. Furthermore, 80-nm diameter latex particles have also been observed. These are the smallest size particle resolved by the PSTM, to the author’s knowledge. A reflection-resonance type PSTM is proposed1 for solving the problem with the low power picked up in a transmissiontype PSTM (demonstrated above), which limits the measurement sensitivity.
Compact atomic force microscope using a linear fiber-optic detection scheme
Authors: Vaez-Iravani M. , Nonnenmarcher M. , Wickramasinghe H. K.
Published: February 2023

The design and operation of an atomic force microscope employing a stable fiber-optic detection system are discussed, and a number of results are presented.
Quantitative 2-D laser Rayleigh temperature measurements
Authors: Leipertz Alfred , Kowalewski Gerd , Kampmann Stefan
Published: February 2023

By forming a laser beam to a 2-D light sheet and collecting the intensity distribution within the sheet by using a 2-D photoelectrical detector, instantaneous 2-D density or temperature measurements are possible in a large number of hydrocarbon-air flames, providing also qualitative visualization as quantitative results over an extended combustion field of interest. The emphasis of our work is in this first stage on the quantitative evaluation of the 2-D Rayleigh images, which is done in laminar premixed flames in comparison to point measurements by spontaneous Raman scattering. In a further step the use for large-scale burners is planned.
Quantitative species concentration measurements in flames using REMPI
Authors: Cool Terrill A.
Published: February 2023

Two laser-based diagnostic methods, resonance-enhanced multiphoton ionization (REMPI) and laser-induced fluorescence (LIF), were used for concentration measurements of seven species, O, H, OH, CH, CO, HCO and CH3, in low pressure methane/oxygen, ethylene/oxygen and ethane/oxygen premixed hydrocarbon flames. For the well-understood methane/oxygen flame, measured density profiles for these seven species were in excellent agreement with flame modeling calculations. This agreement encourages confidence in the experimental procedures and current kinetic modes of C1 chemistry. Indeed, the methane/oxygen flame provides an accurate standard of comparison by which relative density profiles, measured for other hydrocarbon flames, may be placed on an absolute density scale. This approach was used for measurements for the ethylene/oxygen and ethane/oxygen flames.
Moisture resistant oxide coating by dc magnetron sputtering
Authors: Pond B. J. , Du T. C. , Sobczak J. , Carniglia C. K. , Williams F. L.
Published: February 2023

The process of dc magnetron sputtering can lead to the deposition of dense oxide films. Because of the high density of the films, they are resistant to the penetration of moisture. Improvements in magnetron sputtering technology have made it possible to use a lower gas pressure during deposition. This lower pressure reduces the level of water incorporated into the films during deposition. We report the results of a study of single-layer films of the oxides of silicon, aluminum, and titanium. An 8-in. dc magnetron source was used for the deposition. Metal targets were used for each material, and a mixture of argon and oxygen was employed during the deposition. An aluminum dopant was used with the silicon target to minimize contamination. The deposition parameters studied were the target voltage, the total pressure during the deposition, and the partial pressure of the oxygen. Several source geometries were tested in an attempt to optimize the deposition rate. Moisture content of the films was determined by spectral transmission scans over the water absorption bands at 2.7 μm. For total pressures of 2 × 10-4 Torr or less, the films were found to be free of water.
In situ measurements of stress in titanium dioxide thin films produced by ion-assisted deposition
Authors: Bovard Bertrand G. , de Lega Xavier Colonna , Macleod H. Angus
Published: February 2023

A stressometer has been developed to measure the evolution of total stress in thin films during growth. The instrument is based on a cat’s eye interferometer which measures the variations of curvature of a thin substrate during deposition. This instrument is installed on a Balzers-760 box coater equipped with a 12-cm Kaufman ion source. We have used this experimental setup to study stress in thin films of titanium dioxide grown on silicon substrates as a function of bombardment conditions. In this paper, we describe the experimental setup, present the stress measurements for different growth conditions, and discuss the results. In particular, we show how the stress evolves with increasing levels of bombardment, and how it varies with physical thickness.
Optical coatings with cross-section variable thickness: fabrication techniques, applications, and investigations in powerful laser beams
Authors: Lukishova Svetlana G. , Kovtonuk Sergej A. , Ermakov Anatoly A. , Svakhin Aleksej S. , Plavtov Evgeny E. , Sedoruk Oleg E.
Published: February 2023

Close to spherical and different smooth flat-top shape surfaces, which are SiO2, SiO or MgF2 single profiled films with ~0.5-2-μm maximum thickness, were deposited on glass or quartz substrates by electron beam, resistive heating or sputtering techniques. The comparative analysis of rotating mask and noncontacting (fixed) mask methods (the use of shadow effect of the mask on substrate) for preparation of profiled films has been carried out. The advantage of using sputtering units with a large source for preparing flat-top profiled films is discussed. The possibilities of using chemical etching with laser heating for this purpose are examined experimentally. Such profiled film was used in a frustrated total internal reflection amplitude filter; there it separated the hypotenuse faces of two right-angle glass prisms. Results are presented of testing such filters in lasers and laser radiation damage thresholds of different films in optical contact conditions. A comparison of laser damage thresholds of nonconducting films and in optical contact conditions is given.
Time-resolved reflectivity studies of GaAs(100)/oxide and GaAs(100)/ZnSe interfaces
Authors: Cheville R. A. , Haynes W. B. , Halas N. J.
Published: February 2023

The time-resolved reflectivity from a series of variously prepared GaAs interfaces has been observed. GaAs n-type wafers of 2 × 1016 cm-3 doping density were used. The surfaces were prepared in the following ways: growth of a thermal oxide, growth of a photochemically passivated oxide, and growth of an epitaxial ZnSe overlayer using the technique of laser-assisted MOCVD. Reflectivity measurements were performed using a CPM laser (620 nm, pulsewidth <100 fsec) in a standard pump-probe geometry. The time dependence of the reflectivity within the first few picoseconds is highly dependent on surface preparation. This variation of surface treatment is linked to a variation of both the density of states present at the interface and a variation in the space-charge layer on the GaAs side of the interface. Characterization of the GaAs spacecharge layer by contactless optical probing techniques, as well as additional experiments on III–V device structures enable us to make some initial correlations between the time dependence of the optical reflectivities observed and the properties of the GaAs space-charge layer.
Physical properties of the solar corona and the role of x-ray optics
Authors: Spicer Daniel S.
Published: February 2023

Solar coronal magnetized plasmas exhibiting evidence of telescopic fine structure, as first observed by the Skylab ATM soft x-ray grazing incidence telescopes (~5") and the XUV slitless spectroheliographs (≥ 2"), resulted in a profound change in how theoreticians view the solar corona. To better unravel the physical implications of the Skylab data, it became obvious that not only was higher spatial resolution required but also higher temporal resolution. In addition, because the solar corona is causally coupled to the lower solar atmosphere, i.e., the photosphere, both electrodynamically and mechanically, monochromatic or at least narrowband images were required to map structure exhibited at one temperature to structure exhibited at other temperatures. These three requirements made it clear that Skylab type instruments could not obtain the desired data at reasonable cost. However, with the development of inexpensive normal incidence soft x-ray optics, sounding rocket experiments utilizing this new technology have demonstrated that normal incidence soft x-ray optics meet all the requirements noted above.
Computer generated holograms for free-space digital optics
Authors: Morrison R. L. , Walker S. L. , Tooley F. A. P. , McCormick F. B. , Cloonan T. J.
Published: February 2023

AT&T's photonics switching technology group has demonstrated a series of prototype systems of increasing complexity to test and illustrate the feasibility of free-space digital optical systems. Computer generated holograms (CGH) were incorporated into a multistage system demonstration (i) to distribute optical power and illuminate an array of optical processors,1and (ii) to form interconnections between stages. A 64 × 64 spot array was generated by illuminating a CGH with a collimated laser beam. The spot array intensity was required to vary by <20% between minimum and maximum intensity spots. A characterization system was used to ensure that this objective was met. To provide connectivity between channels, the information from each device was routed between modules using a scheme similar to a banyan network. By selectively shielding areas on the processor array, the interconnection was achieved using space invariant 1 × 3 CGHs. Some 1 × 3s were designed for reduced intensities at several higher-order spots.
Improvements of the graphic code of computer generated holograms
Authors: Lohmann Adolf W. , Sinzinger Stefan
Published: February 2023

During recent years, research in the area of computer generated holography (CGH) almost exclusively dealt with the improvement of the algorithms to produce CGHs with enhanced performance. Now we would like to concentrate on improvements of the CGH quality by using certain tricks during the actual manufacturing process. In most CGHs the sampling cells contain one or sometimes two black rectangles. The size of the rectangle is responsible for the local light amplitude. The location of the rectangle determines the phase of the light, which is diffracted at that cell.
Electromagnetic scattering by two rectangular grooves in a ground plane
Authors: Kok Yon-Lin
Published: February 2023

The diffraction of a plane electromagnetic wave by two rectangular grooves corrugated in a perfectly conducting plane is rigorously formulated in terms of a Fourier integral for two orthogonal polarizations. The problem can be treated as a combination of two separate ones, each involved with a single rectangular groove. The resultant matrix leading to the solution consists of submatrices appearing in the single groove scattering problem and others accounting for mutual coupling between grooves. The angular spectrum of the diffracted field is expressed in a series of Bessel functions, which is found to be computationally stable for solutions from the low to the high frequency regions. The diffracted-field patterns in the radiation zone are predicted by evaluating a Fresnel-type integral where contour integration and Watson transform are utilized to convert the original eigenvalue series into a radially fast convergent asymptotic series. Simulation results are generated for arbitrary scattering geometries. The far-field diffraction patterns are found to be a strong function of the ratio of the groove widths, heights, and the separation between them. The solution techniques can be easily generalized to solve the N-groove scattering problem.
Use of surface-relief diffractive optics in helmet-mounted displays
Authors: Faklis Dean , Bowen John P. , Cotton Christopher T. , Morris G. Michael
Published: February 2023

A helmet-mounted display (HMD) provides the pilot with a dedicated visually coupled interface that offers increased vision as well as improved target acquisition and weapons delivery. The HMD presents the wearer with avionics symbology superimposed on sensor imagery or a natural scene. The flight scene may consist of a sunlit terrain or it may consist of the output of a night vision sensor or FLIR. Two recent conferences have examined the latest uses of HMD optical systems in tactical aircraft, rotocraft, simulators, and land vehicles.1,2 Current HMD systems have advanced to the point where reducing the headborne weight and maintaining a reasonable center of gravity is technically difficult. Concentrating on the helmet optical system, it remains possible to achieve weight reductions through the use of optical glasses of lower density and by reducing the overall number of optical elements. For systems consisting of conventional optics, such modifications usually give rise to inferior system performance whether it be decreased field-of-view, reduced unvignetted exit pupil or increased chromatic aberration. We have investigated the use of combinations of refractive and surface-relief diffractive elements in the relay lens to provide increased wavefront and color correction.
Statistical properties of a single-mode semiconductor laser modulated at GHz rates
Authors: Colet Pere , Mirasso Claudio , Miguel Maxi San
Published: February 2023

The statistical properties of the turn-on delay time, pulse width, maximum light intensity and output power are analyzed by solving numerically the stochastic rate equations for the number of photons 1 and carriers number N. We study the influence of the value of the bias current for different frequencies of modulation, in the 1-10 GHz regime. We consider periodic and random signal modulation. Under fast periodic modulation, statistical properties are almost independent of the bias current, contrary to what happens in a slow modulated regime (in the order of MHz) or in repetitive gain switching. Under random signal modulation, appropriate for intensity modulation-direct detection optical communications, statistical properties are reported to be very sensitive to the value of the bias current: for bias above threshold the turn-on delay time and output power probability distributions become multimodal when entering the GHz regime. In this regime the response of the laser to an electrical pulse depends on previous transmitted bits.
Two-dimensional Maxwell’s curl equation simulation of light propagation and reflection in heterostructure laser configurations
Authors: Mayhall David J. , Yee Jick H. , Sieger Gregory E. , Mariella Raymond P.
Published: February 2023

To investigate the propagation and reflection of laser light in slab heterostructure configurations, especially quantum wells, we are developing 2-D finite difference computer codes for self-consistent solution of Maxwell’s curl equations in complicated refractive media. The exact Maxwell’s equations are solved without the approximations inherent in the high-frequency envelope methods. Separate codes treat TE and TM modes. These codes will be used in semiconductor laser research and design. The field gradients in the charge free equations are conveniently approximated by central finite differences on a staggered mesh. The three modal components occupy a triangle of grid points within a four-point computational cell. Appropriate boundary conditions are imposed at the mesh extremities. The global set of ordinary differential equations from this discretization are solved with the well known implicit, variable step size solver LSODE. The propagation of low-order eigenmodes, perturbed eigenmodes, and noneigenmodes in step refractive, parabolic, and quantum well GaAs/AlGaAs structures is investigated.
Polarization properties of optical fibers
Authors: Poole Craig D.
Published: February 2023

This tutorial reviews the intrinsic and extrinsic factors affecting the polarization of light in optical fibers. Among the topics discussed are polarization-maintaining fiber and its limitations; polarization evolution and polarization-mode dispersion in randomly birefringent fiber; and nonlinear interactions in birefringent fiber. Special attention is given to issues affecting ultralong distance data transmission in conventional single-mode fiber.
Fiber ring resonator with power exchange between polarization modes: spectroscopic and sensing applications
Authors: Mouroulis Pantazis , Fan Chenjun
Published: February 2023

Fiber ring resonators made from polarization preserving fiber suffer from well-known polarization mode splitting problems, caused by small amounts of crosstalk at the coupler. The output of such a resonator is generally unsuitable for spectrum analysis or sensing. A solution to this problem has been recently described in the form of a ring resonator in which there is deliberate power exchange between the two birefringent axes. Polarization modal splitting is eliminated, and a significant signal improvement is further possible by separating the output power along the two axes. The resulting device presents simultaneous resonant peaks and resonant dips, and is simple and relatively inexpensive to construct. There are, however, some signal instabilities that are inherent in this type of resonator. These instabilities are quantified, and means of overcoming them are discussed. The resulting stabilized output is useful in very high resolution spectroscopy, since a long loop can be constructed without mechanical alignment problems. The use of the device as a spectrum analyzer is demonstrated.
Skew rays and photon turning points in graded-index multimode fibers
Authors: Aly Moustafa Hussein
Published: February 2023

When rays are transmitted without passing through the fiber axis they are called skew rays. These rays follow a helical path through the fiber. The light ray propagating in a graded-index fiber does not necessarily reach every point in the fiber core. The ray is contained within two cylindrical caustic surfaces, and for most rays a caustic does not coincide with the core-cladding interface. Hence, the caustics define the classical turning points of the light ray within the graded fiber core. These turning points defined by the two caustics may be designated as occuring at r = r0 and r = r1, i.e., the radii where the wavevector’s radial component is zero.
Atomic interferometry using stimulated Raman transitions
Authors: Kasevich Mark , Chu Steven
Published: February 2023

Sodium atoms prepared in hyperfine ground-state 11 > are driven to the other ground-state hyperfine level 12> when two laser beams nearly resonant with an optical transition have a frequency difference equal to the ground-state hyperfine splitting. When the two laser beams are counterpropagating, conservation of momentum between the atom and the light field requires that the atom acquire a velocity kick ~22 ħk/m during the 11> and 12> transition (~6 cm/sec in our experiment). When the lasers are detuned far from the optical transition, spontaneous emission from the intermediate optical level becomes negligible, and the atom behaves as a two-level system coupled to a resonant rf driving field. We have created an interferometer by applying a π/2-π-π/2 Raman pulse sequence: a first π/2 pulse coherently splits the atomic wave packet by putting it in a superposition of states 11> and 12>, a second π pulse occurring a time Δt later redirects each wave packet and a final π/2 pulse recombines the wave packets at time 2Δt. We have observed wave packet interference for wave packet separations of 2.4 mm and, by using the interferometer as an accelerometer, have measured the atom’s acceleration due to gravity to 3 parts in 106.
Broadband stimulated laser cooling
Authors: DeVoe Ralph G.
Published: February 2023

A new method is proposed for laser cooling atoms with Doppler shifts an order of magnitude larger than the homogeneous linewidth of the atomic transition. Two traveling waves cross at a small angle and form standing waves whose wavelength is much longer than that of either traveling wave. This allows one to extend the region in which the laser cooling force is proportional to velocity. The resulting broadband stimulated cooling forces are predicted to stop 0.1% of the flux of a 500-K atomic sodium beam in a distance of 300 μm and a time of a few microseconds. This is more than 100 times faster than current methods. Numerical integration and the method of Gordon and Ashkin have been used to calculate the cooling forces which result when two traveling waves cross at an angle 2a. The stimulated cooling forces are reduced in intensity by sin2a but are proportional to velocity over an interval which is larger by 1/sin a. This allows one to stop a substantial fraction of an atomic beam without chirping the laser or Zeeman tuning the atoms.
Single step recoded signed-digit binary arithmetic using optical symbolic substitution
Authors: Awwal Abdul Ahad S.
Published: February 2023

A hybrid symbolic substitution scheme is proposed based on a recoding of input numbers, so that the optical addition process can be carried out in a single step. In this scheme, the to-be- added numbers are encoded, independently, into MSD numbers so that when added they result in carry-free addition.1 This encoding step can be performed electronically beforehand unlike other single step processes and the addition step can be performed optically. The optic overhead of the process is reduced by distributing the total task between electronics and optics. The overall result is fewer rules to-be-implemented optically without the need to re-encode as in the multiple step processes.2
Butterfly interconnection implementation for an n-bit parallel full adder/subtractor
Authors: Sun De-Gui , Xiang Qian , Hu Guang-Hui , Weng Zhao-Heng , Wang Na-Xin
Published: February 2023

In digital optical computing, optical interconnections are the primitives of algorithm and architecture. In particular, perfect shuffle interconnections, butterfly interconnections, and crossover interconnections are widely studied; not only can they implement some simpler logic operations, they can also constitute more complex and more effective computing systems. Especially, the butterfly interconnection has many advantages over others in implementing digital systems. In this paper, we design an n-bit parallel full adder/subtractor.
Analytical model of corneal surgery
Authors: Howland Howard C. , Rand Richard
Published: February 2023

We present a thin shell model of the mammalian cornea in order to study the changes in its shape resulting from refractive surgery (e.g., radial keratotomy or laser keratomileusis). A simple closed-form solution is given for a thin linearly elastic spherical shell model of the cornea. We assume axisymmetry and isotropy in the shell surface. The surgery is modeled by permitting Young’s modulus and shell thickness to depend on position. The analytical nature of the solution permits principal shell curvatures to be explicitly calculated. The model is used to investigate the effect of surgery on change of corneal shape and refractive power and the associated sensitivity to intraocular pressure changes.
Aspherized human schematic eye with GRIN crystalline lens
Authors: Xu David H. , Katz Milton
Published: February 2023

Blaker1 designed an adaptive human eye model with a gradient-index (GRIN) lens for zero and maximally accommodated states. His GRIN profiles were based on spherical corneal and lens surfaces. We present a computer modeled adaptive schematic eye with aspheric corneal and lens surfaces based on anatomical measurements and a GRIN lens. Our algorithm models up to 10 D of accommodation by continuously varying the axial and radial gradient indices; the anterior chamber and lens thicknesses; and the surface radii and conic constants of the lens. Spherical aberration and longitudinal chromatic aberration computed throughout the range of accommodation agree with empirical data. The astigmatic error of the model eye is compared with several empirical studies. Polychromatic MTFs at each level of accommodation and with pupil diameters of 2-8 mm are presented. We found that the NR1 radial gradient coefficient significantly impacts on paraxial power and can correct spherical aberration, the NR2, and NR3 and NR4 terms increase spherical aberration; and axial gradient terms higher than NZ2 have negligible effect on spherical aberration.
Stationary counterphase gratings elicit temporal-to-nasal optokinetic nystagmus in infants
Authors: Teller Davida Y. , Mar Corinne M. , Succop Annemarie , Mahal Monika R. , Lindsey Delwin T.
Published: February 2023

A stationary 100% contrast counterphase flickering grating can also be described as two identical 50% contrast components moving in opposite directions. Since infants have a temporal→ nasal (T–N) OKN bias, we wondered whether they would show T–N OKN to counterphase gratings. Two-month-old infants monocularly viewed 48 × 48° counterphase grating (0.17 cycles/degree, 6 Hz, or 0.45 cycles/degree, 6.7 Hz). The ratio of contrasts of the two grating components was varied, with a constant sum of 100%. The direction of OKN was judged by an adult observer on each trial. All infants tested showed predominantly T–N OKN in response to the 50% T–N, 50% N–T grating. On the average, contracts of ~25% T–N, 75% N–T were required to null the OKN response. These results suggest that the infant’s visual system analyzes the counterphase grating into its two opposite motion components, and reduces the effective contrast of the N–T component prior to the site of generation of OKN.
Emmetropization in chick eyes: optimizing refractive state by visual feedback control
Authors: Schaeffel Frank
Published: February 2023

From studies of refractive development in humans, it is difficult to derive mechanisms of emmetropization because refractive errors may both be pre-programmed genetically but may also be acquired from environmental factors. By contrast, animal models offer the opportunity to study the cause and effect relationship in controlled conditions. Animals with rapidly growing eyes and good acuity are most appropriate. Many intriguing results were recently obtained in the chicken: it was found that eyes can correct for refractive errors imposed by spectacle lenses by changes in axial eye growth, and this result can also be obtained without functional accommodation. Removing high spatial frequencies from the retinal image during development by translucent occluders induces axial refractive errors (deprivation myopia), and deprivation myopia can be restricted to parts of the visual field only if the deprivation was local. The occurrence of deprivation myopia does not require an intact optic nerve. Eyes even recover from induced myopia and hyperopia without intact optic nerve. The results suggest that (1) refractive state is guided by the quality of the retinal image, and (2) information from the retinal image is used locally to modulate growth of the underlying sclera.