Showing papers on "Physical optics published in 1992"

Spin-orbit interaction of a photon in an inhomogeneous medium

Abstract: As light propagates in an optically inhomogeneous medium, bending and twisting of the beam cause the rotation of the polarization plane. This is the well-known Rytov-Vladimirsky effect or Berry phase. Considering this effect as the result of an interaction between the spin of the photon (polarization) and its orbital motion, one can expect the reverse effect. In fact, the additional angular shift of a trajectory of the circularly polarized beam (CPB) was recently studied for the particular case of an optical fiber. In this paper the spin-orbit interaction Hamiltonian is obtained both in geometrical optics and in wave optics. We have calculated also the effect of the transverse shift of CPB under refraction on the boundary of two media. The expressions for the angular shift of a trajectory of CPB in optical fibers with two types of refractive-index profiles have been obtained. Geometrical optics expressions can be applied for the typical waveguides only at lengths less than 0.05 cm. However, using the geometric optical picture we can successfully describe statistical properties of speckle patterns of laser radiation as it propagates at a considerable distance.

Refraction of diffuse photon density waves.

Abstract: Experiments are performed which illustrate the properties of damped traveling waves in diffusive media. Our observations demonstrate the manipulation of these waves by adjustment of the photon diffusion coefficients of adjacent turbid media. The waves are imaged, and are shown to obey simple relations such as Snell's law. The extent to which analogies from physical optics may be used to understand these waves is further explored, and the implications for medical imaging are briefly discussed.

Bending losses of coated single-mode fibers: a simple approach

Abstract: A new approach for the bending losses of coated optical single-mode fibers is developed based on a modified fiber geometry model, and the result is a simple formula. An improved condition for the peak locations is given, that allows for the wavefront curvature of the leaky mode in the bent fiber, since it is derived by wave optics. Simple explicit relations for both the peak spacings and the peak-to-trough ratio are given. Their asymptotic forms for small bend radii are independent of the fundamental-mode parameters. An interpretation of oscillations in the bend-loss curves in terms of a thin-film filter effect of the triple-layer structure on the lateral leaky-mode radiation fully explains the behavior, especially the loss increase in the peaks compared to the case of an infinite cladding. The agreement with numerical and experimental results of other authors is excellent. >

Diffraction of cylindrical and plane waves by an array of absorbing half-screens

Abstract: Multiple forward diffraction past an array of many absorbing half-screens whose separation is large compared to wavelength is examined. Starting with the physical optics approximation for half-planes that are equally spaced and of equal height, the field incident on successive edges is represented by a multidimensional Fresnel integral, which is then expanded into a series of functions studied by Boersma (1978). When the angle of incidence with respect to the plane containing the edges is small, each edge is in the transition region of the previous edge, which precludes the use of the geometrical theory of diffraction and related asymptotic theories. The solution obtained applies for incidence either from above or below the plane containing the edges, and is especially suited to the case of near-grazing incidence. This method of solution allows for numerical evaluation of a large number of half-screens and shows how the multiple diffracted fields are influenced by the physical parameters. Both incident plane waves and incident cylindrical waves can be treated. >

A versatile wave propagation model for the VHF/UHF range considering three-dimensional terrain

Abstract: A polarimetric wave propagation model for field strength forecasting and coverage prediction in the VHF/UHF frequency range is presented. The model uses a digital terrain data bank and considers multipath propagation. Based on the uniform geometrical theory of diffraction (UTD) and physical optics an approach is described for calculating the propagation effects in natural 3-D terrain, given by topological and morphographical data. The method for field strength forecasting is described and methods for the analysis of the predicted multipath signal are discussed. It is shown how the complex probability density function (PDF) for the receiver field strength and the field strength delay spectrum can be derived. Methods for further evaluation of the transmitting channel characteristics are discussed. >

Hybrid ray optics and parabolic equation methods for radar propagation modeling

Abstract: The use of parabolic equation (PE) methods has become very popular in recent years for modeling radar propagation effects in the lower atmosphere, especially for cases in which the vertical refractive index profile changes along the propagation path. The author presents a hybrid propagation model called the radio physical optics (RPO) model that uses a combination of ray optics (RO) and split-step PE methods to overcome the high computational burden of pure split-step PE methods. RPO considers four regions. At ranges less than 2500 meters and for all elevation angles above 5 degrees, RPO uses a flat Earth (FE) model. For the region beyond the FE region, a full RO model is used. The PE model is used for ranges beyond the RO region. For ranges beyond the RO region and heights above the PE region, an extended-optics (XO) method is used.

Light scattering by closely packed particulate media

Abstract: We have calculated the scattering of light by media consisting of densely packed spherical particles by applying geometric optics and Monte Carlo simulation. We found that when the packing density is increased, dark surfaces are clearly brightened, especially near grazing emergence and incidence. Also, the transmission through a finite layer is reduced with opaque particles but not with transparent ones. The results indicate that previous models that use low-density approximations (Lommel–Seeliger, Hapke, Lumme–Bowell, etc.) are not accurate for typical regoliths.

International Trends in Optics

Abstract: Integrated optics - OEICs or PICs?, H.Kogelnik quantum opto-electronics for optical processing, D.A.B.Miller optics in telecommunications - beyond transmission, P.W.E.Smith microoptics, K.Iga holographic optical elements for use with semiconductor lasers, H.P.Herzig and R.Dadliker fiber optic signal processing, B.Culshaw and I.Adonovic optical memories, Y.Tsunado what are photorefractives good for?, H.Rajbenbach and J.-P.Huignard adaptive interferometry - a new area of applications of photorefractive crystals, S.I.Stepanov water wave optics, J.J.Stamnes about the philosophies of diffraction, A.W.Lohmann the essential journals of optics, J.N.Howard optics in China - ancient and modern accomplishments, Z.-M.Zhang unusual optics - optical interconnects as learned from the eyes of (nocturnal insects), crayfish, shellfish and similar creatures, P.Greguss the opposition effect in volume and surface scattering, K.C.Dainty influence of source-correlations on spectra of radiated fields, E.Wolf quantum statistics and coherence of nonlinear optical processes, J.Perina one photon light-pulses versus attenuated classical light-pulses, A.Aspect and P.Grangier optical propagation through the atmosphere, A.Consortini are the fundamental principles of holography sufficient for the creation of new types of 3D cinematography and artificial intelligence?. Y.N.Denisyuk medical applications of holographic 3D display, J.Tsujiuchi Moire fringes and their applicatons, O.Bryngdahl breaking the boundaries of optical system design and construction , C.H.F.Velzel interferometry - what's new since Michelson?, P.Hariharan curreent trends in optical testing, D.Malacara adaptive optics, F.Merkel triple correlations and dispectra in high-resolution astonomical imaging. H.Weigelt phase retrieval imaging problems, J.R.Fienup blind deconvolution - recovering the seemingly irrecoverable!, R.H.T.Bates and H.Jiang pattern recognition, similarity, neural nets, and optics, H.H.Arsenault and Y.Sheng towards nonlinear optical processing, T.Szoplik and K.Chalasinska-Macukow new apects of optics for optical computing, V.Morozov digital optical computing, S.D. Smith computing - a joint venture for light and electricity?, P.Chavel.

Energy-density distribution inside large nonabsorbing spheres by using Mie theory and geometrical optics.

Abstract: Mie theory and geometrical-optics ray tracing are used to obtain the distribution of electric energy density inside a nonabsorbing micrometer-sized sphere illuminated by a polarized plane wave. The Mie solution shows the multiply reflected geometrical-optics rays inside a sphere having a diameter of ~ 150 free-space wavelengths (size parameter = circumference/wavelength = 500). The geometrical-optics result shows the major features of the Mie solution and provides a physical interpretation of the electromagnetic interactions that result in the observed energy-density distributions. Both solutions show internal on-axis energy-density maxima inside the shadow surface of the sphere. The region of greatest enhanced energy density is approximately one internal wavelength in diameter and approximately twenty internal wavelengths in length.

Self-Fourier objects and other self-transform objects

Abstract: A self-Fourier function (SFF), according to Caola [ J. Phys. A24, L1143 ( 1991)], is a function that is its own Fourier transform. The Gaussian and Dirac combs are well-known examples. Many more SFF’s have been discovered recently by Caola. This discovery might bear some fruit in optics, since the Fourier transform is perhaps the most important theoretical tool in wave optics. We show that Caola discovered all SFF’s. Furthermore, we study other self-transform functions, which are also tied to some transformations that play a role in coherent optics.

RCS of electrically large targets modelled with NURBS surfaces

Abstract: A technique is presented for the RCS computation of electrically large conducting bodies, modelled by NURBS patches, using physical optics (PO) and asymptotic expansion of integrals methods. The NURBS surfaces are transformed in Bezier patches to apply PO. Excellent accuracy is obtained.

Higher order equivalent edge currents for fringe wave radar scattering by perfectly conducting polygonal plates

Abstract: An approach for including higher order edge diffraction in the equivalent edge current (EEC) method is proposed. This approach, which applies to monostatic as well as bistatic radar configurations with perfectly conducting polygonal plates, involves three distinct sets of EECs. All of these sets of EECs contain very few singularity problems. In order to obtain an approximation to the scattered field, the three sets are added and integrated along the circumference of the scatterer. This procedure is straightfoward, and since most singularity problems have been eliminated, it is numerically well behaved. The approach is applied to a configuration involving a square plate. Substantial improvements were achieved. The calculations also illustrate that the edge interaction can be significant, although the direction of incidence is far from the plane of the scatterer. >

Optical caustics in natural phenomena

Abstract: When observing a distant point source of light through a water droplet adhering to a pane of glass near one’s eye or the scattering of light from raindrops, one often sees optical caustics. In this paper, diffraction integrals are used to investigate these caustics. The caustic shapes are related to divergences in the stationary phase method for approximating the diffraction integrals. These divergences correspond to the coalescing of two or more geometrical light rays in ray optics or the coalescing of two or more regions of stationary phase in wave optics. The number of coalescing light rays is related to a polynomial approximation of the phase function in the diffraction integral. Also, the relation between the shape of the resulting caustic and the elementary caustic forms of the catastrophe optics classification scheme is described.

Canonical examples of reflector antennas for high-power microwave applications

Abstract: The suitability of various radiating systems for generating a directive high-power microwave (HPM) beam is considered. It is concluded that offset reflector antenna systems are well suited for this purpose. An HPM reflector antenna may consist of one or two reflectors that are illuminated by single or array feeds. To accurately predict the performance of an HPM reflector antenna, a versatile analysis scheme is used to compute the fields of an array feed with general configurations, and the diffraction techniques of physical optics (PO) and physical theory of diffraction (PTD) are applied to analyze reflectors of conic or shaped surfaces. Design examples of offset dual-reflector antennas for HPM applications are presented. Analysis results are shown with emphasis on both the near-field and far-field radiation characteristics. Applications of optimization (mathematical programming) techniques to the diffraction synthesis of HPM reflector antenna systems are discussed, and examples are given to demonstrate their effectiveness. >

Incremental length diffraction coefficients for an impedance wedge

Abstract: An incremental length diffraction coefficient (ILDC) formulation is presented for the canonical problem of a locally tangent wedge with surface impedance boundary conditions on its faces. The resulting expressions are deduced in a rigorous fashion from a Sommerfeld spectral integral representation of the exact solution for the canonical wedge problem. The ILDC solution is cast into a convenient matrix form which is very simply related to the familiar geometrical theory of diffraction (GTD) expressions for the field on the Keller cone. The scattered field is decomposed into physical optics, surface wave, and fringe contributions. Most of the analysis is concerned with the fringe components; however, the particular features of the various contributions are discussed in detail. >

A uniform ray approximation of the scattering by polyhedral structures including higher order terms

Abstract: A uniform ray representation of the far field scattered by flat plate structures is investigated by postulating an approximation of the surface current on each face of the object, which is subsequently integrated either in closed form or asymptotically in terms of the well-tabulated edge transition function. Specifically, the current on each plate is approximated, in addition to the usual physical optics (PO) component, by a primary nonuniform current, obtained from the canonical solution to the wedge problem and truncated at edges of the plate, as well as a secondary nonuniform current induced by doubly diffracted fields and expressed in terms of an equivalent edge source. The superimposed effect of the rays resulting from the primary and secondary nonuniform current integration improves the agreement of the calculated pattern as compared with method of moments computations. >

A comparison of scattering model results for two-dimensional randomly rough surfaces

Abstract: Bistatic radar cross sections are calculated using two modern scattering models: the small slope approximation (both first- and second-order), and the phase perturbation technique. The problem is limited to scalar-wave scattering from two-dimensional, randomly rough Dirichlet surfaces with a Gaussian roughness spectrum. Numerical results for the cross sections are compared to those found using the classical Kirchhoff, or physical optics, approximation and perturbation theory. Over a wide range of scattering angles, the new results agree well with the classical results when the latter are considered to be accurate. A comparison between the new results shows that the phase perturbation method gives better results in the backscattering region for correlation lengths greater than approximately one wavelength, while both the first- and second-order small slope approximations yield greater accuracy in the forward scattering direction at low grazing angles. >

An asymptotic feature of corner waves scattered by polygonal plates

Abstract: Plane wave scattering from a polygonal plate is investigated within the framework of extended Physical Optics. Reflection and transmission coefficients are used to describe the scattering behavior of various plates, including perfectly reflecting, semi-transparent and perfectly absorbing plates. A far field scattered by such plates is the sum of corner waves. A new asymptotic feature of these waves has been established. The algebraic sum of their directivity patterns is zero for any direction of scattering. Thus the scattering is due to relative phase shifts between corner waves.

Introduction to Nonlinear Guided Wave Optics

Abstract: Nonlinear optics is now almost three decades old as a discipline. Although the early days were characterized by experiments which needed high power lasers, in the modern context semiconductor diode lasers with sub-watt powers can be used for observing many nonlinear phenomena. This development is the result of two factors, the most important being the development of better materials and the second the use of more optimum sample geometries. It is the second which is dealt with here.

High speed method for predicting radio-wave propagation

Abstract: Radio-wave propagation is rapidly predicted by a hybrid computational method that uses Ray Optics techniques to calculate radio field strength above a limiting radio-wave ray, Parabolic Equation techniques to calculate radio field strength below the limiting radio-wave ray and below a predetermined altitude, and a newly created Extended Optics method to compute radio field strength in an area of the atmosphere below the limiting radio-wave ray and above the predetermined altitude. Rays in the extended optics area are initialized from the elevation angle that rays traced through the parabolic equation area make with the predetermined altitude. Where reflected, direct or origin created rays do not exist within the parabolic equation area, the elevation angle for the ray that does exist at the furthest range (optical limit) is used to initiate ray tracing in the extended optics area for ranges beyond the optical limit. Where the refractive index varies along the predetermined altitude, adjustments to the elevation angle used to initialize rays within the extended optics area are made. Propagation factors, determined through the Parabolic Equation method, are assigned to the rays traced through the extended optics area based upon the propagation factors in existence at the predetermined altitude. Field strength or propagation loss within the extended optics area is calculated from an interpolation between propagation factor values assigned to the extended optics rays.

Analysis of aperture blockage in reflector antennas by using obstacle-located blockage currents

Abstract: An improved method is presented to account for blockage effects in the analysis of reflector antennas. Commonly this is done by introducing shadows on the reflector surface according to the location of the obstacles when performing the physical optics integration. By using physical optics blockage currents located at the blocking obstacle instead of at the main reflector surface, the effect of the different locations in the axial direction is accurately accounted for. This can easily be included by a single phase factor in existing computer programs based on physical optics integration. >

Asymptotic computation of the RCS of low observable axisymmetric objects at high frequency

Abstract: A method based on high-frequency asymptotic techniques is described for rapid radar cross section (RCS) computation for arbitrary convex axisymmetric objects whose geometry is described in a computer-aided design (CAD) format. A modified version of the physical theory of diffraction (PTD), which is free from divergence problems at caustics and shadow boundaries and yields good accuracy even for low-RCS objects, is employed. The spurious contributions due to sudden truncation of the physical optics (PO) currents on the shadow boundary, which yield nonphysical results, are removed, and the accuracy of the PTD is enhanced by adding the contributions due to the creeping waves and the fringe-wave currents for discontinuities in the curvature. This modified PTD yields results that are consistent with the geometrical theory of diffraction (GTD) when the stationary phase evaluation of the fields from the induced currents is valid, and also allows the RCS to be computed for the entire range of incidence angles. The results agree well with those computed with an integral equation code. >

Direct PO optimized dual-offset reflector antennas for small Earth stations and for millimeter wave atmospheric sensors

Abstract: An efficient direct numerical synthesis method for dual offset reflector antennas which is directly based on the physical optics procedure for both reflectors (PO-PO-method) and where the reflector surfaces are advantageously characterized in the spatial domain by a 2D Fourier-transformation is described. The method uses an evolution-type optimization algorithm to shape both reflectors simultaneously so as to generate the desired far field with prescribed criteria. The efficiency of the design method is demonstrated for two computer-optimized dual-offset antenna designs for space applications, a very compact optimum shaped Gregorian Earth station antenna with high offset angle (70 degrees ) and small subreflector size (13 lambda ) and a shaped Cassegrain atmospheric sensor antenna for 200 GHz. The theory is verified by available measured results. >

Huygens' principle, 1690-1990 : theory and applications : proceedings of an International Symposium, the Hague/Scheveningen, November 19-22, 1990

Abstract: Historical Background. The life and the work of Christiaan Huygens (E. Wolf). Christiaan Huygens, originator of wave optics (H. de Lang). Geometrical Optics. Microscope objectives for optical disc systems (J.J.M. Braat). The use of characteristic functions in optical design (J.L.F. de Meijere). Huygens' principle in optical engineering (C.H.F. Velzel). Ray Theory. Rays, wavefronts and phase: a picture book of cusps (M. Berry). Some recent research on optical coherence (E. Wolf). Field Theory. Computational modeling of integrated-optical waveguides (N.H.G. Baken). Observable-based wave modeling: wave objects, spectra and signal processing (L.B. Felsen). Reciprocity, causality, and Huygens' principle in electromagnetic wave theory (A.T. de Hoop). Huygens' principle and a field relation (D.S. Jones). Photolithography and the mathematical theory of diffraction (H.P. Urbach). Mathematical Analysis. On the diffraction problem in electromagnetic theory: a discussion based on concepts of functional analysis including an example of practical application (M. Cadilhac, R. Petit). Huygens' principle for linear partial differential equations (J.J. Duistermaat). Des particules aux ondes: quantification geometrique (J.-M. Souriau). Quantum Electronics and Nonlinear Optics. Optical bistability (E. Abraham). Nonlinear optics a historical perspective (N. Bloembergen). Optical solitons in fibers - a theoretical review (A. Hasegawa). Optics with a new law of reflection phase conjugative optics (A. Yariv). Contributed papers by : M.S. Alber, G.B. Altshuler, A.N. Azarenkov, P.M. van den Berg, J. Carminati, B. Colombeau, S. Cornbleet, C. Froehly, W.J.R. Hoefer, H. Hoekstra, B.J. Hoenders, W. Kamminga, S.A. Kozlov, J.M. Krijnen, P.V. Lambeck, A. Lagendijk, D. Lenstra, M.B. van der Mark, R.G. McLenaghan, M. Nieto-Vesperinas, A. Papiernik, D. Pompei, Th.J.A. Popma, G. Pozzi, D. Sanchez-Gil, P.P.M. So, J.M. Soto-Crespo, A.G. Tijhuis, M. Vampouille, M.H. Vogel, O.I. Yordanov, P. Zhongqiu.

Comparison of monostatic Doppler and radar cross-section spectra by rotating multiple skew-plated metal fan blades

Abstract: Comparison of monostatic Doppler and radar cross-section spectra (RCS spectra) for rotating multiple skew-plated metal Tan blades, in the presence of a linearly polarized EM wave, are investigated. The high frequency backscatter of such a slowly rotating and electrically large blade is based on the quasi-stationary method together with PO/PTD (physical optics/physical theory of diffraction) equivalent currents techniques. Only the θθ polarization case is considered here, while the ΨΨ polarization case can be treated in the same way. Three rotating skew-plated blades are taken as an example, and the agreement between the theoretical and experimental results are acceptable. Some significant features corresponding to the Doppler and RCS spectra are also presented.