Showing papers on "Reflection (physics) published in 1989"

Time domain reflection methods for dielectric measurements to 10 GHz

Abstract: Total reflection methods and instrumentation for their use are described for measurements of dielectric permittivity and loss at frequencies to 10 GHz or more. Several cell designs are shown, together with analyses of their performance. Procedures are given for correcting effects of wave propagation in the cells and residual reflections in the cells by bilinear analysis with calibrations using dielectrics of known permittivity. Representative results are presented for highly polar liquids, dilute solutions of polar molecules in nonpolar solvents, electrolyte solutions, and ionic glasses with appreciable ohmic conduction.

Optical interconnection network

Abstract: A crossbar switch (500) with input optical fibers (571, . . . 586) and output optical fibers (511, . . . 526) having ends connected to transmitters (551, . . . 554) and receivers 561, . . . 564), respectively, and other ends in linear arrays (545, 546) that are adjacent to linear micro lens arrays (540, 542) and a linear spatial light modulator (530) with light emitted from an input fiber end reflected back into an output fiber end for pixels deflected in one direction in the spatial light modulator (530) and lost for pixels deflected in another direction. Other embodiments include reflection from a pixel directly back into the same fiber which is bifurcated.

Determining shape and reflectance of hybrid surfaces by photometric sampling

Abstract: A method is presented for determining the shapes of hybrid surfaces without prior knowledge of the relative strengths of the Lambertian and specular components of reflection. The object surface is illuminated using extended light sources and is viewed from a single direction. Surface illumination using extended sources makes it possible to ensure the detection of both Lambertian and specular reflections. Uniformly distributed source directions are used to obtain an image sequence of the object. This method of obtaining photometric measurements is called photometric sampling. An extraction algorithm uses the set of image intensity values measured at each surface point to compute orientation as well as relative strengths of the Lambertian and specular reflection components. The simultaneous recovery of shape and reflectance parameters enables the method to adapt to variations in reflectance properties from one scene point to another. Experiments were conducted on Lambertian surfaces, specular surfaces, and hybrid surfaces. >

A general two-pass method integrating specular and diffuse reflection

Abstract: We analyse some recent approaches to the global illumination problem by introducing the corresponding reflection operators, and we demonstrate the advantages of a two-pass method. A generalization of the system introduced by Wallace et al. at Siggraph '87 to integrate diffuse as well as specular effects is presented. It is based on the calculation of extended form-factors, which allows arbitrary geometries to be used in the scene description, as well as refraction effects. We also present a new sampling method for the calculation of form-factors, which is an alternative to the hemi-cube technique introduced by Cohen and Greenberg for radiosity calculations. This method is particularly well suited to the extended form-factors calculation. The problem of interactive display of the picture being created is also addressed by using hardware-assisted projections and image composition to recreate a complete specular view of the scene.

Frequency-selective reflection and transmission by a periodic dielectric layer

Abstract: The feasibility of using a periodic dielectric layer, composed of alternating bars having dielectric constants epsilon /sub 1/ and epsilon /sub 2/, as a dichroic surface at millimeter-wave frequencies is examined For oblique incidence, it is found that total transmission and total reflection can be obtained at different frequencies for proper choices of epsilon /sub 1/ and epsilon /sub 2/ and the geometric parameters The frequencies of total reflection and transmission can be estimated from wave phenomena occurring in a layer of uniform dielectric constant equal to the average value in the periodic layers For some of the frequencies of total transmission, the bandwidth for 90% transmission is found to be 40% The bandwidth for 90% reflection is always found to be much narrower, the greatest value obtained being 25% >

Theory of light-beam propagation at nonlinear interfaces. I. Equivalent-particle theory for a single interface.

Abstract: A theory is presented that describes the global reflection and transmission characteristics of a self-focused channel propagating at an oblique angle of incidence to an interface separating two or more self-focusing nonlinear dielectric media. The nonlinear wave packet representing the self-focused channel is represented as an equivalent particle moving in an equivalent potential. The dynamics of the particle is described by Newton's equations of motion, with the asymptotic propagation paths of the channel being read off from the associated phase portraits of the equivalent potential. Equilibria of the potential, or equivalently, critical points in the phase plane, represent stationary (stable or unstable) nonlinear surface waves. Stability of the latter follows immediately from a simple inspection of the potential. The shape of the equivalent potential changes with the power in the incident beam. Our theory provides the nonlinear analog of the well-known linear Snell's laws of reflection and transmission. Conditions on the validity of the theory are established in parameter space by extensive numerical solution of the nonlinear partial differential equation describing beam propagation. One important conclusion of the paper is that the predictions of the equivalent-particle theory encompass a wide physical parameter space. As an illustration of an application of the theory, we show how to design an all-optical angle or power adjustable spatial scanning element. Contact is made with earlier numerical studies of beam propagation and nonlinear surface-wave stability at a linear-nonlinear interface.

Reflection of a beam of finite size from a corrugated waveguide

Abstract: The paper is concerned with the influence of the finite size of an incident beam upon both the anomalous-reflection spectrum and the shape of the energy distribution in a reflected beam. It is proved experimentally that the use of corrugated waveguides as a laser-resonator selective mirror improves the spatial coherence of radiation.

Modified optical frequency domain reflectometry with high spatial resolution for components of integrated optic systems

Abstract: An apparatus which allows detection of scatterers and faults as well as measurement of reflections in fiber or integrated optic devices and systems with a spatial resolution in the region of 10-100 mu m is discussed. The dynamic range is sufficient to detect reflection with a reflection coefficient down to 10/sup -10/. The system uses a modified optical frequency domain reflectometry (OFDR) technique whereby signal light and local oscillator light are coupled into the waveguide under test from opposite directions. The measurement principle requires the wavelength of the light source to be swept continuously up or down. It is shown that the experimental relationship between frequency shift and waveguide length is in fairly good agreement with the theoretical estimate. Polarization-sensitive experimental results are given for reflection factors in short, side-polished polarization-maintaining fibers. >

Wave transformation and swash oscillation on gentle and steep slopes

Abstract: The numerical model developed previously for coastal structures is slightly modified and applied to predict the wave transformation in the surf and swash zones on gentle slopes as well as the wave reflection and swash oscillation on relatively steep beaches. The numerical model is one-dimensional in the cross-shore direction and is based on the finite amplitude, shallow water equations, including the effect of bottom friction, which are solved in the time domain for the incident wave train specified as input at the seaward boundary of the computation located outside the breakpoint. The slight modification is related to the effect of the time-averaged current on the seaward boundary condition and improves the agreement between the computed and measured mean water levels on gentle slopes. The modified numerical model is compared with available small-scale test data for monochromatic waves spilling on gentle slopes as well as for monochromatic waves plunging and surging on a relatively steep slope. Additional comparisons are made with small-scale tests conducted using transient monochromatic and grouped waves on a 1:8 smooth slope with and without an idealized nearshore bar at the toe of the 1:8 slope. As a whole, the numerical model is shown to be capable of predicting both time-varying and time-averaged hydrodynamic quantities in the surf and swash zones on gentle as well as steep slopes.

Using polarization to separate reflection components

Abstract: A technique is presented which utilizes the polarization properties of reflected light to separate specular and diffuse components of reflection. This technique works for both dielectric and metal surfaces, regardless of the color of the illuminating light source or the color detail on the object surface. In addition to separating out diffuse and specular components of reflection, the technique can also identify whether certain image regions correspond to a dielectric or metal object surface. Extensive experimentation is presented for a variety of dielectric and metal surfaces, both polished and rough, using a point light source. >

Analysis of second-order gratings

Abstract: The results of an analysis of second-order gratings used as distributed Bragg reflectors in surface-emitting lasers are presented. The gratings provide reflection, output coupling, and power transmission to other gain segments for purposes of injection locking. The analysis determines these quantities for arbitrary-shaped grating teeth and includes the presence of a substrate reflector to reduce the radiated power in that direction. The reflector is shown to be effective, but only if it can be precisely positioned. Examples illustrating variations in dimensions, tooth shapes and heights, waveguide loss, and detuning are included. Second-order, square gratings, whose conventional coupling coefficient is identically zero, exhibit substantial reflectivity which is primarily produced by the radiation reaction. The analysis also forms the basis for calculating the far-field grating coupled radiation patterns. >

Theory of light-beam propagation at nonlinear interfaces. II. Multiple-particle and multiple-interface extensions.

Abstract: The theory presented in the preceding paper is extended to account for incident optical beam breakup into multiple self-focused channels and to deal with multiple reflection and transmission at multiple interfaces. Beam breakup is explained by examining the decomposition of the channel in one medium, into its soliton and radiation components after it has crossed into the new medium. A formula is derived which gives the criterion for the number of channels appearing as a consequence of breakup. This formula also provides analytic expressions for the individual self-focused channel powers and the amount of radiation generated. An important observation here is that the amount of radiation generated at the interface shrinks rapidly as a function of increasing channel number N. Each new component generated can be treated as a separate equivalent particle moving in its own equivalent potential. The theory of the preceding paper [Aceves, Moloney, and Newell, Phys. Rev. A 39, 1809 (1989)] can therefore be applied directly to show that low-power channels generated in the breakup will suffer reflection while higher-power channels will undergo transmission. An added ingredient to allow for mutual-channel interaction is the soliton-collision formula. The multiple-interface extension of the single-interface problem results from patching individual single-interface equivalent potentials together. The theory is illustrated with two applications: (i) a nonlinear version of a directional coupler requiring just two interfaces and (ii) trapping of a channel at an interface by a ramped linear refractive index.

A general two-pass method integrating specular and diffuse reflection

Abstract: We analyse some recent approaches to the global illumination problem by introducing the corresponding reflection operators, and we demonstrate the advantages of a two-pass method. A generalization ...

Achieving greater on-wafer S-parameter accuracy with the LRM calibration technique

Abstract: Since the Introduction of microwave wafer probing In 1983 the dominant vector network analyzer calibration technique has been the short-open-load-thru (SOLT). The thru-reflect-line (TRL) technique has also been used In certain applications, and both approaches have enabled valuable measurements to be made with relative ease and a high degree of accuracy. Each technique, however, has drawbacks which may hinder accuracy or prevent certain applications. A new method,' line-reflect-match (LRM), circumvents many of these drawbacks, thereby allowing a more accurate and more versatile on-wafer calibration. In addition, LRM is simpler to perform because it requires fewer standards.

"Electron acceleration at nearly perpendicular collisionless shocks, 1, One-dimensional simulations without electron scale fluctuations""

Abstract: Under certain conditions electrons can be reflected and effectively energized at quasi-perpendicular shocks. This process is most prominent close to the point where the upstream magnetic field is tangent to the curved shock. A theoretical explanation of the underlying physical mechanism has been proposed which assumes conservation of magnetic moment and a static, simplified shock profile are performed. Test particle calculations of the electron reflection process in order to examine the results of the theoretical analysis without imposing these restrictive conditions. A one-dimensional hybrid simulation code generates the characteristic field variations across the shock. Special emphasis is placed on the spatial and temporal length scales involved in the mirroring process. The simulation results agree generally well with the predictions from adiabatic theory. The effects of the cross-shock potential and unsteadiness are quantified, and the influence of field fluctuations on the reflection process is discussed.

Absorbing boundary condition for the elastic wave equation: Velocity‐stress formulation

Abstract: This paper describes an absorbing boundary condition for finite‐difference modeling of elastic wave propagation in two and three dimensions. The boundary condition is particularly effective for obliquely incident waves, typically quite troublesome for absorbing boundaries. Analytical predictions of the boundary reflection coefficients of a few percent or less for angles of incidence up to 89° are verified in example finite‐difference applications. The algorithm is appropriate for use in a velocity‐stress finite‐difference (vs‐fd) formulation. It is computationally simpler than a similar absorbing boundary given previously for the standard displacement formulation. A second algorithm is presented which may be advantageous when the boundary of interest is exposed to strong evanescent waves. Both algorithms require that the adjacent elastic medium be locally homogeneous.

Laser-amplified motion detector and method

Abstract: Method and apparatus for measuring nanometer or picometer surface displacements in a target surface. A laser beam is directed against the target surface, and time-dependent variations in laser output power are measured. These variations, which are due to non-specular reflection of the incident beam by the target and reentry of the retroreflected light into the laser cavity, are used to determine time-dependent displacements at the target surface, based on a linear relationship between the measured power variations and surface displacements. The invention is useful for determining microscopic surface features of a surface, for high-density laser optical disc data storage and retrieval, and as an ultrasensitive transducer for sound or mechanical vibrations.

Wave transmission over submerged breakwaters

Abstract: Monochromatic wave reflection and transmission over a submerged impermeable breakwater is predicted numerically by slightly modifying the numerical model developed previously for predicting wave reflection and run‐up on rough or smooth impermeable slopes. The slight modification is related to the landward boundary condition required for the transmitted wave propagating landward. In addition to the conservation equations of mass and momentum used to compute the flow field, an equation of energy is derived to estimate the rate of energy dissipation due to wave breaking. The computed reflection and transmission coefficients are shown to be in agreement with available small‐scale test data. The numerical model also predicts the spatial variation of the energy dissipation, the mean water level difference, and the time‐averaged volume flux per unit width, although available measurements are not sufficient for evaluating the capabilities and limitations of the numerical model for predicting these quantities.

Directional wavemaker theory with sidewall reflection

Abstract: A directional wavemaker theory is presented for waves in wave basins with sloping bottoms and reflective sidewalls. The theory includes the refraction, shoaling and diffraction that occur in wave basins with the wavemaker mounted along one end of the basin. A procedure is shown which utilizes the reflection from the sidewalls to produce planar wave trains at a given location in the basin, similar to that which would be obtained by an infinitely long wavemaker.

Pulse reflection sites and effective length of the arterial system

Abstract: The concept of effective length (L) of the arterial system implies that it may be represented by a single viscoelastic tube terminated by an impedance, creating a single reflection site. Although the concept is straightforward, investigators for years have been unable to agree on the value of L. Proposed values range from a few millimeters to a few meters, confounding the identification of arterial reflection sites. This report shows analytically and illustrates with experimental data that the determination of the effective length leaves room for an infinite number of exact solutions for L and the corresponding terminal impedance if the input impedance of the tube is to match the measured input impedance of an arterial system. None of the possible values of L needs to bear any relationship to actual reflection sites.

Method of and apparatus for obtaining object data by machine vision form polarization information

Abstract: A method and apparatus for determining object characteristics such as shape and relative electrical conductivity and for resolving specular and diffuse components of reflection are disclosed. These object characteristics are determined by measuring the following polarization parameters of reflected light from the object surface: (i) the magnitude of the minimum polarization component, (ii) the magnitude of the maximum polarization component, and (ii) the directional orientation of the minimum polarization component. These parameters are used to ascertain at an object point the specular plane and the ratio of the Fresnel reflection coefficients, perpendicular to parallel, with respect to the specular plane. Both of these are used for the determination of the surface normal at object points. The numerical value of the Fresnel reflection coefficient is used to discriminate between surfaces of varying electrical conductivity, lower values indicating highly conductive metals, higher values indicating poorly conducting dielectrics. The numerical value of the Fresnel reflection coefficient is used to resolve specular and diffuse reflection components.

On the derivation of the Schrödinger equation from stochastic mechanics

Abstract: It is shown that the existing formulations of stochastic mechanics are not equivalent to the Schrodinger equation, as had previously been believed. It is argued that this is a reflection of fundamental inadequacies in the physical foundations of stochastic mechanics.