Complex Wave Phenomena Research Articles

Structure of the field of a mode group in a multimode waveguide

I. The present article is concerned with the spatial structure of the field of an antenna excited in a multimode waveguide by a small group of modes with closely spaced orders. It has been shown in several papers (see, e.g., [1-3]) that adjacent modes sum in phase or, alternatively stated, interfere constructively along the geometrical-optics (GO) ray path. It is therefore reasonable to expect a mode group to be capable of generating a beam that is localized in the vicinity of a certain ray [4, 5]. An analogy exists here with free space, where a beam of finite width is formed by a set of plane waves (free-space "modes") propagating at close angles. The objective of the present study is to give an approximate analytical description of the structure of a wave beam in a plane-layered multimode waveguide. The analysis of this comparatively simple example can provide a basis for the qualitative analysis of more complex wave phenomena and aid in developing the intuition needed in order to solve problems in the control of fields in multimode waveguides.

WAVE: Program for simulating onshore-offshore transport in two dimensions using the macintosh™ computer

WAVE is a FORTRAN-77 program for two-dimensional simulation of onshore-offshore transport of sand caused by oscillatory wave motions. Simulation of wave-induced processes is limited to the nearshore area, seaward of the breaker zone, where onshore-offshore transport dominates. The breaker zone is defined by a breaker index of H/ d = 0.78, where H equals wave height and d equals depth. A wave front is propagated over a two-dimensional grid representing a geologic cross section of a beach. Each wave front consists of a wave crest followed by a wave trough. As a wave crest passes over the cross section, bottom velocities are calculated according to Stokes wave theory. Subsequently, a wave trough is passed over the section and bottom velocities are recalculated. Bottom velocities under wave crests are stronger, but of shorter duration, than velocities under wave troughs. Sorting and transport may occur due to these differences. Transport rates are calculated using algorithms based on Bagnold's equations for bedload and suspended-load transport. Wave climate, initial beach slope, and sand-grain sizes are specified by the user. Furthermore, wave climate can remain constant, or can be differed by changing the height of incoming waves according to a Rayleigh probability distribution. Although WAVE simplifies complex wave phenomena, experiments show that simplified two-dimensional models can be used to help predict complex interactions between differing wave climates, beach slope, and available grain sizes.

Rules of refractive index and a potential well model of the optical waveguides

This is the text of an invited paper presented at the North American Radio Science Meeting of the International Union of Radio Science held in the University of Leval in Quebec, June 2–6, 1980. In integrated optics, it has been possible to explain various complex wave phenomena by two simple rules of refractive index which, however, have never been rigorously proved. The purpose of this paper is to examine these rules critically and to define them more precisely based on a Potential well model of the optical waveguides, which we will discuss in detail.

Stress wave propagation in fibres: Effect of crossovers

A direct numerical solution is described which models the wave propagation dynamics of a system of two crossed fibres, one of which has been subjected to transverse ballistic impact. The model provides a means of assessing the influence of fibre materials properties and fibre-fibre slip on the complex wave phenomena occurring at fibre crossovers. This is a matter of considerable importance in rationalising the performance of textile structures used as ballistic protection devices.