Pulse propagation through multimode fibres

To evaluate their communication potential, measurements have been made on multimode glass fibres. Detector limited pulses of 180 psec risetime from a Ga-As laser were transmitted through various lengths of fibre. After a 120 m length the risetime was still not greater than 450 psec. Measurements with a mode locked He-Ne laser, done on shorter lengths of fibre, agreed with the above results.     

Pulse propagation in multimode fibres

The Gloge model for mode-coupled pulse propagation in a step index fibre has been re-examined and a dynamic model proposed to explain the significance of the pulse-broadening regime in which the pulse width varies asL. This leads to the conclusion that the critical factor controlling such propagation is the existence of a particular distribution of power which is a function of space, time and angle.     

Pulse propagation in one-dimensional nonlinear chains

Summary Several numerical computations are carried out to investigate the effects of the propagation of pulses (solitons and quasi-solitons) in one-dimensional nonlinear chains. Numerical results concerning the Toda lattice and a Coulomb-like lattice are discussed and compared. We consider lattices both with and without defects.

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Riassunto Si studiano gli effetti della propagazione di solitoni e di quasi solitoni in reticoli non lineari unidimensionali usando procedure di calcolo numerico. Si considerano il reticolo di Toda ed un reticolo di tipo Coulomb sia in presenza che in assenza di difetti.

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Резюме Используя процедуру численных вычислеий, исследуются эффекты распространения импульсов (солитонов или квази-солитонов) в одномерных нелинейных цепях. Обсуждаются и сравниваются численные редультаты, относящиеся к решетке тода и решетке кулоновского типа. Мы рассматриваем решетки с и вез дефектов.

     

Pulse propagation over smooth irregular terrain

The source of the electromagnetic field is assumed to be a vertical electric dipole at height ξ above the surface of the plane earth with arbitrary time varying moment. The problem of finding the transient field of this dipole when the earth is allowed to be slightly rough is solved by means of a perturbation analysis, repeated application of integral transforms and their inversion on the base of Cagniard's method with the modification of de Hoop.     

Pulse propagation through a nonlinear optical amplifier

We report an investigation of pulse propagation through a recently proposed nonlinear amplifier composed of asymmetrical twin-core fibre. While the pulse is amplified and the associated noise is suppressed, we find that the pulse is strongly chirped. While the chirp in the centre of the pulse can be easily eliminated by inserting a short piece of dispersive fibre right after the amplifier, the chirp in the wings may remain and lead to the eventual destruction of the pulse. This residual chirp can be removed through a damped and radiative oscillation by judicious adjustment of the parameters of the amplifier and the dispersive fibre. Finally, we consider the effect of noise in the pulse. We discovered a threshold of the noise amplitude below which the noise is suppressed (which must be a characteristic asset of the nonlinear amplifier). Above the threshold, the noise tends to shift the centre of the pulse.     

Pulse propagation in randomly fluctuating media.

Pulse propagation in a weakly and randomly inhomogeneous medium is studied using a time-domain progressive wave equation. An eikonal-like approximated solution to the wave equation derived from the path integral representation is used to obtain the time-dependent statistics of pulses propagating through this random medium. This approach yields both a simple way of producing simulations of time series as well as their statistical properties.     

Pulse propagation in a nonlinear dielectric slab waveguide

The evolution of an optical pulse in a single-mode, step index dielectric slab waveguide which is characterized by an intensity dependent dielectric function in the core and cladding regions is treated by means of differential equation techniques. A cubic order non-linearity is considered. The electromagnetic field distribution in the slab waveguide region satisfies a non-linear wave equation. This field can be represented in terms of even TE guided modes with a slowly varying envelope amplitude function.Then using the well known approximation, based on the slowly varying character of the amplitude function, a non linear partial differential equation is obtained for the amplitude function. As the coefficients of this equation depend on the distance across the transverse direction X, an averaging technique over x is applied to reduce the nonlinear partial differential equation into a form that is easily transformed to the so-called non-linear Scroedinger differential equation.This equation is then attacked by means of the well known Inverse Scattering method in the case of reflection less potentials. The single and double soliton solutions are obtained explicitly for a single-mode slab waveguide. Finally numerical results are presented in the time domain.     

Pulse propagation solution for a quantum free electron laser

We calculate the exact solution of the propagation equations describing a quantum free electron laser. The solution is obtained by evaluating the residue in the essential singularities of the Fourier-Laplace transformed optical field, and is expressed as a complete series of special functions. The classical and quantum limits of the solution are discussed and an asymptotic form, valid in the high-gain regime, is obtained.     

Pulse propagation analysis based on the temporal Radon-Wigner transform

Based on the space-time duality and the temporal imaging theory, an optical implementation of the Radon-Wigner transform in the time domain is proposed for analyzing the propagation of ultrashort light pulses in guided dispersive media. As an application of this approach, we discuss the temporal selfimaging or Talbot effect originated by a periodic pulse train. The frequency chirp of the pulses is also considered in order to evaluate its effect on both the integer and the fractional selfimages.     

Pulse propagation of acoustic waves scattered in a channel

When acoustic waves are scattered by random sound-speed fluctuations in a two-dimensional channel the energy is continually transferred between the propagating modes. In the multiple- scattering region the energy flux assumes an asymptotic form in which there is equal energy flux propagating in each mode. Here we shall make use of this well known result to show how to obtain an asymptotic form for a pulse of acoustic energy propagating in the channel. In the multiple-scattering region the speed of the acoustic waves in the pulse continually changes as the energy is transferred between the modes. The process is basically a diffusion process around the mean speed of propagation. We shall first show, using physical arguments, that the diffusion coefficient is proportional to the square root of the propagation distance times the mean free path of scattering. The theory governing the acoustic propagation in the channel is formulated in terms of modal coherence equations and we shall next give a brief review of the definitions of the coherence functions and a discussion of how the equations governing the propagation of the modal coherence functions are derived. We shall then show how the pulse shape and the relevant parameters may be obtained by solving the basic modal coherence equations at large propagation distances.     

Pulse propagation of acoustic waves scattered in a three-dimensional channel

Abstract

In a previous paper (Whitman et al 1999 Waves Random Media 9 1–11) we discussed the scattering of acoustic waves by random sound-speed fluctuations in a two-dimensional channel and presented an asymptotic form for an acoustic pulse propagating in the channel. Here we include the three-dimensional effect of transverse scattering. We find an asymptotic solution in which initially the two-dimensional mode-transfer effect is more important than the transverse scattering effect. However, for large enough propagation distances the transverse scattering effect dominates the pulse spread. In this paper we shall show the form of the pulse shape in both propagation ranges as well as in the transition regime. We shall begin with a discussion of the physics of the problem and then present a mathematical discussion.     

Pulse propagation in an autoionization medium with double Fano profile

We discuss the propagation of a short laser pulse in an auto- ionizing (AI) medium with degenerate double Fano model. By solving numerically the coupled equations for atoms and fields we show that by the proper choice of Fano parameters involved in the problem (contrary to the case considered in (E. Paspalakis, N. J. Kylstra, and P. L. Knight, Phys. Rev. A60 (1999)) we have now two Fano asymmetry parameters) one can eliminate almost completely the absorption in the pulse propagation. It means that we have the transparency in the medium. From the connection between population trapping in short pulsed laser field and transparency in the propagation of the laser pulse which has been fixed by Paspalakis et al., Phys. Rev. A60 (1999) we conclude that this proper choice leads to the presence of the population trapping (or the existence of the “dark” states) in the atomic system. Moreover, instead of one value of the laser detuning for which the dark states exist in the case of one AI level, we find numerically two such values in the case of two AI levels.     

涌浪条件下的浅海表面声道脉冲声传播*

在冬季,海水表面受到海面强风的影响,普遍存在表面声道。当声源位于表面声道中并且声源频率高于表面声道的截止频率时,声能量几乎被完全限制其中,不与海底作用,十分有利于声传播。但当表面声道上边界为较大涌浪所形成的粗糙界面时,这种优良性能会被破坏。在南海北部陆坡海区的一次冬季实验中,发现表面声道以下水听器接收到的首个脉冲的幅度明显增加,通过研究表明,其原因是：存在较大涌浪时,部分表面声道内传播的声能量,经粗糙海面反射作用后进入下层水体中,使得位于表面声道以下的水听器的第一个到达的脉冲幅度增强。     

Pulse propagation in an elastic medium with quadratic nonlinearity (L)

This letter examines the propagation of an acoustic pulse in an elastic medium with weak quadratic nonlinearity. Both a displacement pulse and a stress pulse of arbitrary shapes are used to generate the wave motion in the solid. By obtaining the explicit solutions for arbitrary pulse shapes, it is shown that for a sinusoidal tone-burst, in addition to a second order harmonic field, a radiation induced static strain field is also generated. These results help clarify some confusion in the recent literature regarding the shape of the propagating static displacement pulse.     

Pulse propagation of photon-added coherent states in waveguides with side-coupled nonlinear cavities

We present a theoretical analysis of pulse propagation in a waveguide with a side-coupled Kerr nonlinear cavity. As a specific application, we demonstrate how the nonlinearity has a profound influence on transport properties of a photon-added coherent state. We find that the fields provided by the coherent states facilitate a tunable nonlinearity on the few-photon level, allowing for a robust gating of single photons.     

Pb2CrO5 photovoltaic device for the detecting light-beam position

A light position detector operating through a photovoltaic effect of a Pb₂CrO₅ ceramic disk with a pair of Au planar electrodes is investigated. A fabrication technique and the basic characteristics of the photovoltaic device for position detection are described. A peak photovoltage is obtained around the edge of the electrode for an incident light beam. The incident light beam shape and the electrode pattern are important factors for obtaining a linear relation between the light-beam position and the output signal from the device. A device fabricated for detecting one-dimensional light position has a high position resolution of 0.5 m and a good linearity of ±2 m or less. A two-dimensional device can be fabricated in the same way as the one-dimensional device, except for the electrode pattern. A method for two-dimensional light position detection using a Pb₂CrO₅ photovoltaic cell is demonstrated for a green LED as a light source.