Propagation Of Spatial Solitons Research Articles

FDTD modelling of spatial soliton propagation

The finite difference time domain method is used as a tool to model non-linear optical devices. Following this approach, Maxwell's equations are directly integrated in the time domain, avoiding any mathematical approximation. As an example, spatial soliton propagation and interaction will be modelled by the FDTD technique. Some new results will be discussed, to highlight the envisaged breakthroughs allowed by the method.

Material figures of merit for spatial soliton interactions in the presence of absorption

The effects of linear and two-photon absorption on bright spatial soliton propagation are studied. A spatial soliton switch that achieves gain through the novel mechanism of colliding, dragging, or trapping of two fundamental solitons of different widths is proposed. Figures of merit for use in evaluating the suitability of absorbing nonlinear media for soliton switching applications are presented. The main effect of linear absorption is to limit the propagation distance, which places an upper bound on the width of the soliton in order to fit sufficient characteristic soliton propagation lengths within the device. The optical limiting nature of two-photon absorption places an upper bound on the gain that an interaction can achieve. The combined effects of linear and two-photon absorption are to reduce the gain upper bound imposed by two-photon absorption alone with the addition of the soliton width constraint. A maximized gain upper bound is determined solely by material parameters and is compared among three promising nonlinear materials. It is shown numerically that the spatial soliton dragging interaction requires shorter propagation distances and achieves greater gain than the collision interaction and that both are tolerant to the presence of absorption and can provide, with high contrast, gains of three or greater using measured material parameters. These results warrant pursuing the implementation of spatial soliton-based logic gates.

Effects of optical activity on photorefractive spatial solitons in a biased Bi_12TiO_20 crystal

It is shown that the propagation of steady-state spatial solitons in a bismuth titanium oxide (Bi12TiO20) photorefractive crystal is strongly affected by the presence of concomitant natural optical activity. We assume that the Bi12TiO20 crystal is (110) cut and that the external bias field is along the [001¯] axis. Such orientation introduces self-focusing in one polarization of an optical wave front, whereas it has no effect whatsoever on the component orthogonal to it. Under these conditions, the equations that describe the coupled evolution of the two polarizations of an optical planar beam are derived. Our numerical study of the interaction dynamics shows that, even though the optical beam experiences periodic diffraction in one of the polarization components, it can still recover significantly at particular distances within the crystal. Moreover, it is initially capable of maintaining its solitonlike form over a certain distance of propagation. Relevant examples are provided.

Splitting of high-order spatial solitons under the action of two-photon absorption

We analyze the effect of two-photon absorption on the propagation of high-order spatial optical solitons. The main focus of the paper is the splitting of the soliton bound state which has been recently observed experimentally. Using the results of the adiabatic perturbation theory and the information extracted from the Zakharov-Shabat eigenvalue problem we investigate the evolution of the soliton amplitudes and demonstrate that such a splitting can be understood as resulting from a sequence of the amplitude jumps which finally lead to a structural bifurcation. Different regimes of soliton splitting and decay are analyzed in detail.

Spatial soliton deflection mechanism indicated by FD-TD Maxwell's equations modeling

We present first-time calculations from the time-domain vector Maxwell's equations of spatial optical soliton propagation and mutual deflection, including carrier waves, in a 2-D homogeneous Kerr-type nonlinear dielectric. The nonlinear Schrodinger equation predicts that two co-propagating, in-phase spatial solitons remain bound to each other, executing a periodic separation. This disagrees with our new extensively tested finite-difference time-domain (FD-TD) solution of Maxwell's equations. FD-TD shows that co-propagating in-phase spatial solitons become unbound, i.e. diverge to arbitrarily large separations, if the ratio of soliton beamwidth to wavelength is order 1 or less. Not relying upon paraxial approximations or analogies to temporal soliton interactions, FD-TD appears to be a robust means of obtaining detailed models of the interaction of sub-picosecond pulsed light beams in nonlinear media directly in the space-time domain. >

Temporal modulation of spatial optical solitons

A variational method is used to investigate temporal effects that are experimentally observed in the propagation of spatial solitons in planar systems. These effects appear when the laser beam used to reach the soliton propagation regime is pulsed. In the absence of dispersion, the three-dimensional equation of propagation, including two space and one time variable, becomes a two-dimensional spatial equation. Time is included as a parameter that determines the initial value problem. The main effect derived is a temporal modulation on the spatial width of the soliton. This modulation depends crucially on the temporal envelope shape. The interest of these results is concerned with the potential use of spatial solitons for making gradient-index systems with a controllable index profile.

Is two-photon absorption a limitation to dark soliton switching?

It is shown that two-photon absorption does not always place a fundamental limitation on soliton devices: The steering angle, the key characteristic of switching devices based on the propagation of dark spatial solitons, is almost preserved as the intensity of the background wave decays in the presence of weak two-photon absorption.

Spatial solitons in photorefractive Bi12TiO20 with drift mechanism of nonlinearity

The analysis performed shows that in cubic photorefractive crystals (of Bi12SiO20 and GaAs type in particular) with drift (‘‘quasilocal’’) mechanism of optical nonlinearity spatial soliton propagation can be observed for reasonable external dc electric fields 10–15 kV/cm. These photorefractive solitons which can be excited at very low cw laser power are stable in a broad region of signal(soliton)/incoherent(spatially uniform) intensity ratio, and allow easy switching from bright to dark type. Original experimental results of self-channeling of submicrowatt HeNe laser beam in a cubic Bi12TiO20 sample under external dc field are presented.

Dark optical solitons in saturable nonlinear media

We consider the propagation of dark spatial solitons in a saturable self-defocusing medium. An exact analytical solution to the propagation equation is presented, and its properties are discussed.

Experimental observation of beams’ self-deflection appearing with two-dimensional spatial soliton propagation in bulk Kerr material

The observation of two-dimensional optical spatial solitons in three-dimensional Kerr media requires the use of a two-beam interference technique to stabilize the nonlinear propagation. It is shown that as the spatial soliton is self-trapped, the two interfering beams attract each other. This intensity-dependent self-deflection has been applied to the shortening of picosecond laser pulses.

Novel photonic device using nonlinear corner-bend structure

A novel photonic device is proposed for optical switching by using a corner-bend waveguide structure with a Kerr-like nonlinear dielectric interface. For certain specific input signal power, the device proposed can also function as a power divider. The switching characteristics and spatial soliton propagation in the structure are discussed.

Dark spatial soliton propagation in bulk ZnSe

The propagation of dark spatial solitons was experimentally demonstrated in bulk ZnSe at lambda =532 nm using a picosecond laser system. Several propagation and collision parameters were measured and compared with analytic and numerical predictions. It is shown that the propagation parameters behave in a manner consistent with two-dimensional analytic and three-dimensional numerical predictions. The important result is that it is possible to create pronounced dark spatial solitons on a bright optical pulse which do not disappear due to the self-defocusing and diffraction processes operating in the media of interest.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ion-exchanged optical waveguides for all-optical switching

Current interest in all-optical waveguide devices has created a need for suitable nonlinear materials and fabrication techniques. To meet this need, we have made optical waveguides using ion exchange in two glasses, which were designed both to have large optical nonlinearities and to be compatible with the ion-exchange processing. We find that the choice of alkali metal ion in the glass has a major effect on the exchange process and on the optical quality of the ensuing guides. Guides made in one of these glasses have been used for demonstrations of spatial soliton propagation, which can be used as the basis of an all-optical switch.