Reduction of the nonlinear phase shift induced by stimulated Brillouin scattering for bi-directional pumping configuration system using particle swarm optimization algorithm

H A Al-Asadi

doi:10.2971/jeos.2013.13012

Abstract

We present a theoretical analysis of an additional nonlinear phase shift of backward Stokes wave based on stimulated Brillouin scattering in the system with a bi-directional pumping scheme. We optimize three parameters of the system: the numerical aperture, the optical loss and the pumping wavelength to minimize an additional nonlinear phase shift of backward Stokes waves due to stimulated Brillouin scattering. The optimization is performed with various Brillouin pump powers and the optical reflectivity values are based on the modern, global evolutionary computation algorithm, particle swarm optimization. It is shown that the additional nonlinear phase shift of backward Stokes wave varies with different optical fiber lengths, and can be minimized to less than 0.07 rad according to the particle swarm optimization algorithm for 5 km. The bi-directional pumping configuration system is shown to be efficient when it is possible to transmit the power output to advanced when frequency detuning is negative and delayed when it is positive, with the optimum values of the three parameters to achieve the reduction of an additional nonlinear phase shift.

Highlights

Stimulated Brillouin scattering (SBS) is an inelastic process, and can be described classically as acoustic waves travelling within the fiber core, causing moving periodic variations in the medium density that results in periodic variations in the refractive index and changes in the optical susceptibility through electrostriction
We show from our analysis that the reduction of an additional nonlinear phase shift of backward Stokes wave depends on the optimal numerical aperture of the optical fiber, as well as the optical loss and the pumping wavelength
Our aim in this paper is to find optimum parameters usually chosen to reduce the additional nonlinear phase shift backward Stokes wave through SBS, sine of the maximum half-angle accepted by the optical fiber (N A), pumping wavelength and optical loss coefficient (α)

Summary

INTRODUCTION

Stimulated Brillouin scattering (SBS) is an inelastic process, and can be described classically as acoustic waves travelling within the fiber core, causing moving periodic variations in the medium density that results in periodic variations in the refractive index and changes in the optical susceptibility through electrostriction. The fluctuation of the Stokes wave at the higher Brillouin pump power can be attributed to the additional nonlinear phase shift caused by the spontaneous scattering process that initiates SBS and the gain/loss spectrum [2]–[4]. PSO is a very successful swarm intelligence, as is well known, computationally inexpensive and can be implemented since its CPU speed and memory requirements are low It does not require gradient information of the objective function but only its values [8]. We show from our analysis that the reduction of an additional nonlinear phase shift of backward Stokes wave depends on the optimal numerical aperture of the optical fiber, as well as the optical loss and the pumping wavelength

THEORETICAL ANALYSIS

PARTICLE SWARM OPTIMIZATION

RESULTS AND DISCUSSIONS

CONCLUSION