International Journal of Computer Applications (0975 – 8887) Volume 92 – No.7, April 2014 23 Overview of Stimulated Brillouin Scattering Effect and Various Types of Method to Eliminate this Effect Fahmida Hossain Tithi Department of Electrical and Electronic Engineering, Bangladesh University of Engineering and Technology Dhaka, Bangladesh M. S. Islam Institute of Information and Communication Technology, Bangladesh University of Engineering and Technology Dhaka, Bangladesh Md. Tawhidul Anwar Tanna United International University Dhaka, Bangladesh ABSTRACT Stimulated Brillouin scattering (SBS) is a resonant nonlinear optical interaction with the material that results in transmitted light being scattered back towards the input. Although high power lasers are available to overcome the intrinsic loss of standard single mode optical transmission fibers (0.2 to 0.3 dB/km) but SBS places an upper limit on the optical power that can be transmitted through the link. Usually, SBS normally has a lower threshold power (≤1.4 mW) than other nonlinear effects. In this paper we see the SBS effect in optical fiber transmission system and different types of methods to eliminate this effect. Here we propose two new approaches to eliminate this effect. Keywords Stimulated Brillouin scattering, intrinsic loss, threshold power, nonlinear effects. 1. INTRODUCTION Fiber nonlinearities become a problem when several channels coexist in the same fiber and results high optical power. Interactions among propagating light and the fiber can lead to interference, distortion or excess attenuation of the optical signals. Nonlinear effects are determined by the total power per channel. The most important types of nonlinear scattering within optical fibers are stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS). The non-linear phenomenon of SBS, first observed in 1964 [1, 2]. Once the power launched into an optical fiber exceeds a certain level, which is known as threshold level or threshold power, most of the light is reflected backward direction due to SBS. When light is scattered to the backward direction, the output power is not more increased [3,4] . Over the years, many research works have been carried out to analyze SBS effect SBS on transmission performance and developed many techniques to eliminate this effect. In this paper we have studied and reviewed the different types of research methods and also propose new methods to compensate the delirious SBS effect in optical fiber transmission system. 2. STIMULATED BRILLOUIN SCATTERING EFFECT 2.1 Basic Concepts In scattering effects, energy gets transferred from one light wave to another wave at a longer wavelength or lower energy. The lost energy is absorbed by the molecular vibrations, or phonons, in the medium. Stimulated scattering is affected by the threshold level. The most important types of nonlinear scattering within optical fibers are SBS and SRS. The SRS is a nonlinear parametric interaction between light and molecular vibrations. Optical phonon participates in SRS but acoustic photon participates in SBS. Due to SRS power transferred from shorter wavelength channels to the longer wavelength channels. SRS occurs in both directions, either forward or backward direction. The non-linear phenomenon of SBS and its effect, first detected in 1964 [5].When launched power into an optical fiber exceeds threshold level; most of the light is reflected backward direction. This phenomenon is known as SBS. Input signal is known as pump wave and which signal is generated due to this scattering process that is known as Stokes wave. SBS occurs only in the backward direction i.e., when input power exceeds threshold power, Stokes power shifted to the backward direction. Pump wave losses power while Stokes wave gains power. 2.2 SBS Mechanism The SBS is a nonlinear process that can occur in optical fibers at large intensity. Quantum mechanically the Brillouin shift originates from the photon- phonon interaction. The basic mechanism of SBS phenomenon is illustrated in Fig. 1 Fig.1: Basic SBS mechanism The pump wave creates acoustic wave in transmission medium through a process called electrostriction. The interaction between pump wave and acoustic wave creates the generation of back propagating optical wave which is called Stokes wave. When acoustic waves travel through the solid, transparent glass material, they induce spatially periodic local compressions and expansions which in turn cause local increases and decreases in the refractive index. This phenomenon is known as photoelastic effect. The magnitude of the photoelastic effect increases with increasing input optical power. When the input power reaches a SBS threshold level, the refractive index of the fiber has been acoustically