ISSN: 2278 – 1323 International Journal of Advanced Research in Computer Engineering &Technology (IJARCET) Volume 2, Issue 10 , October 2013 2646 All Rights Reserved © 2013 IJARCET An Accurate Model for Chromatic Dispersion in Optical Fibers under Radiation and Thermal Effects Ahmed Nabih Zaki Rashed 1* , Abd El-Naser A. Mohamed 1 , Imbaby I. Mahmoud 2 , Mohamed S. El_Tokhy 2 , Osama H. Elgzar 2 1 Electronics and Electrical Communications Engineering Department Faculty of Electronic Engineering, Menouf 32951, Menoufia University, EGYPT 1* E-mail: ahmed_733@yahoo.com 2 Engineering Department, Nuclear Research Center, Atomic Energy Authority, P.O. 13759, Inshas, Egypt Abstract - Radiation and temperature influence the optical fiber characteristics. These influences such as increasing the chromatic dispersion were studied and shown to result from the refractive index changes occurring within the fibers induced by radiation and thermal effects. In this paper we present a model and a simulation results to reveals the effect of radiation and temperature on the optical fiber chromatic dispersion by using Vissim environment. We demonstrate the importance of waveguide dispersion in the reduction of the total chromatic dispersion. This formulated treatment provides a mean to control the optical characteristics of fibers in radiation environments. The results are validated against published experimental work and showed good agreement. Keywords- Optical Fiber, Radiation Environments, Thermal and Gamma Radiation Harmful Effects, Chromatic Dispersion, Optical Communication System. I. INTRODUCTION Nowadays the growing demand for high data rate applications, is requires a reliable transmission media such as optical fibers [1]. Optical fiber is the basic element in the modern high capacity and high-bit-rate optical telecommunication systems [2-3]. Optical fibers advantages over other electrical media, including [4], capability to work under strong electromagnetic fields, possibility to carry multiplexed signals (time, wavelength multiplexing); small size and low mass [5], ease of integration [6], the large packing density, mass replication, fast data rate, high signal- to-noise ratio, and high immunity to defects especially when short lengths and flexibility are required [7]. Optical fibers can be classified in to two basic types from the point of view of propagation: single-mode fibers, and multimode fibers [8]. Single-mode optical fiber is extensively used in the telecommunication system because it provides a bandwidth of about 30 GHz [3]. In optical fibers, studies mainly focused on the understanding and on the modeling of radiation-induced attenuation and luminescence. Therefore, it has become essential to investigate the influence of ionizing radiation on the characteristics of many fiber-optic components [9]. Moreover, the investigation of the refractive index changes induced by gamma radiation is of crucial importance in the design of fiber-optic systems including fiber-optic gyroscopes, laser ranging systems for space, and intrasatellite high-speed optical links [9]. Another effect of gamma radiation on optical fiber is the dispersion. It plays a critical role in optical signal propagations of optical pulses through fibers [10]. That subdivided into chromatic and modal dispersion [11]. Chromatic dispersion is resulted from the variations in group velocity for different optical spectral components traveling in an optical fiber [12]. It has several limitations on the optical fiber link. Such as pulse broadening, limiting the data rate of an optical communications system [12], restrict the available wavelength region [13], increasing of bit-error rates [3], and affect transmission performance [14]. Additionally, it determines the maximum bandwidth that can be transmitted through the optical fiber [8]. Chromatic dispersion consists of waveguide and material dispersion. The waveguide dispersion can be adjusted by choosing an appropriate refractive index profile of the fiber. However, the material dispersion is an invariable characteristic of a specific material [15]. Thus, it is important to know the dispersion characteristics of the optical fibers [16]. Consequently, we are interested with evaluation of chromatic dispersion that enables us to calculate the degradation that occurs in optical fiber transmission characteristics under irradiation environment. In addition, it allows predicting operating wavelength, thermal and radiation harmful effects. The arising effects of both material and waveguide dispersion are indispensable in designing high-bit-rate optical communication systems. This work is done by using VisSim environment. VisSim is a Windows-based program for modeling and simulating complex dynamic systems. VisSim combines an intuitive drag-and-drop block diagram interface with a powerful simulation engine. The visual interface offers a simple method for constructing, modifying, and maintaining complex system models. With VisSim, we can rapidly develop software prototypes of systems or processes to demonstrate their behavior prior to building the physical prototype. Furthermore, all modeling and simulation tasks can be completed without writing a line of code. This leads to significant savings in both development time and costs, and a greater assurance that the resultant product will perform as specified. This paper is organized as follows: Section II presents the basic assumptions and modeling of radiation induced dispersion, Section III describes the model results. However section IV is devoted to conclusion. II. BASIC ASSUMPTIONS AND MODELING OF RADIATION INDUCED DISPERSION A pulse, during its propagation through the fiber, experiences a temporal spread known as temporal dispersion or, dispersion as shown in Fig. (1). Therefore, in any communications link through an optical fiber it is observed that the dispersion is the parameter that determines the maximum bandwidth that can be transmitted through the optical fiber [8]. The factors that contribute to the waveform