Tikrit Journal of Pure Science 22 (6) 2017 ISSN: 1813 – 1662 (Print) E-ISSN: 2415 – 1726 (On Line) 108 Estimate the Attenuation and Simulation of dispersion Gaussian pulses propagation in a Single Mode Optical Fiber Mubarak Hamad Oglah Dept. of controlling petroleum systems , College of Petroleum & Minerals Engineering , Tikrit University , Iraq E-Mail: Aukla_mubarak74@yahoo.com Abstract we studied Attenuation in Fiber Optics, we used two type of Fibers (Plastic and glass) with length (0.5,5,20m) and (1,20,100m) respectively and used two wavelength laser (660nm, 850nm), we found attenuation increase with 850nm wavelength and 660nm wavelength are the best for the plastic fiber optics, in addition the attenuation which occur from axial gap, axes rotation, inclination angle, transversal displacement are investigated. Influence three values of linear dispersion on Pulse propagation along fiber at seam distance is investigated by simulation using Fourier Method using MATLAB. Keywords: Single Mode Optical Fiber, Attenuation and Dispersion Simulation. Introduction and review As discussed by [1][2] There are many reasons causing attenuation in the fiber optics like absorption, dispersion, scattering, core and cladding, bending, splicing and connectors, as well as can be affected by temperature [3]. There are three sources majority of light used in fiber optics emits light at one of different wavelengths: 850nm, 1310nm and 1550nm , these wavelengths are attracted because they offer the least amount of attenuation in the glass fiber. The attenuation for 850nm wavelength for long distance around 3dB/km but, for 1310 nm wavelength is given by 0.35dB/km while 1550 nm wavelength is 0.23dB/km [4] [5]. There are many theoretical and experimental studies on the subject of the attenuation in the fiber optics, where, K.A. Lathief discussed how measure the attenuation using Optical Time Domain Reflectometer he found the attenuation limit achieved is 0.43dB/ Km for both 1310 nm signal & for 1550 nm [6]. Sabah Hawar Saeid Al-Bazzaz presents a simulation, using VC++, for testing outputs of some of optical communication components like amplifiers, used in single mode optical fiber systems for compensating the attenuation and dispersion caused by the long distance, he found that The results indicate that these effects increase with increasing the distance through the fiber optic length [7]. M. Grabka et al were investigated the suspended-- core microstructured optical fiber. The fiber exhibits a very high numerical aperture which originates from high refractive-index contrast built-in into the fiber structure. they found experimentally demonstrated that light-coupling efficiency and mode distribution strongly depend on relative position of the fiber’s core and a light beam and light polarization.[8] M. F. M. Salleh & Z. Zakaria studied and examine the reliability of Optical Ground Wire as long distance telecommunication backbone and to discuss the possible factors that contribute to the findings. they found the relationship between bend loss and optical power attenuation on long distance optical fibre and reliability [9]. A. Zendehnam and et al study used different radii of curvature and also up to 40 wrapping turns have been employed, to investigate their effects on bending loss. And also wrapping turns has been suggested, which shows good agreement with the experimental results. they found Influence of torsion stress on core and clad structure. [10] In this study, we will focus on the attenuation in the single mode optical fiber such as dispersion, splicing and connectors experimentally, as well as the effect of the attenuation coefficient on the pulse amplitude transmitted through the optical fiber using MATLAB simulation at same conditions. The simulation will examine the reliability a long distance telecommunication and amplitude of the signal pulse. Theory Attenuation Attenuation is natural phenomenon in the optical fiber manufacturing, which is defined as a logarithm relationship between the optical input power and the optical output power in a fiber optical system [11,12] which measure of the signal decay, or losses in the power of ligth, that occurs as propagate pulses through the fiber length. This decay can be written as: () = (0) − 10 … … (1) Where (x) represent length in kilometers, and the attenuation coefficient(α) is given in decibels per kilometer (dB/km). Because the designers of the fiber optic systems need to know how much light will remain in a fiber after propagating a given distance, one of the most important specifications of an optical fiber is the fiber's attenuation. In particular, the fiber attenuation is the easiest of all fiber measurements to make. All that is required is to launch power from a source into a long length of fiber, measure the power at the far end of the fiber using a detector with a linear response, and then, after cutting off a length of the fiber, measure the power transmitted by the shorter length. The reason for leaving the short length of the fiber at the input end of the system is to make sure that the loss that is measured is due solely to the loss of the fiber Fig. 1 shows a schematic illustration of the measurement system.