Many properties of optical fibers namely power loss, noise, distortion, attenuation,rnabsorption, damping etc are guided by nonlinearities. They must be checked andrncalculated their effects before put into applications. We used a developed an-harmonicrnoscillator model (by Sunita Sharma, S. K. Ghoshal and Devendra Mohan) in whichrntwo oxygen atoms are connected to the silicon atom by springs which undergoes intornan-harmonic vibration. This formulation is targated for nanosecod pulses in long haulrnoptical communication. For such laser signal a nonlinearity is quite prominent. It isrnthis an-harmonic motion that leads to nonlinear effects. The equations for secondorder,rnthird-order, and fifth-order linear and nonlinear susceptibilities are derivedrnfrom this an-harmonic model. The equations for the dielectric constants and for thernindex of refraction are also derived. The power loss due to imaginary part of thernhigher-order nonlinear refractive index for Pure Silica Core Fiber, Dispersion ShiftedrnFiber and Dispersion Compensating Fiber is explicitly calculated. The variation ofrnpower loss with damping constant is also calculated at 2mW. The power loss byrnthe Kerr and the electrostrictive nonlinear refractive index and also the total powerrnradiated is theoretically calculated from the model. Our results demonstrate that thernelectrostriction, the Kerr the damping effects are significant in optical fibers. Thesernresults confirm some of the recent theoretical and experimental observations. Thernmodel is quite general and is suitable for calculating many other nonlinear propertiesrnof fiber materials.