A nonlinear Schrodinger equation has been solved in order to establish the nonlinear optical self phase modulation (SPM) actual magnitude in fiber (within optical domain), the SPM magnitude was simulated at 40 GHz in relation to normalized time and actual distance within the fiber. When the SPM signal comes out of the fiber and enters a pre-designed transimpedance amplifier (TIA) (electronic domain), and according to simulation, the SPM signal corresponds to an input noise spectral density of 320.3 pA 2 /Hz (electronic domain) that enters the TIA. A significant reduction in S 21 scattering parameter, nonlinear optical power and nonlinear noise figure were registered when the 320.3 pA 2 /Hz is entered at the TIA input. That effectively means a reduction in SPM value using the TIA at 40 GHz. A Microwave Office software was used for simulation.