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Ahmad Atieh

Dear Paolo,
Sorry for late response. Please find answers below, which was sent to you by email as well.
[AA] we use +ve sign in the definition of chirp. The sign in the general filed equation is related to the directional of propagation of the optical field.
[AA] please note that the chirp definition is not exactly the derivative of the phase for the gaussian pulse as shown in the attached image and described in the component datasheet. It is derivative of the phase of the optical field E(t) which is related to the gaussian pulse p(t) according to the equation in the attachment.
[AA] as I’ve explained above, there is a difference between the gaussian pulses and the optical field used in the calculation of the propagated signals in the optical fiber.
[AA] please note that the equations in the tutorial on Optiwave website are related to the normalization process of the nonlinear Schrodinger equation. In equation 5, the initial pulse at z=0m, has a chirp parameter which is related to the phase. The field phase is Ct^2/2T^2. You can’t correlate this equation to the chirp definition show in the image for the Gaussian pulse.
[AA] if you derive the phase with respect to t, it gives Ct/T^2, which is linear varying function. The sign should be +ve. Typically, the positive or negative sign indicates the direction of the propagation of the field as I’ve mentioned above.
[AA] I guess the two equations 5 and the Gaussian pulse are different as described in the datasheet of the components.
[AA] the optical fiber components in OptiSystem support attenuation, GVD, Beta2, Beta 3, SPM, XPM, FWM, SBS, SRS, Self-steeping. etc.
You should be able to include all of these physical characteristic in your modeling. Please refer to the Example Library of OptiSystem at the location below for examples covering theses effect.
C:\Users\USER NAME\Documents\OptiSystem 19.0 Samples\Fiber analysis and design
[AA] OptiSystem solves the nonlinear Schrodinger equation using Split-step method. Please refer to the datasheet for the Optical Fiber and Bidirectional Optical Fiber components for more details. Please note that these models have been verified experimentally by many users in the industry and academia.