Higher Order Approximation for Stimulated Raman Scattering Including Walk-off Effect

Abstract

The performance of an optical system is reduced by nonlinear effects. It is known that when optical power is very high then non linear effects tend to manifest themselves, so the study became important in DWDM system. The fiber nonlinearities fall into two categories. One is stimulated scattering (Raman and Brillouin), and the second is known as optical Kerr effect. With these effects the results are changed in the refractive index of fiber with optical power. With different input signals kerr-non-linearity manifests itself in three different effects such as Self-Phase Modulation (SPM), Cross-Phase Modulation (CPM) and Four-Wave Mixing (FWM). At high power level, the inelastic scattering phenomenon can induce stimulated effects such as Stimulated Brillouin-Scattering (SBS) and Stimulated Raman-Scattering (SRS). The Brillouin and Raman scattering can be differentiated as the Brillouin generated phonons (acoustic) are coherent and give rise to a macroscopic acoustic wave in fiber, while in Raman scattering the phonons (optical) are incoherent and no macroscopic wave is generated, So SRS is much less problem than SBS. The threshold of SRS is nearly to 1 Watt, more than thousand times higher than SBS. But the real systems are being expanded with EDFAs having output optical powers of 500 mW (+27 dBm), and this will only go higher. A fiber optic link that includes three such optical amplifiers will reach this limit since the limit drops proportionally by the number of optical amplifiers in series.