Effect of Gain Flattening Filter Placement for Nonlinear-Impairment Mitigation in Multiband Optical Transport Network

The multiband elastic optical technology appears as a near-term solution for solving the optical fiber capacity crunch problem in core optical networks. However, the significant challenges come from several non-linear physical-layer impairments (PLIs), such as inter-channel stimulated Raman scattering (ISRS), and band-dependent transmission impairments, such as attenuation, dispersion, etc. In order to maintain the quality of transmission (QoT) throughout all the bands, the gain flattening filters (GFFs) need to be placed in the network, which can be helpful to enhance the overall capacity of the network while mitigating the effect of PLIs. This paper investigates the effect of GFF placement at different parts of geographically diverse networks in terms of traffic admissibility, QoT, and return on investment (ROI). Reported results show that the placement of GFF at every inline amplifier module instead of its placement at the reconfigurable optical add-drop multiplexer (ROADM) module can provide a maximum gain of nearly 37.7% and 118.7% in traffic admissibility for smaller (such as BT-UK network) and larger networks (such as Indian RailTel networks), respectively. In addition, the effect of launch power and symbol rate variation is also studied in the paper. Numerical results show that the placement of GFF at the ROADM modules outperforms in terms of ROI, whereas the placement of GFF at the EDFA module outperforms in terms of QoT.