Few-mode fibers (FMFs) with weak mode coupling which are used to transmit signals predominantly in the fundamental mode are referred to as quasi-single-mode (QSM) fibers. QSM fibers can be designed to have much larger effective areas for the fundamental propagation mode than conventional single-mode fibers (SMFs). Signal transmission over the fundamental mode of QSM fibers can reduce distortion arising from the fiber Kerr nonlinearity. Random light coupling, however, among QSM fiber modes leads to multipath interference (MPI). Simultaneous reduction of nonlinear distortion and MPI can be achieved by using hybrid fiber spans, each composed of a QSM fiber segment to restrict nonlinear distortion, followed by an ultra-low-loss, large-effective-area SMF segment to suppress MPI.In this invited paper, we review modeling and simulation tools that can be used for the design and optimization of coherent optical communication systems and networks with hybrid QSM fiber/SMF spans. We show that the precise selection of the fiber splitting ratio per span is not critical for the system performance and can be calculated with sufficient accuracy using a modified version of the nonlinear Gaussian noise model for hybrid fiber spans.