Quasi-Single-Mode Fiber Transmission for Optical Communications

The transmission of a single fundamental mode in a fiber with cutoff wavelength above the transmission band is studied as a means of allowing a larger fiber effective area and reducing fiber nonlinearity. The reduction of nonlinear impairments is achieved at the expense of a potential new linear impairment in the form of multipath interference (MPI). We use a power-coupled-mode formalism to analyze the growth of MPI, and the effects of fiber and cable attributes on its magnitude and the required complexity of digital signal processing to combat the MPI. Hybrid fiber spans comprised partially of a quasi-single-mode fiber are also analyzed using a modification of the Gaussian noise model of coherent systems to predict optimal configurations, and results from transmission experiments are presented that demonstrate very high spectral efficiencies and performance surpassing that of a purely single-mode fiber system.