Spatio-temporal mode characterization of disordered weakly nonlinear graded-index multimode fibers

In the transmission of relatively low power telecom signals, the performance of space-division multiplexed (SDM) transmission systems employing multimode graded-index fiber (GIF) is mostly affected by linear random mode-coupling (RMC) [1], [2]. The study and characterization of power exchanges among the propagating modes, owing to fiber imperfections and bending [3], is of utmost importance in SDM systems, because it involves an appropriate optimization of modal multiplexing and de-multiplexing techniques. Here we propose a 3D modal reconstruction method, using as input condition spatio-temporal bullets Ep(x,y,0,t)=Ap(0,t)Fp(x,y) , describing individual modes, while accounting for laser linewidth and pulse temporal shape. The input 3D bullets are independently propagated using the GNLSE, accounting for chromatic and modal dispersion [4]. RMC is accounted by adding a random phase between modes at input, and weighting the output modal power by power fractions |c i | 2 provided by the experiments; hence, the total output bullet field is given by Etot=∑Mi=1ciEi(x,y,z,t) . By integrating |Etot|2 vs. time, the output near-field is obtained; whereas integration vs. (x,y) yields the instantaneous power profile.