Fiber-modes characterization using singular value decomposition

The transverse modes of an optical fiber are essential to understand the propagation properties of electromagnetic fields travelling in the fiber. Characterizing them is key for the analysis of large mode area fibers [1]. The most fundamental and well-developed approach of modal characterization is to numerically solve the Maxwell's equations using the measured refractive index profile of the fiber as boundary condition. The main issue with this approach is that the accuracy of this method is strongly dependent on the quality of the refractive index measurement and the imperfections thereof induced during the manufacturing process. In addition to this theoretical method, some experimental methods were also proposed in the last two decades including the S² imaging [1], low-coherence interferometry [2] and C² imaging [3]. One eminent advantage of these methods is that they are agnostic to the refractive index profile of the fiber. However, due to them employing interferometry and intermodal dispersion, these techniques require broadband/tunable sources and (or) fibers of several meters in length. This limits the applicability of these techniques for some designs, such as the fibers used in high-power ultrafast systems.