Enhancement of modal stability through reduced mode coupling in a few-mode fiber for mode division multiplexing

We demonstrate a novel approach to enhance the modal stability between the modes of a few-mode fiber (FMF) by increasing the effective index differences between these modes. Unlike single mode fibers (SMFs), a FMF guides more than one mode with a larger effective mode area. Mode division multiplexing in FMFs has gained significant importance for potentially high data rate transmission. However, with the increase in the number of modes, a FMF encounters possible coupling between the modes. We proposed two designs of a FMF that supports LP01, LP11, LP21 and LP02 modes, which propagate with larger mode spacing, offering reduced mode coupling and thus enhancing mode stability. The modal stability or effective index difference between the modes is enhanced by more than 26% by introducing a ring of air-holes in the first fiber design. Moreover, a second fiber design is also proposed, where a five modes fiber is transformed to a four modes fiber and the modal stability enhancement is calculated to be more than 30% without affecting the mode quality significantly. It is also shown here that such a FMF is more resilient to both bending loss and mode area variation compared to a standard SMF. Our proposed technique is scalable and can be used for fibers with a higher number of modes to increase the transmission capacity along with reduced mode coupling