Theoretical analysis of transverse mode conversion using transient long-period gratings induced by ultrashort pulses in optical fibers

We study numerically the conversion of transverse modes in a few-mode fiber using long-period gratings that are optically induced by femtosecond pulses. The gratings are transiently generated via the Kerr effect by the modal beating of a high-power write beam that excites a combination of transverse modes. The spectral properties and the influence of pulse walkoff on the conversion are investigated. Furthermore, by delaying the write pulse with respect to the probe pulse and choosing a suitable target mode profile, we show the temporal characteristics of a novel optical switch that can be realized based on this principle.