Interesting effect of optical Kerr nonlinearity in expanding single-mode regime of optical fibers using dispersion-flattened profiles

An interesting effect of optical Kerr nonlinearity is reported from theoretical investigation on the fundamental and first higher mode cutoff frequencies in single-mode fibers doped with highly nonlinear materials like CdS_xSe_1−x with W-type dispersion-flattened profiles. It is observed that whereas the single-mode regime decreases absolutely for dispersion-shifted profiles due to reduction of the first higher order mode cutoff frequency as is evident from earlier studies, it increases for W-type profiles for such nonlinearity taking its effect on the nonzero fundamental mode cutoff frequency into consideration. Thus, one can go further down below the fundamental mode cutoff frequency while using W-fibers in single mode nonlinear fiber devices involving evanescent field coupling in the low V region.