EFFECT OF OPTICAL KERR-EFFECT NONLINEARITY ON LP(11) MODE CUTOFF FREQUENCY OF SINGLE-MODE DISPERSION-SHIFTED AND DISPERSION-FLATTENED FIBERS

A theoretical investigation of the effect of the optical Kerr effect i n the refractive index distribution on the first higher-order mode cut off frequency is carried out for single-mode fibers having dispersion- shifted and dispersion-flattened profiles. It is observed that the eff ect is the least in the case of step and W-profiles and pronounced for fibers having imperfections like a dip in the profiles, Although the nonlinearity-induced cutoff frequency change is negligible in a practi cal nonlinear optical fiber which operates at levels of several watts, our analysis includes a single-mode fiber with weakly nonlinear mater ials like silica under high optical fields or highly nonlinear materia ls under weak fields. These results should be useful as guidelines in minimising the modal noise in single-mode nonlinear fibers of wide int erest.