Measurement of effective nonlinear coefficients in few-mode fibers

Because of random mode coupling, the nonlinear coefficient in few-mode fibers (FMFs) is averaged to an effective value, which can be theoretically modeled and calculated by using the multi-mode Manakov equations. In this Letter, we experimentally measure the effective nonlinear coefficients in a 530-m-long FMF supporting two mode groups, namely, the $ {\rm LP}_{01} $LP₀₁ and $ {\rm LP}_{11} $LP₁₁ mode groups, by exploiting the self-phase and cross-phase modulations of pulsed fields. By using the nonlinear coefficient of the $ {\rm LP}_{01} $LP₀₁ mode as a reference and comparing the spectral broadening of the pulsed fields, we obtain the intra-modal effective nonlinear coefficient of the $ {\rm LP}_{11} $LP₁₁ mode and the inter-modal effective nonlinear coefficient between the $ {\rm LP}_{01} $LP₀₁ and $ {\rm LP}_{11} $LP₁₁ modes. The experimental results are in good agreement with the theoretical predictions of the multi-mode Manakov equations.