Characterization of Effective Nonlinear Coefficient in Randomly Coupled Multi-Core Fiber

We numerically and experimentally investigate the nonlinear characteristics of randomly coupled multi-core fiber (RC-MCF). The numerical results show that the effective area of the modes in RC-MCF change significantly due to the fiber bending angle, whereas the effective nonlinear coefficient (γ_eff) is independent of the angle, thus clarifying that γ_eff characterization is not affected by the twisting condition of the fiber. We also propose a modified continuous wave-self phase modulation (CW-SPM) method to evaluate the γ_eff of the RC-MCF where the wavelength difference between two CW lights is reduced to less than one-tenth that of the conventional setup to suppress the pulse and spectrum distortion owing to the modal dispersion. Our comparison of the measured and simulated values for 2-, 4-, and 12-core fibers demonstrate that they are in good agreement.