2025 年 E108.B 巻 9 号 p. 1038-1051
The eigenvalues in the Zakharov-Shabat problem for the nonlinear Schrödinger equation are invariant quantities with respect to the transmission distance. Therefore, optical eigenvalue modulation is expected to be a novel transmission scheme to overcome the Kerr nonlinearity limit in fiber optic communications. However, there is a concern that optical eigenvalues vary under dispersion fluctuations arising in the manufacturing process of the optical fiber. In this study, we investigate the effects of the dispersion fluctuation on the eigenvalue transmission, including that of multi-eigenvalues, through numerical simulations. For the modeling, we experimentally measure the dispersion distribution of a non-zero dispersion-shifted fiber (NZ-DSF) using the bidirectional optical time domain reflectometer (OTDR) method. The measurement result indicates that the count of dispersion fluctuation could be approximated by the Gaussian distribution. Hence, we investigate the three dependencies of eigenvalue variation: the number of eigenvalues, the standard deviation of dispersion fluctuation, transmission distance, and reference time. The simulation results indicate that multi-eigenvalue transmission was more sensitive to dispersion fluctuation than 1-soliton transmission. Moreover, the direction of the eigenvalue variation depends on the eigenvalue configurations. Nevertheless, the results show that the eigenvalue shift is sufficiently small even for the transmission of the 2-soliton solution in the dispersion fluctuation of practical fibers. However, in the case of the 4-soliton solution, dispersion fluctuations affect eigenvalue transmission under certain conditions.
