Frequency conversion dynamics of vector modulation instability in normal-dispersion high-birefringence fibers

We investigate the frequency conversion associated with the nonlinear stage of vector modulational instability in high-birefringence fibers with normal group-velocity dispersion. A complex heteroclinic structure of instability reveals all possible dynamic trajectories of frequency conversion. It is shown that different Fermi-Pasta-Ulam recurrent regimes are separated by Akhmediev breathers corresponding to a separatrix on the heteroclinic structure. We also demonstrate that the optimal frequency conversion unexpectedly occurs outside the parametric gain bandwidth when the input light is polarized close to 45 degrees from a principal axis of the fiber, whereas the optimal conversion frequency gradually shifts into the gain region when the polarization direction of input light tilts toward the principal axis of the fiber.