Extended four-photon mixing approach to modulational instability

Analysis of modulational instability in optical fibers based on a phase-matched four-photon mixing approach is extended by taking into account higher-order dispersion. Fourth-order dispersion governs the modulation frequency in a region near zero-dispersion wavelength, resulting in frequency saturation. The frequency decreases as group delay dispersion becomes dominant in comparison to the fourth-order dispersion. To deepen the modulation, a phase-matching condition for four-photon mixing must be satisfied. A technique is studied which uses externally controllable birefringence of optical fibers to achieve phase-matching at a given modulation frequency.