MIDIT OFD CATS Modelling, Nonlinear Dynamics Optics and Fluid Dynamics Chaos and Turbulence Studies and Irreversible Thermodynamics Risø National Laboratory Niels Bohr Institute and Technical University of Denmark Building 128 Department of Chemistry Building 321 P.O. Box 49 University of Copenhagen DK-2800 Lyngby DK-4000 Roskilde DK-2100 Copenhagen Ø Denmark Denmark Denmark
by Stefano Trillo
Fondazione Ugo Bordino
Rome, Italy
MIDIT-seminar 455
Tuesday June 29, 1999, 11.00 h
at MIDIT, IMM, Bldg. 305, Room 027, DTU
Abstract: The theory of modulational instability (MI) in optical fibers is briefly reviewed, with specific focus on the polarization arrangements which allow for MI to take place in the normal dispersion regime in bimodal (birefringent) fibers. Specifically, we wish to address the question concerning the most favourable conditions for frequency conversion from a strong pump to the modulational sidebands. According with the standard linearized MI analysis, this condition is obtained at the MI peak gain or phase-matching of the underlying four-photon process. We show, however, that the MI analysis can be prolonged into the nonlinear (strongly depleted) regime revealing a complex homoclinic structure of the system of coupled nonlinear Schroedinger equations which govern the nonlinear mixing process. We show that, as a consequence, the optimum conversion strongly deviates from the phase-matching condition, being obtained even outside the MI gain or parametric bandwidth. A clear experimental evidence for this phenomenon has been recently provided.