Nonlinear vortex modes in dual-core photonic crystal fiber couplers

We study the different families of vortex-type modes that can exist in a photonic crystal fiber with two close defects forming a dual-core coupler and presenting the Kerr nonlinearity. Those complex modes bifurcate from the real double-dipole states leading to different states with different phase structures. When power is high enough, single-and double-vortex modes as well as combinations of vortex and fundamental modes arise. Also, families of discrete vortices formed by multipoles located inside the cores are found. We classify the different families, describe their nontrivial bifurcations, and study the stability of the states identifying different scenarios. (C) 2009 Optical Society of America