Vector normal modes on two-core optical fibers. II. The modal cutoffs

For pt.I see ibid., vol.15, no.7, p.1213-24 (1997). A vector theory based on generalization of the circular harmonics expansion method combined with the finite-element method is formulated to determine cutoff values for higher-order normal modes on the two-core fiber with radially inhomogeneous core index profiles. The method is developed under the transverse magnetic field formulation in order to avoid the spurious solutions. Numerical examples are given for the two-identical-core cases with power-law core index profiles.