A novel boundary condition for a two-dimensional finite-element method (2D-
FEM) is developed to simulate accessing waveguides to planar optical juncti
ons, This new boundary condition is based on a paraxial approximation to th
e field's derivatives over the junction's ports, The formulation is very ea
sily adapted within the 2D-FEM framework while providing good simulation re
sults. Two examples are provided to show the applicability and reliability
of the present method: a waveguide step discontinuity and a sharp waveguide
bend.