Evanescent-field coupling between a monomode fiber and a high-index medium of limited thickness

By applying a coupled-mode theory to the angle degenerate modes of a planar waveguide and to the single mode of a neighboring monomode fiber, we derive an integrodifferential system describing the transfer of light intensity from the fiber to the planar waveguide. By numerically solving this system, the transmission loss of the fiber is computed as a function of various parameters such as the planar-guide thickness, the planar index, and the remaining fiber-cladding thickness.