A novel dielectric waveguide directional coupler with a tapering left-handed slab core located in the coupling region is analyzed by the staircase approximation method, which combines the building block approach and multi-mode network theory with a rigorous mode-matching procedure. Particular attention is directed toward the radiation and coupling characteristics under different structural parameters of the coupler. Numerical results indicate that the proposed coupler is very promising by shortening the coupling length significantly while keeping the radiation loss at a low level.
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