A novel directional coupler utilizing a left-handed material

A novel directional coupler with a left-handed material (LHM) layer between two single-mode (SM) waveguides of usual material is introduced. The coupling system is analyzed with the supermode theory. It is shown that such an LHM layer of finite length can shorten significantly the coupling length for the two SM waveguides. An LHM layer with two slowly tapered ends is used to avoid the reflection loss at the ends.