{HEAD ~ The waveguides} in one section are arranged in the proximity of each other, such that {TAIL ~ an optical field} in the first waveguide can overlap a second waveguide and vice versa and that in said section at least two gratings are arranged for co directional coupling 
{ HEAD ~ The waveguides } in one section are arranged in the proximity of each other , such that { TAIL ~ an optical field } in the first waveguide can overlap a second waveguide and vice versa and that in said section at least two gratings are arranged for co directional coupling
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