In some embodiments, the present disclosure relates to a device having a first waveguide and a second waveguide arranged over a substrate. The first waveguide has a first input terminal and a first output terminal, wherein the first input terminal is configured to receive light. The second waveguide is arranged laterally beside the first waveguide and has a second input terminal and a second output terminal. The second input terminal of the second waveguide is configured to receive light. The first waveguide further includes a first portion that has a different structure than surrounding portions of the first waveguide. The second waveguide further includes a second portion that has a different structure than surrounding portions of the second waveguide. The first waveguide is spaced apart at a maximum distance from the second waveguide at the first portion and the second portion.