US Patent 7095913 Non-active waveguides on planar lightwave circuits

A planar lightwave circuit includes a first active waveguide, a second active waveguide, and a non-active waveguide interposed between the first and the second active waveguides. The circuit further includes a third active waveguide that intersects (1) the first active waveguides at a first cross point, and (2) the second active waveguide at a second cross point. A first active perturbation is located at the first cross point, and a second active perturbation is located at the second cross point. A passive perturbation is located at one of the first, the second, and the third active waveguide.